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Research ArticleEquilibrium and Nonequilibrium Nanoscale Ordering ofPolystyrene-b-poly(NN 1015840-diethylaminoethyl methacrylate)a Block Copolymer Carrying Tertiary Amine Functional Groups

Pedro Navarro-Vega1 Arturo Zizumbo-Loacutepez1 Angel Licea-Claverie1

Alejandro Vega-Rios2 and Francisco Paraguay-Delgado2

1 Instituto Tecnologico de Tijuana Centro de Graduados e Investigacion en Quımica Apartado Postal 1166 22000 Tijuana BCMexico2 Centro de Investigacion en Materiales Avanzados (CIMAV) Complejo Industrial Chihuahua 31109 Chihuahua CHIH Mexico

Correspondence should be addressed to Angel Licea-Claverie aliceactectijuanamx

Received 11 July 2014 Revised 15 October 2014 Accepted 29 October 2014 Published 27 November 2014

Academic Editor Wanqin Jin

Copyright copy 2014 Pedro Navarro-Vega et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Poly(styrene)-b-poly(NN1015840-diethylaminoethyl methacrylate) (PS-b-PDEAEM) block copolymer was synthesized by RAFT free-radical polymerization using a trithiocarbonate type of chain transfer agent (CTA) Several block copolymer compositions wereachieved maintaining low polydispersities by using PS as macro-CTA in the first step Thin films of PS

60-b-PDEAEM40 weredeposited over mica substrate and its equilibrium and nonequilibrium nanostructures were studied Lamellar (equilibrium)bicontinuous (nonequilibrium) and detached nanoflakes (nonequilibrium) were obtained by using different annealing methodsMixing nanocomposites of gold nanoparticlesPDEAEM in the block copolymer resulted in the formation of toroidalnanostructures confining gold nanoparticles to the core of those nanostructures The same toroidal nanostructure was achievedby different annealing methods including irradiation with UV light for 15min Electron micrographs show clearly this differenttype of arrays

1 Introduction

Block copolymers (BCPs) of immiscible blocks are comprisedof two chemically different chains covalently linked at oneend BCPs self-assemble into various morphologies in thinfilms depending on the following parameters volume frac-tions of the blocks (119891) molecular weight of BCP interactionparameter between the blocks (120594) interfacial interactionswith substrate film thickness relative to natural block copoly-mer periodicity and type of solvent used and its evaporationrate [1ndash9] According to the phase diagram by Matsen andBates at thermodynamic equilibrium self-assembly intolamellar cylindrical spherical or gyroid nanostructures canbe achieved depending on 119891 and molecular weight timesinteraction parameter (120594) of the BCPs [3] In principle thesame four nanostructures can be achieved for all BCPs ofimmiscible blocks However one key factor in the practical

use of block copolymers is the control over the orientationand lateral ordering of the morphologies in thin films [10]Generally the order in thin films of block copolymers canbe improved by means of thermal annealing [8 11ndash16] andsolvent annealing [2 7 17 18] among other methods Forthermal annealing there usually exists only a small tem-perature window between the glass transition temperature(119879119892) and the degradation temperature (119879

119863) of the involved

blocks which are usually susceptible to thermal degradation[19] Solvent annealing provides an attractive alternative tothermal annealing since sufficient mobility of the blockchains is easily induced at room temperature without thedanger of degradation of the block copolymer although somelow vapor pressure solvents would need some thermal aidto induce phase separation [20ndash22] The solvent annealingapproach has been usedmore andmorewidely in recent years[23] However the details of solvent annealing remain rather

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 725356 14 pageshttpdxdoiorg1011552014725356

2 Journal of Nanomaterials

unclear since the relevant experimental parameters govern-ing the resultant block copolymer nanoscale morphologies(nature of the solvent the relative solvent vapor pressurethe annealing time etc) are usually complex and difficult tocontrol [24] Among these factors the nature of the solventand the relative solvent vapor pressure are crucial [25] Thenature of the solvent influences the degree of the swelling ofeach block and accordingly has severe effects on the resultingblock copolymer morphologies [7] It has been shown thatthe same block copolymer thin films annealed under differentselective solvents and nonselective solvents result in differentmorphologies and orientations [7 26] On the other handonce a solvent is selected the solvent vapor pressure is thekey factor to control the resultant morphologies [27 28]It has been reported that regular phase separated films canonly be achieved when the copolymer Hildebrand solubilityparameter is very similar to the value of the solvent usedfor annealing [26] A lot of practical know-how has beenreported in order to control the solvent vapor pressuressuch as the use of the flow of N

2 to vary the amount of

solvent in reservoir to close the lid of dish more or lesstightly and to change the ratio between the surface area ofthe solvent and the empty volume of the annealing chamber[17 23 29 30] In thin films the destabilization of films isanother important technical issue that should be consideredfor pattern formation [31] Under certain conditions thelocal fluctuation of film thickness is developed and the filmis retracted from the substrate to create fragmentation ofcontinuous films into isolated droplets

Due to the intrinsic nature of polymer chains theobtained nanostructures (in solution bulk or thin films)maybe kinetically trapped nonequilibrium systems since the con-stituent polymer chainsmay not be able to relax towards theirequilibrium conformation [32]

When polymers carrying functional groups in one of theblocks are investigated towards nanoscale ordering in thinfilms a new factor can be included to increase the rich-ness of self-assembled nanostructures that are achievablesmall molecules capable of forming complexes with thefunctional groups of the one block A well-studied exampleof this approach is the use of poly(styrene)-b-poly(4-vin-ylpyridine) (PS-b-P4VP) in combinationwith 2-(41015840-hydroxy-benzeneazo)benzoic acid (HABA) by Tokarev et al [33]Sidorenko et al [34] Bohme et al [35] and Nandan et al[36]

In our research group we are interested in the studyof equilibrium and nonequilibrium self-assembled nano-structures formed by poly(styrene)-b-poly(NN1015840-diethylam-inoethyl methacrylate) (PS-b-PDEAEM) PDEAEM is a pol-ymer carrying tertiary amine groups capable of acting asproton acceptors and lone pair donors (Bronsted and Lewisbases) and also capable of coordinating with metals havingd and f orbitals with deficit on electrons To the best of ourknowledge the only report on the study of self-assembledthin films of this BCP was recently published [37] PS-b-PDEAEM was studied together with the parent BCPpoly(styrene)-b-poly(NN1015840-dimethylaminoethyl methacryl-ate) (PS-b-PDMAEM) in blends with polystyrene findingthat they formed micellar and donut-like structures over

thin films independent of the parameters changed The maindifference between PDEAEM and PDMAEM blocks is theirhydrophobicity and acidity constant (pKa) while PDMAEMis soluble in water at neutral pH and has a pKa of 81 [38]PDEAEM is only soluble in water at pH values close to 6 andlower while it has a pKa of 69 [39]

In the current report not only the equilibrium and non-equilibrium self-assembly process of PS-b-PDEAEM wasinvestigated in detail but also the interactions of gold nano-particles (AuNPs) and their role in self-assembly process ofthe title BCP was assessed

2 Experimental Section

21 Materials All reagents were purchased from Sigma-Aldrich (Mexico) and were used as received with the excep-tion of those described below Styrene and NN1015840-diethylami-noethylmethacrylate (DEAEM)were distilled under reducedpressure to the highest purity possible 441015840-Azobis(4-cyanovaleric acid) (ACVA Fluka) was recrystallized frommethanol 4-Cyano-4-(dodecylsulfanylthiocarbonyl)sulfanylpentanoic acid (CTA) was synthesized following a procedurereported in the literature [40] and was obtained with 72yield

22 Synthesis of Macro-CTAs by RAFT Polymerization Allpolymerizations were performed in ampoules In all cases4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoicacid and 441015840-Azobis(4-cyanopentanoic acid) were used asCTA and as initiator (ACVA) respectively The appropriateamounts of monomers CTA and ACVA were dissolved inp-dioxane (30mL) under stirring at room temperature Solu-tions were degassed by three freeze-pump-thaw cycles Afterdegassing the ampoules were flame-sealed under vacuumand heated in an oil bath at 90∘C The polymerizationswere terminated by rapid cooling and freezing The hom-opolymers obtained also named macro-CTAs since theyinclude the CTA moiety were purified by repeated pre-cipitations using methanol for polystyrene and petroleumether for poly(DEAEM) Products were dried in vacuumfor 48 h An example of the synthesis of polystyrene isdescribed in detail styrene (1202 g 0115mol) 441015840-Azobis(4-cyanopentanoic acid) (ACVA) (00485 g 01203mmol) and4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoicacid (CTA) (00037 g 00132mmol) were dissolved in p-dioxane (30mL) and poured in a glass ampoule (50mL) con-taining a magnetic stir bar Oxygen was removed using 2freeze-thaw evacuation cycles and the ampoule was sealedwith flame under vacuumThe ampoule containing polymer-ization solution was submerged in an oil bath with mag-netic stirring at 90∘C The polymerization was stopped byrapid cooling at a given time The polymerization yield wasobtained gravimetrically by adding a fivefold excess of coldmethanol The polymer product was purified by dissolutionin theminimumamount of acetone followed by adding a five-fold excess of coldmethanol and filteringThis procedure wasrepeated three times to remove residual monomer followedby drying under vacuum to constant weight

Journal of Nanomaterials 3

23 Synthesis of Block Copolymers The macro-CTAsobtained in the first step were characterized and used forthe synthesis of diblock copolymers The calculated amountof macro-CTA was dissolved in p-dioxane (15mL) beforeadding different amounts of the second monomer and theinitiator The copolymerization procedure was the same asthe synthesis of macro-CTAs by RAFT polymerization Forthe purification of the block copolymers a combination ofsolvent and nonsolvent for each copolymer was settled downaccording to their composition using petroleum ethertet-rahydrofuran(THF)methanol As an example the detailedsynthesis of a polystyrene-b-poly(DEAEM) block copolymerstarting with a macro-CTA of polystyrene is describedpolystyrene (10 g 002443mmol)119872

119899= 40940 gmol ACVA

(2mg 000714mmol) and (39 g 002105mmol) of DEAEMwere dissolved in p-dioxane (15mL) containing a magneticstir bar Oxygen was removed using 3 freeze-thaw evacua-tion cycles and the ampoule was sealed with flame undervacuum The ampoule containing copolymerization solutionwas submerged in an oil bath with magnetic stirring at 90∘CThe polymerization was stopped by rapid cooling at a giventime

Theblock copolymerwas precipitated by adding a fivefoldexcess of cold methanol decanting excess liquid and dissolv-ing the copolymer in the minimum amount of THF precipi-tating again using cold petroleum ether and decanting againThis procedure was repeated three times to remove residualmonomer and possible homopolymers formed Finally theproduct was dried under vacuum to constant weight Thecopolymerization yield was obtained gravimetrically by thisprocess of solution-precipitation of the copolymer

24 Characterization of Block Copolymers

241 Nuclear Magnetic Resonance Spectroscopy (NMR) 1H-NMR measurements were carried out on a Varian mercury(200MHz) NMR instrument using chloroform-d as solventand tetramethylsilane as referenceThe main signals of NMRspectra for one example of each macro-CTA are describedbelow The multiplicity of signal is abbreviated as follows119904 = singlet 119889 = doublet 119905 = triplet and br = prefix for broadsignal

Macro-CTA of PS 119872119899= 23600 gmol PDI = 109 1H-

NMR (CDCl3 200MHz) 120575 71 (3H m (Arom 3CH)) 66

(2Hm (Arom 2CH)) 18 (1HmCH) and 14 (2HmCH2)

Macro-CTA of PDEAEM119872119899= 22500 gmol PDI = 117

1H-NMR (CDCl3 200MHz) 120575 41 (2H m OndashCH

2) 26 (6H

m Nndash(CH2)3) 18 (2H m CH

2) 11 (6H m (CH

3)2) and 08

(3H m CH3)

242 Gel Permeation Chromatography (GPC) The number-average molecular weight (119872

119899) and polydispersity of the

molecular weight distribution (119872119908119872119899) of the polymers

were determined with a GPC Varian 9002 chromatographequipped with two mixed-bead columns in series (Phenogel5 linear and Phenogel 10 linear) and two detectors refractiveindex (Varian RI-4) and triangle light scattering (MINI-DAWN Wyatt Technology)

The measurements were performed in THF at 35∘C at aflow rate of 07mLmin Reported 119889119899119889119862 values for polysty-rene (119889119899119889119862 = 0180mLg) [41] were used for the molec-ular weight evaluation of PST macro-CTA The 119889119899119889119862 ofPDEAEM was determined using a differential refractometerIR Optilab DSP (Wyatt Technology) at 633 nm 40∘C usingnine solutions with concentrations from 0192mgmL to192mgmL in THF obtaining a 119889119899119889119862 value of 0087mLg

For the molecular weight calculation of block copoly-mers the average 119889119899119889119862 was calculated from the 119889119899119889119862values for the corresponding homopolymers in the blocksand itsmolar composition (119883) determined byNMRusing thefollowing equation

(119889119899

119889119862

)

COP= 119883PS (

119889119899

119889119862

)

PST+ 119883PDEAEM (

119889119899

119889119862

)

PDEAEM (1)

243 Differential ScanningCalorimetry (DSC) Thepolymerswere dried and purified in vacuum at 40∘C to constant weightand their glass transition temperatures (119879

119892) were obtained

on a TA Instrument modulated DSC 2920 Analyses wereperformed in a helium atmosphere Samples of 8ndash12mg wereheated in aluminum pans at a heating rate of 5 Kmin in thetemperature range from minus50∘C to 150∘C using a temperaturemodulation of 05 K every 60 sec

244 Thermogravimetric Analysis (TGA) The decomposi-tion temperatures of the polymers were obtained on a TAInstrument SDT 2920 Simultaneous DSC-TGA thermal ana-lyzer Analyses were carried out under nitrogen flow Samplesof 10ndash15mgwere heated in aluminum cups at a heating rate of10 Kmin from room temperature to 700∘C Weight loss andderivative of weight loss are reported

25 Preparation of Thin Films of Block Copolymer Solutionsof PS-b-PDEAEM block copolymers (1 wt) were preparedin toluene or benzene by shaking overnight Solutions werethen spin-coated over freshly cleaved mica using a LaurellTechnologies spin coater (model WS-400B-6NPPLITEAS)at spinning velocities of 2000 to 8000 rpm After spin coatingthe thin films formed were dried overnight at ambient tem-perature

26 Posttreatments of Block Copolymer Thin Films

261 Thermal Annealing Some block copolymer films wereintroduced in a vacuum oven filled with nitrogen gas Avacuum of 10 torr was achieved and the temperature was setto either 40∘C or 90∘C Under such conditions the films wereannealed for different periods of times (24 h up to 80 h) Afterthermal annealing the thin films were cooled down to roomtemperature overnight

262 Solvent Annealing Block copolymer films were intro-duced in a glass desiccator filled with toluene vapor(26mmHg) A Petri dish filled with liquid toluene was alsointroduced in the desiccator to maintain the toluene vaporpressure The desiccator was closed and maintained at room


temperature (25∘C) for different periods of times (24 h up to80 h) After solvent annealing the thin filmswere taken out ofthe glass desiccator and allowed to dry overnight at ambienttemperature

263 UV Degradation of Block Copolymer Thin Films Ithas been reported that poly(methylmethacrylate) (PMMA)domains can be selectively degraded by UV light irradiationof PS-b-PMMA thin films [40ndash43] Since PDEAEM is amethacrylate type of polymer it was tested if these domainscould be also degraded using UV light irradiation Thinfilms of the block copolymers over different substrates weresuspended inside a Rayonet UV reactor with air coolingcontaining 12 lamps (120582 = 254 nm) UV irradiation wasprovided for different times Afterwards the thin films werewashed subsequently with acetic acid to dissolve PDEAEMresidues andmethanol to eliminate acetic acid residues Afterdrying at room temperature the thin films were analyzed

27 Preparation of Block Copolymer Thin Films ContainingGold Nanoparticle PDEAEM decorated with gold nanopar-ticles (Au-NP) was prepared as described previously [44]briefly PDEAEM (119872

119899= 18000 gmol) was dissolved in water

at pH of 48 by stirring to yield a 1mgmL solution After-wards the Au-NP precursor tetrachloroauric acid (HAuCl

4)

was dissolved in the solution and the mixture was heatedto 60∘C under reflux 2mL of a 10mgmL solution of thereducing agent tribasic sodium citrate was added dropwiseand the reaction was continued at 60∘C for 120min Aftercooling the AuNp product was isolated by increasing the pHof the reaction solution to 9 PDEAEMAuNP precipitatesand it was separated by centrifugation (13000 rpm) TheAuNP product was washed with deionized water and theclean product was dried in a vacuum oven overnight

Different amounts of the PDEAEM-AuNP were mixedwith the title block copolymer (PS-b-PDEAEM) from 0 to10wt relative to block copolymer These mixtures weredissolved in toluene to achieve a 1 wt solution by shakingovernight The solutions containing block copolymer andAuNP were spin-coated as described before

28 Characterization of Block Copolymer Thin Films

281 Atomic Force Microscopy (AFM) Surface character-ization of the thin films was performed by means of aSPM 5100 atomic force microscope (Agilent Technologies)in intermittent mode using silicon cantilevers in the 145KHzto 160KHz frequency range using amplitude of 3 to 5V Thescanner (N9520A) operation interval was 10 120583m times 10 120583mImages were edited using the WSxM Develop 30 softwarefrom electronic nanotechnology [45]

282 Scanning Transmission Electron Microscopy (STEM)Thin films morphology was studied by STEM Micrographswere acquired using electron microscope model JEOL JEM-2200-FS working at 200 kV Images were acquired by brightfield and 119885-contrast detectors Samples were observeddirectlywithout staining due to a reasonable contrast between

PDEAEM and PST domains that appear darker comparedto PDEAEM The samples for electron microscope wereobtained by detachment of films in hot water (119879 = 50∘C)Those film pieces were then suspended on triple distilledwater and finally it was picked up over a holey carbon filmon a Cu grid of 400 mesh and driedThe average domain sizedetermination was made using DigitalMicrograph softwarescript and these values were used for basic statistics

3 Results and Discussion

31 Synthesis and Characterization of PS-b-PDEAEM BlockCopolymer The preparation of polystyrene (PS) using theRAFT controlled free-radical polymerization is well estab-lished By adequate selection of a RAFT chain transferagent (CTA) the ratio of monomer to CTA to initiatordetermines the obtention of PS in differentmolecular weightsmaintaining low polydispersity (PDI =119872

119899119872119908) In order to

use the synthesized PS for block copolymer preparation it isimportant to guarantee that the PS is functionalized with theCTAmoiety building amacro-CTA and also to guarantee thatthe CTAmoiety is active in the polymerization of the secondmonomer which is NN1015840-diethylaminoethyl methacrylate(DEAEM) in our case In this study a trithiocarbonate typeof CTA was used since it is reported that trithiocarbonatescan be used in the RAFT polymerization of PS [46] andthe specific CTA used in this work works well in RAFTpolymerization ofmethacrylates [47] Table 1 summarizes theresults obtained in the synthesis of block copolymers Thefirst 3 rows show the characteristics of the PS macro-CTAsused in block copolymer preparation The polydispersitiesare very low and the obtained molecular weights match wellthe theoretical values The fourth row of Table 1 shows thefeeding ratios used for the block copolymer synthesis Againthe polydispersities are low and the obtained molecularweights demonstrate that the PS-macro-CTAs grew into thedesired PS-b-PDEAEM products Figure 1 shows an exampleof chromatograms (GPC traces) where a macro-CTA iscompared with the block copolymer product The peaksare narrow and the retention times decreased for the blockcopolymer since inGPChighmolecular weights are observedat lower retention times due to the separation technique used

The composition of the obtained block copolymers wasdetermined by means of 1H-NMR (Figure 2)

For this purpose the integration of signals at a chemicalshift of 41 ppm corresponding to two methylene protons ofthe DEAEM units attached to oxygen was compared to theintegration of five aromatic protons of styrene units withsignals in the range from 63 to 73 ppm A simple calculationshows that the block copolymer depicted in the NMRspectrum on Figure 2 contains 707mol of styrene and293mol of DEAEM units

Thermal analysis of the block copolymerswas undertakento determine adequate temperatures for thermal annealingof the films of block copolymers Figure 3 shows the resultsIn the case of calorimetry (Figure 3(a)) two distinct glasstransition temperatures (119879

119892) are observed one at minus49∘C

corresponding presumably to the poly-DEAEM units and


Table 1 Characteristics of block copolymers

Macro-CTA First block Block copolymer119872119899

gmol PDIa [119872]0 [PS] [119868]0119872119899

gmol PDIa Yieldb 119891PSc

1198911015840

PSd

Polystyrene 37090 102 84 1 011 45760 109 56 091 085Polystyrene 37090 102 356 1 020 71980 117 53 071 058Polystyrene 24870 109 545 1 019 76280 115 51 060 046aPDI =119872

119908119872119899 bby mass of recovered polymer cmolar fraction of PS by 1H-NMR dmass fraction of PS based on 119891PS

10 20 30 40

Time (min)

RI si

gnal

nor

mal

ized

1

0

PS (37090gmol)PS-b-PDEAEM (71980 gmol)

Figure 1 GPC traces of a PS-macro-CTA (119872119899= 37090 gmol) and

the block copolymer (119872119899= 71980 gmol) prepared from it

ab c d ef g h i jk

Acetone

ab c d ef g h i jjjjjjjjj k

Acetone1207

200

CDCl

3

i gn

nb

h k

OOed

N ffjj

aac c

b

78 6 5 4 3 2 1 0

(ppm)

Figure 2 1H-NMR spectrum of a PS-b-PDEAEM block copolymer(119872119899= 71980 gmol)

the second one at 997∘C corresponding well to the reportedvalues for PS In the case of thermogravimetry (Figure 3(b))thermogram shows that the block copolymer is thermallystable up to 220∘C

These results teach us that at room temperature thePDEAEM units are viscoelastic and that in order to move

the PS units temperature above 105∘C is needed A tempera-ture limit of 200∘C can be established as the highest temper-ature to anneal this block copolymer without degradation

In addition to these facts the calorimetry further con-firms that the block copolymer consists of immiscible blockssince two separate 119879

119892rsquos are observed Furthermore thermo-

gravimetric analysis shows thermal decomposition in twosteps in the first step parts of PDEAEM are detached whilein the second step both PDEAEM residual polymer and PSare decomposed

Results of other block copolymers that were preparedcan be consulted in a supplementary results file (see Sup-plementary Material available online at httpdxdoiorg1011552014725356)

32 Towards Equilibrium Ordering of PS-b-PDEAEM ThinFilms Given the composition of the block copolymers pre-pared we decided to study in deep the block copolymercontaining 60mol PS (46 mass) with a molecular weightof 76 280 gmol This block copolymer is expected to format thermodynamic equilibrium lamellae however a gyroidnanostructure is also a possibility As for solvents toluenebenzene and tetrahydrofuran (THF) were chosen due to theFlory-Huggins polymer-solvent (P-S) interaction parameters(120594P-S) calculated with PS and PDEAEM namely 0347 and0350 for toluene 0341 and 0380 for benzene and 034 and036 for THF values that are very similar to both polymersindicating that in this solvent there is only a slight or not asolvating preference for one of the blocks These parameterswere calculated according to (2) [48] using the solubilityparameters (120575) reported in the literature [49] at room tem-perature (29815 K) with the exception of that of PDEAEMestimated from theHoy theory of group contributions [50] tobe 120575PDEAEM = 177 (MPa)12 For polystyrene the value usedis 120575PS = 186 (MPa)12 Consider

120594P-S =119881SR119879(120575S minus 120575P)

2

+ 034 (2)

119881S is the molar volume of the solvent 119877 is the universal gasconstant and 119879 is the temperature

Simple solubility tests showed that the best solubility forboth types of homopolymers was given by THFNeverthelessthis solvent was discarded due to the high vapor pressureof the solvent that resulted in film detachment and voidformation in the films The following results make use oftoluene and benzene as selected solvents even if the solubilityof PDEAEM is worse than that of PS in those solvents

6 Journal of NanomaterialsRe

v he

at fl

ow (W

g)

DSC

9192∘C

9964∘C(I)

10400∘C

0 50 100 150

Temperature (∘C)Exo up Universal V45A TAminus100 minus50

instruments

minus006

minus004

minus008

minus010

minus741∘C

minus496∘C(I)

minus353∘C

(a)

2464

6854

00

05

10

15

20

0

20

40

60

80

100

120

Wei

ght (

)

0 200 400 600 800

TGA

Temperature (∘C)

Der

iv w

eigh

t (

∘C)

Universal V45A TAinstruments

Y-1 Y-2

minus05

(b)

Figure 3 Thermograms by DSC (a) and TGA (b) of a PS-b-PDEAEM block copolymer (119872119899= 71980 gmol)

(a) (b) (c)

Figure 4AFM topographic images obtained using the intermittent contactmode of PSt60-b-PDEAEM40 thin films prepared froma 1ww

toluene solution over mica substrate as a function of spin coating velocity (a) 2000 rpm (b) 5000 rpm and (c) 8000 rpm

Figure 4 shows thin films prepared from toluene solutionsover mica substrate at room temperature (25∘C) as a functionof spin coating velocity It is clear that no equilibriumstructure is formed and that a spinning velocity of 5000 to8000 rpm seems to favor phase segregation

Figure 5 shows AFM images of thin films prepared usingthe same polymer but in solution in benzene over freshlycleaved mica substrate

In this case a constant spinning velocity was used andthermal annealing at a relatively low temperature was appliedto gain movement of PDEAEM units in the block copolymerthat resulted in a transition from elongated type of aggregatesright after spin coating to a phase separated nanostructureResults show that after 36 h of moderate thermal annealing(40∘C) a knitted pattern resembling a bicontinuous gyroidnanostructure was obtained However longer annealing timedestroyed this nanostructure

Figure 6 shows AFM images from the same block copoly-mer deposited over mica substrate but in this case by using

toluene solution for the start and at constant spinning velocityof 8000 rpm In this case the annealing temperaturewas risento 90∘C a temperature at 10 torr at which the movementsof both PDEAEM and slightly for PS units in the blockcopolymer were expected Results show that after 40 h ofthermal annealing the sameknitted nanostructurewas foundin this case as for thin films prepared from benzene solutionsafter annealing at 40∘C The best order was found after 90 hof thermal annealing however the main features can beobserved already after 40 h

Up to these results it looked like a bicontinuos (gyroid)nanostructure was the equilibrium self-assembled one forthis specific block copolymer however solvent annealingproved to us that we were wrong Figure 7 shows AFMimages of solvent-annealed nanostructures obtained fromthe PS

60-b-PDEAEM40 block copolymer deposited by spincoating over mica substrate Images clearly show that solventannealing in toluene at 25∘C for extended periods of time(80 h) resulted in the most expected equilibrium lamellar


(a) (b) (c)


benzene solution over mica substrate at a spinning velocity of 5000 rpm (a) directly after spin coating (25∘C) and after annealing in vacuum(10 torr) at 40∘C for (b) 36 h and (c) 48 h

(a) (b) (c)

(d) (e)


toluene solution over mica substrate at a spinning velocity of 8000 rpm (a) directly after spin coating (25∘C) and after annealing in vacuum(10 torr) at 90∘C for (b) 20 h (c) 40 h (d) 60 h and (e) 90 h

nanostructures It is also clear that from toluene solutionthe direct spin-coated films show micelle-like features andthat only after prolonged solvent annealing treatment theequilibrium nanostructures are formed

To confirm the lamellar nanoordering polymer filmwas detached from the mica substrate with hot water andthe thin film was studied using scanning transmission elec-tron microscopy (STEM)


(a) (b)

(c) (d)


toluene solution over mica substrate at a spinning velocity of 5000 rpm (a) directly after spin coating (25∘C) and after annealing in a toluenevapor chamber (760 torr 25∘C) for (b) 24 h (c) 36 h and (d) 80 h

(a) (b)

Figure 8 Images of PSt60-b-PDEAEM40 thin films prepared using a 1ww toluene solution over mica substrate at a spinning velocity of

5000 rpm and annealed for 80 h with toluene vapor at 25∘C (a) AFM topographic image obtained using the intermittent contact mode and(b) STEM image (119885-contrast) obtained from detached film

Figure 8 compares STEM images with AFM images forthe thin films prepared confirming the lamellae nanopatternsThe lamellae were measured from AFM and STEM imagesgiving the following results (see statistics in Supplemen-tary Material) In the case of AFM the average diameter of

a (light yellow) lamella is 515plusmn37 nmwhile the interlamellardistance is 736 plusmn 68 nm in the case of STEM image85 plusmn 095 nm is an average diameter of the pale graylamellae (PDEAEM phase) and 55 plusmn 077 nm for the darkgrey lamellae (PS-phase) and the interlamellar distance is


(a) (b) (c)


toluene solution over mica substrate at a spinning velocity of 2000 rpm (a) directly after spin coating (25∘C) and after thermal annealing invacuum (10 torr 170∘C) for (b) 120 h and (c) 138 h

1346 plusmn 127 nm Given the molecular weight of theblock copolymer (76280 gmol) the content and molecu-lar weights of both comonomers we can calculate that thenumber of repetitive units is as the following PS

(119899=239)-

b-PDEAEM(119898=278)

If the block copolymer would be anextended chain its maximal size would be 517 times thecontribution of a monomer unit based on tetrahedral CndashCbond (0254 nm [51]) namely 1313 nm However polymerchains are coiled even if dispersed in a good solvent Forexample for PS in tetrahydrofuran (THF) the relationshipbetween molecular weight and radius of gyration (119877

119892) is

described by the following equation (3) [52]

119877119892(A) = (02092)119872056

119908 (3)

If we consider the whole block copolymer constituted ofstyrene units (517 units) its molecular weight would be closeto 54000 gmol which would yield a 119877

119892of 93 nm only The

end to end distance (extension ℎ) of a coiled polymer chainin a good solvent can be estimated by the following simpleequation [53]

ℎ2= 704119877

2

119892 (4)

In our case ℎwould be 247 nmTherefore domains between25 nm and 130 nm are to be expected in self-assembled filmsof the studied PS

60-b-PDEAEM40 The lamellae observedby AFM are in between the calculated sizes while the STEMimage shows smaller domains possibly by shrinkage as a sideeffect of film detaching and drying procedures

33 Nonequilibrium Ordering of PS-b-PDEAEM Thin FilmThe fact that the PSt

60-b-PDEAEM40 block copolymerformed gyroid-like patterns under certain conditions asa nonequilibrium nanostructure opened the possibility tostudywhich other nanostructures are possible to obtain usingthis block copolymer in a reproducible way

In the following text case examples are presented whichshow the richness of nanostructures that can be producedusing this block copolymer

Figure 9 shows what happens if a not very thin filmof the title block copolymer is prepared and annealed at arelatively high temperature of 170∘C (where both blocks arefreely mobile) The polymer film is detached from the micasubstrate to form ldquonanoflakesrdquo of an average size of 1935 plusmn734 nm (Figure 9(c))

Another case consisted in UV irradiation treatmentof PSt

60-b-PDEAEM40 thin films prepared at 5000 rpmFigure 10 shows AFM images of the thin film directly afterspin coating compared to the film after irradiation with UVlight (120582 = 254 nm) for different periods of time Results showthat partial degradation occurred presumably partial depoly-merization of the PDEAEM phase leading to a rough surfaceRMS values increased from 109 nm (Figure 10(a)) directlyafter spin coating to 353 nm after irradiation for 15min(Figure 10(b)) and to 407 nm after irradiation for 30min(Figure 10(c)) Degradation of polymethacrylate domains byUV irradiation is well known and served as a method togenerate nanotemplates [42 54] This study demonstratesthat nanopatterns can be generated fast (spin coating + 15minUV irradiation) using PS-b-PDEAEM as template howeverno regularly ordered nanostructure can be achieved that fast

It has been reported that the ordered nanostructuresformed by block copolymers can be altered by mixing themwith homopolymers enriching one of the phases [55] orby mixing them with nanoparticles that may show specificinteractions with one of the two blocks [56] In this studywe used a linear PDEAEM (119872

119899= 18000 gmol) that already

contains gold nanoparticles (AuNPs) of an average size of75 nm to study nanostructure modification of PSt

60-b-PDEAEM

40Figure 11 shows results on thin films prepared using

10w of the AuNPs containing PDEAEM and 90w of thetitle block copolymer Images taken at 25∘C directly afterspin coating showed that there is no significant difference tothe previously studied thin films with block copolymer onlyHowever thermal annealing at 90∘C showed a substantialdifference as compared with thin films prepared of blockcopolymers only While the title block copolymer forms


20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)

Figure 10 AFM topographic images obtained using the intermittent contact mode of PSt60-b-PDEAEM40 thin films prepared from a

1ww toluene solution over mica substrate at a spinning velocity of 5000 rpm (a) directly after spin coating (RMS = 109 nm) and after UVirradiation (120582 = 254 nm) for different times (b) 15min (RMS = 353 nm) and (c) 30min (RMS = 407 nm)

(a) (b) (c)

Figure 11 AFM topographic images obtained using the intermittent contact mode of PSt60-b-PDEAEM40PDEAEM-AuNP (9 1) thin

films prepared from a 1ww toluene solution over mica substrate at a spinning velocity of 8000 rpm (a) directly after spin coating (25∘C)and after annealing in vacuum (10 torr) at 90∘C for (b) 24 h and (c) 48 h

a bicontinuous (gyroid like) phase themixture with PDEAEM-AuNP forms micelle-like nanostructures with voids in themiddle A similar nanostructure is reported already withthe name of toroids [57 58] After 48 h annealing timethe micellar nanostructures are kept From the images inFigure 11 there is no clear evidence where PDEAEM-AuNPsare located What we can expect is that AuNPs are located

in vicinity of PDEAEM units since tertiary amine groupsinteract strongly with AuNPs

Electron microscope images obtained by STEM modeshow the uniform size and homogeneous distribution ofAuNPs Figures 12(a) and 12(b) show a comparison betweenAFM image and STEM In both images a similarmorphologyafter the sample was detached from the mica substrate can


(a) (b) (c)

Figure 12 Images of PSt60-b-PDEAEM40PDEAEM-AuNP (9 1) thin films prepared using a 1ww toluene solution over mica substrate

at a spinning velocity of 8000 rpm after annealing in vacuum at 90∘C for 48 h (a) AFM topographic image obtained using the intermittentcontact mode (b) STEM low magnification image obtained from detached film and (c) higher magnification image of a cluster of AuNPsfrom image shown in (b)

(a) (b) (c)


films prepared from a 1ww toluene solution over mica substrate at a spinning velocity of 8000 rpm after different treatment methods(a) after annealing in vacuum (10 torr) at 90∘C for 48 h (b) after annealing in a THF vapor chamber (760 torr 25∘C) for 24 h and (c) after UVirradiation (120582 = 254 nm) by 20min

be seen The tiny dark spots represent the AuNPs whichare dispersed homogeneously in arrays These images showthat PDEAEM-AuNPs are located in the middle part of themicelle-like toroidal nanostructres formed (Figure 12(b))Therefore we postulate that PS domains form the outer layerof the micelles and PDEAEM phase forms the internal partresembling the core-shell morphology

From the images the diameter of these spherical nan-odomains was measured and an average of 261plusmn145 nmwascalculated as diameter of the micelles formed by a core of995 plusmn 319 nm and a shell of variable thickness Figure 12(c)shows bright field image at higher magnification evidencingthat these gold NPs are crystalline and all of them showd-spaces which belong to metallic gold The morphologyobtained by using PDEAEM-AuNP is interesting since ittends to form micelles with voids in the middle that can beused to position AuNPs in a controlled way over a surface

Given these results we decide to test if this morphol-ogy was achievable by other treatment methods This wasimportant since in the case of polystyrene-block-poly(4-vinylpyridine) it was reported that the formation of toroidswas only achievable at specific strong acidic conditions [57] oronly in a combination of a specific surface (gold or substratewith nitrided layer) and annealing with high polarity solventslike ethanol and methanol [58] Figure 13 shows that theformation of toroidal morphology is robust since it can beobtained by using at least three different methods thermaltreatment solvent annealing and also irradiation with UVlight In the latter case the size of the toroids is similarto that obtained by thermal annealing diameter of 268 plusmn36 nm with 875 plusmn 17 nm core These results show thatthe title block copolymer can be combined with PDEAEMattached to nanoparticles to create an ordered surface wherenanoparticles may be deposited in an ordered manner


4 Conclusions

A series of poly(styrene)-b-poly(NN 1015840-diethylaminoethylmethacrylate) block copolymers can be prepared controllingsize and composition by using RAFT free-radical polymer-ization starting with a PS block polydispersities were low(lt12)

Thin films of PS60-b-PDEAEM40 block copolymer

deposited overmica substrates form a lamellar nanostructureat equilibriumThis was achievable only after solvent anneal-ing (toluene) for extended periods of time (80 h)


deposited over mica substrates form several nonequilibriumnanostructures that are reproducible a knitted bicontinuousnanostructure by thermal annealing in vacuum at 90∘C aporous nanotemplate direct after spin coating and UV irra-diation for short time (15min) and toroidal self-assemblednanostructures with PS shell and PDEAEM core whenthe title block copolymer is mixed with a linear PDEAEMattached to gold nanoparticles

PS60-b-PDEAEM40 block copolymer can be combined

with PDEAEM attached to gold nanoparticles to create anordered surface where nanoparticles may be deposited in anordered way This is achievable fast and easy by using forexample UV irradiation This approach may be extended toother types of nanoparticles

Additional AFM images can be found in the Supplemen-tary Material file described before

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This investigation was financed by a grant from the NationalCouncil of Science and Technology of Mexico (CONACYTno SEP2007-60792) The authors acknowledge the NationalNanoscience and Nanotechnology Network of Mexico forsupporting PedroNavarro-Vega for a research stay at CIMAVThey thank A Ochoa and I A Rivero from IT Tijuana forperforming NMR analysis They also thank C Ornelas WAntunez and L De la Torre for their help at CIMAV

References

[1] J N L Albert and T H Epps III ldquoSelf-assembly of blockcopolymer thin filmsrdquoMaterials Today vol 13 no 6 pp 24ndash332010

[2] D H Lee H Cho S Yoo and S Park ldquoOrdering evolutionof block copolymer thin films upon solvent-annealing processrdquoJournal of Colloid and Interface Science vol 383 no 1 pp 118ndash123 2012

[3] M W Matsen and F S Bates ldquoConformationally asymmetricblock copolymersrdquo Journal of Polymer Science Part B PolymerPhysics vol 35 no 6 pp 945ndash952 1997

[4] U Jeong H-C Kim R L Rodriguez et al ldquoAsymmetric blockcopolymers with homopolymers routes tomultiple length scalenanostructuresrdquoAdvancedMaterials vol 14 no 4 pp 274ndash2762002

[5] J-Y Wang W Chen J D Sievert and T P Russell ldquoLamellaeorientation in block copolymer films with ionic complexesrdquoLangmuir vol 24 no 7 pp 3545ndash3550 2008

[6] T G Fitzgerald R A Farrell N Petkov et al ldquoStudy on thecombined effects of solvent evaporation and polymer flow uponblock copolymer self-assembly and alignment on topographicpatternsrdquo Langmuir vol 25 no 23 pp 13551ndash13560 2009

[7] Y Li H Huang T He and Y Gong ldquoSolvent vapor inducedmorphology transition in thin film of cylinder forming diblockcopolymerrdquo Applied Surface Science vol 257 no 18 pp 8093ndash8101 2011

[8] RGuoHHuang BDu andTHe ldquoSolvent-inducedmorphol-ogy of the binary mixture of diblock copolymer in thin film theblock length and composition dependence of morphologyrdquoTheJournal of Physical Chemistry B vol 113 no 9 pp 2712ndash27242009

[9] S W Hong and T P Russell ldquoBlock copolymer thin filmsrdquo inPolymer Science A Comprehensive Reference K MatyjaszewskiandMMoller Eds vol 7 pp 45ndash69 Elsevier BV AmsterdamThe Netherlands 2012

[10] J Bang B J Kim G E Stein et al ldquoEffect of humidity on theordering of PEO-based copolymer thin filmsrdquoMacromoleculesvol 40 no 19 pp 7019ndash7025 2007

[11] M Yoo S Kim S G Jang et al ldquoControlling the orientation ofblock copolymer thin films using thermally-stable gold nano-particleswith tuned surface chemistryrdquoMacromolecules vol 44no 23 pp 9356ndash9365 2011

[12] H-C Kim S-M Park W D Hinsberg and I R DivisionldquoBlock copolymer based nanostructures materials processesand applications to electronicsrdquo Chemical Reviews vol 110 no1 pp 146ndash177 2010

[13] H Wang A B Djurisic M H Xie W K Chan and O KutsayldquoPerpendicular domains in poly(styrene-b-methyl methacry-late) block copolymer films on preferential surfacesrdquoThin SolidFilms vol 488 no 1-2 pp 329ndash336 2005

[14] E Buck and J Fuhrmann ldquoSurface-induced microphase sepa-ration in spin-cast ultrathin diblock copolymer films on siliconsubstrate before and after annealingrdquo Macromolecules vol 34no 7 pp 2172ndash2178 2001

[15] D A Olson L Chen and M A Hillmyer ldquoTemplating nano-porous polymers with ordered block copolymersrdquo Chemistry ofMaterials vol 20 no 3 pp 869ndash890 2008

[16] M Radjabian J Koll K BuhrUAHandge andVAbetz ldquoHol-low fiber spinning of block copolymers influence of spinningconditions on morphological propertiesrdquo Polymer vol 54 no7 pp 1803ndash1812 2013

[17] S Park J-Y Wang B Kim J Xu and T P Russell ldquoA simpleroute to highly oriented and ordered nanoporous block copoly-mer templatesrdquo ACS Nano vol 2 no 4 pp 766ndash772 2008

[18] C Wang S Yang J Xu and M Zhu ldquoMorphology transfor-mation of polystyrene-block-poly(ethylene oxide) vesicle onsurfacerdquo Polymer vol 54 no 14 pp 3709ndash3715 2013

[19] WVanZoelen TAsumaa J RuokolainenO Ikkala andGTenBrinke ldquoPhase behavior of solvent vapor annealed thin films ofPS-b-P4VP(PDP) supramoleculesrdquoMacromolecules vol 41 no9 pp 3199ndash3208 2008


[20] I Zalakain N Politakos R Fernandez et al ldquoMorphologyresponse by solvent and vapour annealing using polystyrenepoly(methyl methacrylate) brushesrdquo Thin Solid Films vol 539pp 201ndash206 2013

[21] S E Mastroianni and T H Epps ldquoInterfacial manipulationscontrolling nanoscale assembly in bulk thin film and solutionblock copolymer systemsrdquo Langmuir vol 29 no 12 pp 3864ndash3878 2013

[22] A Nunns J Gwyther and IManners ldquoInorganic block copoly-mer lithographyrdquo Polymer vol 54 no 4 pp 1269ndash1284 2013

[23] C Sinturel M Vayer M Morris and M A Hillmyer ldquoSolventvapor annealing of block polymer thin filmsrdquo Macromoleculesvol 46 no 14 pp 5399ndash5415 2013

[24] C Park J Yoon and E L Thomas ldquoEnabling nanotechnologywith self assembled block copolymer patternsrdquo Polymer vol 44no 22 pp 6725ndash6760 2003

[25] W-N He and J-T Xu ldquoCrystallization assisted self-assembly ofsemicrystalline block copolymersrdquo Progress in Polymer Sciencevol 37 no 10 pp 1350ndash1400 2012

[26] S OrsquoDriscoll G Demirel R A Farrell et al ldquoThe morphologyand structure of PS-b-P4VP block copolymer films by sol-vent annealing effect of the solvent parameterrdquo Polymers forAdvanced Technologies vol 22 no 6 pp 915ndash923 2011

[27] S P Paradiso K T Delaney C J Garcıa-Cervera H DCeniceros andGH Fredrickson ldquoBlock copolymer self assem-bly during rapid solvent evaporation Insights into cylindergrowth and stabilityrdquo ACSMacro Letters vol 3 no 1 pp 16ndash202014

[28] P Mokarian-Tabari T W Collins J D Holmes and M AMorris ldquoCyclical ldquoflippingrdquo of morphology in block copolymerthin filmsrdquo ACS Nano vol 5 no 6 pp 4617ndash4623 2011

[29] S Y Choi C Lee J W Lee C Park and S H KimldquoDewetting-induced hierarchical patterns in block copolymerfilmsrdquoMacromolecules vol 45 no 3 pp 1492ndash1498 2012

[30] Y S Jung and C A Ross ldquoOrientation-controlled self-assem-bled nanolithography using a polystyrene-polydimethylsilox-ane block copolymerrdquoNano Letters vol 7 no 7 pp 2046ndash20502007

[31] L Xue and Y Han ldquoPattern formation by dewetting of polymerthin filmrdquo Progress in Polymer Science vol 36 no 2 pp 269ndash293 2011

[32] B Bharatiya J-M Schumers E Poggi and J-F GohyldquoSupramolecular assemblies from poly(styrene)-block-poly(4-vinylpyridine) diblock copolymers mixed with 6-Hydroxy-2-naphthoic acidrdquo Polymers vol 5 no 2 pp 679ndash695 2013

[33] I Tokarev R Krenek Y Burkov et al ldquoMicrophase separationin thin films of poly(styrene-block-4-vinylpyridine) copolymer-2-(4rsquo-hydroxybenzeneazo)benzoic acid assemblyrdquo Macromole-cules vol 38 no 2 pp 507ndash516 2005

[34] A Sidorenko I Tokarev S Minko and M Stamm ldquoOrderedreactive nanomembranesnanotemplates from thin films ofblock copolymer supramolecular assemblyrdquo Journal of theAmerican Chemical Society vol 125 no 40 pp 12211ndash122162003

[35] M Bohme B Kuila H Schlorb B Nandan and M StammldquoThin films of block copolymer supramolecular assembliesmicrophase separation and nanofabricationrdquo Physica StatusSolidi (B) vol 247 no 10 pp 2458ndash2469 2010

[36] B Nandan M K Vyas M Bohme and M Stamm ldquoCompo-sition-dependent morphological transitions and pathways inswitching of fine structure in thin films of block copolymer

supramolecular assembliesrdquo Macromolecules vol 43 no 5 pp2463ndash2473 2010

[37] A Bousquet E Ibarboure E Papon C Labrugere and JRodrıguez-Hernandez ldquoStructuredmultistimuli-responsive func-tional polymer surfaces obtained by interfacial diffusion ofamphiphilic block copolymersrdquo Journal of Polymer Science PartA Polymer Chemistry vol 48 no 9 pp 1952ndash1961 2010

[38] C S Patrickios W R Hertler N L Abbott and T A HattonldquoDiblock ABC triblock and random methacrylic polyampho-lytes synthesis by group transfer polymerization and solutionbehaviorrdquoMacromolecules vol 27 no 4 pp 930ndash937 1994

[39] A S Lee A P Gast V Butun and S P Armes ldquoCharacterizingthe structure of pH dependent polyelectrolyte block copolymermicellesrdquoMacromolecules vol 32 no 13 pp 4302ndash4310 1999

[40] S H Thang B Y K Chong R T A Mayadunne G Moadand E Rizzardo ldquoA novel synthesis of functional dithioestersdithiocarbamates xanthates and trithiocarbonatesrdquo Tetrahe-dron Letters vol 40 no 12 pp 2435ndash2438 1999

[41] J Brandrup and E H Immergut Polymer Handbook Wiley-Interscience New York NY USA 3rd edition 1989

[42] A J Hong C-C Liu Y Wang et al ldquoMetal nanodot memoryby self-assembled block copolymer lift-offrdquoNano Letters vol 10no 1 pp 224ndash229 2010

[43] T Kim S Wooh J G Son and K Char ldquoOrientation controlof block copolymer thin films placed on ordered nanoparticlemonolayersrdquo Macromolecules vol 46 no 20 pp 8144ndash81512013

[44] N A Cortez-Lemus A Licea-Claverie F Paraguay-Delgadoand G Alonso-Nunez ldquoControlling the size of gold nanopar-ticles by using poly( NN-diethylaminoethyl methacrylate)rdquoJournal of Nanoparticle Research Under review

[45] I Horcas R Fernandez J M Gomez-Rodrıguez J Colchero JGomez-Herrero and A M Baro ldquoWSXM a software for scan-ning probe microscopy and a tool for nanotechnologyrdquo Reviewof Scientific Instruments vol 78 no 1 Article ID 013705 2007

[46] J Chiefari R T A Mayadunne C L Moad et al ldquoThiocar-bonylthio compounds (S=C(Z)S-R) in free radical polymer-ization with reversible addition-fragmentation chain transfer(RAFT polymerization) Effect of the activating Group ZrdquoMac-romolecules vol 36 no 7 pp 2273ndash2283 2003

[47] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer vol 46 no 19 pp 8458ndash8468 2005

[48] J Brandrup E H Immergut and E A Grulke Polymer Hand-book JohnWileyamp Sons NewYork NYUSA 4th edition 1999

[49] J Brandrup E H Immergut and E A Grulke Polymer Hand-book pp VII688ndashVII707 John Wiley amp Sons New York NYUSA 4th edition 1999

[50] D W van Krevelen Properties of Polymers Elsevier ScienceAmsterdam The Netherlands 3rd edition 1997

[51] D Kafouris andC S Patrickios ldquoSynthesis and characterizationof shell-cross-linked polymer networks and large-core starpolymers effect of the volume of the cross-linking mixturerdquoEuropean Polymer Journal vol 45 no 1 pp 10ndash18 2009

[52] K Venkataswamy A M Jamieson and R G Petschek ldquoStaticand dynamic properties of polystyrene in good solvents ethyl-benzene and tetrahydrofuranrdquoMacromolecules vol 19 no 1 pp124ndash133 1986

[53] K F Arndt and G Muller Polymercharakterisierung CarlHanser Munchen Germany 1996


[54] M M Alam Y-R Lee J-Y Kim and W-G Jung ldquoFabricationof nanopatterns using block copolymer and controlling surfacemorphologyrdquo Journal of Colloid and Interface Science vol 348no 1 pp 206ndash210 2010

[55] M Rosales-Guzman R Alexander-Katz P Castillo-OcampoA Vega-Rıos and A Licea-Claverıe ldquoStrain state of poly(N-isopropylacrylamide) in polystyrene-b-poly(N- isopropylacry-lamide) block copolymers and binary blends with polystyrenerdquoJournal of Polymer Science Part B Polymer Physics vol 51 no18 pp 1368ndash1376 2013

[56] G-K Xu X-Q Feng and S-W Yu ldquoControllable nanos-tructural transitions in grafted nanoparticle-block copolymercompositesrdquo Nano Research vol 3 no 5 pp 356ndash362 2010

[57] MAizawa and JM Buriak ldquoBlock copolymer templated chem-istry for the formation of metallic nanoparticle arrays on sem-iconductor surfacesrdquo Chemistry of Materials vol 19 no 21 pp5090ndash5101 2007

[58] S M OrsquoDriscoll C T OrsquoMahony R A Farrell T G FitzgeraldJ D Holmes and M A Morris ldquoToroid formation in poly-styrene-block-poly(4-vinyl pyridine) diblock copolymers com-bined substrate and solvent controlrdquo Chemical Physics Lettersvol 476 no 1ndash3 pp 65ndash68 2009

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


unclear since the relevant experimental parameters govern-ing the resultant block copolymer nanoscale morphologies(nature of the solvent the relative solvent vapor pressurethe annealing time etc) are usually complex and difficult tocontrol [24] Among these factors the nature of the solventand the relative solvent vapor pressure are crucial [25] Thenature of the solvent influences the degree of the swelling ofeach block and accordingly has severe effects on the resultingblock copolymer morphologies [7] It has been shown thatthe same block copolymer thin films annealed under differentselective solvents and nonselective solvents result in differentmorphologies and orientations [7 26] On the other handonce a solvent is selected the solvent vapor pressure is thekey factor to control the resultant morphologies [27 28]It has been reported that regular phase separated films canonly be achieved when the copolymer Hildebrand solubilityparameter is very similar to the value of the solvent usedfor annealing [26] A lot of practical know-how has beenreported in order to control the solvent vapor pressuressuch as the use of the flow of N

2 to vary the amount of

solvent in reservoir to close the lid of dish more or lesstightly and to change the ratio between the surface area ofthe solvent and the empty volume of the annealing chamber[17 23 29 30] In thin films the destabilization of films isanother important technical issue that should be consideredfor pattern formation [31] Under certain conditions thelocal fluctuation of film thickness is developed and the filmis retracted from the substrate to create fragmentation ofcontinuous films into isolated droplets

Due to the intrinsic nature of polymer chains theobtained nanostructures (in solution bulk or thin films)maybe kinetically trapped nonequilibrium systems since the con-stituent polymer chainsmay not be able to relax towards theirequilibrium conformation [32]

When polymers carrying functional groups in one of theblocks are investigated towards nanoscale ordering in thinfilms a new factor can be included to increase the rich-ness of self-assembled nanostructures that are achievablesmall molecules capable of forming complexes with thefunctional groups of the one block A well-studied exampleof this approach is the use of poly(styrene)-b-poly(4-vin-ylpyridine) (PS-b-P4VP) in combinationwith 2-(41015840-hydroxy-benzeneazo)benzoic acid (HABA) by Tokarev et al [33]Sidorenko et al [34] Bohme et al [35] and Nandan et al[36]

In our research group we are interested in the studyof equilibrium and nonequilibrium self-assembled nano-structures formed by poly(styrene)-b-poly(NN1015840-diethylam-inoethyl methacrylate) (PS-b-PDEAEM) PDEAEM is a pol-ymer carrying tertiary amine groups capable of acting asproton acceptors and lone pair donors (Bronsted and Lewisbases) and also capable of coordinating with metals havingd and f orbitals with deficit on electrons To the best of ourknowledge the only report on the study of self-assembledthin films of this BCP was recently published [37] PS-b-PDEAEM was studied together with the parent BCPpoly(styrene)-b-poly(NN1015840-dimethylaminoethyl methacryl-ate) (PS-b-PDMAEM) in blends with polystyrene findingthat they formed micellar and donut-like structures over

thin films independent of the parameters changed The maindifference between PDEAEM and PDMAEM blocks is theirhydrophobicity and acidity constant (pKa) while PDMAEMis soluble in water at neutral pH and has a pKa of 81 [38]PDEAEM is only soluble in water at pH values close to 6 andlower while it has a pKa of 69 [39]

In the current report not only the equilibrium and non-equilibrium self-assembly process of PS-b-PDEAEM wasinvestigated in detail but also the interactions of gold nano-particles (AuNPs) and their role in self-assembly process ofthe title BCP was assessed

2 Experimental Section

21 Materials All reagents were purchased from Sigma-Aldrich (Mexico) and were used as received with the excep-tion of those described below Styrene and NN1015840-diethylami-noethylmethacrylate (DEAEM)were distilled under reducedpressure to the highest purity possible 441015840-Azobis(4-cyanovaleric acid) (ACVA Fluka) was recrystallized frommethanol 4-Cyano-4-(dodecylsulfanylthiocarbonyl)sulfanylpentanoic acid (CTA) was synthesized following a procedurereported in the literature [40] and was obtained with 72yield

22 Synthesis of Macro-CTAs by RAFT Polymerization Allpolymerizations were performed in ampoules In all cases4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoicacid and 441015840-Azobis(4-cyanopentanoic acid) were used asCTA and as initiator (ACVA) respectively The appropriateamounts of monomers CTA and ACVA were dissolved inp-dioxane (30mL) under stirring at room temperature Solu-tions were degassed by three freeze-pump-thaw cycles Afterdegassing the ampoules were flame-sealed under vacuumand heated in an oil bath at 90∘C The polymerizationswere terminated by rapid cooling and freezing The hom-opolymers obtained also named macro-CTAs since theyinclude the CTA moiety were purified by repeated pre-cipitations using methanol for polystyrene and petroleumether for poly(DEAEM) Products were dried in vacuumfor 48 h An example of the synthesis of polystyrene isdescribed in detail styrene (1202 g 0115mol) 441015840-Azobis(4-cyanopentanoic acid) (ACVA) (00485 g 01203mmol) and4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoicacid (CTA) (00037 g 00132mmol) were dissolved in p-dioxane (30mL) and poured in a glass ampoule (50mL) con-taining a magnetic stir bar Oxygen was removed using 2freeze-thaw evacuation cycles and the ampoule was sealedwith flame under vacuumThe ampoule containing polymer-ization solution was submerged in an oil bath with mag-netic stirring at 90∘C The polymerization was stopped byrapid cooling at a given time The polymerization yield wasobtained gravimetrically by adding a fivefold excess of coldmethanol The polymer product was purified by dissolutionin theminimumamount of acetone followed by adding a five-fold excess of coldmethanol and filteringThis procedure wasrepeated three times to remove residual monomer followedby drying under vacuum to constant weight



119899= 40940 gmol ACVA










2) 26 (6H


2) 11 (6H m (CH

3)2) and 08

(3H m CH3)







(119889119899

119889119862

)

COP= 119883PS (

119889119899

119889119862

)

PST+ 119883PDEAEM (

119889119899

119889119862

)

PDEAEM (1)















4)









119899119872119908) In order to










gmol PDIa [119872]0 [PS] [119868]0119872119899


1198911015840

PSd



10 20 30 40

Time (min)

RI si

gnal

nor

mal

ized

1

0




ab c d ef g h i jk

Acetone


Acetone1207

200

CDCl

3

i gn

nb

h k

OOed

N ffjj

aac c

b

78 6 5 4 3 2 1 0

(ppm)










120594P-S =119881SR119879(120575S minus 120575P)

2

+ 034 (2)




v he

at fl

ow (W

g)

DSC

9192∘C

9964∘C(I)

10400∘C

0 50 100 150


instruments

minus006

minus004

minus008

minus010

minus741∘C

minus496∘C(I)

minus353∘C

(a)

2464

6854

00

05

10

15

20

0

20

40

60

80

100

120

Wei

ght (

)

0 200 400 600 800

TGA

Temperature (∘C)

Der

iv w

eigh

t (

∘C)


Y-1 Y-2

minus05

(b)


(a) (b) (c)











(a) (b) (c)



(a) (b) (c)

(d) (e)






(a) (b)

(c) (d)



(a) (b)






(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





119899= 40940 gmol ACVA










2) 26 (6H


2) 11 (6H m (CH

3)2) and 08

(3H m CH3)







(119889119899

119889119862

)

COP= 119883PS (

119889119899

119889119862

)

PST+ 119883PDEAEM (

119889119899

119889119862

)

PDEAEM (1)















4)









119899119872119908) In order to










gmol PDIa [119872]0 [PS] [119868]0119872119899


1198911015840

PSd



10 20 30 40

Time (min)

RI si

gnal

nor

mal

ized

1

0




ab c d ef g h i jk

Acetone


Acetone1207

200

CDCl

3

i gn

nb

h k

OOed

N ffjj

aac c

b

78 6 5 4 3 2 1 0

(ppm)










120594P-S =119881SR119879(120575S minus 120575P)

2

+ 034 (2)




v he

at fl

ow (W

g)

DSC

9192∘C

9964∘C(I)

10400∘C

0 50 100 150


instruments

minus006

minus004

minus008

minus010

minus741∘C

minus496∘C(I)

minus353∘C

(a)

2464

6854

00

05

10

15

20

0

20

40

60

80

100

120

Wei

ght (

)

0 200 400 600 800

TGA

Temperature (∘C)

Der

iv w

eigh

t (

∘C)


Y-1 Y-2

minus05

(b)


(a) (b) (c)











(a) (b) (c)



(a) (b) (c)

(d) (e)






(a) (b)

(c) (d)



(a) (b)






(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









4)









119899119872119908) In order to










gmol PDIa [119872]0 [PS] [119868]0119872119899


1198911015840

PSd



10 20 30 40

Time (min)

RI si

gnal

nor

mal

ized

1

0




ab c d ef g h i jk

Acetone


Acetone1207

200

CDCl

3

i gn

nb

h k

OOed

N ffjj

aac c

b

78 6 5 4 3 2 1 0

(ppm)










120594P-S =119881SR119879(120575S minus 120575P)

2

+ 034 (2)




v he

at fl

ow (W

g)

DSC

9192∘C

9964∘C(I)

10400∘C

0 50 100 150


instruments

minus006

minus004

minus008

minus010

minus741∘C

minus496∘C(I)

minus353∘C

(a)

2464

6854

00

05

10

15

20

0

20

40

60

80

100

120

Wei

ght (

)

0 200 400 600 800

TGA

Temperature (∘C)

Der

iv w

eigh

t (

∘C)


Y-1 Y-2

minus05

(b)


(a) (b) (c)











(a) (b) (c)



(a) (b) (c)

(d) (e)






(a) (b)

(c) (d)



(a) (b)






(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






gmol PDIa [119872]0 [PS] [119868]0119872119899


1198911015840

PSd



10 20 30 40

Time (min)

RI si

gnal

nor

mal

ized

1

0




ab c d ef g h i jk

Acetone


Acetone1207

200

CDCl

3

i gn

nb

h k

OOed

N ffjj

aac c

b

78 6 5 4 3 2 1 0

(ppm)










120594P-S =119881SR119879(120575S minus 120575P)

2

+ 034 (2)




v he

at fl

ow (W

g)

DSC

9192∘C

9964∘C(I)

10400∘C

0 50 100 150


instruments

minus006

minus004

minus008

minus010

minus741∘C

minus496∘C(I)

minus353∘C

(a)

2464

6854

00

05

10

15

20

0

20

40

60

80

100

120

Wei

ght (

)

0 200 400 600 800

TGA

Temperature (∘C)

Der

iv w

eigh

t (

∘C)


Y-1 Y-2

minus05

(b)


(a) (b) (c)











(a) (b) (c)



(a) (b) (c)

(d) (e)






(a) (b)

(c) (d)



(a) (b)






(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




v he

at fl

ow (W

g)

DSC

9192∘C

9964∘C(I)

10400∘C

0 50 100 150


instruments

minus006

minus004

minus008

minus010

minus741∘C

minus496∘C(I)

minus353∘C

(a)

2464

6854

00

05

10

15

20

0

20

40

60

80

100

120

Wei

ght (

)

0 200 400 600 800

TGA

Temperature (∘C)

Der

iv w

eigh

t (

∘C)


Y-1 Y-2

minus05

(b)


(a) (b) (c)











(a) (b) (c)



(a) (b) (c)

(d) (e)






(a) (b)

(c) (d)



(a) (b)






(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b) (c)



(a) (b) (c)

(d) (e)






(a) (b)

(c) (d)



(a) (b)






(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)



(a) (b)






(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b) (c)




(119899=239)-

b-PDEAEM(119898=278)


119892) is


119877119892(A) = (02092)119872056

119908 (3)




ℎ2= 704119877

2

119892 (4)












60-b-PDEAEM




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

1050nm

(a)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2174nm

(b)

20

18

16

14

12

10

8

6

4

2

0

0 200 400 600 800 10001200

Z(n

m)

X (nm)

000nm

2606nm

(c)



(a) (b) (c)







(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b) (c)



(a) (b) (c)







4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




4 Conclusions











Acknowledgments


References





































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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