1 nanoparticles: definition and significance synthesis and characterization stabilization ordering...
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1
NANOPARTICLES:
•Definition and Significance
•Synthesis and Characterization
•Stabilization
•Ordering
•Optical Properties
•Magnetic Properties
•Catalysis
•Other Applications
Acknowledgements: M. D. Porter
2
Definitions*Nanoparticle- Particle with 1 dimension in the 10-100 nm size range.
Colloid- Particle with dimensions in the 1 nm – 1 mm (?) size range.
Quantum Dot- Particle with all 3 dimensions in the 1-10 nm size range.
Latex- Aqueous suspension of polymer particles.
Natural- Contains Protein Impurities; May Cause Allergies
Synthetic- Made via Emulsion Polymerization
SignificanceThe size of Nanoparticles leads to unique characteristics.
*These definitions are constructed from a compilation of literature, and represent the most commonly used verbiage over a span of years
3
Metallic Nanoparticle Synthesis
M++ Reductant Nanoparticle
M+
M+
M+
M+
M+
M++ ne-
M
M = Au, Pt, Ag, Pd, Co, Fe, etc.
Reductant = Citrate, Borohydride, Alcohols
Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.
4
Control FactorsAverage Size
Reductant Concentration
Stirring Rate
Temperature
Size Distribution
Rate of Reductant Addition
Stirring Rate
Fresh Filtered Solutions
Stabilization
Solution CompositionHayat, M. A. , Ed., Colloidal Gold: Principles, Methods, and Applications; Academic Press: San Diego, 1989; Vol 1.
5
Functionalized Reductions
M+
+ ReductantFunctionalizedNanoparticleSurfactant
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
Y
X
YX
YX
Y
Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.
6
Bimetallic Nanoparticle
Core-Shell
Mixed Alloy
M1 M1 M2
+ M2+ + Reductant
M1M1+ + Reductant
M1+ + M2
+ + Reductant
Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, 1179-1201.
7
Semiconductor Nanoparticles(Q-dots)
R
RNC
Se
SeCd
Se
SeCN
R
R
TOP/TOPO200ºC
PO CdSe OP
POO
P
Pickett et al. The Chemical Record 2001, 1, 467-479
8
Semiconductor Nanoparticles
Mix Intermicelle exchange
Cd 2+
S2-
Cd 2+
S2-
CdS
CdS
Thiol capping
Micelle disruption
CdSCdS
Functionalized particles can be isolated by centrifugation or by precipitation Shipway et al.
Chemphyschem 2000, 1, 18-52
CdCl2
Na2S
9
10
CharacterizationTechnique Information
TEM/SEM Size/Shape/Size Distribution
UV/vis absorbance Size/Size Distribution
AFM Size/Shape/Size Distribution
X-ray Composition
IR Functionality
11
Stabilization of Polymer Nanoparticles•Stable Dispersion- All particles exist as single entities; order or disorder
•Aggregation- General term for unstable states
•Flocculation- Disorder, with weak attraction
•Coagulation- Disorder, with strong attraction
Figure adapted from: Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp 1-49.
Low [electrolyte]
Strong repulsion
Order
Intermediate [electrolyte]
Repulsive contacts
Disorder High [electrolyte]
Stable
Aggregated
Coagulated
Flocculated
12
Forces
1. Electrostatic- Charged surfaces and stabilizers
2. Steric- Geometric effects/solvation effects
3. van der Waals- Attraction of hydrocarbon chains towards each other
X
XXXX
X
XXXX
X
X
XXXX
X
X XX X
X
X
XXXX
X
X
X
X
X
X
X
XXXX
X
X
X
X
X
X
Y
YYY
Y
Y
YY
Y
Y
X, Y = Cationic, Anionic, or Nonionic Functional Groups
Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp 1-49.
13
Ionic Groups
-
--
-
- ---
--
-
-Stabilizer
-
--
-
- ---
--
-
-
+
+
+
+
++
+
Neutralization of surface charge causes aggregation -
-
--
-
- ---
--
-
-
--
-
--
-- -
Tails bind via hydrophobic attraction- enhanced stability
OR
Hydrophobic attraction binds tails, leading to an excess of positive charge
Stabilization
-
--
-
- ---
--
-
-
++
+
+
+
+
+More Stabilizer
+
+
+
14
Nonionic Groups
-
-
-
-
- --
---
-
-
Hydrophobic interactions bind the tail group to the NP, while the polar head groups extend into solution
Polar head groups are hydrated, providing a steric barrier to prevent aggregation
15
Surface Charges
arsr e
r
a
Where:
IkT
Ne A
1000
8 2
2
Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, 1948.
r = Potential at distance r from NP surface
s = Potential at NP surface
a = radius of NP
r = distance from NP surface
e = elementary charge
NA = Avogadro’s number
= Permittivity of free space
k = Boltzmann’s constant
T = Temperature
I = Ionic Strength
-
--
-
- ---
--
-
-+
+
+
+
+
+
+
+
+
--
-+
++
+
+
+
+
16
Effect of Electrolyte Concentration on Potential Profiles
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 1 2 3 4 5 6 7 8 9 10
Distance
C1 > C2
C1
C2
Low C
High C
17
Interaction Energy
Vt = Vr + Va
Where
Vr = Potential energy of electrostatic interactions (may include contribution from steric interactions)
Va = Potential energy of van der Waals interactions
Vr Double layer term (DLVO theory) surface charge & environment (electrolyte & solvent); thickness and density of adsorbed layer and interaction with solvent
Va Material nature (dispersion frequency, static polarizability, density)- Hamaker constants*
•Derjaguin, B. V., Landau, L., Acta Physicochim. USSR, 1941, 14, 633
•Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, 1948.
•Hamaker, H. C., Physica, 1937, 4, 1058.
*An estimate of the Hamaker constant may be determined from AFM measurements: Argento, C.; French, R. H. Journal of Applied Physics 1996, 80, 6081-6090.
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19
Nanoparticle Films
20
Ligand Directed Assembly
Bifunctional ligand
nanoparticle
substrate+
+
Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.
21Natan, M. J.; et. al. Chem. Materials 2000, 12, 2869-2881
Tapping mode AFM (1m x 1m) of HSCH2CH2OH linked Au colloid multilayers: (A) monolayer; (B) 3 Au treatments; (C) 5 Au treatments; (D) 7 Au treatments; (E) 11 Au treatments.
• Monolayer formed by adsorption of Au particles on 3-mercaptopropyltrimethoxysilane derivatized SiO2 surface
• Multilayers constructed by immersion in a 5 mM solution of 2-mercaptoethanol for 10 min. followed by immersion in Au particle solution for 40 – 60 min.
22
Electrostatic Assembly
• Polycationic polymer
• Very stable in most solvents
• Control inter-layer spacing
• Conductive, semiconductive, or insulating
- --- -
--- --
+ ++
+- -- - --
Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.
23
Convective Self Assembly
• Definition: Particles are allowed to freely diffuse. As the solvent evaporates, particles crystallize in a hexagonally close-packed array.
• Optimize: Particle concentration Particle/substrate charge Evaporation
Top View
Colvin, V.L.; et al. J. Am. Chem. Soc. 1999, 121, 11630-11637.
24
Microcontact Printing
• PDMS stamp to “ink” a capture monolayer on a substrate followed by nanoparticle adsorption
• PDMS stamp to “ink” the nanoparticles directly onto the substrate
Side View
Top View
Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.
25
AFM of Microcontact Patterned Nanoparticle Array
Natan, M. J.; et al. Chem. Mater. 2000, 12, 2869-2881
AFM scan (10 m x 10 m) of microcontact printed Au surfaces. HOOC(CH2)15SH is initially stamped on substrate. The surface is then exposed to 1.0 mM 2-mercaptoethylamine followed by exposure to a 17 nM solution of 12 nm Au nanoparticles.
26
27
Optical Properties and Applications of Nanoparticles
Plasmon Absorbance
Surface-Enhanced Raman Spectroscopy (SERS)
Fluorescence Spectroscopy
28
Plasmon Absorbance - Background
• Surface Plasmon (SP): Coherent oscillation in e-density at the metal and dielectric interface when e-field (of incident light) forces loosely held conduction electrons to move with the field
• Plasmon Absorbance: absorption of EM radiation of SP at a particular energy
29
Plasmon Absorbance - Factors
• Surface functionality, temperature, and the solvent
• Particle concentration and particle size
S. Link et al. J. Phys. Chem. B 1999, 103, 4212-4217
30
GOLD QUANTUM DOTSVARIOUS DIAMETERS
31
Plasmon Absorbance - Applications• Coupled – Plasmon
Absorbances
Storhoff et al. J. Am. Chem. Soc., 120 (9), 1959 -1964, 1998.
1
2
32
Plasmon Absorbance – Applications (continued)
Storhoff et al. J. Am. Chem. Soc., 120 (9), 1959 -1964, 1998.
AB
S of
D
NA
33
Surface Enhanced Raman Spectroscopy
SERS • Enhanced e-magnetic field as a consequence of SP and
the appearance of new electronic states in the absorbate as a consequence of absorption
• Enhancement occurs when the exciting radiation is coincident with the plasmon absorbance of the nanoparticles
Creighton et al. J. Chem. Soc. Faraday Trans. 2 1979, 75, 790-798
• Aggregated nanoparticles have additional plasmon resonances associated with interparticle plasmon coupling
34
SERS - Factors• Particle size
Nie et al. J. Am. Chem. Soc. 1998, 120, 8009-8010
35
SERS - Applications
Au nanoparticle with Raman label and antibody
Antibody
Antigen (analyte)
Linker molecule
Raman signal to detector
Laser
Raman Reporter molecule
0.8 cm
Porter group
36
Application - Analysis of Prostate Specific Antigen (PSA)
1000 ng/mL
100 ng/mL
10 ng/mL
0 ng/mL
Antibody Anti-PSA (prostate specific antigen)
Antigen PSA
Raman label
DSNB
Integration time
60 seconds
PSA-Prostate cancer marker-Different forms-Analysis of composition change gives information of the malignancy
37
38
Binds w/o Mg2+
Binds & cuts w Mg2+
39
Fluorescence – Applications
Nie et al. Anal. Chem., 72 (9), 1979 -1986, 2000.
40
Dye addedto DNA
Nanoparticle fluor.Random binding via histones
41
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POTENTIAL APPLICATIONS
RAPID GENE MAPPING
FUND. STUDY OF PROTEIN – DNA INTERACTIONS
-HOW DOES PROTEIN FIND SPECIFIC BINDING SITEAMONG MANY NONSPECIFIC SITES?
-HOW DOES RNA POLYMERASE MOVE DURING TRANSCRIPTION?
ALL ON SINGLE-MOLECULE BASISINTEGRATE AVG. PROPS. OF ENSEMBLE OF MOLECULES
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46
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PARTIAL FILLING
TIC
RIC for nortriptylineAnalytes 10 ppm
1 = nortriptyline 2 = salbutamol 3 = diphenhydramine
50
?
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52
AC 2004, 362A
53
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MICROPARTICLES HOST CODING ELEMENTS -ORG. SOLVENT, POLYMER PARTICLES SWELL OPEN CODING ELEMENTS ENTER IN WATER, PARTICLES CLOSE, TRAPPED
-CODING ELEMENTS BOUND TO PARTICLE SURFACE ALSO CONTAIN CAPTURE REAGENTS
CODING ELEMENTS (COLORED)
-FLUORESCENT ORGANIC DYES (Δλ = 50 to 200 nm)
-FLOUR. SEMICON NANOCRYSTALS (Δλ = 10 to 20 nm)
-IR, RAMAN REPORTERS
55
Au
Ag
GaAs
GaP
Al stripeson Si
Photolith.& etching
56
Particles coated with antihuman IgG+ flourescein tagged human IgG
Particles coated with anti-rabbit IgG+ Texas red tagged rabbit IgG
IMMUNOASSAY
Was istlos?
57
Magnetic Nanoparticles
• Small size implies superparamagnetism
• Ferrofluids: a colloidal mixture of magnetic nanoparticles
• Generally made through a reduction reaction, however, other methods have been used– Hydrothermal Synthesis– Laser Ablation
58
Magnetic Cell Sorting
MP MP
Modify MP by attaching an effector
Roger, Pons, Massart, et al. Eur. Phys. J. AP 5, 321-325 (1999)
59
Bind to Specific Cells
MP
MP
MP
MPMP
+
Cell
MP
MP
MP
MPCell
MP
Cell Cell
60
Uses for magnetically labeled cells
A: Cell sorting B: Magnetic Fluid Hyperthermia
Jordan, A. et al. J Magn Mater, 201 (1999) 413-419
Roger, J.; et. al. Eur Phys. J. AP 5, 321-325 (1999)
61
Drug TargetingGene Transfection
Both are methods of delivery using magnetic fields.
Magnetic particles with the appropriate ligands attached are injected into the body and manipulated to the positions where they will be activated using magnetic fields.
At this point, the gene/drug will be taken up by the cell and act as it is supposed to (depending on the application)
Often used in conjunction with MFH (mag. fluid hyperthermia)
Scherer, F; et al. Gene Therapy, 9 p. 102-109 (2002)
62
Other Possible Uses for Magnetic Nanoparticles
• MRI Contrast Enhancementa
• GMR Detection Methodsb
• Magnetocaloric Refrigerationc
a: Ahrens, E. T; et al. Proc. Natl. Acad. Sci. USA: 95 p. 8443-8448 (1998)
b: Tondra, M; Porter, M; Lipert R; J. Vac. Sci. Tech. A: 18 p. 1125-1129 (2000)
c: McMichael, R. D.; et al. J. Magn. Magn. Mater. 111 p. 29-33 (1992)
63
Magnetic Fluid Hyperthermia (MFH)
• Also known as magnetocytolysis• Inject fluid containing MP’s into patient • Use constant magnetic field to maneuver
particles to desired location (tumor, for example)
• Expose area to oscillating magnetic field to cause extremely localized heating
• Prototype unit being built in Germany
Jordan, A. et al. J Magn Magn Mater, 201 (1999) 413-419
64
Animal Test Results
Jordan, A. et. al. J. Magn Magn Mater, 201 (1999) 413-419
65
Magnetic Recording MediaCan be manufactured through a 6 step process
Todorovic, M. Schultz, S. Wong, J. Scherer, A. App. Phys. Lett. 1999 (74) 2516-2518
Left: synthesis scheme.
Right: SEM image of substrate. a)before step (f). b)same array filled with nickel c) MFM (12m x 12 m) image of array.
66
Magnetic Recording MediaEach nickel “column” has dimensions on the order of 170 nmdiameter, 200 nm high and 2 m apart. This leads to a particledensity below that of today’s hard drives (by approximatelya factor of 10), however, it demonstrates that other methods for data storage are feasible.
This method can be used with current read/write heads
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Magnetic Recording Media
• Current methods of recording are proprietary (i.e. very little information about how they work is available)
• Theoretical density limit for data storage is on the order of 100 Gbits/in2
• Theoretical density limit for reliable data storage is only on the order of 40 Gbits/in2
68
Nanomotors/Generators using Ferrofluids
Zahn, M. J. Nano. Rsrch, 3: 73-78, 2001
69
Nanomotors/Generators using Ferrofluids
• Currently, few applications explored (mostly theoretical)
• Paradoxical results– below a critical magnetic field strength,
ferrofluids move opposite an AC field.– Fluid viscosity is dependent on the field
strength (zero viscosity fluid reported)
Ref’s in review: Zahn, M. J. Nano. Rsrch. 3: 73-78, 2001
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CatalysisAu nanoparticles supported on TiO2 substrates show high activity for oxidation of CO at room temperature and below.
TiO2 Support
Oxygen Adsorption (on TiO2)
CO adsorption (on Au)
Haruta, M.; Date, M. Applied Catalysis A: General 2001, 222, 427-437.
Reaction proceeds at corner, step, and edge sites of Au
2-3 Atoms high
12 Atoms in length
3.5 nm Au nanoparticle
72
Bimetallic Catalysis
Figure taken from: Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, 1179-1201 and references therein.
Geometric effects lead to higher activity and selectivity for certain reactions.
CH2=CH-CN + H2O CH2=CH-CONH2
Reaction proceeds most favorably with Pd-Cu particles, and is 100% selective when using a 3:1 Cu:Pd ratio.
CH3-CH-CN
OH
73
Effect of Composition
Catalytic activity as a function of nanoparticle composition for the hydrogenation of 1,3-Cyclooctadiene
Figure taken from: Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, 1179-1201.
Interaction of the two metals:
Pd Pt
e- density
C=C bond prefers e- deficient sites (donor acceptor interactions); leads to selective hydrogenation
74
Electrochemical Reactions•Electrochemistry using a roughened silver electrode has been compared to that using an array of silver nanoparticles on a support.
•Different molecules adsorb differently on the two surfaces; i.e. there are different types of active sites.
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CVs of methylviologen in 0.1 M Na2SO4 at (a) EC roughened electrode, and (b) NP array electrode
Surface Properties
Couple 1: -0.66 V & 0.72 V; Ep = 60 mV
pi
Couple 2: -0.53 V & -0.55 V; Ep = 60 mV
pi
(a)
(b)No adsorption of MV!
No active sites for adsorption of MV on nanoparticle array
Zheng, J.; Li, X.; Gu, R.; Lu, T. Journal of Physical Chemistry B 2002, 106, 1019-1023.
76
Surface ComparisonSEM images of (A) EC roughened electrode and (B) NP array electrode
Ag Electrode polished, then roughened by potential steps in 0.1 M KCl
NP array made by dipping an Indium-Tin Oxide (ITO) electrode in poly-L-lysine for two hours, then into a colloidal silver solution overnight
Defect sites on the EC roughened electrode must be active for MV adsorption.
Zheng, J.; Li, X.; Gu, R.; Lu, T. Journal of Physical Chemistry B 2002, 106, 1019-1023.
77
Applications of Latex Particles•Butadiene
•Tires, Belts, Cables, Shoes, etc.
•Oil-resistant Products
•Styrene
•Linoleum, Plastics, Coatings
•Vinyl Acetate
•Adhesives and Paints
•Acrylate
•Adhesives, Paints, Primers, and Leather Finishing
•Chloroprene
•Belts, Hoses, Cables, etc.
•Natural Rubber Latex
•Gloves
•Condoms
78
Drying of Paint
http://www.pcimag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,1846,268,00.html
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Rings…
Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, 3441-3445.
Rings form as the contact line between the liquid and dry substrate undergoes pinning and de-pinning cycles, while mass transport occurs toward the boundary (rate of evaporation highest at edge). Particles build-up at the interface during each pinning cycle so that rings are left when the liquid dries.
80
Pinning and De-pinning
Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, 3441-3445.
Where a particle adheres to the surface a pinning event takes place. Mass transfer builds-up particles at this pinning site until there are no more particles in the vicinity of the edge. At this point, the contact line becomes de-pinned, and will move back until there is another adhered particle. This mechanism leads to the formation of rings when a polymer nanoparticle is left to dry on a glass slide.
81
Ordering in Rings
Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, 3441-3445.
Mass transfer during a pinning event drives ordering in ring-forming systems such that a closest-packed layer of particles forms.
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84
85
Periodic Table of the Elements
103Lr
(260)
102No
(259)
101Md
(258)
100Fm
(257)
99Es
(252)
98Cf
(251)
97Bk
(247)
96Cm
(247)
95Am
(243)
94Pu
(244)
93Np
(237)
92U
238
91Pa
231
90Th
232
71Lu
175
70Yb
173
69Tm169
68Er
167
67Ho
165
66Dy
162
65Tb
159
64Gd
157
63Eu
152
62Sm150
61Pm
(145)
60Nd
144
59Pr
141
58Ce
140
8A18
7A17
6A16
5A15
4A14
3A13
Lanthanides
Actinides
109Une
(266)
108Uno
(265)
107Uns
(262)
106Unh
(263)
105Ha
(262)
104Rf
(261)
89Ac
227
88Ra
226
87Fr
(223)
83Bi
209
82Pb
207
81Tl
204
80Hg
201
79Au
197
78Pt
195
77Ir
192
76Os
190
75Re
186
74W
184
73Ta
181
72Hf
178
57La
139
56Ba
137
55Cs
133
51Sb
122
50Sn
119
49In
115
48Cd
112
47Ag
108
46Pd
106
45Rh
103
44Ru
101
43Tc
(98)
42Mo
95.9
41Nb
92.9
40Zr
91.2
39Y
88.9
38Sr
87.6
37Rb
85.5
86Rn
(222)
85At
(210)
84Po
(209)
52Te
128
53I
127
54Xe
131
36Kr
83.8
35Br
79.9
34Se
79.0
33As
74.9
32Ge
72.6
31Ga
69.7
30Zn
65.4
29Cu
63.5
28Ni
58.7
27Co
58.9
26Fe
55.8
25Mn
54.9
24Cr
52.0
23V
50.9
22Ti
47.9
21Sc
45.0
20Ca
40.1
19K
39.1
18Ar
39.9
17Cl
35.4
16S
32.1
15P
31.0
14Si
28.1
13Al
27.0
2He
4.00
10Ne
20.2
9F
19.0
8O
16.0
7N
14.0
6C
12.0
5B
10.88B
2B12
1B111098
7B7
6B6
5B5
4B4
3B3
12Mg
24.3
11Na
23.0
4Be
9.01
3Li
6.94
2A2
1A1
1H
1.01
86
Organic Nanoparticles
Organic compound
+ Lipophilic solvent
Water +
Stabilizer
Emulsification
Separation of solvent
Hydrosol of organic compound
Horn et al.
Angew. Chem. Int. Ed
2001, 40, 4330-4361
Polymer Nanoparticle Synthesis
Initiator
X
XXXX
X
XXXX
X
X
XXXX
X
X XX X
X
X
XXXX
X
X
X
X
X
X
X
XXXX
X
X
X
X
X
X
Monomer
Micelle formed from emulsifier
Polymer
Stability Sphere
•Colloid Science, Kruyt, H. R., Ed.; Elsevier: New York, New York, 1952; Vol. 1
•Mysels, K. J. Introduction to Colloid Chemistry; Interscience: New York, 1959
•Irja Piirma, Ed., Emulsion Polymerization; Academic Press: New York, 1982
•Eliseeva, V. I.; Ivanchev, S. S.; Kuckanov, S. I.; Lebedev, A. V. Emulsion Polymerization and its Applications in Industry; Plenum: New York, 1981
•Bovey, F. A.; Kolthoff, I. M.; Medalia, A. I.; Meehan, E. J. In High Polymers; Mark, H., Melville, H. W., Marvel, C. S., Whitby, G. S., Eds.; Interscience: New York, 1955; Vol. IX
88
Other Techniques
Laser Ablationa
Electrochemistryb
Hydrothermal Synthesisc
(Supercritical water)
Sol-Geld
a: Neddersen, J; et al. Appl. Spec. 47 p. 1959-1964 (1993)b: Lu, D; Tanaka, K. J. Phys. Chem. 100 p. 1833-1837 (1996)c: Cabanas, A; Poliakoff, M. J. Mater. Chem. 11 p. 1408-1416 (2001)d: Moreno, E; et al. Langmuir 18 p. 4972-4978 (2002)
89
DLVO Theory
•Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp 1-49.
•See also DLVO theory : Derjaguin, B. V., Landau, L., Acta Physicochim. URSS, 1941, 14, 633, and Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, 1948.
Vr + Va
0
Separation Distance (nm)0 200
Repulsion
Attraction
90
Photolithography Patterning
• Typically pattern the capture monolayer followed by particle adsorption
• Few examples of patterning
after nanoparticle deposition
91
Photolithography Patterned Nanoparticles
SEM image of Au nanoparticles adsorbed onto a patterned (3-mercaptopropyl)-trimethoxysilane monolayer on SiO2 coated silicon wafer.
AFM image (80 m x 80 m) of a three-layer coating of nanoparticles followed by photopatterning.
Chen, D.; et al. Thin Solid Films, 1998, 327-329, 176-179.
Pris, A.D.; Porter, M. D. Nano Lett. 2002, 2(10), 1087-1091.
92
Electron Beam Lithography
• Coat substrate with polymer film
Write pattern with e- beam
Dissolve exposed polymer
Evaporate metal into “holes”
Somorjai, G. A.; et al. J. Chem. Phys. 2000, 113(13), 5432-5438.
93
Images of Nanoparticle Arrays Formed by Electron Beam Lithography
AFM and SEM of Pt nanoparticle array. Particles are 40 nm in diameter and spaced 150 nm apart.
Somorjai, G. A.; et al. J. Chem. Phys. 2000, 113(13), 5432-5438.
Spin-coat PMMA on Si (100) wafer with 5 nm thick SiO2 on surface.
Beam current: 600 pA
Accelerating Voltage: 100 dV (100 kV?)
Beam diameter: 8 nm
Exposure time: 0.6 s at each site
Pt deposition: 15 nm by e- beam evaporation
94
Nanosphere Lithography
Hulteen, J.C.; Van Duyne, R.P. J. Vac. Sci. Technol. A 1995, 13(3), 1553-1558.
(A) Representation of a single-layer nanosphere mask formed by convective self assembly.
(B) Illustration of the exposed sites on the substrate with single-layer mask
(C) AFM image (1.7 m x 1.7 m) of Ag deposited on mica with a mask of 264 nm diameter nanoparticles.
Mask preparation: Spin coat 267 nm polystyrene nanoparticles at 3600 rpm.
Deposition: Ag vapor deposition
Mask removal: sonicate 1-4 min. in CH2Cl2
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