physical structure induced hydrophobicity analyzed from

Research ArticlePhysical Structure Induced Hydrophobicity Analyzed fromElectrospinning and Coating Polyvinyl Butyral Films

Shuo Chen1 Guo-Sai Liu1 Hong-Wei He 1 Cheng-Feng Zhou 2

Xu Yan 134 and Jun-Cheng Zhang4

1 Industrial Research Institute of Nonwovens and Technical Textiles College of Textiles and Clothing Qingdao UniversityQingdao 266071 China

2State Key Laboratory of Bio-Fibers and Eco-Textiles Qingdao University Qingdao 266071 China3Collaborative Innovation Center for Eco-Textiles of Shandong Province Qingdao University Qingdao 266071 China4Collaborative Innovation Center for Nanomaterials and Optoelectronic Devices College of Physics Qingdao UniversityQingdao 266071 China

Correspondence should be addressed to Cheng-Feng Zhou chengfengzhouqdueducn and Xu Yan yanxu-925163com

Received 5 November 2018 Accepted 5 March 2019 Published 1 April 2019

Academic Editor Golam M Bhuiyan

Copyright copy 2019 Shuo Chen et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Surface wettability of a film plays a critical role in its practical applications To control the surface wettability modification onthe physical surface structures has been a useful method In this paper we reported the controlling physical surface structure ofpolyvinyl butyral (PVB) films by different film-forming methods spin-coating bar-coating and electrospinningThewettability ofthese PVB films was examined and the surface morphologies and roughness were investigated The results indicated that coatingPVB films were hydrophilic while electrospun films were hydrophobic The physical surface structure was the key role on theinteresting transition of their surface wettability Theoretical analyses on these results found that the coating PVB films showeddifferent mechanism with electrospun ones These results may help to find the way to control the PVB film surface wettability andthen guide for applications

1 Introduction

The wetting behavior of solid surfaces by a liquid as avery important aspect of surface properties has been afocused interest for a long time [1ndash4] and has shown a widevariety of practical applications in various fields such asprotecting clothes [5] medical care [6ndash8] and filtration [9]Consequently great efforts have been made to find the way tocontrol the surface wettability [10ndash13]

According to the term biomimetic ldquolotus leaves effectrdquoindicates that the cooperation of hierarchical structures andother specific components on the natural surfaces resultsin the desired wettability [1ndash3 14] Moreover from thetheoretical view such as Youngrsquos equation [15]Wenzel model[16] and Cassie model [17] the surface roughness playsa critical role in surface wettability [18ndash21] Furthermorethe rough surface is extended to porous surfaces and evenmicro-nano structures [22ndash24] To achieve these structures

especially in film structures several methods are developedsuch as solution cast and electrospinning [5ndash10 19 21]

Among variousmaterials polyvinyl butyral (PVB) whichis characterized by high adhesion to glass excellent mechani-cal strength excellent biocompatibility nontoxicity and goodsolubility in alcohol has been applied to many fields suchas an adhesive interlayer in safety glass wound dressingand coating film [5ndash7 10 11] Moreover PVB shows bothhydrophobic and hydrophilic properties due to its chemicalstructure with both vinyl butyral group and vinyl hydroxylgroup [10 25] And previous study has suggested that elec-trospun PVB nanofibrous structures and patterns showedlarger water contact angle (WCA) than that of the solutioncasting film [7 10 11]However theseworksmost focus on theelectrospun PVB meshes and rarely discuss the comparisonof the structures between the different methods

In this paper we focused on the comparison of PVB filmsmade by several methods spin-coating bar-coating and

HindawiAdvances in Condensed Matter PhysicsVolume 2019 Article ID 6179456 5 pageshttpsdoiorg10115520196179456

2 Advances in Condensed Matter Physics

Table 1 The SWCA of the prepared PVB films by different methods

Methods SWCA (∘) SWCA (∘) SWCA (∘) ASWCA (∘)Concentrationsparameters 8 wt 10 wt 12 wt

Spin-coating250 rs 77767 78800 78900

78593300 rs 74300 82600 79933350 rs 76033 82733 76267

Bar-coating6 120583m 86438 83297 84303

830678 120583m 81255 82626 8143710 120583m 81093 81360 85796

Positive electrospinning15 cm 135833 130833 131933

13240420 cm 132167 133600 12970025 cm 131667 135400 130500

Negative electrospinning15 cm 131033 135733 130867

13161520 cm 128633 135100 13336725 cm 128300 133233 128267

electrospinning The WCAs on these films were measuredand the morphologies and surface roughness of them werealso examined By analyzing these results we want to find away to control the surface wettability

2 Materials and Methods

21Materials Polyvinyl butyral (PVB) (MWsim100000 Sino-pharm Chemical Reagent Co Ltd China) was dissolved inethyl alcohol (analytical reagent 99) at 8 wt 10 wt and12 wt firstly and then stirred for 2 h at room temperature

22 Preparation of the Films The PVBalcohol solutionswere used to produce films by spin-coating bar-coating andelectrospinning respectively During spin-coating processPVBalcohol solutions were dripped onto cover slips (20mmtimes20 mm) with 5 120583l and then set on the spin-coater (KW-4A Institute of Microelectronics of the Chinese Academyof Sciences) The spinning velocities were selected at 250rs 300 rs and 350 rs and spinning time was set at 30seconds In bar-coating process 10 120583l PVBalcohol solutionswere dripped onto slide glasses (76mmtimes26mm) and the barswere selected with 6 120583m 8 120583m and 10 120583m film thickness Forelectrospun meshes both positive electrospinning and neg-ative electrospinning were processed PVBalcohol solutionswere firstly loaded into syringes (5 ml) and then set on theelectrospinning apparatus (DW-P303-1ACF5 (positive) DW-N303-1ACDF0 (negative) Dongwen China) the electrospin-ning voltage was set at 15 kV and -15 kV and the distanceswere selected at 15 cm 20 cm and 25 cm

23 Characterization The static water contact angles(SWCA) of the prepared films were examined by an opticaltensiometer (Attension Theta Biolin Scientific Germany)with a 2 120583L water droplet for three sites at room temperatureand analysis was performed by fitting drops with a Young-Laplace formula using the Theta software The surfaceroughness was also measured by optical tensiometer with 3Dsurface roughness module The morphologies of the filmswere examined by a scanning electron microscope (SEM

Phenom ProX Phenom Scientific Instruments Co LtdChina) at 10 kV and all samples were coated with gold for30 s before analysis The fiber diameters were analyzed byNano Measurer software The Fourier transform infraredspectroscopy (FTIR) spectrums were measured by aThermoScientific Nicolet iN10 spectrometer

3 Results and Discussion

To ensure the wettability of the prepared PVB films SWCAwere measured and shown in Table 1 One can find that thespin-coating and bar-coating PVB films showed hydrophilic-ity with SWCA lt90∘ while the electrospun films showedhydrophobicity with SWCAgt90∘ which agreed with theprevious study [7 10 11] Moreover the bar-coating PVBfilms had larger SWCA than spin-coating ones generallyThe SWCA of electrospun PVB films with positive elec-trospinning process is mostly larger than that of negativeelectrospinning Nevertheless as seen from Figure 1 theprepared PVB films showed similar absorption peaks whichindicated that these films had same chemical structures It isinteresting that the samematerial showed different wettabilityfor its different film-forming methods

To understand the interesting PVB film wettability wefirstly examined the morphologies of selected PVB films(10 concentration) with spin-coating 250 rs bar-coating6120583m and positive and negative electrospinning with distanceof 15 cm As shown in Figure 2(a) the spin-coating PVBfilm showed a macroscopically relative smooth surface withSWCA 788∘ the bar-coating film also had a smooth surfacewith SWCA 833∘ (Figure 2(b)) Both smooth films showedhydrophilicity Meanwhile both the positive and negativeelectrospun PVB films showed porous rough surfaces as canbe found in Figures 2(c) and 2(d) and the SWCAwere 1308∘and 1357∘ respectively Both the porous rough electrospunfilms showed hydrophobicity According to these results itseems that the surface roughness determined the wettabilityof the films

For further investigation we examined the roughnessof the selected films as shown in Figure 3 It is strange

Advances in Condensed Matter Physics 3

Tran

smiss

ivity

[au

]

800 1600 2400 3200 4000

Wave number (cＧ-1)

spin-coatingbar-coating

positive electrospinningnegative electrospinning

Figure 1 FTIR spectra of PVB films made by different methods

743∘

100 m

10 m

(a)

833∘

100 m

10 m

(b)

1308∘

100 m

10 m

76543210

Cou

nt

08 10 12 14 16 18

Diameter (m)

128plusmn028 m

(c)

100 m

10 m

6

5

4

3

2

1

0

Cou

nt

Diameter (m)04 06 08 10 12 14 16 18 20

099plusmn037 m

1357∘

(d)

Figure 2 SEM images of the PVB films made by spin-coating 250 rs (a) bar-coating 6 120583m (b) positive electrospinning 15 cm (c) andnegative electrospinning 15 cm (d) The upper inset images showed the water droplet onto these films and the lower inset images showed theelectrospun fiber diameter distributions

that the macroscopical smooth surfaces shown in Figure 2have higher roughness than the electrospun films In ouropinion this case may result from the different surfacestructures of the films that coating films showed relative densesurface structure while electrospun films had porous surfacestructure as can be seen in Figure 2 For the hydrophobiliccoating PVB films [seen in Figures 3(a) and 3(b)] bar-coating ones showed higher roughness than the spin-coatingones with r=3715gt2351 where r is the factor of the surfaceroughness According to the Wenzel model [1 22]

cos 1205791015840 = 119903 cos 120579119888 (1)

where 120579119888lt 90∘ the larger the factor of roughness r is the

smaller 1205791015840 will get and the increasing roughnesswillmake thefilmmore hydrophilicThe case in coating PVBfilms followedthe Wenzel model consequently the bar-coating films withmore roughness showed smaller SWCA than spin-coatingones Meanwhile for the electrospun films the porous andmicro-nano surface structures made the Wenzel model notwork As suggested in Figures 3(c) and 3(d) and Figures2(c) and 2(d) the positive electrospun PVB film with moreroughness (r=1106) had smaller SWCA (1308∘) than that ofnegative electrospinning PVB film (r=1076 SWCA 1357∘)In this case the Cassie model which gives a composite state


(a) (b) (c) (d)

Figure 3 3D surface roughness of the prepared PVB films under spin-coating 250 rs (a) bar-coating 6 120583m (b) positive electrospinning 15cm (c) and negative electrospinning 15 cm (d) The inset images showed the 2D surface roughness of these films

that liquids are assumed to only contact the solid through thetop of the asperities and air pockets are assumed to be trappedunderneath the liquid [1 22] may be considered the functioncan be expressed as

cos 1205791015840 = minus1 + 119891119904(1 + 119903 cos 120579

119888) (2)

where 119891119904are the area fractions of the solid on the surface

From (2) one can find that the smaller 119891119904is the more

hydrophobicity will be obtained Specifically to the electro-spun PVB films the smaller the fiber diameter is the smaller119891119904will be achieved and then higher hydrophobicity will be

shown [5 7 10 11] From lower inset images in Figure 2we can obviously find that negative electrospun PVB fibershad smaller diameters and less uniform and consequentlyexhibited higher SWCA

4 Conclusions

In conclusion we have prepared several kinds of PVB filmsthrough spin-coating bar-coating and electrospinning TheFTIR spectra suggested that these films have the samechemical structures Meanwhile these films showed differentwettability that coating films were hydrophilicity and elec-trospun films were hydrophobicity SEM images indicatedthat the different films showed different physical surfacestructures which may introduce the different wettabilityFurther investigation on the surface roughness confirmedthat the wettability of coating films obeyed theWenzelmodelwhile the electrospun films agreed with the Cassie modelThese results may help to understand the mechanism of thePVB films and then guide for its practical application

Data Availability

The data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This work was supported by the National Natural ScienceFoundation of China (51703102 51373082 and 51673103)the Shandong Provincial Natural Science Foundation China(ZR2016EMB09 and ZR2017BEM045) and the QingdaoPostdoctoral Applied Research Project

References

[1] K Liu X Yao and L Jiang ldquoRecent developments in bio-inspired special wettabilityrdquo Chemical Society Reviews vol 39no 8 p 3240 2010

[2] T L Sun L Feng X F Gao and L Jiang ldquoBioinspired surfaceswith special wettabilityrdquo Accounts of Chemical Research vol 38no 8 pp 644ndash652 2005

[3] L Feng S Li Y Li et al ldquoSuper-hydrophobic surfaces fromnatural to artificialrdquo Advanced Materials vol 14 no 24 pp1857ndash1860 2002

[4] J C Zhang C Pan Y F Zhu et al ldquoAchieving thermo-mechano-opto-responsive bitemporal colorful luminescencevia multiplexing of dual lanthanides in piezoelectric particlesand its multidimensional anticounterfeitingrdquo Advanced Mate-rials vol 30 Article ID 1804644 2018

[5] M N Liu X Yan and M H You ldquoReversible photochromicnanofibrous membranes with excellent waterwindproof andbreathable performancerdquo Journal of Applied Polymer Sciencevol 135 no 23 Article ID 46342 2018

[6] H Xu H Li and J Chang ldquoControlled drug release froma polymer matrix by patterned electrospun nanofibers withcontrollable hydrophobicityrdquo Journal of Materials Chemistry Bvol 1 no 33 p 4182 2013

[7] G S Liu X Yan F F Yan et al ldquoIn situ electrospinningiodine-based fibrous meshes for antibacterial wound dressingrdquoNanoscale Research Letters vol 13 Article ID 309 2018

[8] J Zhang S Li D Ju et al ldquoFlexible inorganic core-shellnanofibers endowed with tunable multicolor up conversionfluorescence for simultaneous monitoring dual drug deliveryrdquoChemical Engineering Journal vol 349 pp 554ndash561 2018

[9] N Wang Y Si J Yu H Fong and B Ding ldquoNano-fibernetstructured electrospun PVA membrane effects of formic acidas solvent and crosslinking agent on solution properties and


membrane morphological structuresrdquoMaterials and Corrosionvol 120 pp 135ndash143 2017

[10] X Yan M H You T Lou et al ldquoColorful hydrophobicpoly(vinyl butyral)cationic dye fibrous membranes via a col-ored solution electrospinning processrdquo Nanoscale ResearchLetters vol 11 no 540 2016

[11] H Wu R Zhang Y Sun et al ldquoBiomimetic nanofiber patternswith controlled wettabilityrdquo So Matter vol 4 no 12 p 24292008

[12] S S Liu C H Zhang J G He et al ldquoWetting state transitionon hydrophilic microscale rough surfacerdquo Acta Physica Sinicavol 62 no 20 Article ID 206201 2013

[13] J Yang Y Pu D Miao and X Ning ldquoFabrication of durablysuperhydrophobic cotton fabrics by atmospheric pressureplasma treatment with a siloxane precursorrdquo Polymers vol 10Article ID 460 2018

[14] J B Boreyko and C H Chen ldquoRestoring superhydrophobicityof lotus leaves with vibration-induced dewettingrdquo PhysicalReview Letters vol 103 no 17 Article ID 174502 2009

[15] T Young ldquoAn essay on the cohesion of fluidsrdquo PhilosophicalTransactions of the Royal Society London vol 95 pp 65ndash87 1805

[16] R N Wenzel ldquoResistance of solid surfaces to wetting by waterrdquoIndustrial and Engineering Chemistry vol 28 no 8 pp 988ndash994 1936

[17] A B D Cassie and S Baxter ldquoWettability of porous surfacesrdquoTransactions of the Faraday Society vol 40 pp 546ndash551 1944

[18] D Quere ldquoWetting and roughnessrdquoAnnual Review of MaterialsResearch vol 38 pp 71ndash99 2008

[19] H Ems and S Ndao ldquoMicrostructure-alone induced transitionfrom hydrophilic to hydrophobic wetting state on siliconrdquoApplied Surface Science vol 339 pp 137ndash143 2015

[20] M Khorasani H Mirzadeh and Z Kermani ldquoWettabilityof porous polydimethylsiloxane surface morphology studyrdquoApplied Surface Science vol 242 no 3-4 pp 339ndash345 2005

[21] Y Zhang X Chen F Liu et al ldquoEnhanced coffee-ring effectvia substrate roughness in evaporation of colloidal dropletsrdquoAdvances in Condensed Matter Physics vol 2018 Article ID9795654 9 pages 2018

[22] K Lum D Chandler and J DWeeks ldquoHydrophobicity at smalland large length scalesrdquoe Journal of Physical Chemistry B vol103 no 22 pp 4570ndash4577 1999

[23] S Rajamani T M Truskett and S Garde ldquoHydrophobichydration from small to large lengthscales Understandingand manipulating the crossoverrdquo Proceedings of the NationalAcadamy of Sciences of the United States of America vol 102 no27 pp 9475ndash9480 2005

[24] X B Li and Y Liu ldquoWetting mechanisms and models on solidsurfacesrdquo Journal of FunctionalMaterials vol 38 pp 3919ndash39242007 (Chinese)

[25] W Chen D J David W J MacKnight and F E KaraszldquoMiscibility and Phase Behavior in Blends of Poly(vinyl butyral)and Poly(methyl methacrylate)rdquo Macromolecules vol 34 no12 pp 4277ndash4284 2001

Hindawiwwwhindawicom Volume 2018

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Table 1 The SWCA of the prepared PVB films by different methods

Methods SWCA (∘) SWCA (∘) SWCA (∘) ASWCA (∘)Concentrationsparameters 8 wt 10 wt 12 wt

Spin-coating250 rs 77767 78800 78900

78593300 rs 74300 82600 79933350 rs 76033 82733 76267

Bar-coating6 120583m 86438 83297 84303

830678 120583m 81255 82626 8143710 120583m 81093 81360 85796

Positive electrospinning15 cm 135833 130833 131933

13240420 cm 132167 133600 12970025 cm 131667 135400 130500

Negative electrospinning15 cm 131033 135733 130867

13161520 cm 128633 135100 13336725 cm 128300 133233 128267

electrospinning The WCAs on these films were measuredand the morphologies and surface roughness of them werealso examined By analyzing these results we want to find away to control the surface wettability

2 Materials and Methods

21Materials Polyvinyl butyral (PVB) (MWsim100000 Sino-pharm Chemical Reagent Co Ltd China) was dissolved inethyl alcohol (analytical reagent 99) at 8 wt 10 wt and12 wt firstly and then stirred for 2 h at room temperature

22 Preparation of the Films The PVBalcohol solutionswere used to produce films by spin-coating bar-coating andelectrospinning respectively During spin-coating processPVBalcohol solutions were dripped onto cover slips (20mmtimes20 mm) with 5 120583l and then set on the spin-coater (KW-4A Institute of Microelectronics of the Chinese Academyof Sciences) The spinning velocities were selected at 250rs 300 rs and 350 rs and spinning time was set at 30seconds In bar-coating process 10 120583l PVBalcohol solutionswere dripped onto slide glasses (76mmtimes26mm) and the barswere selected with 6 120583m 8 120583m and 10 120583m film thickness Forelectrospun meshes both positive electrospinning and neg-ative electrospinning were processed PVBalcohol solutionswere firstly loaded into syringes (5 ml) and then set on theelectrospinning apparatus (DW-P303-1ACF5 (positive) DW-N303-1ACDF0 (negative) Dongwen China) the electrospin-ning voltage was set at 15 kV and -15 kV and the distanceswere selected at 15 cm 20 cm and 25 cm

23 Characterization The static water contact angles(SWCA) of the prepared films were examined by an opticaltensiometer (Attension Theta Biolin Scientific Germany)with a 2 120583L water droplet for three sites at room temperatureand analysis was performed by fitting drops with a Young-Laplace formula using the Theta software The surfaceroughness was also measured by optical tensiometer with 3Dsurface roughness module The morphologies of the filmswere examined by a scanning electron microscope (SEM

Phenom ProX Phenom Scientific Instruments Co LtdChina) at 10 kV and all samples were coated with gold for30 s before analysis The fiber diameters were analyzed byNano Measurer software The Fourier transform infraredspectroscopy (FTIR) spectrums were measured by aThermoScientific Nicolet iN10 spectrometer

3 Results and Discussion

To ensure the wettability of the prepared PVB films SWCAwere measured and shown in Table 1 One can find that thespin-coating and bar-coating PVB films showed hydrophilic-ity with SWCA lt90∘ while the electrospun films showedhydrophobicity with SWCAgt90∘ which agreed with theprevious study [7 10 11] Moreover the bar-coating PVBfilms had larger SWCA than spin-coating ones generallyThe SWCA of electrospun PVB films with positive elec-trospinning process is mostly larger than that of negativeelectrospinning Nevertheless as seen from Figure 1 theprepared PVB films showed similar absorption peaks whichindicated that these films had same chemical structures It isinteresting that the samematerial showed different wettabilityfor its different film-forming methods

To understand the interesting PVB film wettability wefirstly examined the morphologies of selected PVB films(10 concentration) with spin-coating 250 rs bar-coating6120583m and positive and negative electrospinning with distanceof 15 cm As shown in Figure 2(a) the spin-coating PVBfilm showed a macroscopically relative smooth surface withSWCA 788∘ the bar-coating film also had a smooth surfacewith SWCA 833∘ (Figure 2(b)) Both smooth films showedhydrophilicity Meanwhile both the positive and negativeelectrospun PVB films showed porous rough surfaces as canbe found in Figures 2(c) and 2(d) and the SWCAwere 1308∘and 1357∘ respectively Both the porous rough electrospunfilms showed hydrophobicity According to these results itseems that the surface roughness determined the wettabilityof the films

For further investigation we examined the roughnessof the selected films as shown in Figure 3 It is strange


Tran

smiss

ivity

[au

]

800 1600 2400 3200 4000





743∘

100 m

10 m

(a)

833∘

100 m

10 m

(b)

1308∘

100 m

10 m

76543210

Cou

nt

08 10 12 14 16 18

Diameter (m)

128plusmn028 m

(c)

100 m

10 m

6

5

4

3

2

1

0

Cou

nt

Diameter (m)04 06 08 10 12 14 16 18 20

099plusmn037 m

1357∘

(d)



cos 1205791015840 = 119903 cos 120579119888 (1)




(a) (b) (c) (d)



cos 1205791015840 = minus1 + 119891119904(1 + 119903 cos 120579

119888) (2)





4 Conclusions


Data Availability




Acknowledgments


References































Shock and Vibration





Volume 2018














Geophysics



Volume 2018




Volume 2018






Journal of

Chemistry




RotatingMachinery






Tran

smiss

ivity

[au

]

800 1600 2400 3200 4000





743∘

100 m

10 m

(a)

833∘

100 m

10 m

(b)

1308∘

100 m

10 m

76543210

Cou

nt

08 10 12 14 16 18

Diameter (m)

128plusmn028 m

(c)

100 m

10 m

6

5

4

3

2

1

0

Cou

nt

Diameter (m)04 06 08 10 12 14 16 18 20

099plusmn037 m

1357∘

(d)



cos 1205791015840 = 119903 cos 120579119888 (1)




(a) (b) (c) (d)



cos 1205791015840 = minus1 + 119891119904(1 + 119903 cos 120579

119888) (2)





4 Conclusions


Data Availability




Acknowledgments


References































Shock and Vibration





Volume 2018














Geophysics



Volume 2018




Volume 2018






Journal of

Chemistry




RotatingMachinery






(a) (b) (c) (d)



cos 1205791015840 = minus1 + 119891119904(1 + 119903 cos 120579

119888) (2)





4 Conclusions


Data Availability




Acknowledgments


References































Shock and Vibration





Volume 2018














Geophysics



Volume 2018




Volume 2018






Journal of

Chemistry




RotatingMachinery


























Shock and Vibration





Volume 2018














Geophysics



Volume 2018




Volume 2018






Journal of

Chemistry




RotatingMachinery





physical structure induced hydrophobicity analyzed from

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