Preparation of Thin Poly(vinyl chloride) Films with Size-controlled Nanopores
Ichiro Tanabe, Hajime Yasuda, and Tetsu Tatsuma*
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505(Received April 20, 2013; CL-130371; E-mail: tatsuma@iis.u-tokyo.ac.jp)

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Vol.42 No.9

2013 p.966–968
CMLTAG
September 5, 2013

The Chemical Society of Japan
Published on the web June 1, 2013; doi:10.1246/cl.130371

doi:10.1246/cl.130371
Published on the web June 1, 2013966

Preparation of Thin Poly(vinyl chloride) Films with Size-controlled Nanopores
Ichiro Tanabe,³ Hajime Yasuda, and Tetsu Tatsuma*
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505(Received April 20, 2013; CL-130371; E-mail: tatsuma@iis.u-tokyo.ac.jp)
Thin poly(vinyl chloride) ﬁlms with size-controlled nanopores (40­150 nm diameter) are prepared by a new and simple
method on ITO-coated glass plates and TiO2 substrates by using
monodisperse Au nanoparticles. These ﬁlms are expected to be
applied to nanomasks for nanoelectrode ensembles and templates for deposition of size-controlled metal nanoparticles.
Thin ﬁlms with size-controlled nanopores or nanoholes
have attracted much attention because of their wide variety ofapplications.1­4 For example, a nanoporous ﬁlm can be used as atemplate for nanoparticles. Size-controlled metal nanoparticles
can be prepared on a substrate by spattering or evaporating metalon the template followed by its removal (lift-oﬀ method).1,2
Electrodeposition can also be used for preparation of nanoparticles in the pores.3 In addition, an electrode coated with athin insulating ﬁlm with nanopores or micropores serves as anano- or microelectrode ensemble. They are studied for electrochemical analysis or applications such as advanced electrochemical capacitors, because of enhanced mass transport andcurrent density.4 Thin ﬁlms with size-controlled nanopores arethus important. For these applications, the thin ﬁlms must bestable and durable chemically and mechanically. In addition, forapplications to a template for electrodeposition or a nanomask
for nanoelectrode ensembles, it is preferable that the ﬁlm isinsulating. From these points of view, poly(vinyl chloride)(PVC) is an ideal material, because it is highly insulating, tough,ﬂexible, and resistant to both acidic and alkaline solutions.
Therefore, in this study, we develop a simple method for
preparation of thin PVC ﬁlms with size-controlled nanopores.
Previously reported methods for preparing nanoporous ﬁlms
are not necessarily easy to apply to PVC ﬁlms. For example,
methods of ﬁlm preparation from polymer nanoparticles and aﬁlm precursor solution5,6 are convenient but applicable only tooxide ﬁlms such as titania (TiO2) and alumina (Al2O3), because
the polymer nanoparticles are decomposed and removed byannealing. Although polymer nanoparticles can also be removed
by dissolution into organic solvents, the solvents for the polymer
nanoparticles may also dissolve organic thin ﬁlms such as PVC.
Anode oxidation methods are also used for the preparation of
nanoporous metal oxide ﬁlms.7 Electron beam lithography is a
powerful method,1,2 but the ﬁlm must be electroconductive. In
addition, it requires huge and expensive equipment. A track etchmethod,8 which is used for production of membrane ﬁlters, alsoneeds an expensive radiation device.
In this study, we employ monodisperse gold (Au) nanoparticles, which are chemically and thermally stable. Monodisperse Au nanoparticles with a wide variety of sizes (3­150nm diameter) are commercially available. Here we use Au
nanoparticles with 40, 100, and 150 nm diameter purchased from
Tanaka Kikinzoku. Figure 1 illustrates the present method for
preparing the nanoporous PVC ﬁlm. In the ﬁrst step (Figure 1a),Chem. Lett. 2013, 42, 966­968

Figure 1. Preparation of a PVC ﬁlm with size-controlled
nanopores by using monodisperse Au nanoparticles.
Au nanoparticles are immobilized onto a solid substrate. Here
we cast aqueous suspension of spherical Au nanoparticles
protected with citric acid (diameter: 150 nm, pH ca. 4)(50 ¯L cm¹2) on an ITO-coated glass plate modiﬁed with(3-aminopropyl)triethoxysilane9 and left for about 3 h in thedark. Intact Au nanoparticles were found on the substrate(ca. 108 particles cm¹2) by atomic force microscopy (AFM,Figure 2a) and scanning electron microscopy (SEM, Figure 2b).
AFM measurements (NanoNavi Station/SPA400, SII Nanotechnology) were performed in a tapping mode with a siliconcantilever (SI-DF20, SII Nanotechnology). The AFM images
were corrected with a Morphology Filter (SII Nanotechnology)
to avoid overestimation of the particle size due to the AFM
tip curvature radius (= 10 nm). If necessary, the packing andspacing of Au nanoparticles would be controlled by changing
the surface charges of the nanoparticles and the substrate.10
In the next step (Figure 1b), thin PVC ﬁlm is formed bya standard dip-coating technique (withdrawal rate was 1­2mm s¹1) on the substrate with Au nanoparticles from atetrahydrofuran (THF) solution containing 1 wt % PVC (degreeof polymerization is about 1100, Wako Pure Chemical Industries). The substrate was heated at 80 °C for 30 min in order toevaporate THF. Finally, saturated aqueous solution of iodine (I2)
containing 36 mM potassium iodide (KI) was cast on the PVCcoated substrate (50 ¯L cm¹2) and left for at least 30 min. Afterthe sample was rinsed with pure water in order to remove theions, AFM (Figures 2c and 2d) and SEM (Figure 2e) images
showed nanopores on the PVC ﬁlm instead of Au nanoparticles.
These results indicate that the Au nanoparticles are oxidized anddissolved by I3¹ and I¹ contained in the cast solution, according
to the following reaction 1.11

© 2013 The Chemical Society of Japan

2Au þ I3  þ I ¼ 2½AuI2 ð1Þ

www.csj.jp/journals/chem-lett/967

Figure 2. Typical (a, c) AFM and (b, e) SEM images of (a, b)
immobilized Au nanoparticles (150 nm diameter) and (c­e)
nanoporous PVC ﬁlms prepared on ITO-coated glass plates.
(d) A cross-sectional image of the nanopore.
The pore diameter is 151.7 « 7.3 nm (average « standard
deviation, n = 10), which coincides with the diameter of the Aunanoparticles. The cross-sectional AFM image (Figure 2d)shows that the PVC ﬁlm thickness is about 20 nm and that thethickness around the oriﬁce is about 50 nm because of a meniscus
formed around the nanoparticle. The thin PVC ﬁlm exhibited
good insulation. The AFM cantilever used with 10 nm curvatureradius and 13° half-cone angle can reach the bottom of a pore of150 nm diameter unless it is deeper than 310 nm. The surface
roughness of PVC ﬁlms was 5­10 nm. When the withdrawal rate
for the dip-coating was as low as 0.1 mm s¹1, PVC did not cover
the substrate completely and ITO was partially exposed. On theother hand, the rate as high as 5 mm s¹1 gave PVC ﬁlms too thickwithout nanopores because PVC covered the Au nanoparticles
completely. Tsuboi and co-workers have also prepared polymer
ﬁlms with nanopores by the use of 20 and 40 nm Au nanoparticles.12 They vaporized the Au nanoparticles by pulsed laser.
Their method, therefore, needs expensive laser equipment andgives polydisperse pores larger than Au nanoparticles. Incontrast, the diameter of the nanopores formed in this study isin good agreement with that of Au nanoparticles.
We also prepared nanoporous ﬁlms on a TiO2 substratein the same way. We have found plasmon-induced charge
separation, which takes place at the interface between plasmonic
metal (Au, Ag, or Cu) nanoparticles and a semiconductor
such as TiO2.13­19 The charge separation can be applied tophotovoltaics,15,16 photocatalysis,16 photochromism,13,14,19 andothers.18,19 Coating TiO2 with a thin insulating ﬁlm with sizecontrolled nanopores would allow deposition of size-controlled
metal nanoparticles and thereby materials and devices with sharp
spectra. A TiO2 ﬁlm was prepared on a Pyrex glass plate from aethanolic titanium alkoxide solution (NDH-510C, Nippon Soda)
by dip-coating (withdrawal rate was 2 mm s¹1), followed byChem. Lett. 2013, 42, 966­968

Figure 3. Typical AFM images of (a, c, e) immobilized Au
nanoparticles (150, 100, and 40 nm diameter, respectively) and(b, d, f) nanoporous PVC ﬁlms prepared on TiO2-coated glassplates. Inset images are typical AFM images of Au nanospheres
and cross-sectional images of the nanopores.
calcination at 500 °C for 1 h. The colloidal solution of Au
nanoparticles (150 nm diameter) was cast on the TiO2 ﬁlm andleft for 30 min in the dark. Figure 3a shows an AFM image of
the Au nanoparticles immobilized on TiO2. Since the TiO2
surface is charged positively due to partial protonation (­OH2+),
negatively charged Au nanoparticles protected by deprotonatedcitric acid (­COO¹) are electrostatically adsorbed onto the TiO2
surface in the solution at about pH 4. Subsequently, a PVC ﬁlm
was formed and Au nanoparticles were dissolved as describedabove. As a consequence, a PVC ﬁlm with nanopores wasformed on the TiO2 substrate (Figure 3b).
We also used Au nanoparticles of 40 and 100 nm diameter.
As a result, thin PVC ﬁlms with nanopores of corresponding size
were obtained (Figures 3c­3f). In the cases of 40, 100, and150 nm Au nanoparticles, the pore diameters were 40.4 « 2.6,101.7 « 3.3, and 150.5 « 5.2 nm, respectively (n = 10).
In summary, we developed a new and simple method for
preparation of thin PVC ﬁlms with size-controlled nanopores byusing commercially available monodisperse Au nanoparticles
and a conventional method for etching Au with iodine.
This work was supported in part by a Grant-in-Aid for
Scientiﬁc Research on Priority Area “Coordination Programming” (Area No. 2107) No. 24108708 and a Grant-in-Aid for
Scientiﬁc Research No. 25288063. IT thanks a JSPS Research
Fellowship for Young Scientists.

© 2013 The Chemical Society of Japanwww.csj.jp/journals/chem-lett/968
References and Notes³ Present address: Department of Chemistry, School ofScience and Technology, Kwansei Gakuin University,Sanda, Hyogo 669-1337
1 T. D. Corrigan, S.-H. Guo, H. Szmacinski, R. J. Phaneuf,Appl. Phys. Lett. 2006, 88, 101112.
2 N. A. A. Hatab, J. M. Oran, M. J. Sepaniak, ACS Nano 2008,
2, 377.
3 Y. Takahashi, T. Tatsuma, Nanoscale 2010, 2, 1494.
4 P. Simon, Y. Gogotsi, Nat. Mater. 2008, 7, 845.
5 M. Kuemmel, J. Allouche, L. Nicole, C. Boissière, C.
Laberty, H. Amenitsch, C. Sanchez, D. Grosso, Chem.
Mater. 2007, 19, 3717.
6 S. Matsushita, T. Miwa, A. Fujishima, Chem. Lett. 1997,925.
7 H. Masuda, K. Fukuda, Science 1995, 268, 1466.
8 J. C. Hulteen, C. R. Martin, J. Mater. Chem. 1997, 7, 1075.
9 D. V. Leﬀ, P. C. Ohara, J. R. Heath, W. M. Gelbart, J. Phys.

Chem. Lett. 2013, 42, 966­968

Chem. 1995, 99, 7036.
10 A. N. Shipway, E. Katz, I. Willner, ChemPhysChem 2000, 1,18.
11 O. Seitz, M. M. Chehimi, E. Cabet-Deliry, S. Truong, N.
Felidj, C. Perruchot, S. J. Greaves, J. F. Watts, Colloids
Surf., A 2003, 218, 225.
12 K. Yamada, T. Itoh, Y. Tsuboi, Appl. Phys. Express 2008, 1,087001.
13 Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota,A. Fujishima, Nat. Mater. 2003, 2, 29.
14 K. Naoi, Y. Ohko, T. Tatsuma, J. Am. Chem. Soc. 2004, 126,3664.
15 Y. Tian, T. Tatsuma, Chem. Commun. 2004, 1810.
16 Y. Tian, T. Tatsuma, J. Am. Chem. Soc. 2005, 127, 7632.
17 T. Yamaguchi, E. Kazuma, N. Sakai, T. Tatsuma, Chem. Lett.
2012, 41, 1340.
18 I. Tanabe, T. Tatsuma, Nano Lett. 2012, 12, 5418.
19 T. Tatsuma, Bull. Chem. Soc. Jpn. 2013, 86, 1.

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