fabrication and characterization of photocurable inorganic–organic hybrid materials using...

6
Fabrication and characterization of photocurable inorganic–organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin Dong Jun Kang * , Dong Hee Han, Dong Pil Kang Advanced Materials and Application Research Laboratory, Korea Electrotechnology Research Institute, 28-1 Sungju-dong Changwon, Gyeongsangnam-do 641-120, Republic of Korea article info Article history: Received 17 October 2008 Received in revised form 13 January 2009 Available online 21 February 2009 PACS: 81.07.Pr 81.20.Fw 82.33.Ln Keywords: STEM/TEM Hardness Indentation, microindentation Atomic force and scanning tunneling microscopy Nanoparticles FT-IR measurements Organic–inorganic hybrids abstract Photocurable inorganic–organic hybrid materials were prepared from colloidal-silica nanoparticles syn- thesized through the sol–gel process and using acryl resin. The synthesized colloidal-silica nanoparticles had uniform diameters of around 20 nm and were organically modified, using methyl and methacryl functional silanes, for efficient hybridization with acryl resin. The organically modified and stabilized col- loidal-silica nanoparticles could be homogeneously hybridized with acryl resin without phase separation. The successfully fabricated hybrid materials exhibit efficient photocurability and simple film formation due to the photopolymerization of the organically modified colloidal-silica nanoparticles and acryl resin upon UV exposure as well as an excellent optical transmission of above 90% in the visible region and an enhanced surface smoothness of around 1 nm RMS roughness. They likewise exhibit improved thermal and mechanical characteristics, much better than those of acryl resin. Lastly and most importantly, these photocurable hybrid materials fabricated through the synergistic combination of colloidal-silica nanopar- ticles with acryl resin are candidates for optical and electrical applications. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Inorganic–organic nanohybrid materials (IONHMs) have at- tracted much attention of late as candidates for optical and electri- cal applications due to their outstanding properties, including thermal stability, mechanical strength, high transparency, and good processibility [1–6]. Thus, intensive research on the design and fabrication of IONHMs has been conducted, using a variety of methods, including a sol–gel process of organically modified sil- icon alkoxide, the embedment of inorganic particles in polymers, the embedment of organic dyes in sol–gel matrices, and the simul- taneous formation of interpenetrating organic–inorganic networks [7–10]. In general, IONHMs can be classified into two types, depending on the strength of the bonds between the organic and the inorganic phase [8]. One type of IONHM is that with weak bonds, such as van der Waals or hydrogen bonding, fabricated through the ex-situ physical mixing of the inorganic and organic components. The other type of IONHM is that with strong chemical bonds, such as covalent or ionocovalent chemical bonding, between the inorganic and the organic phase, synthesized by in-situ chemical routes [7–15]. ION- HMs with weak bonds exhibit good performance, which the respec- tive materials cannot exhibit, through the effective combination of their inorganic and organic components. These materials appear, however, during phase separation due to the agglomeration of the inorganic particles or the organic components, and due to the inter- facial defects between the two phases resulting from physical mix- ing, which leads not only to the degradation of the properties but also to a decrease in the stability and reproducibility of the materi- als. On the other hand, the IONHMs with strong chemical bonds be- tween the two phases are uniform and stable materials. Thus, film formation is easier when these materials are used, and the overall film properties are better. The sizes of the inorganic components of the described IONHMs, however, are mostly below several nm. Thus, they cannot contribute to the enhancement of the properties shown in the results. To highlight the better properties of IONHMs, the size control of the inorganic particles with several tens of nm diameters, and their stable dispersion in organic matrices, are very important, and chemical networking between the inorganic parti- cles and the organic components is required. Thus, in this study, monosized colloidal-silica nanoparticles with diameters of around 20 nm were synthesized, and surface- modified, using organically modified silicon alkoxide, for the 0022-3093/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2009.01.013 * Corresponding author. Tel.: +82 55 280 1614; fax: +82 55 280 1590. E-mail address: [email protected] (D.J. Kang). Journal of Non-Crystalline Solids 355 (2009) 397–402 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol

Upload: dong-jun-kang

Post on 15-Oct-2016

214 views

Category:

Documents


2 download

TRANSCRIPT

Page 1: Fabrication and characterization of photocurable inorganic–organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

Journal of Non-Crystalline Solids 355 (2009) 397–402

Contents lists available at ScienceDirect

Journal of Non-Crystalline Solids

journal homepage: www.elsevier .com/locate / jnoncrysol

Fabrication and characterization of photocurable inorganic–organic hybridmaterials using organically modified colloidal-silica nanoparticles and acryl resin

Dong Jun Kang *, Dong Hee Han, Dong Pil KangAdvanced Materials and Application Research Laboratory, Korea Electrotechnology Research Institute, 28-1 Sungju-dong Changwon, Gyeongsangnam-do 641-120, Republic of Korea

a r t i c l e i n f o a b s t r a c t

Article history:Received 17 October 2008Received in revised form 13 January 2009Available online 21 February 2009

PACS:81.07.Pr81.20.Fw82.33.Ln

Keywords:STEM/TEMHardnessIndentation, microindentationAtomic force and scanning tunnelingmicroscopyNanoparticlesFT-IR measurementsOrganic–inorganic hybrids

0022-3093/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.jnoncrysol.2009.01.013

* Corresponding author. Tel.: +82 55 280 1614; faxE-mail address: [email protected] (D.J. Kang).

Photocurable inorganic–organic hybrid materials were prepared from colloidal-silica nanoparticles syn-thesized through the sol–gel process and using acryl resin. The synthesized colloidal-silica nanoparticleshad uniform diameters of around 20 nm and were organically modified, using methyl and methacrylfunctional silanes, for efficient hybridization with acryl resin. The organically modified and stabilized col-loidal-silica nanoparticles could be homogeneously hybridized with acryl resin without phase separation.The successfully fabricated hybrid materials exhibit efficient photocurability and simple film formationdue to the photopolymerization of the organically modified colloidal-silica nanoparticles and acryl resinupon UV exposure as well as an excellent optical transmission of above 90% in the visible region and anenhanced surface smoothness of around 1 nm RMS roughness. They likewise exhibit improved thermaland mechanical characteristics, much better than those of acryl resin. Lastly and most importantly, thesephotocurable hybrid materials fabricated through the synergistic combination of colloidal-silica nanopar-ticles with acryl resin are candidates for optical and electrical applications.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

Inorganic–organic nanohybrid materials (IONHMs) have at-tracted much attention of late as candidates for optical and electri-cal applications due to their outstanding properties, includingthermal stability, mechanical strength, high transparency, andgood processibility [1–6]. Thus, intensive research on the designand fabrication of IONHMs has been conducted, using a varietyof methods, including a sol–gel process of organically modified sil-icon alkoxide, the embedment of inorganic particles in polymers,the embedment of organic dyes in sol–gel matrices, and the simul-taneous formation of interpenetrating organic–inorganic networks[7–10].

In general, IONHMs can be classified into two types, dependingon the strength of the bonds between the organic and the inorganicphase [8]. One type of IONHM is that with weak bonds, such as vander Waals or hydrogen bonding, fabricated through the ex-situphysical mixing of the inorganic and organic components. The othertype of IONHM is that with strong chemical bonds, such as covalentor ionocovalent chemical bonding, between the inorganic and the

ll rights reserved.

: +82 55 280 1590.

organic phase, synthesized by in-situ chemical routes [7–15]. ION-HMs with weak bonds exhibit good performance, which the respec-tive materials cannot exhibit, through the effective combination oftheir inorganic and organic components. These materials appear,however, during phase separation due to the agglomeration of theinorganic particles or the organic components, and due to the inter-facial defects between the two phases resulting from physical mix-ing, which leads not only to the degradation of the properties butalso to a decrease in the stability and reproducibility of the materi-als. On the other hand, the IONHMs with strong chemical bonds be-tween the two phases are uniform and stable materials. Thus, filmformation is easier when these materials are used, and the overallfilm properties are better. The sizes of the inorganic componentsof the described IONHMs, however, are mostly below several nm.Thus, they cannot contribute to the enhancement of the propertiesshown in the results. To highlight the better properties of IONHMs,the size control of the inorganic particles with several tens of nmdiameters, and their stable dispersion in organic matrices, are veryimportant, and chemical networking between the inorganic parti-cles and the organic components is required.

Thus, in this study, monosized colloidal-silica nanoparticleswith diameters of around 20 nm were synthesized, and surface-modified, using organically modified silicon alkoxide, for the

Page 2: Fabrication and characterization of photocurable inorganic–organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

398 D.J. Kang et al. / Journal of Non-Crystalline Solids 355 (2009) 397–402

homogenous dispersion with acryl resin. In addition, the stable dis-persion of the colloidal-silica nanoparticles in acryl resin and thedegree of the chemical networking through the UV-induced poly-merization of the organically modified colloidal-silica nanoparti-cles and acryl resin were investigated. The optical and surfacecharacteristics of the developed IONHM films, newly formed usingthe synthesized colloidal-silica nanoparticles and acryl resin, werelikewise examined, and the influence of the colloidal-silica nano-particles in acryl resin on the thermal and mechanical propertieswas investigated.

2. Experimental section

2.1. Synthesis of the colloidal-silica nanoparticles

The colloidal-silica nanoparticles in IONHMs were synthesizedusing tetraethyl orthosilicate (TEOS, Aldrich), ethanol (Aldrich),concentrated ammonia (Aldrich), and distilled water as reagents.The formation of colloidal-silica nanoparticles takes place throughthe hydrolysis and condensation reactions, using TEOS as a startingmaterial, in an alcoholic ethanol solution consisting of water andammonia. Ammonia plays the role of a catalyst for hydrolysisand condensation. Furthermore, to obtain monosized colloidal-sil-ica nanoparticles, it is important to use the following working con-ditions: a constant temperature reaction and appropriated molarconcentrations of the reagents. Therefore, the reactions were real-ized at a constant room temperature and using the following molarratio: 1 M TEOS, 3 M distilled water, 0.34 M NH3, and 33.1 M etha-nol. Ethanol, distilled water, and NH3 were mixed and stirred for5 min at room temperature, in a reaction flask, and were combinedwith TEOS. The mixture was stirred for 24 h, with a stirring rate of800 rpm, using a magnetic stirrer. Subsequently, monosized colloi-dal-silica nanoparticles were obtained through hydrolysis andcondensation.

2.2. Synthesis of the MTMS-MPTMS-modified colloidal-silicananoparticles

The surfaces of the colloidal-silica nanoparticles were modifiedwith methyltrimethoxysilane (MTMS, Aldrich, 0.2 M) for 24 h, un-der a stirring rate of 800 rpm and using a magnetic stirrer, at roomtemperature. The molar ratio of MTMS to TEOS was 1:5. Then,methacryloxypropyltrimethoxysilane (MPTMS, Aldrich, 0.2 M)was reacted with the MTMS-treated colloidal-silica nanoparticlesunder magnetic stirring for 24 h, with a stirring rate of 800 rpmand at room temperature, for chemical polymerization with acrylresin. The molar ratio of MPTMS to TEOS was 1:5.

2.3. Fabrication of Photocurable IONHMs using the MTMS-MPTMS-modified colloidal-silica nanoparticles and acryl resin

After the reaction to the synthesis of the methyl and the meth-acryl-silane-treated colloidal-silica nanoparticles, any residualproduct (such as alcohol and water) was replaced with propyleneglycol monomethyl ether acetate (PGMEA, Aldrich) at 40 �C, usingan evaporator, for the hybridization of the organically modifiedcolloidal-silica nanoparticles with acryl resin (SK CYTEC, UP 053).The organically modified colloidal-silica nanoparticles were homo-geneously dispersed in PGMEA, and their solid content in PGMEAwas 30-wt%. To adequately mix and hybridize it with acryl resin,acryl resin was diluted with the PGMEA solvent, and acryl resin di-luted in PGMEA with 30-wt% solid contents was fabricated. Then,the organically modified colloidal-silica nanoparticles and the di-luted acryl resin with 30-wt% solid contents were efficiently mixedat a stirring speed of 800 rpm, using a magnetic stirrer, for 1 h.

Finally, the homogeneous photocurable hybrid solutions in PGMEAwere fabricated. The 0- to 80-wt% organically modified colloidal-silica nanoparticles that were stabilized through surface modifica-tion were homogeneously embedded in diluted acryl resin. In addi-tion, 1-wt% solid benzyldimethylketal (BDK, Aldrich) was added asa photoinitiator to the solutions composed of organically modifiedcolloidal-silica nanoparticles and acryl resin. After stirring thesolutions for 1 h at a stirring rate of 800 rpm and at room temper-ature, homogeneous and photocurable IONHMs were obtained.These photocurable IONHM solutions were filtered and werespin-coated onto clean glass substrates and wafers.

2.4. Fabrication of photocurable IONHM films using UV-inducedpolymerization

The coated IONHM films were then subjected to UV-(500 W HgLamp, <365 nm, Oriel97453)-induced polymerization under anitrogen atmosphere, after pre-drying at 90 �C for 3 min. Conse-quently, photocured IONHM films were fabricated.

2.5. Characterization

Transmission electron microscopy (TEM, 300 kV, JEM 3010 ofJEOL) was employed for the analysis of the size and dispersion ofthe organically modified colloidal-silica nanoparticles. The changesin the chemical structure of the photocurable IONHMs were exam-ined using Fourier transform infrared (FT-IR, JASCO 680 Plus) spec-troscopy, before and after UV irradiation. The optical transparencyand surface properties of the photocurable IONHM films wereexamined, respectively, through ultraviolet visible near-infrared(UV/Vis/NIR) spectroscopy and atomic-force measurement (AFM,SFI 3800N, SEIKO). In addition, the influence of the colloidal-silicananoparticles on the thermal stability and mechanical propertiesof the photocurable IONHM films was determined through ther-mogravimetric analysis (TGA) and the use of a nanoindentator(Nanoindenter XP, MTS Nano Instruments).

3. Results and discussion

3.1. FT-IR spectroscopy and transmission electron microscopy ofmonosized and homogeneous dispersed MTMS-MPTMS-modifiedcolloidal-silica nanoparticles

Fig. 1 shows the FT-IR spectra of the colloidal-silica nanoparti-cles and MTMS- and MTMS-MPTMS-modified colloidal-silica nano-particles. As shown in Fig. 1, in the organically modified silicananoparticles, the alkoxy groups and CH bond of the methyl groupsin the 2900- to 2700-cm�1 regions are shown, as well as the C@Cpeak at 1638–1615 cm�1 and the C@O peak at around 1725 cm�1

in the methacryl groups of MPTMS. On the other hand, the unmod-ified colloidal-silica nanoparticles had no FT-IR spectra within theabove ranges, except for the silica peaks within the 1000–1100 cm�1 range. Therefore, the surface modification of MTMSand MPTMS on the fabricated colloidal-silica nanoparticles wasconfirmed through the FT-IR spectra analysis.

Fig. 2 shows the TEM images of the colloidal-silica nanoparticleswith diameters of around 20 nm, indicating (a) the monosized andhomogeneous dispersion with surface modification of the func-tional silanes on the colloidal-silica nanoparticles, and (b) theagglomerated colloidal-silica nanoparticles due to the absence ofsurface modification in the functional silanes on the colloidal-silicananoparticles. Such monosized and homogeneous dispersion of thecolloidal-silica nanoparticles is due to the surface modificationof the methyl and methacryl silanes on the colloidal-silica nano-particles through the sol–gel technique. The organically modified

Page 3: Fabrication and characterization of photocurable inorganic–organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

Fig. 1. FT-IR spectra of the unmodified colloidal-silica nanopartilces and of theMTMS- and MTMS-MPTMS-modified colloidal-silica nanoaprticles.

Fig. 2. TEM images of the colloidal-silica nanoparticles with diameters of around20 nm, indicating (a) the monosized and homogeneous dispersion with surfacemodification of the functional silanes on the colloidal-silica nanoparticles, and (b)the agglomerated colloidal-silica nanoparticles without surface modification of thefunctional silanes on the colloidal-silica nanoparticles.

D.J. Kang et al. / Journal of Non-Crystalline Solids 355 (2009) 397–402 399

colloidal-silica nanoparticles were not agglomerated and phase-separated even upon exposure to a high-energy electron beam(i.e., 200 kV TEM), as shown in Fig. 2(a). Moreover, the colloidal-sil-ica nanoparticles could be homogeneously mixed with acryl resin,and the mixed IONHM solutions remained transparent and stable,without phase separation and precipitation, within all the compo-sition ranges. On the other hand, the colloidal-silica nanoparticleswithout the surface modification of the organically modified func-

tional silanes were not only agglomerated but also phase-sepa-rated and precipitated, by mixing them with acryl resin.

3.2. Photocurability of the fabricated IONHMs determined via FT-IRspectroscopy

These well-dispersed and stabilized IONHM solutions consist-ing of organically modified colloidal-silica nanoparticles in acrylresin have photocurable groups, such as acryl and methacryl moi-eties. Thus, the IONHM solutions can be cured through UV poly-merization, and the IONHM films can be simply fabricatedthrough UV irradiation. Fig. 3 shows the FT-IR spectra of the photo-curable IONHM films with (a) 20- and (b) 40-wt% organically mod-ified colloidal-silica nanoparticles in acryl resin on the Sisubstrates, as a function of UV dose (left: FT-IR spectra of thephotocurable IONHM films within the 4000–400 cm�1 range;right: FT-IR spectra of the photocurable IONHM films within the1850–1550 cm�1 range). The FT-IR measurements were performedwithin the 4000–400 cm�1 range, with a 4 cm�1 resolution. Indi-rectly, the FT-IR shows that the polymerization or crosslinking ofthe acryl or methacryl groups in the photocurable IONHM films oc-curred during the UV curing process. For both composition ranges,it was found that the intensity of the C@C peak at 1638–1615 cm�1

had been reduced, and that the C@O peak at 1725 cm�1 had shiftedto longer wavenumbers as the UV dose increased. This representsthe consumption of the C@C bonds and the loss of the conjugationwith the C@C bond because of the photopolymerization of therespective photocurable IONHM films. On the other hand, the inte-grated area of the C@O bond at 1725 cm�1 remained constant[7,16]. The conversion degree of the C@C bond calculated fromthe integrated peak intensities of the C@C and C@O bonds wasplotted as a function of the organically modified colloidal-silicananoparticle contents at a UV dose of 1.4 J/cm2, as shownFig. 3(c). The conversion degree of the C@C bond increased up to85–88% within the composition ranges of 0–40-wt% of the organi-cally modified colloidal-silica nanoparticles in acryl resin. As theorganically modified colloidal-silica nanoparticles in acryl resin in-creased to 80-wt%, the conversion degree decreased to 50%. It wasfound that the photocurable IONHM film with a low content of col-loidal-silica nanoparticles in acryl resin has a faster and higherconversion degree compared to that with a high content of colloi-dal-silica nanoparticles in acryl resin. This is because more colloi-dal-silica nanoparticles screen the polymerization of the acryl ormethacryl radicals in the photocurable IONHM solutions. The con-version degree, however, which indicates the extent of the poly-merization, reached almost 90–50%, which is enough to cure thephotocurable IONHMs within all the composition ranges. There-fore, the IONHM films could be fabricated within wide compositionranges through simple UV irradiation because of the efficientphotocurability of the developed IONHM solutions, which can beapplied to the electrical- and optoelectrical-device formation pro-cess using the photolithography technique.

3.3. Optical transparency of the photocured IONHM films via UV/Vis/NIR spectroscopy

Fig. 4 shows the optical transparency of the IONHM films thatwere photocured with 0- to 80-wt% organically modified colloi-dal-silica nanoparticles in acryl resin. The analysis of the opticaltransmission of the photocured IONHM films that had been usedto coat the quartz substrate was carried out at visible wavelengthsof 400–800 nm, using ultraviolet visible near-infrared (UV/Vis/NIR)spectroscopy. All the photocured IONHM films were optically trans-parent despite the incorporation therein of colloidal-silica nanopar-ticles in acryl resin. The spectra show that the photocured IONHMfilms within all the composition ranges are highly transparent, with

Page 4: Fabrication and characterization of photocurable inorganic–organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

Fig. 3. FT-IR spectra of the photocurable IONHM films with (a) 20- and (b) 40-wt% organically modified colloidal-silica nanoparticles in acryl resin on the Si substrates as afunction of UV dose (left: FT-IR spectra of the photocurable IONHM films within the 4000–400 cm�1 range; right: FT-IR spectra of the photocurable IONHM films within the1850–1550 cm�1 range), and (c) conversion degrees of the C@C bond calculated from the integrated peak intensities of the C@C and C@O bonds plotted as a function of theorganically modified colloidal-silica nanoparticles in acryl resin content at a UV dose of 1.4 J/cm2.

400 D.J. Kang et al. / Journal of Non-Crystalline Solids 355 (2009) 397–402

around 90% transmittance in the visible spectrum regions of400–800 nm. This is due not only to the homogeneous dispersionof the organically modified colloidal-silica nanoparticles in acryl re-

sin without phase separation but also to its high photodurability,without transparency decrease and discoloration, upon UVirradiation

Page 5: Fabrication and characterization of photocurable inorganic–organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

Fig. 4. Optical transparency of the IONHM films photocured with 0- to 80-wt%organically modified colloidal-silica nanoparticles in acryl resin.

D.J. Kang et al. / Journal of Non-Crystalline Solids 355 (2009) 397–402 401

3.4. Surface properties of the photocured IONHM films determined viaatomic-force microscopy

To characterize the surface quality of the photocured IONHMfilms, their surface roughness was observed through atomic-forcemicroscopy (AFM, SFI 3800N, SEIKO). Fig. 5(a)–(e) shows the 3DAFM images of the photocured IONHM films with 0- to 80-wt%

Fig. 5. AFM 3D images of the IONHM films photocured with (a) 0-wt%, (b) 20-wt%, (c) 40-acryl resin, and (f) RMS roughness of the photocured IONHMs as a function of the organ

organically modified colloidal-silica nanoparticles in acryl resin.The AFM images in Fig. 5(f) reveal that the IONHM films thathad been photocured through the incorporation and chemicalnetworking of organically modified colloidal-silica nanoparticleswith acryl resin have smoother and more homogeneous surfaces,with a low root-mean-square (RMS) roughness of below 1 nm,compared to the base acryl resin, which has an RMS roughness ofaround 10 nm. This is because the incorporation and photoinducedchemical networking of the organically modified colloidal-silicananoparticles with acryl resin could reduce the shrinkage of acrylresin during UV curing.

3.5. Thermal stabilities of the photocured IONHMs measured via TGA

In addition, the thermal stabilities in the photocured IONHMswere investigated depending on the organically modified colloi-dal-silica nanoparticle content, and were compared with that of ac-ryl resin. Fig. 6 shows the dynamic thermogravimetric curvesexhibiting the different inorganic residual weight losses of thephotocured IONHMs as a function of the colloidal-silica nanoparti-cle content. The 5-wt% weight loss temperature in the photocuredIONHMs was around 320–370 �C, and it increased in proportion tothe incorporated colloidal-silica nanoparticles in acryl resin con-tent. Rapid weight loss of the photocured IONHMs did not occuruntil 400 �C. More importantly, the residual weights of the photo-cured IONHMs were proportional to their colloidal-silica nanopar-ticle in acryl resin contents and could be efficiently enhanced bythe incorporation of the colloidal-silica nanoparticles into acryl re-sin, as shown in Fig. 6.

wt%, (d) 60-wt%, and (e) 80-wt% organically modified colloidal silica nanoparticles inically modified colloidal-silica nanoparticles in acryl resin content.

Page 6: Fabrication and characterization of photocurable inorganic–organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

Fig. 6. Dynamic thermogravimetric curves exhibiting the different inorganicresidual weight losses of the photocured IONHMs as a function of the organicallymodified colloidal-silica nanoparticles in acryl resin content.

Fig. 7. Hardness of the photocured IONHMs as a function of the organicallymodified colloidal-silica nanoparticles in acryl resin content.

402 D.J. Kang et al. / Journal of Non-Crystalline Solids 355 (2009) 397–402

3.6. Mechanical properties of the photocured IONHM films determinedvia nanoindentation

In addition, the mechanical properties, such as Young’s modulusand the hardness of the photocured IONHM films, were investigatedthrough nanoindentation (Nanoindenter XP, MTS Nano Instru-ments), using a three-sided-pyramid Berkovich indenter. Nanoin-dentation is a superficial technique for quasi-statisticallymeasuring the penetration generated by increasing the loadsapplied to a material [17–18]. Fig. 7 exhibits the hardness of the

photocured IONHMs as a function of the organically modified colloi-dal-silica nanoparticle in acryl resin content. The hardness of thephotocured IONHM films within all the composition ranges wasmeasured via nanoindentation and was compared with that of baseacryl resin without colloidal-silica nanoparticles, as shown in Fig. 7.Moreover, no measured IONHM film was found to have a crack orfracture after nanoindentation. The hardness of the photocured ION-HM films was enhanced by increasing their colloidal-silica nanopar-ticle contents, and it was almost one and a half times higher thanthat of the acryl-resin-coated film under the same curing conditions.This means that the mechanical properties of IONHMs can beefficiently enhanced through the homogenous dispersion andUV-induced chemical networking of the organically modified colloi-dal-silica nanoparticles in acryl resin.

4. Conclusions

Photocurable IONHMs were successfully fabricated from organ-ically modified colloidal-silica nanoparticles in acryl resin withoutphase separation and precipitation. The successfully fabricatedIONHMs exhibit efficient photocurability, chemical networking be-tween the two phases, and simple film formation upon UV expo-sure, as well as an excellent optical transmission of above 90% inthe visible regions and an enhanced surface smoothness of around1 nm RMS roughness. In addition, the IONHM films exhibit im-proved thermal and mechanical characteristics, much better thanthose of acryl resin, with the incorporation and chemical network-ing of organically modified colloidal-silica nanoparticles in acrylresin. Lastly and most importantly, these photocurable IONHMsfabricated through the synergistic combination of organically mod-ified colloidal-silica nanoparticles with acryl resin, which showoverall enhanced properties, are candidates for solution-process-ible materials for optical and electrical applications.

References

[1] B.M. Novak, Adv. Mater. 5 (1993) 422.[2] M. Sternitzke, B. Derby, R.J. Brook, J. Am. Ceram. Soc. 81 (1998) 41.[3] T. Kikukawa, K. Kuraoka, K. Kawabe, K. Yasuda, K. Hirao, T. Yazawa, J. Am.

Ceram. Soc. 87 (2004) 504.[4] H.J. Chung, K. Ohno, T. Fukuda, R.J. Composto, Nano. Lett. 5 (2005) 1878.[5] J.H. Kim, J.H. Ko, B.S. Bae, J. Sol–Gel Sci. Technol. 41 (2007) 249.[6] X. Song, X.Wang.H. Wang, W. Zhong, Q. Du, Mater. Chem. Phys. 109 (2008) 143.[7] D.J. Kang, B.S. Bae, Acc. Chem. Res. 40 (2007) 903.[8] P. Judeinstein, C. Sanchez, J. Mater. Chem. 6 (1996) 511.[9] A. Ulman, Adv. Mater. 2 (1990) 573.

[10] G. Cao, H.G. Hong, T.E. Mallouk, Acc. Chem. Res. 25 (1992) 420.[11] P. Judeinstein, Chem. Mater. 4 (1992) 4.[12] S. Diré, F. Babonneau, C. Sanchez, J. Livage, J. Mater. Chem. 2 (1992) 239.[13] M.W. Ellesworth, B.M. Novak, Chem. Mater. 5 (1993) 839.[14] S. Xiong, Q. Wang, Y. Chen, Mater. Chem. Phys. 103 (2007) 450.[15] L. Jiang, W. Wang, D. Wu, J. Zhan, Q. Wang, Z. Wu, R. Jin, Mater. Chem. Phys.

104 (2007) 230.[16] W.S. Kim, R. Houbertz, T.H. Lee, B.S. Bae, J. Polym. Sci., Part B: Polym. Phys. 42

(2004) 1979.[17] W.C. Oliver, G.M. Pharr, J. Mater. Res. 7 (1992) 1564.[18] J. Ballarre, D.A. López, A.L. Cavalieri, Thin Solid Films 516 (2008) 1082.