Facile and Versatile Platform Approach for the Synthesis of

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Facile and Versatile Platform Approach for the Synthesis of Submicrometer-Sized Hybrid Particles with Programmable Size, Composition, and Architecture Comprising Organosiloxanes and/or Organosilsesquioxanes Margot Segers,†,‡ Ryan van Zandvoort,‡ Marjolein Sliepen,† Nanning Arfsten,† Marcel Verheijen,§,∥ Helmut Keul,‡ Pascal Buskens,*,†,‡ and Martin Möller*,‡ †

The Netherlands Organisation for Applied Scientific Research (TNO), De Rondom 1, 5612 AP, Eindhoven, The Netherlands DWI − Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, 52056 Aachen, Germany § Philips Innovation Services, High Tech Campus 11, 5656 AE, Eindhoven, The Netherlands ∥ Department of Applied Physics, Eindhoven University of Technology, 5600 MB, Eindhoven, The Netherlands ‡

S Supporting Information *

ABSTRACT: We present a facile and versatile platform approach for the synthesis of submicrometer-sized hybrid particles based on an oil-in-water emulsion. These particles comprise organosiloxanes and/or organosilsesquioxanes formed via hydrolysis and polycondensation of alkyl- or aryltrimethoxysilane, and polystyrene or poly(methyl methacrylate) formed through radical polymerization of styrene and methyl methacrylate, respectively. In this synthesis, the alkyl- or aryltrimethoxysilane fulfills three different roles: (i) it is part of the oil phase, (ii) serves as monomer for the formation of the organosiloxane network, and (iii) forms a surface active species that stabilizes the emulsion. Size, composition and architecture of the resulting hybrid particles are programmable in this synthetic approach, as demonstrated for the combination phenyltrimethoxysilane/styrene. The versatility of the approach is demonstrated by preparing hybrid particles based on following precursor/ monomer combinations: phenyltrimethoxysilane/methyl methacrylate, methyltrimethoxysilane/styrene, (3-acryloxypropyl)trimethoxysilane/styrene and (3-mercaptopropyl)trimethoxysilane/styrene. Latter combination yields hybrid spheres with thiol groups suited for further functionalization.

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the particle surface.6,12,13 Other routes for the production of such hybrid nanoparticles include construction of hybrid block copolymers containing reactive siloxane units,14,15 miniemulsion polymerization,16,17 surface functionalization of silica nanoparticles with oligomers/polymers,18−23 loading of microgels with silicon containing materials,24 and deposition of silica on polymeric micellar and vesicular structures.25,26 Most of these methods are cost-intensive and multistep synthesis routes. In some cases, di- or triblock copolymers are required14,15,25,26 and some processes are intrinsically difficult to perform on industrial scale.27 Hence, polymer particles comprising silica or organosiloxanes with a programmable size, composition, and architecture are costly and/or technically difficult to obtain on an industrial scale. Under appropriate reaction conditions, organosilsesquioxanes can form through hydrolytic conversion of alkyl- or

INTRODUCTION Submicrometer-sized, hybrid particles comprising an organic polymer and silica or organosiloxanes are interesting building blocks for the production of nanocomposites. Furthermore, such particles are particularly suited for functionalization with metals and metaloxides.1−3 Especially, particles with a programmable size, composition, and architecture are of interest, because they form the base for advanced composites with tailored functionalities. Examples of products comprising such hybrid particles, or hollow or porous particles produced thereof are scratch and abrasion resistant coatings,4,5 chromatographic materials,6 materials for water purification,6 optical coatings,7−9 catalyst supports,10 and materials for encapsulation and controlled release.11 In spite of the large potential of such hybrid particles, they are not yet widely used in commercial applications. This is mainly due to the limitations of the synthesis routes developed to date. In many cases, polymer nanoparticles are used as templates to produce such hybrid particles. In those cases, the silicon containing material either grows inside the particle or on © XXXX American Chemical Society

Received: July 18, 2014 Revised: September 3, 2014

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dx.doi.org/10.1021/cm5026415 | Chem. Mater. XXXX, XXX, XXX−XXX

Chemistry of Materials

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aryltrialkoxysilanes.28 These are interesting building blocks for composite materials, and are for example used for enhancing the thermal oxidative stability of polyethylene in air,29 increasing the glass transition and decomposition temperature of polystyrene,30 and preventing crystallization and lowering the glass transition temperature of poly(ethylene oxide).31 Furthermore, they are applied in advanced functional composites, e.g., to prevent interchain interactions in polyfluorene leading to a reduction in undesired emission and improvement of thermal stability of organic light-emitting diodes,32 or to improve the reactive ion etching behavior of resists used in lithography processes.33 Here, we present a facile and versatile platform approach for the synthesis of submicrometer-sized hybrid particles with programmable size, composition and architecture comprising organosiloxanes and/or organosilsesquioxanes. In this approach, an emulsion is formed of a mixture of alkyl- or aryltrimethoxysilane (R-TMS) and an organic monomer styrene or methyl methacrylate (MMA)in aqueous ammonia (Figure 1).

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EXPERIMENTAL SECTION

Materials. Ph-TMS (deposition grade, 98%), MPTMS (95%), potassium peroxodisulfate (Fluka, 99%), and styrene (≥99%, contains 4-tert-butylcatechol) were ordered from Sigma-Aldrich. MMA (99%, contains 10−110 ppm MEHQ) was ordered from Acros. APTMS (95%) and Me-TMS (98%) were ordered from ABCR. Ammonium hydroxide solution (25 wt % in water) was ordered from Merck. Styrene and MMA were degassed and stored under nitrogen. Prior to use they were purified by column chromatography on aluminum oxide to remove the inhibitor. All other chemicals were used as received. Synthesis of Hybrid Particles from the Mixture Ph-TMS/ Styrene (Prototypical Example). Demineralized water (113 mL) was degassed and heated to 60 °C in a 250 mL round-bottom flask under a nitrogen atmosphere. Ammonium hydroxide solution was then added (25 wt %, 5 mL). Third, Ph-TMS (0.5 mL) was added and the mixture was stirred for 5 min using a magnetic stirring bar. Subsequently, styrene (0.5 mL) and potassium peroxodisulfate (0.04 molar eq to styrene) were added. The mixture was heated to 80 °C and stirred for 4 h. The obtained dispersion was filtered over a paper filter (Macherey-Nagel MN 615 1/4 ø240 mm). The filtered dispersion was centrifuged at 3214 xG for 20 min, after which the supernatant was removed and the residue was dispersed in demineralized water using an ultrasound bath for 15 min. The resulting dispersion was centrifuged a second time, after which the supernatant was removed and the residue was dispersed in demineralized water. Pendant Drop Experiments. Interfacial tension measurements were performed using a conventional pendant drop technique setup with a 1.8 mm needle, using the Krüss DSA 100 equipped with DSA software. Images of the drop were taken every 10 s. Thermogravimetric Analysis. TGA analysis was performed using a Discovery TGA (TA Instruments). Samples were loaded in platinum pans and ramped at 10 °C/min to 700 or 900 °C under dry air with a flow rate of 20 mL/min. X-ray Diffraction (XRD) Analysis. XRD measurements were carried out on a Bruker Discover D8 using Cu Ka radiation, with Ni filter for CuKb filtering on primary side. Bragg−Brentano setup was used with fixed sample illumination of 10 mm, and 2.5° Soller slits. On secondary side Soller slits of 2.5° were used with a Lynxeye detector. Suppression of air scattering and direct beam detection was done by using a knife-edge at 4 mm above the sample. Samples were prepared by drying an aqueous particle dispersion at 50 °C onto a “low background” sample of silicon. Infrared (IR) Spectroscopy. IR spectra were either recorded on a Nicolet 6700 FTIR spectrometer (Thermo Scientific) in the ATR mode (diamond crystal) or on a Nicolet Nexus 470 FTIR spectrometer (Thermo Scientific) using KBr pallets. Raman Spectroscopy. Raman spectra were recorded on a Bruker RFS 100/S equipped with a YAG laser 1064 nm of 200 mW, using 100 scans. Samples were dried prior to the measurement. Scanning Electron Microscopy. SEM measurements were carried out using a FEI, quanta 600 microscope. Samples were prepared by drying a dispersion droplet on a cleaned microscope slide and were subsequently sputtered with a gold coating. The accelerating voltage used was 15 kV. Transmission Electron Microscopy. TEM studies were performed using a JEOL ARM 200 probe corrected TEM, operated at 200 kV. Imaging of the particles was performed in high-angle annular dark field (HAADF)−scanning TEM (STEM) mode. Energydispersive X-ray spectrocopy (EDS) spectra were recorded using a 100 mm2 Centurio SDD detector. EDS mappings were obtained in STEM mode by acquiring full spectra in grids of either 256 × 256 or 512 × 512 pixels. All mappings were obtained by summation of 50−100 frames, each having 0.1 ms acquisition time per pixel per frame. In this way, the particles remained unaffected by the impact of the incident electron beam.

Figure 1. Schematic representation of the synthesis of submicrometersized hybrid particles.

Through hydrolytic conversion of R-TMS, a surface active species is formed, as recently reported by our research group.34 This stabilizes the emulsion, and through hydrolysis and polycondensation an organosiloxane and/or organosilsesquioxane network is formed. Simultaneously, the organic monomer is polymerized using conventional radical polymerization. This results in hybrid nanoparticles with a programmable composition, i.e., ratio of organosiloxane/organosilsesquioxane to organic polymer, that depending on this ratio, display different architectures ranging from homogeneous spheres to multidomain and core−shell type particles, as shown for the combination phenyltrimethoxysilane (Ph-TMS)/styrene. The particle size can be programmed independently of the composition. Additionally, we demonstrate the versatility of the approach by preparing hybrid particles based on following combinations: Ph-TMS/MMA, methyltrimethoxysilane (MeTMS)/styrene, (3-acryloxypropyl)trimethoxysilane (APTMS)/ styrene, and (3-mercaptopropyl)trimethoxysilane (MPTMS)/ styrene. B



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RESULTS AND DISCUSSION To obtain stable and well-defined particles from the mixture Ph-TMS/styrene, it is important to tune the reaction parameters in such way that a stable emulsion is formed prior to the formation of the phenylsiloxane network and polymerization of styrene. As reported previously, a surface active species is formed within a few minutes through hydrolytic conversion of Ph-TMS in aqueous ammonia of pH 11 at 60 °C, resulting in an oil-in-water (o/w) emulsion of Ph-TMS in aqueous ammonia.34 To acquire information on the rate of formation of the surface active species in reaction mixtures comprising Ph-TMS, styrene, and aqueous ammonia, and to obtain more information on its characteristics, we performed pendant drop experiments analyzing the change in shape of a droplet of aqueous ammonia (pH 11) in four Ph-TMS/styrene mixtures with a volume ratio Ph-TMS:styrene of 2:3, 3:7, 1:4, and 1:9, respectively. This measurement setup was selected because the density of the aqueous phase is higher than the density of the organic phase. Mixtures with volume ratios higher than 2:3 could not be analyzed because of an insufficient difference in density between both phases. These experiments were performed at room temperature. The evolution of the droplet shape in this experiment directly relates to the evolution of the interfacial tension (IFT, Figure 2).

centrifugation and subsequently dispersed in water at neutral pH. Using a volume ratio Ph-TMS:styrene of 1:1, we obtained particles with an average diameter Dav of 512 nm and a narrow size distribution (σ/Dav) of 0.05 (Figure 3).35

Figure 3. SEM image of hybrid particles obtained from the mixture Ph-TMS/styrene (volume ratio Ph-TMS:styrene = 1:1).

Additionally, we determined the composition of these particles using thermogravimetric analysis (TGA, Figure 4).

Figure 2. Evolution of the IFT; volume ratio Ph-TMS:styrene = 2:3 (red), 3:7 (purple), 1:4 (blue), and 1:9 (green). Figure 4. TGA analysis of hybrid particles obtained from the mixture Ph-TMS/styrene (volume ratio Ph-TMS:styrene = 1:1).

As displayed in Figure 2, the IFT sharply drops to a plateau value of 44 mN m−1 for the volume ratio 2:3 and to about 23 mN m−1 for the other three volume ratios, in the first 5 min of the experiment. Consequently, rapid emulsion formation is expected, and the use of additional surfactants for the synthesis of hybrid particles from Ph-TMS/styrene mixtures seems redundant. Hence, for the synthesis of submicrometer-sized hybrid spheres, we added Ph-TMS directly to an aqueous ammonia solution of pH 11 at 60 °C. On the basis of the IFT measurements presented above and the fact that hydrolysis and condensation of organotrialkoxysilanes proceed faster at elevated temperatures, we assumed that the surface active species was formed within 5 min and subsequently added styrene and potassium peroxodisulfate (volume ratio oil:water = 1:118). Subsequently, the reaction mixture was heated to 80 °C to facilitate further hydrolysis and polycondensation of PhTMS and initiate the radical polymerization of styrene. The reaction mixture was then stirred at 80 °C for 4 h. The hybrid particles were separated from the reaction mixture through

As displayed in Figure 4, the hybrid particles decompose in two steps: polystyrene decomposes at about 300 °C, and the phenylsiloxane network decomposes at about 600 °C. After the second decomposition step, all organic material is removed, leaving SiO2 as residue. The SiO2 residue corresponds to 21 wt % of the original sample, which is in agreement with the expected theoretical value of 18 wt %. Hence, Ph-TMS not only forms the surface active species to facilitate the emulsion polymerization of styrene but also is converted to a phenylsiloxane network that blends into hybrid particles with polystyrene. Figure 5 shows the X-ray diffractogram (Figure 5a) and FTIR spectrum (Figure 5b) of the particles formed using a 1:1 volume mixture of Ph-TMS and styrene. The relatively sharp peak in the X-ray diffractogram at 7.34° and the broad peak at 18.46° confirm the presence of phenylsilsesquioxane(s) in the C



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defined particles for volume ratios Ph-TMS:styrene from 1:9999 to 9:1. After purification via centrifugation and subsequent dispersion in water at neutral pH, the resulting dispersions were stable for at least 2 weeks. The size of the particle depends on the volume ratio Ph-TMS: styrene (Figure 7). For volume ratios ranging from 3:2 to 9:1, the diameter of

Figure 7. Particle size as a function of the volume ratio PhTMS:styrene (volume ratio oil:water = 1:118).

the resulting hybrid particles is approximately 600 nm. For volume ratios ranging from 1:9999 to 3:7, the resulting spheres have an approximate size between 300 and 350 nm. In the intermediate region between 3:7 and 3:2, the particle size gradually increases from about 350 to about 600 nm. To validate the composition of these particles, we performed TGA analysis (Figure 8). From these results, we conclude that

Figure 5. (a) X-ray diffractogram and (b) FT-IR spectrum of hybrid particles obtained from the mixture Ph-TMS/styrene (volume ratio Ph-TMS:styrene = 1:1).

hybrid particles.36−38 The X-ray reflections represent the chainto-chain and intrachain distances of 1.20 and 0.48 nm, respectively. The presence of phenylsilsesquioxane(s) was confirmed by FT-IR analysis. In the FT-IR spectrum, the OH functionality is represented by the very weak absorption at 3622 cm−1. The peaks in the region between 1200 and 1000 cm−1 correspond to Si−O−Si stretching vibrations. The distinct absorption maximum at 1128 cm−1 is indicative for the presence of the so-called T10 silsesquioxane.34,39 To provide conclusive evidence for the formation of hybrid particles, and to obtain insight in the architecture of the particles, we performed STEM-EDS element mappings (Figure 6). From the STEM images, we conclude that hybrid particles

Figure 8. Theoretical (line) and measured amount of SiO2 (dots) as a function of the volume ratio Ph-TMS: styrene (volume ratio oil:water = 1:118).

the particle composition matches the expected theoretical value for all particles. Ergo, the composition of these hybrid particles is programmable by the volume ratio Ph-TMS:styrene. Furthermore, FT-IR analysis was performed for all particles (see the Supporting Information, Figures S8−S24). The results are similar to the results obtained for the particles produced using a Ph-TMS:styrene ratio of 1:1. Ergo, all particles comprise phenylsilsesquioxane(s). To obtain more information on the architecture of the hybrid particles produced at different volume ratios Ph-TMS: styrene, we performed STEM-EDS mappings (Figure 9). As displayed in Figure 9, the architecture of the hybrid spheres directly depends on the volume ratio Ph-TMS: styrene. Using a small amount of styrene (volume ratio Ph-TMS: styrene = 9:1), we obtained homogeneous hybrid spheres. When increasing the amount of styrene (volume ratio Ph-TMS: styrene = 3:2), multidomain particles are formed, caused by phase separation

Figure 6. STEM-EDS mapping of hybrid particles obtained from the mixture Ph-TMS/styrene (volume ratio Ph-TMS: styrene = 1:1). The light blue areas are Si-rich and the dark blue areas are C-rich.

are formed. Within these particles, multiple domains are formed through phase separation of polystyrene and phenylsilsesquioxane. The typical size of these domains is on the order of about 50−300 nm. To obtain more insights in the scope and limitations of this synthetic approach, we prepared hybrid particles using different volume ratios Ph-TMS:styrene. We managed to prepare wellD



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Figure 9. Different particle architectures as a function of the volume ratio Ph-TMS: styrene: (a) volume ratio = 9:1, (b) volume ratio = 3:2, (c) volume ratio = 1:9. The light blue areas are Si-rich and the dark blue areas are C-rich. Note: in the left upper corner of a, particles are stacked on top of each other causing a higher brightness than the five individual particles displayed in this image. In c, the EDS sensitivity for Si is just above the detection limit. Hence, the bright pixels in the background do not represent silica oligomers, but rather illustrate the limited signal-to-noise level of this mapping.

of phenylsilsesquioxane and polystyrene. Using large amounts of styrene (volume ratio Ph-TMS:styrene = 1:9), we obtained core−shell particles with a polystyrene core and phenylsilsesquioxane shell. Ergo, the architecture of these hybrid particles is programmable by the volume ratio Ph-TMS: styrene. The size of hybrid particles based on Ph-TMS/styrene can be programmed independently from the particle composition. To demonstrate this, we performed three experiments at a volume ratio Ph-TMS:styrene of 1:1: one at the standard volume ratio oil:water (1:118), one at a lower volume ratio (1:236), and one at a higher volume ratio (1:59). All other reaction parameters were kept constant. Lowering the volume ratio oil:water from 1:118 to 1:236 resulted in a decrease in particle size from 512 to 280 nm, increasing the ratio from 1:118 to 1:59 resulted in an increase in particle size from 512 to 899 nm (Figure 10). Thus, we demonstrated that the particle size is programmable independent from the particle composition.

Figure 11. SEM images of hybrid particles based on a 1:1 volume mixture of (a) Ph-TMS/MMA (Dav = 177 nm, size distribution = 0.18), (b) Me-TMS/styrene (Dav = 295 nm, size distribution = 0.08), (c) APTMS/styrene (Dav = 139 nm, size distribution = 0.16) and (d) MPTMS/styrene (Dav = 347 nm, size distribution = 0.21).

Figure 10. SEM images of hybrid particles obtained at an oil:water volume ratio of (a) 1:236, (b) 1:118, and (c) 1:59 (volume ratio PhTMS:styrene = 1:1). Figure 12. STEM-EDS mappings of hybrid particles based on a 1:1 volume mixture of (a) Ph-TMS/MMA, (b) Me-TMS/styrene, (c) APTMS/styrene, and (d) MPTMS/styrene. The light blue areas are Si-rich and the dark blue areas are C-rich.

To demonstrate the versatility of this synthetic approach, we synthesized hybrid particles using following combinations of RTMS and organic monomer in a 1:1 volume ratio: Ph-TMS/ MMA, Me-TMS/styrene, APTMS/styrene, and MPTMS/ styrene. The volume ratio oil:water was kept constant at 1:118. In all cases, we demonstrated that hybrid particles were formed using SEM and STEM-EDS mappings (Figure 11 and Figure 12). The mixture Ph-TMS/MMA yielded particles with a Dav of 177 nm comprising PMMA and phenylsilsesquioxane, as demonstrated by STEM-EDS mapping (Figure 12a). The particles contain 22 wt % silica, which is in agreement with the 1:1 volume ratio Ph-TMS to MMA (see the Supporting Information, Figure S42). The combination Me-TMS/styrene and APTMS/styrene yielded hybrid spheres with a Dav of 295 and 139 nm, respectively. However, for these two combinations, the composition of the resulting hybrid particles is not in

agreement with the theoretical value, as demonstrated by TGA analysis (see the Supporting Information, Figure S40 and S41). The respective particles both contain less silica than expected (0.3 wt % vs. 31 wt % for Me-TMS/styrene and 2 wt % vs. 16 wt % for APTMS/styrene). On the basis of the reactivity of the acrylic moiety in APTMS, we assume that it participates in the radical polymerization process. Hence, we do not expect that the resulting hybrid particles comprise acrylic groups suited for further functionalization. Proving this unambiguously, however, is impossible due to the small amount of APTMS incorporated into the particles (2 wt % silica, vide supra). In these cases, small organosiloxane oligomers are formed as side product. E



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In case all five requirements are fulfilled, well-defined hybrid particles can be formed with a chemical composition reflecting the volume ratio R-TMS/monomer. This is the case for the combination Ph-TMS/styrene and Ph-TMS/MMA under the experimental conditions presented in this study. In case one or more of these requirements are not fulfilled, either no particles are formed or particles are formed with a chemical composition that does not reflect the volume ratio R-TMS/monomer used in the synthesis. The latter is the case for the combinations MeTMS/styrene, APTMS/styrene, and MPTMS/styrene under the experimental conditions presented in this study.

They are dispersed in the aqueous phase and can be removed through centrifugation. This is confirmed by SEM analysis of the crude reaction mixture (see the Supporting Information, Figures S44−S47) and the hybrid particles purified via centrifugation (Figures 11b, c and 12b, c). Using a 1:1 volume ratio of MPTMS/styrene, we obtained hybrid spheres with an average outer diameter of 347 nm (Figures 11d and 12d). The spheres contained 32 wt % silica, which deviates from the expected silica content of 20 wt %. This discrepancy is caused by incomplete conversion of styrene to polystyrene. Particles produced from MPTMS only have a silica content of 46 wt %, which confirms that the particles produced from the mixture MPTMS/styrene comprise both (3mercaptopropyl)siloxane and polystyrene. This is corroborated by FT-IR analysis (see the Supporting Information, Figure S24). The resulting hybrid particles contained functional thiol groups for further modification. This was demonstrated by Raman spectroscopic analysis (Figure 13). The signal at 2567

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CONCLUSIONS We developed a facile and versatile platform approach for the synthesis of submicrometer-sized hybrid particles comprising organosiloxanes/organosilsesquioxanes and organic polymers. In this approach, which is based on an oil-in-water emulsion, organotrialkoxysilanes fulfill three essential roles: (i) they form the surface active species that stabilizes the emulsion, (ii) are part of the oil phase and (iii) serve as monomer for the formation of the organosiloxane/organosilsesquioxane network through hydrolysis and polycondensation. The organic monomer forms the second part of the oil phase, and is converted into the corresponding polymer using conventional radical polymerization. This synthetic approach allows programming of particle composition, size and architecture, as demonstrated for the combination Ph-TMS/styrene. Using different ratios of Ph-TMS to styrene, we managed to produce hybrid spheres composed of polystyrene and phenylsilsesquioxane(s) of a size between 285 and 603 nm. The composition of these spheres reflected the Ph-TMS to styrene ratio used in the synthesis. The architecture ranged from homogeneous to multidomain and core−shell particles. Controlling the architecture can be of key importance for specific applications, incl. the production of tailored porous or hollow nanoparticles. The particle size could be programmed independent from the composition through variation of the oil to water ratio in the emulsion. To demonstrate the versatility of this approach, we prepared hybrid particles based on following combinations: PhTMS/MMA, Me-TMS/styrene, APTMS/styrene, and MPTMS/styrene. In all four cases hybrid spheres were produced. However, in the last three cases the composition of the hybrid spheres did not reflect the volume ratio R-TMS: styrene used in the synthesis. For the combination MPTMS/ styrene, hybrid spheres with functional thiol groups were formed. Currently, further work is ongoing in our laboratories to optimize the synthesis conditions for the combinations MeTMS/styrene, APTMS/styrene and MPTMS/styrene in order to obtain hybrid particles with a chemical composition reflecting the ratio R-TMS:monomer used in the synthesis. Additionally, we are working on further functionalization of the hybrid particles with metals and metal oxides. For that purpose, three strategies are pursued: (1) addition and conversion of suited precursors during particle synthesis, (2) inclusion of metal or metal oxide structures during particle synthesis, or (3) postmodification of the hybrid particles.

Figure 13. Raman spectrum of hybrid particles based on a 1:1 volume mixture of MPTMS/styrene.

cm−1 can be assigned to thiol groups. The absence of strong signals between 550 and 700 cm−1 indicates that hardly any S− S-bonds have formed. The strong signals at 1003, 2913, and 3053 cm−1 can be assigned to respectively antisymmetrical Si− O−Si stretching, antisymmetrical and symmetrical stretching of −CH2−, and C−H stretching in the phenyl ring of polystyrene. To obtain a uniform dispersion of well-defined, submicrometer-sized hybrid particles using a mixture of R-TMS and organic monomer, a set of requirements needs to be fulfilled, including: 1. A surface active species should be formed through hydrolytic conversion of R-TMS to stabilize the emulsion prior to polycondensation of the organosiloxane precursor and radical polymerization of the organic monomer. 2. R-TMS and the organic monomer should be miscible. 3. R-TMS, the organic monomer and their respective oligomers/polymers should be dissolved/dispersed in the oil phase or at the oil−water interface. 4. R-TMS or oligomers/particles formed thereof should not hinder the radical polymerization of the organic monomer. 5. The organic monomer or oligomers/polymers formed thereof should not hinder the formation of the organosiloxane network via hydrolysis and polycondensation of R-TMS.

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ASSOCIATED CONTENT

S Supporting Information *

(1) X-ray diffraction (XRD) analysis; (2) infrared (IR) spectroscopy; (3) thermogravimetric analysis (TGA); (4) scanning electron microscopy (SEM). This material is available free of charge via the Internet at http://pubs.acs.org/. F



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(30) Romo-Uribe, A.; Mather, P. T.; Haddad, T. S.; Lichtenhan, J. D. J. Polym. Sci., Part B: Polym. Phys. 1998, 36, 1857. (31) Yen, Y. J.; Cheng, C. C.; Kuo, S. W.; Chang, F. C. Macromolecules 2010, 43, 2634. (32) Lee, J.; Cho, H.; Jung, B.; Cho, N.; Shim, H. Macromolecules 2004, 37, 8523. (33) Wu, H.; Hu, Y.; Gonsalves, K. E.; Yacaman, M. J. J. Vac. Sci. Technol. B 2001, 19, 851. (34) Segers, M.; Arfsten, N.; Buskens, P.; Möller, M. RSC Adv. 2014, 4, 20673. (35) The average outer particle diameter, Dav, and the standard deviation, σ, were calculated from 50 measured particles in SEM. (36) de A. Prado, L. A. S.; Radovanovic, E.; Pastore, H. O.; Yoshida, I. V. P.; Torriani, I. L. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 1580. (37) Wang, X.; Li, J.; Wu, L. Polym. Adv. Technol. 2011, 22, 2151. (38) Adrianov, A. A.; Zhdanov, A. A.; Levin, V. Y. Annu. Rev. Mater. Sci. 1978, 8, 313. (39) Brown, J. F., Jr.; Vogt, L. H., Jr.; Prescott, P. I. J. Am. Chem. Soc. 1964, 86, 1120.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Solliance, a solar energy R&D initiative of ECN, TNO, Holst, TU/e, imec, and Forschungszentrum Jülich, and the Dutch province of Noord-Brabant are acknowledged for funding the TEM facility. The authors thank Bastiaan Ingenhut (TNO) for TGA analyses and Harmen Rooms (TNO) and Fieke van den Bruele (TNO) for XRD analyses.

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