Percy M J, Amalvy J I, Randall D P, Armes S P, Greaves S J, Watts J F
Department of Chemistry, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QJ, United Kingdom.
Langmuir. 2004 Mar 16;20(6):2184-90. doi: 10.1021/la035868s.
The surfactant-free synthesis of vinyl polymer-silica nanocomposite particles has been achieved in aqueous alcoholic media at ambient temperature in the absence of auxiliary comonomers. Styrene, methyl methacrylate, methyl acrylate, n-butyl acrylate, and 2-hydroxypropyl methacrylate were homopolymerized in turn in the presence of three commercially available ultrafine alcoholic silica sols. Stable colloidal dispersions with reasonably narrow size distributions were obtained, with silica contents of up to 58% by mass indicated by thermogravimetric analysis. Particle size distributions were assessed using both dynamic light scattering and disk centrifuge photosedimentometry. The former technique indicated that the particle size increased for the first 1-2 h at 25 degrees C and thereafter remained constant. Particle morphologies were studied using electron microscopy. Most of the colloidal nanocomposites comprised approximately spherical particles with relatively narrow size distributions, but in some cases more polydisperse or nonspherical particles were obtained. Selected acrylate-based nanocomposites were examined in terms of their film formation behavior. Scanning electron microscopy studies indicated relatively smooth films were obtained on drying at 20 degrees C, with complete loss of the original particle morphology. The optical clarity of solution-cast 10 microm nanocomposite films was assessed using visible absorption spectrophotometry, with 93-98% transmission being obtained from 400 to 800 nm; the effect of long-term immersion of such films in aqueous solutions was also examined. X-ray photoelectron spectroscopy studies indicated that the surface compositions of these nanocomposite particles are invariably silica-rich, which is consistent with their long-term colloidal stability and also with aqueous electrophoresis measurements. FT-IR studies suggested that in the case of the poly(methyl methacrylate)-silica nanocomposite particles, the carbonyl ester groups in the polymer are hydrogen-bonded to the surface silanol groups. According to differential scanning calorimetry studies, the glass transition temperatures of several poly(methyl methacrylate)-silica and polystyrene-silica nanocomposites can be either higher or lower than those of the corresponding homopolymers, depending on the nature of the silica sol.
在无辅助共聚单体的情况下，于室温的醇水介质中实现了乙烯基聚合物 - 二氧化硅纳米复合颗粒的无表面活性剂合成。苯乙烯、甲基丙烯酸甲酯、丙烯酸甲酯、丙烯酸正丁酯和甲基丙烯酸2 - 羟丙酯在三种市售的超细醇基二氧化硅溶胶存在下依次进行均聚。获得了具有合理窄尺寸分布的稳定胶体分散体，热重分析表明二氧化硅含量高达58%（质量分数）。使用动态光散射和圆盘离心光沉降法评估粒径分布。前一种技术表明，在25℃下，粒径在前1 - 2小时内增大，此后保持恒定。使用电子显微镜研究颗粒形态。大多数胶体纳米复合材料由尺寸分布相对较窄的近似球形颗粒组成，但在某些情况下会得到多分散性更强或非球形的颗粒。对选定的丙烯酸酯基纳米复合材料的成膜行为进行了研究。扫描电子显微镜研究表明，在20℃干燥时可获得相对光滑的薄膜，原始颗粒形态完全消失。使用可见吸收分光光度法评估溶液浇铸的10微米纳米复合薄膜的光学透明度，在400至800纳米范围内获得93 - 98%的透过率；还研究了此类薄膜在水溶液中长期浸泡的影响。X射线光电子能谱研究表明，这些纳米复合颗粒的表面组成总是富含二氧化硅，这与其长期的胶体稳定性以及水性电泳测量结果一致。傅里叶变换红外光谱研究表明，对于聚（甲基丙烯酸甲酯） - 二氧化硅纳米复合颗粒，聚合物中的羰基酯基团与表面硅醇基团形成氢键。根据差示扫描量热法研究，几种聚（甲基丙烯酸甲酯） - 二氧化硅和聚苯乙烯 - 二氧化硅纳米复合材料的玻璃化转变温度可能高于或低于相应均聚物的玻璃化转变温度，这取决于二氧化硅溶胶的性质。
