Zhang Lijuan, D'Acunzi Maria, Kappl Michael, Auernhammer Günter K, Vollmer Doris, van Kats Carlos M, van Blaaderen Alfons
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Langmuir. 2009 Mar 3;25(5):2711-7. doi: 10.1021/la803546r.
Core-shell polystyrene-silica spheres with diameters of 800 nm and 1.9 microm were synthesized by soap-free emulsion and dispersion polymerization of the polystyrene core, respectively. The polystyrene spheres were used as templates for the synthesis of silica shells of tunable thickness employing the Stöber method [Graf et al. Langmuir 2003, 19, 6693]. The polystyrene template was removed by thermal decomposition at 500 degrees C, resulting in smooth silica shells of well-defined thickness (15-70 nm). The elastic response of these hollow spheres was probed by atomic force microscopy (AFM). A point load was applied to the particle surface through a sharp AFM tip, and successively increased until the shell broke. In agreement with the predictions of shell theory, for small deformations the deformation increased linearly with applied force. The Young's modulus (18 +/- 6 GPa) was about 4 times smaller than that of fused silica [Adachi and Sakka J. Mater. Sci. 1990, 25, 4732] but identical to that of bulk silica spheres (800 nm) synthesized by the Stöber method, indicating that it yields silica of lower density. The minimum force needed to irreversibly deform (buckle) the shell increased quadratically with shell thickness.
分别通过无皂乳液聚合和分散聚合法合成了直径为800纳米和1.9微米的核壳聚苯乙烯-二氧化硅球，其中聚苯乙烯核采用上述两种方法制备。聚苯乙烯球用作模板，采用施托伯法（[格拉夫等人，《朗缪尔》，2003年，第19卷，6693页]）合成厚度可调的二氧化硅壳。通过在500摄氏度下热分解去除聚苯乙烯模板，得到厚度明确（15 - 70纳米）的光滑二氧化硅壳。通过原子力显微镜（AFM）探测这些空心球的弹性响应。通过尖锐的AFM探针在颗粒表面施加点载荷，并逐渐增加直至壳破裂。与壳理论的预测一致，对于小变形，变形随施加力呈线性增加。杨氏模量（18 +/- 6吉帕）比熔融二氧化硅的杨氏模量（[安达奇和坂加，《材料科学杂志》，1990年，第25卷，4732页]）小约4倍，但与通过施托伯法合成的块状二氧化硅球（800纳米）的杨氏模量相同，表明它产生的是低密度二氧化硅。使壳发生不可逆变形（屈曲）所需的最小力随壳厚度呈二次方增加。
