Schmitt Michael, Hui Chin Ming, Urbach Zachary, Yan Jiajun, Matyjaszewski Krzysztof, Bockstaller Michael R
Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, USA.
Chemistry Department, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA 15213, USA.
Faraday Discuss. 2016;186:17-30. doi: 10.1039/c5fd00121h.
Recent progress in the area of surface-initiated controlled radical polymerization (SI-CRP) has enabled the synthesis of polymer-grafted colloids with precise control over the architecture of grafted chains. The resulting 'particle brush materials' are of interest both from a fundamental as well as applied perspective because structural frustrations (associated with the tethering of chains to a curved surface) imply a sensitive dependence of the interactions between brush particles on the architecture of surface-tethered chains that offers new opportunities to design hybrid materials with novel functionalities. An important prerequisite for establishing structure-property relations in particle brush materials is to understand the role of homopolymer impurities that form, for example, by thermal self-initiation. This contribution presents a detailed discussion of the role of homopolymer additives on the structure and mechanical properties of particle brush materials. The results suggest that the dissolution of homopolymer fillers follows a two-step mechanism comprised of the initial segregation of homopolymer to the interstitial regions within the array and the subsequent swelling of the particle brush (depending on the respective degree of polymerization of brush and linear chains). Addition of even small amounts of homopolymer is found to significantly increase the fracture toughness of particle brush assembly structures. The increased resistance to failure could enable the synthesis of robust colloidal crystal type materials that can be processed into complex shapes using 'classical' polymer forming techniques such as molding or extrusion.
表面引发的可控自由基聚合（SI-CRP）领域的最新进展使得能够精确控制接枝链的结构来合成聚合物接枝胶体。由此产生的“粒子刷材料”无论从基础研究还是应用角度来看都备受关注，因为结构上的阻碍（与链在弯曲表面上的 tethering 相关）意味着刷状粒子之间的相互作用对表面接枝链的结构具有敏感依赖性，这为设计具有新颖功能的混合材料提供了新机会。在粒子刷材料中建立结构-性能关系的一个重要前提是了解例如通过热自引发形成的均聚物杂质的作用。本文详细讨论了均聚物添加剂对粒子刷材料的结构和力学性能的作用。结果表明，均聚物填料的溶解遵循两步机制，包括均聚物最初偏析到阵列内的间隙区域以及随后粒子刷的溶胀（取决于刷状链和线性链各自的聚合度）。发现即使添加少量均聚物也能显著提高粒子刷组装结构的断裂韧性。增强的抗破坏能力能够合成坚固的胶体晶体类材料，这些材料可以使用“经典”的聚合物成型技术（如模塑或挤出）加工成复杂形状。
