微凝胶胶体晶体研究进展

Progress in the Study of Microgel Colloidal Crystals

Poly(N-isopropylacrylamide)(PNIPAM)微凝胶粒子是一种软的胶体粒子.和单分散的SiO_2、PS、PMMA等硬的胶体粒子一样,单分散的PNIPAM微凝胶粒子也可以自组装成为高度有序的胶体晶体.微凝胶粒子软物质的特性及其对外部刺激的响应性赋予其不同于硬球的组装行为.微凝胶胶体晶体的高度有序结构及其刺激响应性使其在诸多领域有重要用途.本文分别介绍了三维及二维微凝胶胶体晶体组装的研究进展,并对已开发的基于微凝胶胶体晶体的应用进行了总结.

Monodisperse hard colloid particles, such as SiO2, PS and PMMA colloids, can self-assemble into highly ordered colloidal crystals, and have important applications in a wide range of fields, including photonic crystals, surface patterning, chemical and biosensing, etc. Monodisperse PNIPAM microgel, a soft colloid, can also self-assemble into highly ordered colloidal crystals. Monodisperse PNIPAM microgel particles with size varying from tens of nanometers to several microns can be facilely synthesized by free-radical precipitation polymerization. Thanks to its soft nature and ability to respond to external stimuli, PNIPAM microgels exhibit self-assembly behavior different from that of hard colloids. The volume fraction, which is a key parameter for the crystallization of a colloidal dispersion, can be facilely tuned by temperature. In addition, because of the soft nature of the microgel spheres, microgel colloidal crystals are intrinsically defect-tolerant. Therefore large arrays of colloidal crystals with highly ordered structure can be facilely fabricated from these spheres. The highly ordered structure and the unique responsiveness to external stimili also make the microgel colloidal crystals highly promising for applications in various fields. Here we review the progress in the fabrication of both 3D and 2D microgel colloidal crystals. The general features of microgel colloidal crystals, such as crystallization and melting kinetics, and packing structures, were summarized. Emphasis was put on the recent efforts, e.g., the assembly of binary microgel colloidal crystals, the stabilization of the highly ordered structure of microgel colloidal crystals, the introduction of artificial defects into microgel colloidal crystals, and the assembly of large area, highly ordered 2D microgel colloidal crystals. The applications of microgel colloidal crystals already emerged were also reviewed, including their applications as colloidal atoms to study the process of crystallization and melting of the real crystals, as template to synthesize new materials with ordered structure and microgel clusters with ordered crystalline structure, and optical switcher and sensors.