柔性可调核壳微凝胶的旋转运动与形状起伏的耦合
Coupling of Rotational Motion with Shape Fluctuations of Core-shell Microgels Having Tunable Softness
摘要：
利用动态光散射（DLS）和去偏振光散射（DDLS）研究了形状起伏对水溶液中可变形温敏微凝胶的影响。所研究的系统由聚苯乙烯的固体核和交联聚（N-异丙基丙烯酰胺）（PNIPA）的热敏外壳组成，没有和嵌入钯纳米粒子。PNIPA可溶于水，但其临界溶解温度较低，为32 ℃（LCST）。在LCST以下，PNIPA壳溶胀。在这里，我们发现，除了平移和旋转扩散，粒子表现出额外的动态形状波动。这导致旋转扩散系数的显著增加。在转变温度以上，壳层塌陷，形成一个相当紧密的核壳。在这种状态下，壳层的动力学被冻结，核-壳粒子的行为就像硬球一样。一个简单的物理模型，捕捉和解释的旋转运动和形状波动的耦合的本质。
英文摘要：
The influence of shape fluctuations on deformable thermosensitive microgels in aqueous solution is investigated by dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS). The systems under study consist of a solid core of polystyrene and a thermosensitive shell of cross-linked poly(N-isopropylacrylamide) (PNIPA) without and with embedded palladium nanoparticles. PNIPA is soluble in water, but has a lower critical solution temperature at 32 C (LCST). Below the LCST the PNIPA shell is swollen. Here we find that besides translational and rotational diffusion, the particles exhibit additional dynamics resulting from shape fluctuations. This leads to a pronounced apparent increase of the rotational diffusion coefficient. Above the transition temperature the shell collapses and provides a rather tight envelope of the core. In this state the dynamics of the shell is frozen and the core-shell particles behave like hard spheres. A simple physical model is presented to capture and explain the essentials of the coupling of rotational motion and shape fluctuations.
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