互穿聚合物网络微凝胶的弛豫动力学、柔软度与脆性
Relaxation dynamics, Softness and Fragility of Microgels with Interpenetrated Polymer Networks
AI总结：
本研究通过X射线和光散射技术，探究了PNIPAM/PAAc互穿网络微凝胶的动力学，发现通过调节柔软度可控制脆性，并观察到临界浓度下的动力学交叉及异常扩散行为。
摘要：
微凝胶是具有弹性和可变形性的颗粒，其性质介于聚合物和胶体之间，并且相对于硬胶体表现出非常规行为。我们通过相干X射线和光散射技术，研究了由PNIPAM和PAAc互穿聚合物网络构成的软微凝胶的动力学。通过改变PAAc含量来调节颗粒柔软度，我们可以随意调控IPN微凝胶的脆性。有趣的是，我们发现在临界重量浓度处出现动力学交叉，这导致结构弛豫时间从超Arrhenius行为演变为比Arrhenius更慢的行为，强度自相关函数的形状参数达到最小值，并出现颗粒运动的独特异常机制。这种复杂现象可以用极低浓度下的Fickian扩散、中间浓度下的有效非Fickian异常扩散以及由模式耦合理论很好描述的弹道运动来诠释。
英文摘要：
Microgels are elastic and deformable particles with a hybrid nature between that of polymers and colloids and unconventional behaviours with respect to hard colloids. We investigated the dynamics of a soft microgel made of interpenetrated polymer networks of PNIPAM and PAAc by means of coherent X-ray and light scattering techniques. By varying the particle softness through PAAc content we can tune at wish the fragility of IPN microgels. Interestingly we find the occurrence of a dynamical crossover at a critical weight concentration which leads to an evolution of the structural relaxation time from a super-Arrhenius to a slower than Arrhenius behaviour, a minimum for the shape parameter of intensity autocorrelation function and the emerging of distinct anomalous mechanisms for particle motion. This complex phenomenology can be described by a Fickian diffusion at very low concentrations, an effective non Fickian anomalous diffusion at intermediate values and a ballistic motion well described within the Mode Coupling Theory.
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