【作者】 洪伟； 许国智； 欧晓钢； 王涛； 孙尉翔； 童真；

【Author】 Wei HONG;Guozhi XU;Xiaogang OU;Tao WANG;Weixiang SUN;Zhen TONG;Research Institute of Materials Science, South China University of Technology;

【机构】 华南理工大学材料科学研究所；

【摘要】 采用多粒子示踪法研究了胶体探针在发生临界凝胶化转变的介质中的动力学(dynamics)。阐明了介质的临界凝胶点粘弹谱与探针的均方位移的关系。基于这一认识,由探针的均方位移,可分别通过损耗角准则和time-cure叠加原理确定明胶的临界凝胶点及其临界指数n,且两种方法所得到的结果一致。对明胶在凝胶化过程中的时间和空间尺度演化进行了进一步的分析发现,在前凝胶阶段,测量的空间尺度与体系的空间尺度先后发生两次耦合。在与之相应的凝胶化阶段,探针位移的概率密度函数也显示了两次瞬态的非高斯峰。在后凝胶阶段,探针位移的概率密度函数出现第三个非高斯峰,暗示了凝胶网络的不均匀性。通过对概率密度函数进行去卷积得到探针扩散系数涨落的分布发现,非高斯具体来自扩散系数的分岔。以上研究表明,探针的非高斯动力学不是介质的直接等价,而是空间尺度耦合效应。更多还原

【Abstract】 The dynamics of the colloidal probes in a gelatin solution during the time-dependent sol-gel transition was investigated by multi-particle tracking. The relationship between the relaxation of the medium at the critical gel point and the mean square displacement of the probes were elucidated. Based on this understanding, the critical gel point of gelatin and the corresponding critical exponent n was unambiguously determined by the loss angle criterion and the time-cure superposition. The shift factors of the latter are further used to estimate the time/length scale evolution of the gelatin during the sol-gel transition. The growth of the medium length scale crossed with the two measuring length scales successively at the pre-gel regime. Coincide with the length scale crossovers, the probability density function(PDF) of the probe displacements displayed two transient peaks of non-Gaussianity. In the post-gel regime, the third peak of Gaussianity suggested the inhomogeneity in the gel network. The non-Gaussianity results from the bifurcation of diffusivity. The present work showed that the non-Gaussian dynamics of the probes are not the direct equivalence of that of the medium, but an effect of length scale coupling.更多还原