用探针粒子示踪微流变法测量明胶的动态不均匀性  

Dynamic Heterogeneity of Gelatin Study by Probe Particle Tracking Microrheology

作　　者：洪伟[1] 许国智 孙尉翔[1] 童真[1] 

机构地区：[1]华南理工大学材料科学研究所,广州510640

出　　处：《高分子学报》2017年第9期1488-1496,共9页Acta Polymerica Sinica

基　　金：国家自然科学基金(基金号21427805;21574047)资助项目

摘　　要：利用探针粒子示踪微流变法对明胶溶液等温凝胶化过程的动态不均匀性进行了观测.通过向体系中引入探针粒子,利用广义的Stokes-Einstein关系由探针粒子的位移建立了体系结构的空间分布.进而利用van Hove函数和非高斯因子描述了凝胶化转变前后动态不均匀性的变化,结果表明在凝胶化后体系动态在空间和时间尺度上都是不均匀的,与凝胶化前相比,凝胶化后的快动态有更高的贡献.为了进一步探究这种动态不均匀性在空间和时间上相关的变化,本工作在粒子示踪技术的基础上,实现了四点相关函数和极化率的测量.实验结果表明,凝胶化前体系的快松弛可以原位独立完成,而慢松弛则需要周围的结构单元协同完成;凝胶化后体系的快松弛和慢松弛均需要协同完成.Vitrification and gelation are two main paths for matters to transform from liquid to solid in nature.During these transition processes, the dynamics of the systems becomes slower, and there appears a relatively fastand slow dynamics, which finally results in the heterogeneous distribution of dynamics in the space and time. Thisdynamic heterogeneity in the space and time has been reported to diverge following the power law whenapproaching to the glass transition. However, it is still unclear for the dynamic heterogeneity evolution whenapproaching to the gelation. In this work, the dynamic heterogeneity in a gelatin solution during isothermalgelation at 22 ℃ was monitored by the probe particle tracking microrheology. The gel point was determined asthe waiting time tw ： 8 min through the ensemble averaged dynamic modulus, which was obtained from the meansquare displacement of the particles using the generalized Stokes-Einstein relation （GSER）. The spatialdistribution of the loss angle tang was established from the particle trajectories to represent heterogeneousviscoelasticity in the gelatin during the gelation. Then, the dynamic heterogeneity change during the gelation wasquantitatively evaluated by the van Hove function and the non-Gaussian parameter a2. The dynamics was found tobe heterogeneous after gelation in both respects of space and time, and the fast dynamics contributed more aftergelation when compared with that before gelation. To further investigate the spatial and time correlation for thisdynamic heterogeneity, the 4-point correlation function and 4-point susceptibility were measured on the base ofparticle tracking statistics. The results indicated that, before gelation of the gelatin solution, the fast relaxationproceeded independently, while the slow relaxation occurred with a large spatial correlation containing moresurrounding units. On the other hand, after gelation both the fast and slow relaxations processed correlatively andcooperatively with more surrounding units. This was consistent

关 键 词：凝胶化 动态不均匀性 VAN Hove函数 四点极化率 

分 类 号：O648.17[理学—物理化学]