Teixeira A V, Geissler E, Licinio P
Universidade Federal de Viçosa, Departamento de Física, CCE, Av. P. H. Rolfs s/n - Campus - UFV, 36570-000 Viçosa, Brazil.
J Phys Chem B. 2007 Jan 18;111(2):340-4. doi: 10.1021/jp064338c.
We present dynamic light scattering (DLS) measurements of soft poly(methyl-methacrylate) (PMMA) and polyacrylamide (PA) polymer gels prepared with trapped bodies (latex spheres or magnetic nanoparticles). We show that the anomalous diffusivity of the trapped particles can be analyzed in terms of a fractal Gaussian network gel model for the entire time range probed by DLS technique. This model is a generalization of the Rouse model for linear chains extended for structures with power law network connectivity scaling, which includes both percolating and uniform bulk gel limits. For a dilute dispersion of strongly scattering particles trapped in a gel, the scattered electric field correlation function at small wavevector ideally probes self-diffusion of gel portions imprisoning the particles. Our results show that the time-dependent diffusion coefficients calculated from the correlation functions change from a free diffusion regime at short times to an anomalous subdiffusive regime at long times (increasingly arrested displacement). The characteristic time of transition between these regimes depends on scattering vector as approximately q(-2), while the time decay power exponent tends to the value expected for a bulk network at small q. The diffusion curves for all scattering vectors and all samples were scaled to a single master curve.
我们展示了对含有捕获体（乳胶球或磁性纳米颗粒）的软质聚甲基丙烯酸甲酯（PMMA）和聚丙烯酰胺（PA）聚合物凝胶进行的动态光散射（DLS）测量。我们表明，对于DLS技术探测的整个时间范围，可以根据分形高斯网络凝胶模型来分析捕获颗粒的反常扩散率。该模型是对线性链的Rouse模型的推广，扩展到具有幂律网络连通性标度的结构，其中包括渗流和均匀本体凝胶极限。对于捕获在凝胶中的强散射颗粒的稀分散体系，小波矢处的散射电场相关函数理想地探测了囚禁颗粒的凝胶部分的自扩散。我们的结果表明，从相关函数计算出的随时间变化的扩散系数在短时间内从自由扩散状态转变为长时间的反常亚扩散状态（位移越来越受限）。这些状态之间转变的特征时间与散射矢量近似为q(-2)相关，而时间衰减幂指数在小q时趋向于本体网络预期的值。所有散射矢量和所有样品的扩散曲线都被缩放到一条单一的主曲线上。
