论文标题
压力和介电弛豫的二分法行为在肿胀的热园水凝胶微粒的密集悬浮液中
Dichotomous behaviors of stress and dielectric relaxations in dense suspensions of swollen thermoreversible hydrogel microparticles
论文作者
论文摘要
假设：虽然已经对大型剪切流对复杂流体中显微镜结构的机械破坏进行了广泛的研究，但施加菌株对大分子聚集体介电性能的影响却受到了较少的关注。可以使用同时的流变学和介电实验来研究跨越几十年的时空尺度上剪切胶体悬浮液的动力学。 实验：使用精确的阻抗分析仪，我们研究了在不同温度下强烈剪切的热可厌食水凝胶聚凝胶聚凝胶聚凝胶聚凝胶聚凝胶聚凝胶（N-异丙基丙烯酰胺）（PNIPAM）颗粒的介电行为。我们还执行应力松弛实验，以发现大变形对这些悬浮液的大体机械模量的影响。 发现：所有剪切PNIPAM悬浮液的复杂介电渗透率的实际部分在低频和高频制度中表现出明显的松弛过程。在低于较低的固定溶液温度（LCST）的温度下，高度密集的PNIPAM悬浮液的介电性的实际和虚部都随着施加的振荡性应变振幅的增加而降低。同时，我们注意到介电松弛动力学的违反直觉减速。与我们在相同条件下进行的批量流变实验相反，我们的大量流变实验揭示了剪切稀释的动力学，并增加了应变幅度的增加。我们提出了剪切诱导的肿胀的pnipam颗粒脆弱簇的破裂，以解释我们的观察结果。 关键词：Rheo-Dielectric；热响应水凝胶；分段运动；反式极化；界面极化；密集的悬架；流变学；剪切。
Hypothesis: While the mechanical disruption of microscopic structures in complex fluids by large shear flows has been studied extensively, the effects of applied strains on the dielectric properties of macromolecular aggregates has received far less attention. Simultaneous rheology and dielectric experiments can be employed to study the dynamics of sheared colloidal suspensions over spatiotemporal scales spanning several decades. Experiments: Using a precision impedance analyzer, we study the dielectric behavior of strongly sheared aqueous suspensions of thermoreversible hydrogel poly(N-isopropylacrylamide) (PNIPAM) particles at different temperatures. We also perform stress relaxation experiments to uncover the influence of large deformations on the bulk mechanical moduli of these suspensions. Findings: The real parts of the complex dielectric permittivities of all the sheared PNIPAM suspensions exhibit distinct relaxation processes in the low and high frequency regimes. At a temperature below the lower consolute solution temperature (LCST), both real and imaginary parts of the permittivities of highly dense PNIPAM suspensions decrease with increase in applied oscillatory strain amplitudes. Simultaneously, we note a counter-intuitive slowdown of the dielectric relaxation dynamics. Contrary to our rheo-dielectric findings, our bulk rheology experiments, performed under identical conditions, reveal shear-thinning dynamics with increasing strain amplitudes. We propose the shear-induced rupture of fragile clusters of swollen PNIPAM particles to explain our observations. Keywords : Rheo-dielectric; Thermoresponsive hydrogels; Segmental motion; Counterion polarization; Interfacial polarization; Dense suspensions; Rheology; Shear-thinning.
