Caputo Franklin E, Burghardt Wesley R, Krishnan Kasiraman, Bates Frank S, Lodge Timothy P
Department of Chemical Engineering, Northwestern University, Evanston, IL 60208, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2002 Oct;66(4 Pt 1):041401. doi: 10.1103/PhysRevE.66.041401. Epub 2002 Oct 21.
In situ synchrotron x-ray scattering is used in conjunction with a novel annular cone and plate shear cell to study the nonequilibrium structure factor of a polymer bicontinuous microemulsion within the flow-gradient plane. At equilibrium the scattering is well described by the Teubner-Strey structure factor. In steady shear, the structure factor becomes highly anisotropic, owing to loss of scattering intensity along the flow direction and growth of intensity in peaks that progressively rotate towards the velocity-gradient direction. These results contrast with the predictions of a time-dependent Landau-Ginzburg model of Pätzold and Dawson, which generally predicts suppression of scattered intensity. The model assumption of a uniform velocity profile at the microemulsion length scale may be inappropriate owing to high viscosity contrast between the constituents of this sample. While the model anticipates a "stress-x-ray" rule, the data do not support its existence in this system. Nevertheless, strong connections do exist between x-ray anisotropy and stress during transient flow inception experiments. These connections break down upon flow cessation, where stress decays much more rapidly than anisotropy in the structure factor. The mechanical response of this sample exhibits a Rouse-like spectrum of relaxation times, whereas the second moment tensor used to characterize anisotropy in the structure factor exhibits nearly single-exponential relaxation. A phenomenological upper-convected-Maxwell/Lodge model for the second moment tensor provides essentially quantitative predictions of the structural response in step strain and oscillatory shear flow at moderate strains, although additional nonlinearity is found at higher strains.
原位同步加速器X射线散射与一种新型环形锥板剪切池结合使用，以研究聚合物双连续微乳液在流动梯度平面内的非平衡结构因子。在平衡状态下，散射可以很好地用托伊布纳-施特雷结构因子来描述。在稳定剪切中，结构因子变得高度各向异性，这是由于沿流动方向的散射强度损失以及峰强度的增加，这些峰逐渐向速度梯度方向旋转。这些结果与帕佐尔德和道森的时间相关朗道-金兹堡模型的预测形成对比，该模型通常预测散射强度会受到抑制。由于该样品成分之间的高粘度对比，在微乳液长度尺度上均匀速度分布的模型假设可能不合适。虽然该模型预期存在“应力-X射线”规则，但数据不支持其在该系统中的存在。然而，在瞬态流动起始实验中，X射线各向异性和应力之间确实存在很强的联系。在流动停止时，这些联系会失效，此时应力衰减比结构因子中的各向异性快得多。该样品的力学响应表现出类似劳斯的弛豫时间谱，而用于表征结构因子各向异性的二阶矩张量表现出几乎单指数弛豫。二阶矩张量的唯象上随体麦克斯韦/洛奇模型在中等应变下对阶跃应变和振荡剪切流中的结构响应提供了基本定量的预测，尽管在更高应变下发现了额外的非线性。
