Quantitative rheo-microscopy of soft matter

Abstract

Direct observation of the microscopic material structure and dynamics during rheological shear tests is the goal of rheo-microscopy experiments. Microscopically, they shed light on the many mechanisms and processes that determine the mechanical properties at the macroscopic scale. Moreover, they permit for the determination of the actual deformation field, which is particularly relevant to assess shear banding or wall slip. While microscopic observation of the sample during mechanical probing is achieved by a variety of custom and commercial instruments, the possibility of performing quantitative rheology is not commonly available. Here, we describe a flexible rheo-microscopy setup that is built around a parallel-sliding-plate, stress-controlled shear cell, optimized to be mounted horizontally on a commercial microscope. Mechanically, soft materials with moduli ranging from few tens of Pa up to tens of kPa can be subjected to a variety of waveforms, ranging from standard step stress and oscillatory stress to more peculiar signals, such as triangular waves or any other signal of interest. Optically, the shear cell is designed to be compatible with different imaging methods (e.g. bright field or confocal microscopy). Most of the components of the shear cell are commercially available, and those that are not can be reproduced by a standard machine shop, easing the implementation of the rheo-microscopy setup in interested laboratories.

Study on microstructure evolution of waxy crude oil emulsions under dynamic cooling conditions

“…In this study, the motion behavior of microscopic units in waxy crude oil emulsions during the dynamic cooling process was observed using rheo-microscopy 28,29 in situ synchronous measurement technology. 46 Additionally, the impact of gradual growth of wax crystals on water droplets aggregates microstructure, distribution characteristics, and motion behavior were analyzed.…”

“…Notably, some researchers have successfully achieved in situ microscopic observation by rheo-microscopy 18,19 in many elds, such as blood, 20 colloidal suspensions, 21,22 crystals, 23,24 bers, 25,26 so materials 27 and other complex multiphase system rheology and microstructure studies. Villa 28 constructed a rheo-microscopic device that combined a stress-controlled rheometer with differential dynamic microscopic analysis of particle tracking to test the advantages and limitations of the sample under test. Keshtkar 29 studied the rheological properties of ber suspensions with different Young's modulus and different exibility through the rheo-microscopy method.…”