Linear and nonlinear rheology of oil in liquid crystal emulsions
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Linear and nonlinear rheology of oil in liquid crystal emulsions Zhiwei Liu 1 & Kai Yang 1,2 & Wei Yu 1 Received: 26 May 2020 / Revised: 12 September 2020 / Accepted: 16 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract While the majority of experimental and numerical studies focus on yield stress fluids with short-range repulsive interactions, the effect of long-range interaction is rarely known. In this work, we studied the linear and nonlinear rheological behavior of a model oil in nematic liquid crystal emulsions, which exhibit long-range droplet-droplet interaction. The characteristic of long-range interaction, attractive at large droplet separation and repulsive at a small surface distance, was inferred from the morphology and thixotropy of emulsions. We suggested a model accounting for the plateau modulus purely due to the long-range repulsive interaction. We further illustrated that neither the yield stress nor the relaxation time followed a simple power-law scaling with respect to the distance to jamming. The rescaled steady and dynamic flow curves could not collapse on master curves above jamming transition when the long-range and short-range repulsive interactions contribute simultaneously. Keywords Yield stress fluids . Jamming transition . PDMS/8CB . Free energy model
Introduction The yield stress fluids (YSFs) are widely encountered in foodstuff, chemical, pharmaceutical, and personal care products (Bonn et al. 2017; Nelson and Ewoldt 2017). A deep understanding of the relationship between yield stress and composition, as well as their flow behaviors, is of fundamental and practical importance (Bonn et al. 2017; Chen et al. 2010; Nelson and Ewoldt 2017). Dispersions of particles with the different softness (such as solid particles, droplets, or bubbles) in another fluid are the typical approach to prepare yield stress fluids (Vlassopoulos and Cloitre 2014). The physical origin of yield stress has been widely investigated, and the inter-particle interactions are critical for the emergence of apparent yield stress. In the hard-sphere limit, apparent yield stress can Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00397-020-01244-2) contains supplementary material, which is available to authorized users. * Wei Yu [email protected] 1
Advanced Rheology Institute, Frontiers Science Center for Transformative Molecules, State Key Laboratory for Metal Matrix Composite Materials, Department of Polymer Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
2
Malvern Instruments, Shanghai, China
appear due to the colloidal glass transition when the thermal motion of colloidal particles is dynamically arrested at packing fraction above ϕG (~ 0.58) (Petekidis et al. 2004; Pusey and van Megen 1986). The relevant stress scale for the yield stress is the Brownian stress, σT = kBT/a3with kB is the Boltzmann constant, T is the temperature, and a is the particle diamete
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