|Title||Contact tribology also affects the slow flow behavior of granular emulsions|
|Author(s)||Workamp, Marcel; Dijksman, Joshua A.|
|Source||Journal of Rheology 63 (2019)2. - ISSN 0148-6055 - p. 275 - 283.|
|Department(s)||Physical Chemistry and Soft Matter|
|Publication type||Refereed Article in a scientific journal|
|Availibility||Full text available from 2020-03-01|
Recent work on suspension flows has shown that contact mechanics plays a role in suspension flow dynamics. The contact mechanics between particulate matter in dispersions should depend sensitively on the composition of the dispersed phase: Evidently, emulsion droplets interact differently with each other than angular sand particles. We, therefore, ask: What is the role of contact mechanics in dispersed media flow? We focus on slow flows, where contacts are long-lasting and hence contact mechanics effects should be most visible. To answer our question, we synthesize soft hydrogel particles with different friction coefficients. By making the particles soft, we can drive them at finite confining pressure at all driving rates. For particles with a low friction coefficient, we obtain a rheology similar to that of an emulsion, yet with an effective friction much larger than expected from their microscopic contact mechanics. Increasing the friction coefficient of the particles, we find a flow instability in the suspension. Particle-level flow and fluctuations are also greatly affected by the microscopic friction coefficient of the suspended particles. The specific rheology of our "granular emulsions" provides further evidence that a better understanding of microscopic particle interactions is of broad relevance for dispersed media flows.