Rheology of Weakly Attractive Soft Particles

by Ehsan Irani
Doctoral thesis
Date of Examination:2016-08-10
Date of issue:2016-12-14
Advisor:Dr. Claus Heussinger
Referee:Dr. Claus Heussinger
Referee:Prof. Dr. Annette Zippelius
Persistent Address: http://dx.doi.org/10.53846/goediss-6025

 

 

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Abstract

English

We study the rheology of a soft particulate system with attractive interactions. Lees-Edwards boundary conditions are used to simulate a shear-controlled flow. Unlike repulsive systems, it is found that in systems with a damping force directed normally to the contact point, attractive interactions result in a finite yield stress, and an iso-static structure emerges below the jamming point. The rheology can be explained by a scaling argument that exploits the vicinity to the isostatic state. In addition, flow curves exhibit non-monotonic behavior, resulting in persistent shear-banding in large systems. Furthermore we investigate the role of dissipation mechanism by implementing several models for the dissipation of energy. A tangential damping gives rise to the monotonic flow curves and the development of a viscous flow in the over-damped regime. However in that case, decreasing the damping factor introduces the inertial time-scale, leading again to non-monotonic flow curves and inertia-induced shear-banding, which are intrinsically different from the above mentioned shear bands. Finally we introduce thermal fluctuations to our system and investigate the interplay of temperature and attraction with respect to flow properties and particles' dynamics. Namely a phase-separation at intermediate values of the underlying parameters is observed to occurs, the amount and rate of which has been quantified in this work by introducing a properly chosen order parameter. Our results shed some light on the rich and complex rheological response of attractive particles, in terms of interaction details, such as the dissipation model, thermal noise and range of the attraction.
Keywords: Physics; Soft Matter; Rheology; Complex Fluid; Attractive Interactions; Shear Bands
 
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