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Title:Role of strong attractive forces on the dynamics and mechanics of glass and gel forming soft materials
Author(s):Ghosh, Ashesh
Director of Research:Schweizer, Kenneth S
Doctoral Committee Chair(s):Schweizer, Kenneth S
Doctoral Committee Member(s):Moore, Jeffrey S; Sing, Charles E; Makri, Nancy
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Glassy Dynamics
Polymer Physics
Abstract:The increasing interest in understanding the slow dynamics of glass and gel forming polymeric and colloidal systems is due to their wide applicability in biology, medicine, chemical physics, soft matter and material science. Although phenomenological and empirical models for slow local dynamics exist, along with coarse-grained scaling level analysis for polymeric systems that allow qualitative understanding of some aspects of chain dynamics, a large unsolved challenge is creating an unified predictive microscopic theory of these systems for local and chemistry-specific relaxation processes at the level of forces that relates interactions, structure, dynamics and mechanics. A major specific interest is how strong short-range attractive interactions that induce long-lived physical bonds impact activated dynamics, structural relaxation, and mechanics of very dense glass and gel forming colloid suspensions, associating copolymer liquids, and related soft materials. This thesis constructs and applies new microscopic statistical mechanical theories of activated dynamics of ultra-dense colloid and nanoparticle fluids that captures the interplay of physical bonding and steric caging. One primary goal is to understand phenomena such as re-entrant solidification, non-monotonic activated structural relaxation, a novel attractive glass state, and small length/time scale ‘in-cage’ dynamical processes. Extension of the new ideas to associating copolymers is achieved by combining it with the PRISM integral equation theory of structure to address unentangled network forming melts as a function of density, temperature, tunable strong attractive forces, and the degree of sticky group functionalization. Both the questions of sticky group modification of segmental relaxation and Tg, and sticky group bond lifetime, are addressed. A unifying theme for colloids and polymers is to predict local activated hopping events involving de-caging and bond-breaking, and their consequences on the relaxation time(s) and dynamic modulus as a function of experimentally controllable variables. Another largely unexplored area of slow relaxation is how deformation modifies dynamic caging constraints and the role of collective elastic effects in determining stress or strain induced liquification and nonequilibrium flow of a glass. This problem is addressed based on nonlinear Maxwell models of how deformation modifies packing structure and reduces the structural relaxation time and softens the elastic modulus. Questions such as yielding, steady state flow, shear-thinning and stress overshoots are theoretically analyzed for ultra-dense repulsive hard sphere fluids and colloidal suspensions. The results are favorably compared with existing simulations and experiments, and predictions are made.
Issue Date:2020-08-27
Rights Information:Copyright 2020 Ashesh Ghosh
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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