Paper Number
GG7 

Session
Out of Equilibrium Systems: Gels and Glasses

Title
Microscopic theory of spatially heterogeneous dynamics, elasticity and vitrification in confined colloidal suspensions and polymer melts

Presentation Date and Time
October 21, 2019 (Monday) 1:55

Track / Room
Track 7 / Room 306C

Authors (Click on name to view author profile)

1. Phan, Anh (University of Illinois, Department of Physics)
2. Schweizer, Kenneth S. (University of Illinois at Urbana-Champaign, Department of Materials Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Anh Phan¹ and Kenneth S. Schweizer^2
1Department of Physics, University of Illinois, Urbana, IL; ²Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Schweizer, Kenneth S.

Text of Abstract
Spatially heterogeneous structural relaxation, diffusion and mechanical properties in glass-forming liquids induced by a surface is a rich but poorly understood problem. Depending on the physical nature of the confining interface, dynamics can be enormously sped up, slowed down, or hardly affected. For example, a vapor surface can effectively melt a nonequilibrium glass, and a rough solid substrate can effectively vitrify a liquid, often over surprisingly long length scales near the interface. We address this problem by building on our microscopic force-level theory of the alpha relaxation in bulk colloidal, molecular and polymeric fluids in which the fundamental activated rearrangement event has a mixed local-nonlocal character involving cage scale hopping strongly coupled to a collective elastic distortion of the surrounding medium. A new description of how dynamical caging constraints at surfaces are modified and spatially transferred into a film has been formulated and integrated with the bulk theory concepts. This allows quantitative calculation of spatial gradients of the shear modulus, relaxation times and other properties for thick and thin films, and their film-averaged consequences. New predictions include an exponential spatial variation of the amplitude of dynamic caging constraints, the near factorization of the temperature and spatial location dependences of the activation barrier, a double exponential form of the structural relaxation time gradient, position-dependent power law decoupling of the relaxation time from its bulk analog, a more (less) mobile layer near a vapor (solid) surface that thickens with cooling or densification, and spatial variation of the glass transition temperature. Representative numerical results will be presented as a function of the nature of the surface (vapor, rough and smooth hard wall), chemical structure, and thermodynamic state, and key results compared with simulations and experiments.