Microscopic Theory of the Elastic Shear Modulus and Length-Scale-Dependent Dynamic Re-Entrancy Phenomena in Very Dense Sticky Particle Fluids

TL;DR

This paper develops a microscopic theory combining hybrid PDT and ECNLE to explain the non-monotonic elastic modulus and dynamic re-entrancy phenomena in dense sticky particle fluids, aligning well with experimental observations.

Contribution

It introduces a novel hybrid PDT-ECNLE framework that captures the interplay of attractive and repulsive forces causing re-entrant elastic behavior in dense colloidal glasses.

Findings

Predicts localization length and elastic modulus re-entrancy consistent with experiments.

Shows non-monotonic alpha relaxation time as a function of attraction strength.

Captures large dynamical heterogeneity and non-Gaussian behavior in attractive glasses.

Abstract

We apply the hybrid Projectionless Dynamic Theory (hybrid PDT) formulation of the Elastically Collective Nonlinear Langevin Equation (ECNLE) activated dynamics approach to study dense fluids of sticky spheres with short range attractions. Of special interest is the problem of non-monotonic evolution with attraction strength of the elastic modulus ("re-entrancy") at high packing fractions far beyond the ideal mode coupling theory (MCT) nonergodicity boundary. The dynamic force constraints explicitly treat the bare attractive forces that drive transient physical bond formation, while a projection approximation is employed for the singular hard-sphere potential. The resultant interference between repulsive and attractive forces contribution to the dynamic vertex results in the prediction of localization length and elastic modulus re-entrancy, qualitatively consistent with experiments. The non-monotonic evolution of the alpha time predicted by ECNLE theory with the hybrid PDT approach is explored in depth as a function of packing fraction, attraction strength, and range. Isochronal dynamic arrest boundaries based on activated relaxation display the classic non-monotonic glass melting form. Comparisons of these results with the corresponding predictions of ideal MCT and the ECNLE and NLE activated theories based on projection reveal large qualitative differences. The consequences of stochastic trajectory fluctuations on intra-cage single particle dynamics with variable attraction strengths are also studied. Large dynamical heterogeneity effects in attractive glasses are properly captured. These include a rapidly increasing non-Gaussian parameter with packing fraction and a non-monotonic evolution with attraction strength, in accord with recent simulations. Extension of the microscopic theoretical approach to treat double yielding in attractive glass nonlinear rheology is possible.