Active interaction switching controls the dynamic heterogeneity of soft colloidal dispersions

M. B. and J. D. acknowledge support by the state of BadenWurttemberg through bwHPCand the German Research Foundation (DFG) through grant no INST 39/963-1 FUGG (bw ForCluster NEMO) and by the Deutsche Forschungsgemeinschaft (DFG) via grant WO 2410/2-1 within the framework of the Research Unit FOR 5099 ``Reducing complexity of nonequilibrium'' (project No. 431945604). P. I. H. and A. M.-J acknowledge the financial support provided by the Spanish Ministry and Agencia Estatal de Investigacio ' n (AEI) through Grants PID2020-113681GB-I00 and FIS2017-84256-P, the Junta de Andaluci ' a and European Regional Development Fund Consejeri ' a de Conocimiento, Investigacion y Universidad, Junta de Andaluci ' a (Projects PY20-00241, A-FQM-90-UGR20, A-FQM175-UGR18 and SOMM17/6105/UGR), and the program Visiting Scholars of the University of Granada (Project PPVS2018-08). Finally, we thank Nils Goth for inspiring discussions and useful comments, and the computational resources and assistance provided by PROTEUS, the supercomputing center of Institute Carlos I for Theoretical and Computational Physics at the University of Granada, Spain.
We employ Reactive Dynamical Density Functional Theory (R-DDFT) and Reactive Brownian Dynamics (R-BD) simulations to investigate the dynamics of a suspension of active soft Gaussian colloids with binary interaction switching, i.e., a one-component colloidal system in which every particle stochastically switches at predefined rates between two interaction states with different mobility. Using R-DDFT we extend a theory previously developed to access the dynamics of inhomogeneous liquids [Archer et al., Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys., 2007, 75, 040501] to study the influence of the switching activity on the self and distinct part of the Van Hove function in bulk solution, and determine the corresponding mean squared displacement of the switching particles. Our results demonstrate that, even though the average diffusion coefficient is not affected by the switching activity, it significantly modifies the non-equilibrium dynamics and diffusion coefficients of the individual particles, leading to a crossover from short to long times, with a regime for intermediate times showing anomalous diffusion. In addition, the self-part of the van Hove function has a Gaussian form at short and long times, but becomes non-Gaussian at intermediates ones, having a crossover between short and large displacements. The corresponding self-intermediate scattering function shows the two-step relaxation patters typically observed in soft materials with heterogeneous dynamics such as glasses and gels. We also introduce a phenomenological Continuous Time Random Walk (CTRW) theory to understand the heterogeneous diffusion of this system. R-DDFT results are in excellent agreement with R-BD simulations and the analytical predictions of CTRW theory, thus confirming that R-DDFT constitutes a powerful method to investigate not only the structure and phase behavior, but also the dynamical properties of non-equilibrium active switching colloidal suspensions.
BadenWurttemberg through bwHPC
German Research Foundation (DFG) INST 39/963-1 FUGG WO 2410/2-1 FOR 5099 431945604
Spanish Ministry and Agencia Estatal de Investigacion (AEI) PID2020-113681GB-I00 FIS2017-84256-P
Junta de Andalucia
European Regional Development Fund Consejeria de Conocimiento, Investigacion y Universidad, Junta de Andalucia PY20-00241 A-FQM-90-UGR20 A-FQM175-UGR18 SOMM17/6105/UGR
University of Granada PPVS2018-08