# Multi-Particle Collision Dynamics for a coarse-grained model of soft colloids

## TL;DR

This paper extends Multi-Particle Collision Dynamics (MPCD) to model soft, polymeric colloids, enabling accurate simulation of hydrodynamic effects in complex colloidal suspensions, including microgels and dendrimers.

## Contribution

It introduces two novel MPCD-based approaches for simulating soft colloids, incorporating effective monomers and penetrable soft colloids, validated against monomer-resolved simulations.

## Key findings

- Effective monomer method works well for linear chains.
- PSC method provides accurate results for star polymers.
- Methods enable simulation of complex soft colloids at finite concentrations.

## Abstract

The growing interest in the dynamical properties of colloidal suspensions, both in equilibrium and under an external drive such as shear or pressure flow, requires the development of accurate methods to correctly include hydrodynamic effects due to the suspension in a solvent. In the present work, we generalize Multi-Particle Collision Dynamics (MPCD) to be able to deal with soft, polymeric colloids. Our methods build on the knowledge of the monomer density profile that can be obtained from monomer-resolved simulations without hydrodynamics or from theoretical arguments. We hereby propose two different approaches. The first one simply extends the MPCD method by including in the simulations effective monomers with a given density profile, thus neglecting monomer-monomer interactions. The second one considers the macromolecule as a single penetrable soft colloid (PSC), which is permeated by an inhomogeneous distribution of solvent particles. By defining an appropriate set of rules to control the collision events between the solvent and the soft colloid, both linear and angular momenta are exchanged. We apply these methods to the case of linear chains and star polymers for varying monomer lengths and arm number, respectively, and compare the results for the dynamical properties with those obtained within monomer-resolved simulations. We find that the effective monomer method works well for linear chains, while the PSC method provides very good results for stars. These methods pave the way to extend MPCD treatments to complex macromolecular objects such as microgels or dendrimers and to work with soft colloids at finite concentrations.