Curvature-Controlled Geometrical Lensing Behavior in Self-Propelled Colloidal Particle Systems

TL;DR

This study uses simulations to show how surface curvature influences the collective behavior of active colloidal particles, revealing curvature-dependent phase separation and dynamic phases.

Contribution

It demonstrates how Gaussian curvature controls motility-induced phase separation and cluster dynamics in active colloids, introducing curvature-engineered surface designs.

Findings

Curvature shifts the critical density for phase separation.

Positive curvature lowers the critical density, negative raises it.

Engineered surfaces produce novel dynamic phases.

Abstract

In many biological systems, the curvature of the surfaces cells live on influence their collective properties. Curvature should likewise influence the behavior of active colloidal particles. We show using molecular simulation of self-propelled active particles on surfaces of Gaussian curvature (both positive and negative) that curvature sign and magnitude can alter the system's collective behavior. Curvature acts as a geometrical lens and shifts the critical density of motility-induced phase separation (MIPS) to lower values for positive curvature and higher values for negative curvature, which we explain theoretically by the nature of parallel lines in spherical and hyperbolic space. Curvature also fluidizes dense MIPS clusters due to the emergence of defect patterns disrupting the crystalline order inside the clusters. Using our findings, we engineer three confining surfaces that strategically combine regions of different curvature to produce a host of novel dynamic phases, including cyclic MIPS on sphercylinders, wave-like MIPS on spherocones, and cluster fluctuations on metaballs.