Diffusiophoresis in a Weakly Viscoelastic Fluid

Self-propelling active colloids (AC) provide insights in the behavior of non-equilibrium systems by producing enhanced diffusive motion. Our model system consists of synthetic Janus (Pt/Si) microspheres undergoing diffusiophoresis (via local concentration gradient) in presence of H₂O₂. In this study, we aim to address for the first time the single-particle dynamics in a weakly viscoelastic fluid. Experimentally, Janus particles were dispersed in dilute PVP water solutions. The solution presented Newtonian shear viscosity with a finite but relatively short (~3ms) relaxation time. The Deborah number, based on the motion of the particles, was calculated to be in the order of 10^-4. Within this regime, we attempt to investigate the coupling between the solute concentration field and the phoretic particle's motility (MSD, velocity and diffusivity analyzed via MPT) because of the weak viscoelastic medium. These findings are the foundations to understand collective motion of ACs in complex media and to study the interplay between particle organization ^[1] and fuel concentration in the limit of low Péclet number. Since any biological fluid is a viscoelastic fluid, the characterization of swimming dynamics is of high relevance for potential drug delivery applications.