A Novel Regularity in Transport Phenomena: Linear Mobility of Colloids from the Triple to Critical Point.

Abstract

Self-diffusion is a cornerstone of transport phenomena in liquids, yet its behavior, particularly along the liquid-gas coexistence line, remains insufficiently understood compared to that in gases and solids. This work presents a comprehensive experimental and computational study that reveals a fundamental regularity in liquid-phase diffusion. We utilized a model system comprising a monolayer of silica colloids where long-range, dipole-like attractions were induced and precisely controlled by a rotating electric field. This technique allowed us to systematically navigate the liquid branch of the binodal, from the triple point up to the critical point, by varying the field strength which serves as an effective inverse temperature. Particle dynamics were directly observed and quantified using single-particle tracking, while complementary molecular dynamics (MD) simulations were performed to validate the experimental findings. Our primary result is the discovery of a robust linear increase in particle mobility with effective temperature along the entire liquid binodal. This linearity holds true for both the experimental system and the MD simulations, despite quantitative differences attributed to many-body interactions inherent in the experiment. This finding confirms previous theoretical predictions for generalized Lennard-Jones systems and suggests the existence of a yet-unidentified small parameter governing transport in liquids. The uncovered linear relationship provides a crucial benchmark for future theories of liquid dynamics and has implications for controlling transport in microfluidics and materials science.

Speaker

Ivan Kushnir
Bauman Moscow State Technical University
Russia

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