Two-Particle Microrheology of quasi-2D Viscous Systems

TL;DR

This study investigates how colloidal particles move in a quasi-2D system at an air-water interface, revealing a transition from interface-dominated to bulk fluid-dependent behavior as surface viscosity varies, and introduces a master curve for flow characterization.

Contribution

It presents the first detailed analysis of correlated particle motions across different surface viscosities in quasi-2D systems, establishing a master curve for flow behavior.

Findings

Transition from 2D interface to bulk fluid behavior with decreasing surface viscosity

Correlated motions scale onto a master curve capturing flow features

Two-particle MSD aligns with rheological measurements

Abstract

We study the correlated motions of colloidal particles in a quasi-2D system (Human Serum Albumin (HSA) protein molecules at an air-water interface) for different surface viscosities $\eta_{s}$. We observe a transition in the behavior of the correlated motion, from 2-D interface dominated at high $\eta_{s}$ to bulk fluid-dependent at low $\eta_{s}$. The correlated motions can be scaled onto a master curve which captures the features of this transition. This master curve also characterizes the spatial dependence of the flow field of a viscous interface in response to a force. From the flow field and the correlated particle motions, we calculate a two-particle MSD (mean square displacement) for direct comparison with rheological measurements.