Interplay between Kinetics and Dynamics of Liquid-Liquid Phase Separation in a Protein Solution Revealed by Coherent X-ray Spectroscopy

TL;DR

This study investigates the microscopic dynamics during liquid-liquid phase separation in a protein solution using x-ray spectroscopy, revealing decoupled relaxation kinetics and hyper-diffusive motions supported by simulations.

Contribution

It provides a novel experimental framework combining spectroscopy and simulations to analyze early-stage phase separation dynamics in complex fluids.

Findings

Structural relaxation is up to 40 times slower than dynamics.

Kinetic decay rate is inversely proportional to time early on.

Microscopic motions are hyper-diffusive with relaxation time growing exponentially then as a power law.

Abstract

Microscopic dynamics of complex fluids in the early stage of spinodal decomposition (SD) is strongly intertwined with the kinetics of structural evolution, which makes a quantitative characterization challenging. In this work, we use x-ray photon correlation spectroscopy to study the dynamics and kinetics of a protein solution undergoing liquid-liquid phase separation (LLPS). We demonstrate that in the early stage of SD, the structural relaxation kinetics is up to 40 times slower than the dynamics and thus can be decoupled. The kinetic decay rate is inversely proportional to time in the early stage, followed by a nearly constant behavior during the coarsening stage. The microscopic dynamics can be well described by hyper-diffusive ballistic motions with a relaxation time exponentially growing with time in the early stage followed by a power-law increase with fluctuations. These experimental results are further supported by simulations based on the Cahn-Hilliard equation. The established framework is applicable to other condensed matter and biological systems undergoing phase transitions and may also inspire further theoretical work.