Aging Maxwell fluids

TL;DR

This paper presents a mesoscopic model explaining aging rheological behavior of protein condensates as Maxwell fluids with increasing viscosity and non-Newtonian properties, aligning with experimental observations.

Contribution

It introduces a phase transition-based mesoscopic model that captures aging dynamics and viscoelastic properties of protein condensates, providing a theoretical framework for observed aging phenomena.

Findings

Protein condensates behave as aging Maxwell fluids with increasing relaxation time.

The model predicts non-Newtonian behavior with shear stress increasing over time.

It explains experimental data and offers testable predictions.

Abstract

Many experiments show that protein condensates formed by liquid-liquid phase separation exhibit aging rheological properties. Quantitatively, recent experiments by Jawerth et al. (Science 370, 1317, 2020) show that protein condensates behave as aging Maxwell fluids with an increasing relaxation time as the condensates age. Despite the universality of this aging phenomenon, a theoretical understanding of this aging behavior is lacking. In this work, we propose a mesoscopic model of protein condensates in which a phase transition from aging phase to non-aging phase occurs as the control parameter changes, such as temperature. The model predicts that protein condensates behave as viscoelastic Maxwell fluids at all ages, with the macroscopic viscosity increasing over time. The model also predicts that protein condensates are non-Newtonian fluids under a constant shear rate with the shear stress increasing over time. Our model successfully explains multiple existing experimental observations and also makes general predictions that are experimentally testable.