Rheology, Structure and Dynamics of Colloid-Polymer Mixtures: from Liquids to Gels

TL;DR

This study explores how colloid-polymer mixtures transition from liquids to gels by examining their viscoelastic properties, structural changes, and comparing experimental results with theoretical models.

Contribution

It provides new insights into the gelation process, including the location of the gelation boundary and the behavior of viscoelastic moduli, supported by experimental and theoretical analysis.

Findings

Significant changes in viscoelastic properties near gelation boundary

Formation of clusters and transient networks in liquids

Qualitative rheological changes indicating gel formation

Abstract

We investigated the viscoelastic properties of colloid-polymer mixtures at intermediate colloid volume fraction and varying polymer concentrations, thereby tuning the attractive interactions. Within the examined range of polymer concentrations, the samples ranged from fluids to gels. Already in the liquid phase the viscoelastic properties significantly changed when approaching the gelation boundary, indicating the formation of clusters and transient networks. This is supported by an increasing correlation length of the density fluctuations, observed by static light scattering and microscopy. At the same time, the correlation function determined by dynamic light scattering completely decays, indicating the absence of dynamical arrest. Upon increasing the polymer concentration beyond the gelation boundary, the rheological properties changed qualitatively again, now they are consistent with the formation of colloidal gels. Our experimental results, namely the location of the gelation boundary as well as the elastic (storage) and viscous (loss) moduli, are compared to different theoretical models. These include consideration of the escape time as well as predictions for the viscoelastic moduli based on scaling relations and Mode Coupling Theories (MCT).