Drying of Soft Colloidal Films

TL;DR

This paper investigates the drying behavior of soft colloidal films made of microgels on different substrates, revealing how substrate wettability and particle softness influence the resulting microstructure and drying dynamics.

Contribution

It introduces a combined experimental and simulation approach to understand how microgel softness and substrate type affect drying behavior and microstructure formation in colloidal films.

Findings

Dried microstructure is more accurately replicated on hydrophobic substrates.

Softer colloids lead to more uniform and controlled drying outcomes.

Experiments and simulations qualitatively agree on the influence of substrate and particle softness.

Abstract

Thin films made of deformable micro- and nano-units, such as biological membranes, polymer interfaces, and particle-laden liquid surfaces, exhibit a complex behavior during drying, with consequences for various applications like wound healing, coating technologies, and additive manufacturing. Studying the drying dynamics and structural changes of soft colloidal films thus holds the potential to yield valuable insights to achieve improvements for applications. In this study, we employ interfacial monolayers of core-shell microgels with varying degrees of softness as model systems and investigate their drying behavior on differently modified solid substrates (hydrophobic vs. hydrophilic). By leveraging on video microscopy, particle tracking, and thin film interference, we shed light on the interplay between microgel adhesion to solid surfaces and the immersion capillary forces that arise in the thin liquid film. We discovered that a dried replica of the interfacial microstructure can be more accurately achieved on a hydrophobic substrate relative to a hydrophilic one, particularly when employing softer colloids as opposed to harder counterparts. These observations are qualitatively supported by experiments with a thin film pressure balance which allows mimicking and controlling the drying process and by computer simulations with coarse-grained models.