The effect of internal architecture on the assembly of soft particles at fluid interfaces

TL;DR

This study investigates how the internal architecture of microgel particles influences their structural and mechanical behavior at fluid interfaces, combining synthesis, experiments, and simulations to inform tailored material design.

Contribution

It provides a comprehensive analysis linking microgel internal structure, tunable via core removal, to their interfacial assembly and mechanical response, advancing understanding of soft particle behavior.

Findings

Hollow microgels are mechanically stable in bulk conditions.

Removing the core causes microgels to flatten and become disk-like at interfaces.

At high compression, particles deform orthogonally due to absence of a core.

Abstract

Monolayers of soft colloidal particles confined at fluid interfaces have been attracting increasing interest for fundamental studies and applications alike. However, establishing the relation between their internal architecture, which is controlled during synthesis, and their structural and mechanical properties upon interfacial confinement, which define the monolayer's properties, remains an elusive task. Here, we propose a comprehensive study elucidating this relation for a system of microgels with tunable architecture. We synthesize core-shell microgels, whose soft core can be chemically degraded in a controlled fashion, yielding particles ranging from analogues of standard batch-synthesized to completely hollow microgels after total core removal. We characterize the internal structure of these particles, their swelling properties in bulk and their morphologies upon adsorption at an oil-water interface via a combination of numerical simulations and complementary experiments. In particular, we confirm that hollow microgels are mechanically stable in bulk aqueous conditions and that the progressive removal of the core leads to a significant flattening of the microgels, which become disk-like particles, at the interface. At low compression, the mechanical response of the monolayer is dominated by the presence of loosely crosslinked polymers forming a corona surrounding the particle within the interfacial plane, regardless of the presence of a core. By contrast, at high compression, the absence of a core enables the particles to deform in the direction orthogonal to the interface. These findings shed new light on which structural features of soft particles determine their interfacial behaviour, enabling new design strategies for tailored materials.