3D Visualization Reveals the Cooling Rate Dependent Crystallization near a Wall in Dense Microgel Systems

TL;DR

This study uses confocal microscopy to explore how cooling rates influence crystallization and glass formation near a wall in dense microgel suspensions, revealing the microscopic mechanisms behind these phase transitions.

Contribution

It demonstrates how cooling rate controls the transition from glassy to crystalline states and affects crystal alignment near a wall in microgel systems, providing new microscopic insights.

Findings

Rapid cooling leads to glassy structures

Slow cooling results in crystalline arrangements

Cooling rate influences crystal alignment with the wall

Abstract

Controlled crystallization, melting and vitrification are important fundamental processes in nature and technology. However, the microscopic details of these fundamental phenomena still lack understanding, in particular how the cooling rate and presence of a wall influence the crystal nucleation and glass formation. Thermoresponsive microgels provide the possibility to study phase transitions on a single-particle level, owing to the ability to tune the particle size with temperature. In this study, we employ composite microgels consisting of a hard core and a crosslinked poly(N-isopropyl acrylamide-co-methacrylic acid) shell to study the crystallization of dense suspensions of soft colloids near a wall using confocal microscopy. We investigate the effect of cooling rate on the fluid-to-solid transition close to the sample wall. The structures formed during cooling range from glassy in case of a rapid temperature quench, to crystalline when a slow cooling rate is used. Detailed analysis of the final structure reveals that the cooling rate also sets the degree of alignment of the crystal domains with the wall as a result of a balance between homogeneous and heterogenous crystal nucleation. The results presented here yield valuable insight into the microscopic details of temperature-controlled crystallization near a wall. This understanding will help pave the way towards optimal crystallization conditions for microgel applications.