Effects of chemical and geometric micro-structures on crystallization of surface droplets during solvent exchange

TL;DR

This study explores how micro-structured surfaces and solvent exchange conditions influence droplet crystallization, revealing controllable crystal shapes and detachment properties, with implications for material fabrication.

Contribution

It demonstrates that flow conditions and surface micro-structures can precisely control crystallization outcomes during solvent exchange on patterned surfaces.

Findings

Flow rate affects crystal fiber length.

Surface roughness facilitates crystal detachment.

Different flow conditions produce varied crystal morphologies.

Abstract

In this work, we investigate crystallization from droplets formed on micro-patterned surfaces. By solvent exchange in a micro-chamber, a ternary solution consisting of a model compound beta-alanine, water, and isopropanol, was displaced by a flow of isopropanol. In the process, oiling-out droplets formed and crystallized. Our results showed that the shape and size of the crystals on micro-patterned surfaces could be simply mediated by the flow conditions of solvent exchange. Varying flow rate, concentration, or channel height led to the formation of a thin film with micro-holes, connected network of crystals, or small diamond-shaped crystals. Rough micro-structures on the surface allowed the easy detachment of crystals from the surface. Beyond oiling-out crystallization, we demonstrated that the crystal formation from another solute dissolved in the droplets could be triggered by solvent exchange. The length of crystal fibers after the solvent exchange process was shorter at a faster flow rate. This study may provide further understanding to effectively obtain crystallization from surface droplets through the solvent exchange approach.