Disentangling kinetics from thermodynamics in heterogeneous colloidal systems

TL;DR

This paper demonstrates how to separate the effects of kinetics and thermodynamics in colloidal phase separation, enabling control over structure and properties beyond traditional nucleation and growth paradigms.

Contribution

The authors introduce a microfluidic approach to disentangle kinetics from thermodynamics in colloidal systems, revealing new phenomena and enabling the fabrication of complex multicomponent liquid crystals.

Findings

Shorter phase separation timescales by orders of magnitude

Wider accessible phase diagram regions

Internal cholesteric structures not seen in conventional LLPS

Abstract

Nucleation and growth (N&G) - the emergence of a new phase within an initially homogeneous one - is one of the most important physical phenomena by which gas-liquid, liquid-liquid and solid-liquid phase separation takes place. Accordingly, thermodynamics sets the asymptotic boundaries towards which the system must evolve, while kinetics tries to cope with it by imposing the transport rates at which phase separation is realized. In all heterogeneous colloidal systems observed in nature, the composition, shape, structure and ultimately physical properties result from the trade-off between thermodynamics and kinetics. In this work we demonstrate, by carefully selecting colloidal systems and controlling phase separation in microfluidic devices, that it becomes possible to go beyond N&G, disentangling kinetics effects from thermodynamics in composition, structure and physical properties of the final system. Using amyloid fibril and cellulose nanocrystal filamentous colloids for which the binodal curve defining the two-phase region in the phase diagram is given by two separate vertical lines, we extrude a solution set at one thermodynamic branch inside the other branch, realizing nematic or cholesteric droplets where the composition is set by thermodynamics, while the structure and morphology are defined by dynamic flow parameters. We demonstrate that departing from the N&G paradigm unveils new physical phenomena, such as orders of magnitude shorter timescales, a wider phase diagram and internal cholesteric structures that are not observable via conventional LLPS. We also show that by co-dispersing plasmonic gold nanoparticles within colloidal liquid crystalline droplets, our approach enables on-demand fabrication of multicomponent heterogeneous liquid crystals, enhancing their potential, and introducing original fundamental and technological directions in multicomponent structured fluids.