Single-Step Control of Liquid-Liquid Crystalline Phase Separation by Depletion Gradients.

Fine-tuning nucleation and growth of colloidal liquid crystalline (LC) droplets, also known as tactoids, is highly desirable in both fundamental science and technological applications. However, the tactoid structure results from the trade-off between thermodynamics and non-equilibrium kinetics effects, and controlling liquid-liquid crystalline phase separation (LLCPS) in these systems is still work in progress. Here we introduce a single-step strategy to obtain a rich palette of morphologies for tactoids formed via nucleation and growth within an initially isotropic phase exposed to a gradient of depletants. We show the simultaneous appearance of rich LC structures along the depleting potential gradient, where the position of each LC structure is correlated with the magnitude of the depleting potential. Changing the size (nanoparticles) or the nature (polymers) of the depleting agent provides additional, precise control over the resulting LC structures through a size-selective mechanism, where the depletant may be found both within and outside the LC droplets. The use of depletion gradients from depletants of varying size and nature offers a powerful toolbox to manipulation, templating, imaging and understanding heterogeneous colloidal LC structures. This article is protected by copyright. All rights reserved.