Liquid-liquid crystalline phase separation of filamentous colloids and semiflexible polymers: experiments, theory and...

Liquid-liquid crystalline phase separation (LLCPS) is the process by which an initially homogenous single-phase solution composed of a solvent-most frequently water- and a solute-typically rigid or semiflexible macromolecules, polymers, supramolecular aggregates, or filamentous colloids-demixes into two (or more) distinct phases in which one phase is depleted by the solute and features properties of isotropic solutions, whereas the other is enriched by the solute and exhibits liquid crystalline anisotropic properties. Differently from the more common liquid-liquid phase separation (LLPS) of flexible macromolecules, which is a trade-off between entropy and enthalpy, LLCPS is mostly an entropy-controlled process in which the morphology, composition and properties of the new phases depend primarily on kinetics and thermodynamic factors and, unexpectedly, on the history followed to reach a specific point in the phase diagram. This review aims to comprehensively discuss the process of LLCPS from experimental, theoretical, and simulation standpoints. We discuss the main systems and experimental approaches followed over the past decades to induce and control LLCPS, then we delve into the main theoretical and modeling approaches available to rationalize this process, and finally, we expand on how numerical simulations can significantly enrich the understanding of LLCPS. A final section touches on possible applications and the significance of LLCPS beyond pure physics, that is, in the broader context of biology, nanotechnology, and everyday life.