Growth dynamics of nanoplatelet liquid crystals by directionally drying colloidal suspensions in a confined channel

Abstract

Unidirectional solvent evaporation has been increasingly concerned as a versatile microfluidic agent in manipulating the self-assembly dynamics of shape anisotropic colloids by precisely governing a confined nanofluid flow in a microcell. Here we develop a theoretical framework upon unidirectional drying-induced growth of nematic liquid crystals (LC) in nanoplatelet suspension confined to a Hele–Shaw (H–S) channel. The nematic order-dependent permeability assembled in modified Darcy's law and the interactions between nanoplatelets for nematic LC are both explicitly incorporated in a confined nanofluid flow. The growth dynamics of nematic LC that is highly correlated with drying rate (drying Peclet number), nanoplatelet aspect ratio, and geometric confinement have been rationalized by our numerical measurements. Unlike the spherical colloids, the nematic LC grows nonlinearly over time indicating a time-dependent instantaneous growth velocity. The final length of LC, when subjected to an enhanced drying rate, is seen to be compressed toward the drying end, but its time-averaged growth velocity increases significantly. Besides, the LC formed by the thicker nanoplatelets gets the shorter final length, while whether its average growth velocity is affected by nanoplatelet types depends on the drying rate. Importantly, we confirm a noticeable promotion in the growth of LC as the enhanced geometric confinement is imposed. A state diagram we produce suggests a universal signature of enhancement in solvent drying flux with enhanced confinement. However, our results highlight the favorable water retention in nanoplatelet nematic LC with compacted layered architecture prevailing over the spherical colloids deposits with the porous percolation architecture.