Liquid crystalline behaviour of self-assembled Laponite PLL-PEG nanocomposites

TL;DR

This study introduces a method to prevent aging in Laponite-PLL-PEG nanocomposites, enabling the formation of liquid crystalline phases and hierarchical transparent films through polymer grafting and evaporation techniques.

Contribution

A novel polymer grafting approach that suppresses aging in Laponite nanocomposites, allowing access to liquid crystalline and crystalline phases.

Findings

Aqueous Laponite dispersions can be stabilized against aging with PLL-PEG grafting.

Liquid crystalline textures are observed upon evaporation-induced concentration.

Transparent hierarchical films are produced by drying the nanocomposite films.

Abstract

Synthetic Laponite-clay particles with platelet-like shape display strong aging when dispersed in aqueous solutions, preventing latter from reaching their natural liquid-crystalline equilibrium state. Here we introduce a facile method that successfully prevents this aging behaviour and enables accessing the systems' liquid-crystal and crystalline phases. We graft the comb-like polymer, poly(L-lysine)-g-poly(ethylene glycol) (PLL-PEG), onto the clay surfaces from solution, thereby screening the negative surface charges and thus ensuring steric stabilisation. We show zeta-sizer and rheology measurements, respectively, confirming complete steric coating and that aging of dilute samples is completely suppressed even after a year. Using evaporation as means to concentrate the particles, we observe various liquid crystalline textures under a polarized optical microscope (POM). Upon sequential spreading and drying, we are also able to obtain transparent films with hierarchical architecture.