Partitioning and self assembly of silica and hematite particles at grain boundaries of hexagonal liquid crystals: Implications on rheology

Abstract

We investigate the rheological implications of partitioning and self-assembly of colloidal particles at the grain boundaries (GBs) of hexagonal (H1) liquid crystal (LC) phase as a function of particle loading, shape and phase transition kinetics. The rheology of spherical silica particles (SiO2, diameter = 140 nm)/H1 and irregular hematite particles (Fe2O3, size = 110 nm)/H1 composites is measured as the samples are cooled from an isotropic to H1 phase at 2 and 0.2 °C/min. At 2 °C/min, SiO2/H1 composites show a consistent increase in G′ as the particle loading increases from 0.5 to 7.5 wt. % while Fe2O3/H1 composites exhibit a small drop in G′ above 2.5 wt. % particle loading. On the other hand, SiO2/H1 and Fe2O3/H1 composites show a monotonic increase in G′ with particle loading at a cooling rate of 0.2 °C/min. Microscopy observations reveal that at 0.2 °C/min, both SiO2 and Fe2O3 particles aggregate at the H1 GBs. The different rheological responses of SiO2/H1 and Fe2O3/H1 composites at 2 °C/min are due...