We investigate the rheological implications of partitioning and self-assembly of colloidal particles at the grain boundaries (GBs) of hexagonal (H-1) 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)/(H)1 and irregular hematite particles (Fe2O3, size = 110 nm)/H-1 composites is measured as the samples are cooled from an isotropic to H1 phase at 2 and 0.2 degrees C/min. At 2 degrees C/min, SiO2/H-1 composites show a consistent increase in G' as the particle loading increases from 0.5 to 7.5wt. % while Fe2O3/H-1 composites exhibit a small drop in G' above 2.5wt. % particle loading. On the other hand, SiO2/H-1 and Fe2O3/H-1 composites show a monotonic increase in G' with particle loading at a cooling rate of 0.2 degrees C/min. Microscopy observations reveal that at 0.2 degrees C/min, both SiO2 and Fe2O3 particles aggregate at the H-1 GBs. The different rheological responses of SiO2/H-1 and Fe2O3/H-1 composites at 2 degrees C/min are due to the segregation of Fe2O3 particles inside the H1 domains. We further show that the moving H-1 front cannot accommodate the larger sized Fe2O3 particle aggregates during phase transition, leading to a reduction in the particle partitioning efficiency (fp) at the H-1 GBs. Our results indicate that fp of particles of different shapes and sizes are determined only by the average area of the H-1 domains. (C) 2017 The Society of Rheology.