Influence of cooling rate on the self-assembly and rheology of hematite and silica nano-particles in hexagonal liquid crystal

Abstract

Liquid crystals (LCs) are a fascinating state of matter due to their ability to demonstrate both solid as well as liquid properties. Non- ionic surfactant nonaethylene glycol dodecyl ether (C12 added to water organizes into different mesophases depending upon the surfactant concentration. In the present work, we focus on H1 LC phase which is formed when the surfactant concentration is 35-70%. Liquid crystals act as a tunable solvent for the self- Eassembly of nanoparticles (NPs). The NP-LC composites gives enhanced LC properties including electrical, magnetic, optical and mechanical properties. In this study, we investigate the rheological and microstructural properties of irregular Fe2 spherical SiO2 (140 nm) composites in H1O3 (110 nm long) LC phase. Oscillatory and rotational rheology measurements are carried out to understand the effect of particle loading on H1LC phase. We choose 7 different particle loading ranging from 0.5 to 10 wt% which when added to the LC matrix, form a network around the LC domains as indicated by microscopy. The particle network makes the system stiffer and stronger and thus the elasticity increases. The composites exhibit increase in gel strength with increasing particle loading. The Fe2 particles surprisingly seem to deviate from this behavior at 2°C/min cooling rate due to the heterogeneity at 50 wt% surfactant concentration rogenerated by the entrapment of particles within the domains. Microscopy showed evidence of particle entrapment within domains leading to this behavior beyond 2.5 wt% loading. At 0.2 %min, the small number of domains nucleated slowly and grew larger in size than at 2 o C/min. The creep rheology affirms that the composites do not recover completely on relieving the stress. and O3Moreover, viscosity versus shear rate plots reveal their shear-thinning behavior

We also synthesized silica spheres and rods of varying size.The common inference of all the synthesis is the role of silica precursor tetraethyl orthosilicate (TEOS). The size and yield of particles synthesized depend upon the amount of TEOS in the reaction mixture. Higher amount of TEOS gives higher particle size and lower amount gives smaller particles. Synthesis yield increases on increasing the amount of reactants accordingly