Abstract:
Liquid crystals are a state of matter between solid and liquid which act as tunable solvents for particles self-assembly. These self-assembled structures can have unique mechanical, optical, electrical and magnetic properties [1,7, 17].
We report the self-assembly of 104 nm Rhombohedral Fe2O3 (iron oxide) particles in hexagonal phase of lyotropic liquid crystal. Visually, the sample is a low viscosity liquid above TH and turns into a soft solid as the temperature is lowered. This is also manifested in the rheological properties of this material where the storage modulus (G’) shows several orders of magnitude increase at the isotropic-hexagonal transition temperature and almost plateaus as the temperature is further lowered. Rheological measurements show that the storage modulus of the material depends on two factors: 1) Particle loading 2) The rate at which the sample is cooled. As observed for cooling rates of 0.5°C/min
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and 1°C/min, G’ increases with an increase in particle loading up to 1.5wt% however, such monotonic increase with cooling rate is not observed as the particle loading is varied from 2.5-10wt%. However when cooled at 2°C/min, the increase in modulus with particle loading is pronounced at higher particle loading. Interestingly, the modulus of the particle free sample shows hardly any effect of cooling rate. The rheological data suggest that the final microstructure and mechanical properties are dictated by interplay between the rate at which the hexagonal domains nucleate and how fast the particles are swept by these domains to form a compact particle layer at the hexagonal liquid crystal and isotropic fluid interface. The process has been observed under polarised microscopy for lower particle loadings. The packing of the particles is very much dependent on the cooling rate as well as particle fraction. Therefore, both particle loading and cooling rate affect the mechanical properties of final structure.
We have synthesized silica nano-rods with different total volume of reactants to see its effect on size of rods and also the effect of Tetraethyl orthosilicate (TEOS) [26]. Increase in the total volume of reactant led to decrease in the size of rods with lesser effect on diameter, while the variation in TEOS concentration showed similar effect but with marginal effect on diameter.