The high surface area to volume ratio and interfacial tailorability of nanoparticles typically promotes host matrix property-enhancing functionalities and enables an ever-increasing array of emergent applications in composite systems. To extend these benefits to take advantage of the anisotropic activity of liquid crystals (LCs), challenges such as nanoparticle-induced molecular alignment distortion and LC-induced elastic force perturbation effects must be effectively managed. These issues generally impose limited nanoparticle compatibility with LCs as dispersibility and phase stability are poor, which results in inhomogeneous distribution and particle aggregation, at times in the formation of discrete nanoparticle networks. Strategies to improve dispersibility and solution stability in LCs rely on surface functionalization with mesogen compatible moieties. A range of surface functionalizing agents are surveyed for improving silica nanoparticle compatibility in 4-cyano-4’-pentylbiphenyl (5CB). The effects of surface functionalizing agent and particle size, and their respective concentrations, on the phase morphology and thermal stability of the nanocomposite are examined by means of rheometry and microscopy for phase diagram development. The dynamics of aggregation are highlighted to map the time-scale evolution of phase instability in the nanocomposite with respect to the mesogenic phase. In particular, the surface functionalizing agents are assessed towards synthesizing hemispheric silica-core Janus nanoparticles to produce anisotropic surfaces capable of directing discrete, phase stable, thermally-triggerable assemblies. Preliminary results on this effort will be presented as a comparative supplement to the discussion on isotropic functionalized nanoparticles and the resultant colloidal meso-phases that manifest from competing effects of LC alignment and elastic forces.

Rheology and phase morphology of liquid crystal dispersed silica-core nanoparticles

256th National Meeting (2018)

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