Coarse-Grained Molecular Monte Carlo Simulations of Liquid Crystal-Nanoparticle Mixtures
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Liquid crystals are a unique and complicated class of phases of matter, also called “mesophases”, which exhibit properties such as solid-like elasticity and anisotropy, and liquid-like flow. The industrial application of liquid crystals in display technology has revolutionized our lives. Most notably, it has enabled the development of thin light displays presently found in many portable devices such as digital watches (and smartwatches), cellphones, laptops, desktop computer monitors and large screen televisions. With the recent advances in nanotechnology, liquid crystals have attracted much interest as a medium for dispersing and organizing nanoparticles, the presence of which also alters the properties of the liquid crystal host and gives rise to new composite materials. The possible applications of these new materials reach far beyond displays. However, in order to understand how to design devices based on liquid crystal-nanoparticle mixtures, it is first essential to understand the structure of the latter at molecular resolution. To this end, computer simulation can provide invaluable insights. This thesis presents a study using a pairwise intermolecular potential capable of describing interactions between liquid crystal molecules and nanoparticles in a liquid crystal-nanoparticle mixture. The so-called Zewdie-Corner potential is a Lennard-Jones type anisotropic pairwise potential where strength (energy scale) and range (length scale) parameters are expanded in terms of an orthogonal basis set of functions with respect to relative orientation and separation distance. This molecular coarse-grained methodology has been employed to represent liquid crystal molecules with cylinder-like shapes and nanoparticles with spherical shapes. Equilibrium structures of domains comprised exclusively of liquid crystal molecules, as well as domains with varying number fractions of liquid crystal molecules and nanoparticles, have been investigated using the Monte Carlo simulation technique in the isobaric-isothermal ensemble. Thermodynamic observables have been calculated and used to draw conclusions as to the molecular-scale structure and thermodynamics of the simulated liquid crystal-nanoparticle mixtures.