Physics

This thesis presents a series of studies of quenched random disorder (QRD) on liq-uid crystals. We have used high-resolution AC-Calorimetry, high-resolution X-Ray Diffraction (XRD), X-Ray Intensity Fluctuation Spectroscopy (XIFS), Turbidity, Integrated Low-Angle Light Scattering (ILALS), as well as Polarizing Microscopy to characterize the effects of a nano-colloidal dispersions of aerosils in the phase transitions of several liquid crystals. The aerosil (SIL) is made of 70 A ̊ diam-eter SiO2 particles coated with hydroxyl (-OH) groups. The coating allows the SIL particles to hydrogen-bond together, to form a very low density gel in an organic solvent. This provides the quenched random disorder. The liquid crys-tals of interest are: octyloxycyanobiphenyl (8OCB), 4-n-pentylphenylthiol-4’-n-octyloxybenzoate (8̄S5), 4’-transbutyl-4-cyano-4-heptyl-bicyclohexane (CCN47), and octylcyanobiphenyl (8CB). Studies have been carried out as a function of aerosil concentration and temperature spanning the following phase transitions, Isotropic to Nematic (I-N), nematic to smectic-A (N-SmA), smectic-A to smectic