Worcester Polytechnic Institute Electronic Theses and Dissertations Collection

Title page for ETD etd-042705-123130


Document Typedissertation
Author NameRoshi, Aleksander
Email Address sandrino01 at yahoo.com
URNetd-042705-123130
TitleQuenched Random Disorder Studies In Liquid Crystal + Aerosil Dispersions
DegreePhD
DepartmentPhysics
Advisors
  • Germano S. Iannacchione, Advisor
  • Carl W. Garland, Committee Member
  • Rafael Garcia, Committee Member
  • Keywords
  • smectic-A to smectic-C
  • nematic to smectic-A
  • isotropic-nematic
  • phase transition
  • quenched random disorder
  • liquid crystal
  • gel structure
  • turbidity
  • gel dynamics
  • x-ray intensity fluctuation spectroscopy ( XIFS )
  • ac-calorimetry
  • x-ray difraction
  • Date of Presentation/Defense2005-04-26
    Availability unrestricted

    Abstract

    This thesis presents a series of studies of quenched random disorder (QRD) on liquid 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~AA~ diameter SiO$_{2}$ 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 crystals of interest are: octyloxycyanobiphenyl ($8OCB$), 4-extit{n}-pentylphenylthiol-4'-extit{n}-octyloxybenzoate (ar{8}$S5), 4'-transbutyl-4-cyano-4-heptyl-bicyclohexane ($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 (emph{I-N}), nematic to smectic-emph{A} (emph{N-SmA}), smectic-emph{A} to smectic-emph{C} (emph{SmA-SmC}), and crystallization.

    Files
  • AlexRoshi-DissertationFinal.pdf

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