AC-Calorimetry and Dielectric Spectroscopy on Anisotropic Liquid Crystal and Aerosil Dispersions

Cruceanu, Florentin I.

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AC-Calorimetry and Dielectric Spectroscopy on Anisotropic Liquid Crystal and Aerosil Dispersions

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This thesis presents an experimental study of the influence of an external field and alignment upon a colloid of a liquid crystal (octycyanobiphenyl denoted 8CB) and a silica gel of aerosil nano-particles. The first techniques used was an AC-calorimetry (alternating current heating) and the systems under investigation were firstly put under the influence of a magnetic field at John Hopkins University in Baltimore by professor Leheny's group. The experiments revealed changes in transition temperatures, nematic range and critical coefficient that could account for what we called a 'memory' of the above mentioned structures. The second technique, dielectric spectroscopy, was applied to the same very densities of mixture s mentioned in the first paragraph. The samples were applied in one procedure an increasingly higher alternating electric field. An overall increase of the capacitance of the sample was measured. The second experiment was to reproduce the application of the magnetic field from the AC-calorimetry experiment now with an electric field. In dielectric spectroscopy case, an increase in transition temperature after the application of the procedure was revealed.

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