Thermal Properties ofp-n-Octadecyloxybenzoic Acid (Part II)

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Abstract
Thermal properties of metastable and liquid crystalline properties of p-n-octadecyloxybenzoic acid were investigated by differential scanning calorimetry. The glass transition found in the metastable crystal obtained by cooling the smectic phase suggested the existence of a disordered phase. Heat capacities of thermally stable and metastable crystals of the deuterated acid also support this conclusion. From measurements of infrared absorption spectra of the original and the deuterated acids with increasing temperature, the differences in molecular conformation among phases is discussed. It is concluded that the molecules of the carboxylic acids are associated in pairs by hydrogen bonds in the thermally stable crystal, while the hydrogen bonds are partially destroyed in the metastable crystal and in the smectic phase.