TEMPERATURE-DEPENDENCE OF MOLECULAR-CONFORMATION AND LIQUID STRUCTURE OF CIS-9-OCTADECENOIC ACID

The temperature dependence of molecular conformation and liquid structure for cis-9-octadecenoic acid in the neat state has been studied by means of differential scanning calorimetry (DSC) and by measurement of the density, viscosity, self-diffusion coefficient, infrared spectrum, fluorescence polarization of DPH dissolved in the acid, ESR order parameter for four kinds of spin probe incorporated in the acid, H-1 and C-13 NMR relaxation T1 and T2, and X-ray diffraction. On the basis of the experimental results, it is concluded that the acid has three kinds of liquid structure depending on temperature: (1) The first structure, in temperatures from the melting point to 30-degrees-C, consist of clusters of a quasi-smectic liquid crystal; the clusters ae randomly orientated and their sizes are smaller than the wavelength of visible light. (2) The second one, in the temperature range between 30 and ca. 55-degrees-C, presumably consists of clusters having a less ordered structure. (3) The third one appears to be an isotropic liquid above ca. 55-degrees-C.