Resonance Raman study on phase transition and molecular orientation in black soap films

Polarized resonance Raman spectra of black soap films (BSF), withdrawn from the 0.01 mol/l aqueous solution of cetyltrimethylammonium chloride (CTAC) containing 0.01 mol/l methyl orange (MO), are recorded below and above the gel-to-liquid crystal phase transition temperature (Tc) of the film. Quantitative description of the molecular orientation of MO at the CTA+ interface is made with the application of the uniaxial orientation distribution model. It was revealed that the temperature-induced phase transition causes increasingly random distribution of MO in the liquid crystalline BSF.