A SPECTROSCOPIC STUDY ON BLACK SOAP FILMS

Black soap films （BSFs） have been prepared from the aqueous solution of cetyltrimeth-ylammonium bromide （CTAB） containing methyl orange （MO）. The dynamic process ofthe formation of the BSFs was examined by electronic absorption and FT-IR spectroscopies.The thickness of the aqueous core of the BSF was found to decrease with the increase of MOconcentration, altering from common BSFs to Newton ones. The spectral features of CH2stretching vibrations of methylene chain and the π--π* absorption of MO show that boththe CTAB and MO molecules are in oriented liquid crystalline state in the two types of theBSFs. Theoretical consideration of Raman scattering activity has been made of uniaxiallyoriented molecules. From the polarized resonance Raman measurements of the BSFs, it wasknown that the long axes of the MO molecules were tilted with a large angle of about 80°with the surface normal in the two types of the BSFs.