SIMULTANEOUS DETERMINATION OF MOLECULAR-ORIENTATION AND SURFACE CONCENTRATION IN ANISOTROPIC MONOLAYERS ON LIQUID SUBSTRATES

A new method is developed for the simultaneous determination of chain orientation and surface concentration in monolayers on liquid substrat es. The method is based on the use of s- and p-polarized reflection-ab sorption (RA) infrared intensities in conjunction with an optical mode l that includes anisotropy in the optical constants. The advantages an d limitations of the method are explored in detail. A modeling assessm ent of the RA(p)/RA(p) ratio leads to information on how the ratio can be used to qualitatively interpret RA spectra. Spectral simulations a re given that address the issues of frequency shifting and band distor tion in reflection-absorption due solely to optical considerations. Ex perimental spectra of sodium dodecyl sulfonate are collected as solubl e monolayers at the air/water interface. The spectral intensities are used to calculate the chain orientation, the surface concentration, an d the associated errors. The surface concentration is compared with th at predicted from surface tension isotherms.