REFLECTANCE INFRARED SPECTROSCOPIC ANALYSIS OF POLYMERS AT THE AIR-WATER-INTERFACE .4. MICROSTRUCTURE OF POLY(DIMETHYLSILOXANE)

At room temperature, monolayer films of poly(dimethylsiloxane) spread on the air-water interface display nearly constant surface pressures i n the region between surface concentrations of 0.75 and 1.6 mg/m(2). S tudies of these films in this region by epifluorescence microscopy and external reflectance infrared spectroscopy are reported. Two surface phases were detected by the epifluorescence micrographs. The infrared reflectance spectra in the 1000-1100 cm(-1) region and at concentratio ns between 0.75 and 1.6 mg/m(2) can be fit as a mixture of infrared fe atures observed at these surface concentration limits. At 0.75 mg/m(2) , the infrared reflectance data are consistent with a random chain in which the oxygen atoms are largely exposed to the water surface, descr ibed by earlier workers as a twisted caterpillar, or a two-dimensional random coil with as many oxygen atoms as possible exposed to water. A t 1.6 mg/m(2), the infrared data indicate that the oxygen atoms are la rgely excluded from contact with water and suggest the presence of a m ore ordered structure consistent with helical segments which have the helix axis parallel to the water surface.