No abstract

The Rayleigh factors and depolarization ratios at 6328 A have been measured for carbon disulfide, toluene, benzene, chloroform, carbon tetrachloride, cyclohexane, butanone, acetone, methanol, and water using an improved model of the low-angle laser light-scattering (LALLS) photometer. Small errors in some of the Rayleigh factors published using an earlier model of this instrument have been revealed. Depolarization ratios are measured by a new method involving detection of the full cone of forward scattered light.

A new method for the calculation of the Rayleigh factor from low angle light scattering measurements is developed. This method does not require a uniform intensity illuminating beam, hence efficiently utilizes all the beam from a focused laser source. Scattering volume is then very small, reducing sample volume and interference from contaminant particles. All the parameters necessary for the calculation of the Rayleigh factor (including the exact dependence on sample refractive index) are measurable, hence absolute calibration is possible. Over-all error is estimated to be less than 2.3% under specified conditions. Measurements are possible at scattering angles as small as 2 degrees obviating the need for angular extrapolations in the determination of molecular weight of most dissolved samples. Rayleigh factors at 22 degrees C, 633 nm, and a scattering angle of 4 degrees for water, methanol, benzene, and toluene, were found to be, respectively, 0.907, 2.56, 12.15, and 13.45 x 10(-6) cm(-1).

SynopsisEffluent from a gel-permeation chromatographic column has been simultaneously and continuously monitored with a differential refractometer and a low-angle laser light-scattering (LALLS) photometer. This provides a true and direct determination of molecular weight distribution rathcr than through a calibration method as obtained by conventional GPC techniques. Computer misted data reduction provides a rapid determination of am, a,,, gW/gm, as well as a plot of molecular weight distribution.Samples of very narrow molecular weight distribution (MWD) polystyrene from Pressure Chemicals Co. and relatively wide MWD samples of poly(methy1 methacrylate) in chloroform have been characterized.