SCREENING LENGTHS IN CONCENTRATED POLYSTYRENE SOLUTIONS IN TOLUENE DETERMINED USING SMALL-ANGLE NEUTRON AND SMALL-ANGLE X-RAY-SCATTERING

Screening lengths have been measured for the polystyrene/toluene system using small angle neutron scattering and small angle X-ray scattering over the concentration interval 0.1-0.9 g/mL and in the temperature range from 5 to 70-degrees-C. At the lower concentrations covering the semidilute regime (c < 0.3g/mL) the concentration dependence agrees well with literature values: xi(s) = (2.7 +/- 0.1)C-0.72+/-0.01/angstrom. At higher concentrations there is a stronger decrease in xi(s) to an approximately constant value: xi(s) almost-equal-to 1.8 angstrom. The observed intensities (I(0)) contain contributions from both density and concentration fluctuations and show a change in slope from a strong (T > T(g)) to a weak (T < T(g)) temperature dependence at the glass transition temperature.