Screening Lengths in Concentrated Polystyrene Solutions in Toluene

Macromolecules 1992,25, 6904-6908

6904

Screening Lengths in Concentrated Polystyrene Solutions in Toluene Determined Using Small Angle Neutron and Small Angle X-ray Scattering Wyn Brown* Department of Physical Chemistry, University of Uppsala, Box 532, 751 21 Uppsala, Sweden

Kell Mortensen Ris0 National Laboratory, Physics Department, DK-4000 Roskilde, Denmark

George Floudas Max-Planck Institut fur Polymerforschung, Mainz, 0-6500 Germany Received June 22, 1992; Revised Manuscript Received September 9, 1992

ABSTRACT 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 0.14.9 g/mL and in the temperature range from 5 to 70 OC. At the lower concentrations covering the semidilute regime (c < 0.3 g/mL) the concentration dependence agrees well with literature values: & = (2.7 f O . ~ ) C ~ . ~ ~ * O . O ~ At / A . higher concentrations there is a stronger decrease in F. to an approximately constant value: & = 1.8A. The observed intensities (I(0))contain contributions from both density and concentration fluctuations and show a change in slope from a strong (T > Tg) to a weak ( T