ORDERING PHENOMENA OF STAR POLYMER SOLUTIONS APPROACHING THE THETA STATE

The liquid-state ordering phenomena of a semidilute polybutadiene 64-arm star polymer solution were investigated by small-angle neutron scattering. For this purpose, we used deuterated 1,4-dioxane, which is a \ensuremath{\Theta} solvent for the star at $31.5\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ Its quality was modified by varying the temperature in the range between $40\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and $80\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ Besides a swelling of the star, with increasing temperature the development of a strong correlation peak was observed in the experiment. The experimental data were described theoretically by employing an effective pair potential between stars which was introduced earlier by Mewis et al. [J. Mewis, W. J. Frith, T. A. Strivens, and W. B. Russel, AIChE J. 35, 415 (1989)].