Thermally driven collapse of a polymer brush in a polymer matrix

The segment density profile of end-functionalized deuterated polystyrene $(d-\mathrm{PS})$ brush in a miscible poly(vinyl methyl ether) (PVME) polymer matrix was studied using neutron reflectivity. Brushes were chemically anchored to a silicon substrate. PVME has a favorable interaction with PS at room temperature. As the temperature increases, the interaction between PS and PVME becomes more unfavorable until in the bulk phase separation would occur. From the reflectivity experiments, it was found that the PVME was expelled from the brush as the temperature was increased. This process was reversible for temperatures up to $90°\mathrm{C}$; above this the volume fraction in the brush approached unity and macroscopic dewetting occurred. The height of the brush was sufficiently well predicted by a scaling theory, which predicts a cube root dependence on the Flory-Huggins interaction parameter.