Flow-induced deformation and desorption of adsorbed polymers

The influence of shear flow of solvent past poly(methyl methacrylate) chains adsorbed onto germanium oxide from dilute carbon tetrachloride solution (a near-θ solvent) was studied at shear rates from 0 to 4 × 10⁴ s^-1 with the new apparatus described in this paper. Both the adsorbed amount and the flow-induced surface orientation (surface dichroism) were measured. The method involved measurements of infrared spectroscopy in attenuated total reflection (FTIR-ATR) using a hemispherical ATR crystal whose position with respect to the incident infrared source was rotated by 90° during the experiment in order to measure infrared absorbance in orthogonal directions, shear flow appeared to flatten the adsorbed PMMA layer relative to the surface. However, alignment of the polymer orientation in the direction of flow was found to be small. This suggests that shear-induced desorption (controlled by stress) and relaxation in response to deformation within the adsorbed layer (controlled by time) may be largely independent.