Swelling and dissolution rate measurements of polymer thin films in supercritical carbon dioxide

The first interferometric dissolution rate monitor (DRM) to probe polymer swelling and dissolution in supercritical carbon dioxide (scCO2) is reported. Refractive index measurements of scCO2 as a function of pressure agree with literature and calculated values using the Lorenz–Lorentz equation, even for short equilibration times. The reflected intensity plot with <2 min of pressure and thermal equilibration time shows ±10−3 deviation from calculation. Maximum swollen film thickness for a scCO2 soluble random copolymer of tetrahydropyranyl methacrylate (35 mol%) and 1H,1H-perfluorooctyl methacrylate (65 mol%) is estimated for pressures 128–197 bar. Dissolution rates show anomalous thickness dependence that can be explained in terms of polymer/surface interactions. It was found that complete film removal requires more than 1000 s below and less than 90 s above ∼191 bar.