Neutron reflectivity study of glassy polymer brushes in density fluctuating supercritical carbon dioxide

Abstract

By using in situ neutron reflectivity, we measured the swelling behavior of two types of polymer brushes, deuterated polystyrene with a trichlorosilane end group and deuterated polystyrene-block-poly(4-vinylpyridine) block copolymer, in supercritical carbon dioxide (scCO 2 ). The measurements were conducted in the pressure range of 0.1-20 MPa at 36°C. The pressure dependence of the brush height clearly showed an anomalous peak at the density fluctuation ridge (pressure ϭ 8.2 MPa) that defined the maximum long-range density fluctuation amplitude in the pressure-temperature phase diagram of carbon dioxide (CO 2 ). The density profile of the brush, which could be approximated by a simple step function, and the magnitude of the brush height both indicated that the solvent quality of scCO 2 for the deuterated polystyrene brushes was still poor even at the density fluctuation ridge. In addition, atomic force microscopy images for the frozen polystyrene brush prepared by the rapid drying of CO 2 showed a phase-separated structure, as predicted from the numerical calculations of Grest and Murat, as a function of the variable N, where N is the polymerization index and is the grafting density.

Role of interfacial interactions on the anomalous swelling of polymer thin films in supercritical carbon dioxide

“…Anomalous adsorption has been rationalized by the fact that long‐range density fluctuations of CO 2 , affects the Gibbs excess adsorption of CO 2 under critical conditions 33. The swelling of polymer thin films in CO 2 also exhibits anomalous maximum in the vicinity of the critical point 25, 34–39. Specifically, Sirard et al first discovered the anomalous maxima in the swelling isotherms of PMMA thin films in CO 2 by in situ spectroscopic ellipsometry 25.…”

“…Specifically, Sirard et al first discovered the anomalous maxima in the swelling isotherms of PMMA thin films in CO 2 by in situ spectroscopic ellipsometry 25. Koga et al used neutron reflectivity to explore the anomalous swelling of polymer thin films with thickness h less than 10 R g in Sc‐CO 2 34–36, 38, 39. The effect of CO 2 on the welding kinetics of colloidal crystals of PS was examined by in situ measurement of Bragg diffraction and by scanning electron microscopy 40.…”

Surface modification of polymeric nanocomposite thin films using supercritical carbon dioxide

“…This ridge is a locus of points that define the maximum long-range density fluctuation amplitude in CO 2 . A large enhancement in the solvent quality was observed to occur for all polymer films, even when the bulk miscibility with CO 2 was very poor [5][6][7][8][9][10]. We also showed that when the polymer films were glassy at room temperature, it was possible to rapidly evaporate the CO 2 and preserve the swollen structures as it was [11].…”

Green thin polymer film metallization using supercritical carbon dioxide

“…Specifically, we have found that, along the pressure-temperature portion of the phase diagram known as the 'density fluctuation ridge', excess swelling of ultrathin polymer films occurs (Koga et al, 2002;Koga, Seo, Shin et al, 2003;Koga et al, 2004). It was also found that, when the gas was released rapidly, the polymer was quickly vitrified and the swollen structure could be preserved as it was (Koga et al, 2002).…”