The Role of Elasticity in the Anomalous Swelling of Polymer Thin Films in Density Fluctuating Supercritical Fluids

Abstract

In situ neutron reflectivity was used to investigate the effects of density fluctuations on the solubility of supercritical carbon dioxide (scCO 2) in polymer thin films. Deuterated polystyrene, deuterated polybutadiene, and the corresponding random copolymer, deuterated styrene-randombutadiene copolymer, as well as deuterated poly(methyl methacrylate) were investigated. Data were obtained as a function of pressure under two isothermal conditions (T) 36 and 50°C). All the polymer films used showed anomalous swelling and CO 2 sorption on the density fluctuation ridge in the P-T phase diagram of CO2. We found that the magnitude of the swelling was a function of the elasticity of the films rather than the bulk solubility of CO2. The enhanced miscibility of the rubber/CO2 systems, which are very poor in bulk, was found to be almost identical to that of the silicon rubber/CO2 mixture, which is one of the highly miscible polymeric materials under moderate CO2 conditions.

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].…”

“…The films were then placed in a high pressure chamber [9] containing scCO 2 at T ¼ 36°C and P ¼ 8.2 MPa for 3 h. These conditions were chosen since they correspond to the density fluctuation ridge in the vicinity of the critical point and can be still tuned within the experimental resolution. In order to preserve the swollen structure, the films were quickly depressurized to atmospheric pressure at constant temperature, typically within 10 s.…”

Green thin polymer film metallization using supercritical carbon dioxide

“…From the best-fitting results, we found that the initial thickness, L 0 = 107 Å , had increased to L = 131 Å . This increase in thickness corresponds to the linear dilation, S f = (L À L 0 )/L 0 = 0.22, and the degree of dilation is much larger than in the bulk PS film (0.07) (Koga, Seo, Shin et al, 2003). In addition, the density, , of the exposed PS layer, which can be calculated by the value, decreased ( = 910 kg m À3 ) by 15% compared with that of the bulk or without exposure ( = 1040 kg m…”

“…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).…”

Positron Annihilation Studies of the Free Volumes in Nylon12/PVA Films Treated by Supercritical Carbon Dioxide

“…Over the past three decades, numerous polymers [1][2][3][4][5][6][7][8] including bulk materials and thin films, either amorphous or semi-crystalline polymers, have been found to be able to dissolve or swell in ScCO 2 with large density fluctuations [9][10][11]. However, very little is clearly known about the interaction between CO 2 and the polymers.…”