Swelling of Poly(n-butyl methacrylate) Films Exposed to Supercritical Carbon Dioxide: A Comparative Study with Polystyrene

Abstract

We report here the swelling and relaxation properties of confined poly(n-butyl methacrylate) (PBMA) films having thicknesses of less than 70 nm under supercritical carbon dioxide (scCO2) using the X-ray reflectivity technique. Swellability is found to be dominant in thinner films compared to thicker ones as a consequence of the confinement-induced densification of the former. Swellability is proportionately increased with the density of the film. PBMA films exhibit a more significant swelling than do PS films, and their differences become more prominent with the increase in film thickness. A comparison between the results obtained for polystyrene (PS) and PBMA ultrathin films reveals that the swellability is dependent upon the specific intermolecular interaction between CO2 and the chemical groups available in the polymers. Owing to strong Lewis acid-base interactions with scCO2 and the lower glass-transition temperature (bulk Tg ≈ 29 °C), PBMA films exhibit a greater amount of swelling than do PS films (bulk Tg ≈ 100 °C). Though they reach to the different swollen state upon exposition, identical relaxation behavior as a function of aging time is evidenced. This unprecedented behavior can be ascribed to the strong bonding between trapped CO2 and PBMA that probably impedes the release of CO2 molecules from the swollen PBMA films manifested in suppressed relaxation.

REFLEX: a program for the analysis of specular X-ray and neutron reflectivity data

“…More examples of the use of REFLEX can be found in selected papers (Bal et al, 2014(Bal et al, , 2015(Bal et al, , 2016Vignaud et al, 2014;Vignaud, Gibaud, Paris et al, 1998).…”

Trimethylaluminum Diffusion in PMMA Thin Films during Sequential Infiltration Synthesis: In Situ Dynamic Spectroscopic Ellipsometric Investigation

“…The difference in the swelling behavior of PMMA and PS is a signature of the different solubility of TMA in the two polymers. The solubility of TMA in polymers containing C=O groups, as PMMA, is larger than the solubility of TMA in polymers without C=O groups, such as PS, because of the effective intermolecular interaction between TMA and C=O groups, commonly identified in a Lewis acid−base interaction 35 . Starting from collected SE data, we argue that the initial PMMA thickness increase during first TMA exposure is due to TMA molecules diffusing in the polymer film and in small percentage forming an adduct with the carbonyl groups of PMMA.…”

Potential Use of Annona Genus Plants Leaf Extracts to Produce Bioactive Transdermal Patches by Supercritical Solvent Impregnation

“…This seems to indicate that the affinity of the active substance with the polymer matrix may be governed by the hydrophobic/hydrophilic nature of each particular polymer. Furthermore, the degree of crystallinity of the material and its glass transition temperature are also crucial factors to determine the swelling of the polymer in the presence of scCO 2 [ 41 , 42 ].…”