Relaxation of Ultrathin Polystyrene Films Hyperswollen in Supercritical Carbon Dioxide

Abstract

Relaxation of highly swollen (∼20−80%) ultrathin (≤21 nm) polystyrene films exposed to supercritical carbon dioxide (at 35°C and 80 bar) is studied by monitoring the evolution of thickness as a function of time using X-ray reflectivity. Correlations between their swelling (that determines the departure from equilibrium), depressurization time, thickness relaxation rate and aging time are established. Swollen films that are depressurized very slowly (depressurization time ≈1 h) exhibit a small swelling and a very low relaxation rate at ambient condition, whereas fast depressurized films (depressurization time ≈2 min) show a large swelling and a high relaxation rate. The rate of depressurization not only impacts their out of equilibrium state but also their relaxation rate. The relaxation time is essentially governed by the temperature following an Arrhenius law below T g and a strong temperature-dependent behavior above T g and by the relative departure from equilibrium.

Vitamin C/Stearic Acid Hybrid Monolayer Adsorption at Air–Water and Air–Solid Interfaces

“…39 Notably, EDP provides film thickness, electron density, and interfacial roughness of films. 39,40 Analysis of XRR data was carried out using the matrix technique. 39…”

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).…”

Direct experimental evidences of the density variation of ultrathin polymer films with thickness

“…[1][2][3][4] As the thickness of the films decreases and approaches the characteristic length scale of the individual polymer molecules (gyration radius, Rg), confinement effects and interactions due to the presence of two interfaces are likely to strongly alter various physical properties of the films. Indeed, diverse studies have shown that the conformation [5][6][7] , dynamics 8 , dewetting behavior [8][9][10] , viscosity 11 , mass density [12][13] and physical aging [14][15] of the polymer thin films are profoundly modified in comparison to their bulk counterpart. In the case of polystyrene (PS) thin films supported on silicon wafers for example, despite a notably abounding and growing literature, it is still not fully understood why such films exhibit a large depression in their glass transition temperature, Tg.…”