Effect of cold plasma surface treatment on the properties of supported ionic liquid membranes

The aim of the work is to study the impact of the cold plasma treatment on the elaboration and stability of the supported ionic liquid membranes (SILMs). The porous support was prepared from Matrimid® 5218 by the water vapor induced phase inversion. The porous structure characterized by SEM showed a spongy, interconnected and relatively symmetrical structure with macropores ranging between 10 and 15 µm. A porous Matrimid® membrane was treated with either hydrophobic (CF4) or hydrophilic (N2 or O2) plasma using a radio frequency discharge according to the optimum plasma parameters for each gas. The porous membrane was then impregnated with [C4C1im][BF4] and [C4C1im][PF6] using the direct immersion method. An acceleration of the room temperature ionic liquid (RTIL) impregnation in the case of N2 and O2 plasma treatments was observed due to both the grafted polar functions on the surface and the increase of surface roughness. On the other hand, the nonpolar surface functionalization after the CF4 plasma treatment slowed and delayed the RTIL impregnation. The SILMs were composed of ∼60% of the RTIL phase, and no effect of the plasma treatments on the RTIL uptake mass was found. The bubble point method was used to evaluate the SILM stability. Although the bubble point pressure was independent of the plasma treatments, the retention of the RTIL phase inside the membrane was found to be improved.