Functionalization of Surface by Plasma Treatment

AFM study of membranes is often combined with the plasma smface treatment. The purpose of plasma treatment in AFM studies is twofold first, for the modification of the membrane surface and second, for the removal of thin layers, one after another, from the membrane surface to reveal the structme of the membrane beneath. The second type of treatment is called plasma etching. 

The capability of plasmas to modify the chemical and physical properties of the surface without affecting the bulk properties of the base material has been advcinta-geous in several cases [35-38]. Either surface modification or thin film deposition can create specific surface chemistries for optimization of membrane performances in separation processes [39]. It is well known that the surface wettabihty and the adhesion of polymer can be significantly improved by plasma treatment with non-polymer-forming gases. The plasma treatment also leads to the formation of radicals [35] that are promoters of surface cross-linking functionahzation. 

Dreux et al. studied the effect of CF4 and CO2 plasma treatment on the barrier properties of polyamide 12 (PA12, ATOFINA, Serquigny, France) toward permeant molecules of opposing characters, i.e., water and toluene [44]. While CF4 treatment made the surface more hydrophobic, CO2 treatment made it more hydrophilic. The surfaces were studied by AFM and XPS. 

Compared to CF4 plasma treatment, CO2 plasma treatment led to a change in the morphology toward the less homogeneous, and the change covered practically the whole surface. In both cases, the alteration of the topography cannot be the result of deposition because CF4 and CO2 are known not to be polymerized by plasma [46, 47]. Rather, the alteration is a modification of the surface by substitution followed by cross-linking and degradation phenomena. 

Samples Nodules (nm) Nodule aggregates (nm) Supernodular aggregates (nm) 

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