XPS studies of radiation grafted PTFE-g-polystyrene sulfonic acid membranes

Abstract

Structural investigations of PTFE-g-polystyrene sulfonic acid membranes prepared by radiation grafting of styrene onto PTFE were conducted by X-ray photoelectron spectroscopy (XPS). The analyzed materials included original PTFE film as a reference material, grafted film, and sulfonated membrane samples having various degrees of grafting. Interest is focused on C1s, F1s, O1s, and S2p of narrow XPS spectra as the basic elemental components of the membrane. The original PTFE film was found to undergo structural changes in terms of chemical composition and shifting in binding energy induced by incorporation of sulfonated polystyrene grafts, and the amount of such changes depends on the degree of grafting. The atomic ratio of F/C was found to decrease with the increase in the degree of grafting, while that for S/C and O/C were found to increase.

XPS analysis of glassy carbon electrodes chemically modified with 8‐hydroxyquinoline‐5‐sulphonic acid

“…The S2p 3/2 BE at 167.6 eV of the unique 2p doublet assigned to sulfur, obtained by fitting the relevant detailed scan of the HQSA standard (see Fig. (b)) seems quite lower than that assigned to sulfonic groups present in the quite different matrices considered in the available references (from sulfonated styrene and styrene copolymers to naphthol[1,8‐ cd ]1,2‐dithiole to α‐naphthalene sulfonate‐doped polypyrrole and to radiation grafted polytetrafluoroethylene‐ g ‐polystyrene sulfonic acid membranes). Available data are 168.1 eV, 168.3 eV, 168.9 eV, 170,0 eV .…”

Cation exchange membranes by radiation-induced graft copolymerization of styrene onto PFA copolymer films. II. Characterization of sulfonated graft copolymer membranes

“…Based on the aforementioned results, it may be stated that the membranes are thermally stable up to ∼320°C under the present experimental conditions. Details of the thermal stability investigations and thermal degradation behavior of PFA‐ g ‐polystyrene sulfonic acid membranes were discussed elsewhere 36…”

Surface modification of radiation‐grafted polymer films and membranes by crosslinking

“…This indicates that part of the hydrocarbons at the surface does not belong to sulfonated polystyrene. The same is most likely valid for the noncrosslinked samples of Nasef et al17–19 These authors too, reported high surface concentrations of poly(styrenesulfonic acid) and at the same time S/C ratios that are significantly below the theoretical values. In addition to this, the different grafting technique of Nasef et al (simultaneous instead of preirradiation grafting) may have contributed to the differences as well.…”

“…Contrary to this, Nasef et al have determined for similar—but noncrosslinked—materials a significant surface enrichment of the sulfonated and nonsulfonated polystyrene grafts over a wide range of graft levels 17–19. These diverging results stimulated us to investigate more closely the effect of crosslinking on the surface properties of radiation‐grafted membranes, a parameter that had been ignored in earlier investigations (e.g.,17–20). Only very recently, while this manuscript was still in preparation, Li et al have reported on the surface analysis of radiation‐crosslinked poly(tetrafluoroethylene) (PTFE) grafted with styrene and divinylbenzene (DVB) 21.…”

“…Recently, we have reported that the performance in fuel cells of our own crosslinked poly(tetrafluoroethylene‐ co ‐hexafluoropropylene) (FEP) and poly(styrenesulfonic acid) based membranes suffers from a very hydrophobic surface that is depleted in ionic groups 11. Contrary to this, Nasef et al have determined for similar—but noncrosslinked—materials a significant surface enrichment of the sulfonated and nonsulfonated polystyrene grafts over a wide range of graft levels 17–19. These diverging results stimulated us to investigate more closely the effect of crosslinking on the surface properties of radiation‐grafted membranes, a parameter that had been ignored in earlier investigations (e.g.,17–20).…”