Adsorption of anionic surfactant on porous and non-porous polyethylene terephthalate films

Abstract

We study the adsorption of anionic surfactant, sodium dodecyl diphenyloxide disulfonate (SDDD) on three types of polyethylene terephthalate substrates from aqueous solutions of SDDD of different concentrations. Neutral electrolyte (KCl) was added to the solutions to vary the ionic strength. The three types of substrates were: (1) original polymer film, (2) etched non-porous film, which was obtained from pristine film by chemical etching and bears negative charge on the surface, (3) etched porous membranes, which were fabricated from pristine film by ion irradiation and subsequent chemical etching. The membranes have negative charge on the flat surface and on the inner pore walls. The comparison of original and etched nonporous films shows that the negative charge on the flat surface has weak effect on adsorption of the anionic surfactant. The comparison of etched non-porous and porous films shows that the SDDD adsorption on the inner walls of pores is much weaker than on flat surface—even in case the pore radius is significantly larger than the Debye length. This “exclusion” effect strongly depends on ionic strength of solution. For the porous films, the effect of the pore size and shape on the anionic surfactant adsorption is presented and discussed.