Disjoining pressure study of formamide foam films stabilized by surfactants

Gunther Andersson, E Carey, C Stubenrauch

    Research output: Contribution to journalArticle

    11 Citations (Scopus)

    Abstract

    A thin film pressure balance was used to investigate the disjoining pressure π as a function of the film thickness h of surfactant-stabilized formamide foam films. Nonionic (alkylpoly(ethylene glycol)s) and cationic surfactant (alkyltrimethylammonium bromides (CnTAB) with n = 14 and 16) solutions were studied in the absence and presence of electrolyte. The resulting π-h curves were fitted with the DLVO theory from which we extracted surface charge densities q0 and surface potentials ψ0. Investigating formamide foam films is of interest for studying the electrostatic component of the stabilizing forces in foam films. We know that the aqueous foam films are stabilized via electrostatic forces. In this case the self-dissociation of water contributes to the charges in the foam film. As formamide has a dissociation constant which is about 2 orders of magnitude lower than that of water, the number of charges in the solution due to self-dissociation is much smaller, which, in turn, should lead to lower electrostatic forces. Indeed, we found that formamide solutions of nonionic surfactants did not form stable foam films at concentrations below the critical micelle concentration. Regarding the cationic surfactants, the main difference between the formamide and the aqueous foam films is the fact that the concentration of ionic surfactants to form stable foam films is about 2 orders of magnitude higher compared to water. Consequently, the screening length for the electrostatic interaction and thus the film thickness are much smaller compared to films formed by the respective aqueous solutions.

    Original languageEnglish
    Pages (from-to)7752-7760
    Number of pages9
    JournalLangmuir
    Volume26
    Issue number11
    DOIs
    Publication statusPublished - 1 Jun 2010

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