A disjoining pressure study of foam films stabilized by tetradecyl trimethyl ammonium bromide C14TAB

Abstract

In the present study disjoining pressure versus thickness curves (Π–h curves) of the cationic surfactant tetradecyl trimethyl ammonium bromide (C₁₄TAB) were measured as a function of the surfactant concentration and of the electrolyte concentration. The former measurements were used to determine the dissociation degree of C₁₄TAB in a confined geometry, i.e. in a thin common black film (CBF). The latter measurements allowed us to determine the electrolyte concentration at which a Newton black film (NBF) is formed and to study the influence the foam film type (CBF or NBF) has on the stability of the respective foam. Last but not least, CBFs were studied in a temperature gradient and it was found that water diffuses from cold to hot regions which can be explained with a negative Soret coefficient of H₂O. All of these examples demonstrate that Π–h curves provide much more information about foam films than simply the interaction forces.