Abstract
Surface tension isotherms ofn-alkylthiopolyoxyerhylene glycols:n-C x H2x+1S(CH2CH2O) y H, wherex=5 to 8,y=3 or 4, were approximated with orthogonal polynomials to get good quality values of surface pressure (II) and molar area of the adsorbed layer (σ). The modified Volmer (Π*(δ−δ0)=Z′*R*T) van der Waals and virial equations of state were used to correlate Π and σ in terms of real two-dimensional gas. The combination of Volmer and van der Waals equations of state made it possible to determine the interaction energy, e, which was prescribed to cohesion of hydrophobic chains in the adsorption layer. The value of e for the amphiphiles in question was in the range 0.97−1.91R*T and the average contribution per methylene group was ca. 0.21R*T. The Lennard-Jones potentials calculated from second virial coefficient were of the same range as e, but no clear relation was found between their values and number of structure elements of the alkylthiopolyoxyethlene glycols.
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