Surface properties of cationic polyelectrolytes hydrophobically modified

Poly (N,N-dimethyl-N,N-diallyl ammonium) chloride, a highly hydrophilic polyelectrolyte, was hydrophobically modified and the surface properties of the resulting amphipathic polyelectrolytes were determined. The surface activity increases with the polyelectrolyte side chain length despite the ability of this type of polyelectrolyte to form hydrophobic micro domains in solution. The standard free energy of the adsorption process, ΔG°ads, were a linear function of the number of carbon atoms in the lateral chain as well as their transfer and interfacial contributions to the adsorption process with −1.73 kJ mol−1 of methylene group to ΔG°ads. From the dependence of the surface tension with the temperature the ΔS°ads was determined. The latter parameter was always positive regardless the polyelectrolyte side chain length, thus the main driving force to ΔG°ads arises from the large positive ΔS°ads values.

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► The surface properties amphipathic cationic polyelectrolytes are studied.
► The surface activity increases as the length of the alkyl side chain increases.
► The adsorption is mainly determined by the process efficiency.
► As in anionic systems the polyelectrolyte adsorption is controlled by entropy.