Surface dilatational properties of Gemini surfactants containing multiple hydroxyl groups

Surfactant adsorption films at the air/water interface, which usually exert a significant influence over system behaviour, are closely related to the surfactant molecular structure. In this research, a series of Gemini surfactants containing four hydroxyl groups at the head groups, namely: alkanediyl-α,ω-bis[di(2-hydroxylethyl) dodecylammonium bromide], abbreviated to 12(2OH)-s-12(2OH), where s = 3, 6, 8 and 10, respectively, were investigated by using interfacial dilatational rheological measurements. The effects of oscillating frequency, bulk concentration and spacer length on the dilatational behaviour of 12(2OH)-s-12(2OH) were investigated. The variation of dilatational modulus of 12(2OH)-8-12(2OH) with concentrations showed two peaks which were attributed to different configurations adopted by the spacer, revealing the effects of dynamic configuration of the spacer on surfactant interfacial adsorption. The fit to the results, with that data available, using the Lucassen/van den Tempel (LVT) model showed that the presence of hydroxyl groups near the head groups of Gemini surfactants enhanced the interfacial elasticity of the adsorption films.