Surface rheological behavior of gelatin/ionic liquid-type imidazolium gemini surfactant mixed systems

Abstract

The surface properties of gelatin solutions without and with ionic liquid-type imidazolium gemini surfactants have been investigated via surface shear and dilational rheology as well as surface tension measurements. Both the surface shear and dilational rheological properties show that the strength of gelatin film is enhanced in the presence of 0.005 mmol L⁻¹[C₁₂-4-C₁₂im]Br₂, and the storage modulus is larger than loss modulus for gelatin/[C₁₂-4-C₁₂im]Br₂, indicating that gelatin/[C₁₂-4-C₁₂im]Br₂ is an elastic film. With increasing the concentration of imidazolium gemini surfactant, the dilational modulus increases firstly and then passes through a maximum value, due to the electrostatic and hydrophobic interactions between surfactant molecules and gelatin chains. Although the surface tension of gelatin/surfactant mixed solution is identical to that of the pure surfactant solution at high surfactant concentration, the dilational modulus suggests that the surfactant molecules are unable to fully replace gelatin molecules from the air/water surface. The structure of the gemini surfactant has great effect on the surface viscoelastic modulus of gelatin, it is found that the gelatin film in the presence of imidazolium gemini surfactant with longer hydrophobic chain or longer spacer reveals the larger strength.