Aggregation behaviors of gelatin with cationic gemini surfactant at air/water interface

The dilational rheological properties of gelatin with cationic gemini surfactant 1,2-ethane bis(dimethyl dodecyl ammonium bromide) (C12C2C12) at air/water interface were investigated using oscillating barriers method at low frequency (0.005–0.1 Hz), which was compared with single-chain surfactant dodecyltrimethyl ammonium bromide (DTAB). The results indicate that the maximum dilational modulus and the film stability of gelatin-C12C2C12 are higher than those of gelatin-DTAB. At high concentration of C12C2C12 or DTAB, the dilational modulus of gelatin-surfactant system becomes close to that corresponding to pure surfactant, suggesting gelatin at interface is replaced by surfactant. This replacement is also observed by surface tension measurement. However, it is found that gelatin-C12C2C12 system has two obvious breaks but gelatin-DTAB has not in surface tension isotherms. These phenomena are ascribed to the double charges and strong hydrophobicity of C12C2C12. Based on these experimental results, a mechanism of gelatin-surfactant interaction at air/water interface is proposed.