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

The dilational theological 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 Rational 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 inter-face 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. (c) 2006 Elsevier B.V. All rights reserved.