Interfacial Dilational Rheology of the Novel Zwitterionic Surfactants

The dilational rheological properties of series branched betaine surfactants: Guerbet p-(n-tetradecyl)-benzyl carboxybetaine (C(14)GCB), Guerbet p-(n-dodecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C(12)GE(2)CB), Guerbet p-(n-tetradecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C(14)GCB) and Guerbet p-(n-hexadecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C(16)GCB), were investigated by drop shape analysis method at the water-decane interface. The dilational properties of surfactants were investigated as a function of time, frequency and concentration. The experimental results show that the time dependence was complex. It was also found that the dilational modulus were almost independent of frequency in the experimental concentration range for C(14)GE(2)CB and C(16)GE(2)CB, while the dilational modulus of C(14)GCB and C(12)GE(2)CB increased with the increase of frequency, sharing the same results with conventional zwitterionic surfactants. The results indicated the appearance of a more elastic film for the C(14)GE(2)CB and C(16)GE(2)CB due to the internal compression and expansion of oxyethylene units (EO). On the other hand, the surfactant with branched alkyl chain came forth a higher maximum value of dilational modulus compared with the straight chain surfactants with the increase of concentration, which means the branching of alkyl chain was another important factor to control the interfacial film.