See Micelles Clearly
Bei Wei, Ye Fan, Chao Chen, Yongchun Pan, Biao Jiang, Lingyu Bao, Meng Zhu,
The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education; School of Chemical & Material Engineering, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu 214122, P. R. China
Abstract: Small spherical micelles may be the self-assemblies of surfactants with the simplest morphology, which has become the fundament to further explore complex amphiphilic systems and life phenomenon. Although it is possible to theoretically infer that micellar diameter is about twice stretch length of a hydrophobic chain length of a surfactant (3-5 nm) and laser light scattering experiment provides some indirect evidence of the particle size, there is a lack of a powerful technique to give direct visualization for characterizing surfactant micelles. Due to spherical surfactant micelles having small particle size; unstable cluster structure and weak ability to scatter electrons, even if by a combination technique of the advanced electron microscopy with other special sample preparation techniques (cryogenic, freeze fracture, etc), the images of the small micelles are still unclear as presented in Fig.1A. To solve the problems in this paper, sodium conjugated linoleate (SCL), a type polymerizable anionic surfactant was synthesized, and spherical SCL micelles were self-assembled in pH 13 at the concentration of 3 mmol·L-1, and then the SCL micelles were tethered by moderated UV irradiation to insure its original fragile micellar structure maintained. The morphology of the self-crosslinked SCL micelles was characterized by high-resolution transmission electron microscopy (TEM). As you can see in Fig.1B, the clearest TEM image of spherical micelles of surfactants by far was obtained successfully, and provided the direct evidence of the micellar diameter indeed twice stretch length of a surfactant hydrophobic chain (3-5 nm). This investigation gives you a chance of seeing small spherical surfactant micelles clearly for the first time. By the way, in situ reduction and gold doping-TEM coupling technology is applying to investigate morphology of spherical surfactant micelles in order to further improve the TEM image contrast.
Keywords: sodium conjugated linoleate, self-assembly, micelle
Fig.1 The cryo-TEM image of the SCL-micelles (A) and the TEM image of the self-crosslinked SCL-micelles (B)