(256v) See Micelles Clearly

See Micelles Clearly

Bei Wei, Ye Fan, Chao Chen, Yongchun Pan, Biao Jiang, Lingyu Bao, Meng Zhu,

Yun
Fang*

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)