High performance controlled reactors from micellar assemblies of aromatic amino acid amphiphiles for nanoparticle synthesis.

The micellar assemblies of lauryl esters of tyrosine (LET) and phenylalanine (LEP) show extraordinary emulsification properties. The structural similarity in respect of the aromatic ring between the dispersed phase, styrene, and the surfactants facilitates solubilization of styrene up to four times the weight of LEP and 11 times that of LET. We propose that the solubilization site varies between core in the LEP and shell in the LET micelles. LET affords double emulsions, water in oil in water (w/o/w) over a narrow phase composition, for example at R=7.15, where R represents ratio of weight of styrene to LET. A schematic model depicting the solubilization site of styrene at different regions in LET and LEP micelles has been proposed. On polymerization, the emulsions with LET and LEP micelles generated high molecular weight polymer nanoparticles of size 12-49 nm with low polydispersity index (P(d)). This demonstrates that micellar assemblies act as templating controlled reactors for the polymerization reaction. We demonstrate that PS nanoparticle dispersion of size 49 nm with polymer weight fraction as high as 42.80% could be produced from emulsions with the LET surfactant, in contrast to LEP that is 50% less efficient. Polymerization of these emulsions occurs predominantly through a micellar nucleation mechanism. It is significant to note that under the same conditions, the control experiments with sodium dodecylsulfate (SDS) micelles resulted in polymers with broad distribution, P(d)>3.0 in molecular weight.