Structural transition of self-assembled nanostructures from dodecyl chain grafted poly(2-hydroxyethyl aspartamide) in aqueous solution

Abstract

A series of amphiphilic graft copolymers, poly (2-hydroxyethyl aspartamide) grafted with dodecyl chains with different degree of substitution (DS) were synthesized, and their aggregates with various morphologies in aqueous media were prepared by a direct dissolution method. In this study, the multiple morphologies of poly (2-hydroxyethyl aspartamide) grafted with dodecyl chain $(PHEA-g-C_{12})$ in aqueous media were investigated as a function of DS of the dodecyl chains, which are related to hydrophobic/hydrophilic ratio, and polymer concentration. At the same polymer concentration condition, the self-assembled structures are changed from spherical micelle to wormlike micelle, tubular networks, and vesicles in orders of increase of DS of dodecyl chains. And also, packing parameter for each polymer is calculated from π-A isotherm of Langmuir monolayer. These structural transitions can be explained in terms of interfacial energy and packing parameter. Polymer concentration is also an important factor affecting self-aggregates behaviors. Although there are no structural changes in case of spherical micelle and wormlike micelle solution, tubular networks and vesicle structures show some structural changes according to the change of concentration. In case of tubular networks solution, there is a phenomenal increase of viscosity according to the increase of concentration. Vesicles at concentrated solution are usually large (~200nm in diameter) and quite polydisperse in size. Consequently, self-aggregates behaviors and their structures are affected profoundly by the DS of the grafted hydrophobic chains and polymer concentration.