Self-assembled transient networks of surfactant based nano-worms

Surfactant molecules posses an amphiphilic structure leading to aggregation in aqueous medium. They can form polymer-like nano-worms, co-called wormlike micelles. The wormlike micelles are enormously long flexible cylindrical... [ view full abstract ]

Surfactant molecules posses an amphiphilic structure leading to aggregation in aqueous medium. They can form polymer-like nano-worms, co-called wormlike micelles. The wormlike micelles are enormously long flexible cylindrical micelles of a surfactant, which may be self-assembly formed by long tail ionic surfactant molecules due to balance of hydrophobic interactions of the tails and electrostatic interactions of the heads. Similarly to polymer chains in semidilute regime these long entangled self-assembled micellar chains forming transient network impact viscoelastic properties into a solution up to gel-like state. The wormlike micelles are widely used as thickening agents in food, pains, cosmetics, oilfield industry.

In contrast to polymer chains such micellar chains incessantly break and recombine as result of weak hydrophobic interaction. They reorganize easily and can transform into droplets of microemulsions if the hydrocarbons were added, then the network of the entangled chains broken. This is one of the numerous specific highly responsive properties. Thus the other general issue is interactions and self-assembly in surfactant/polymer systems.

Polymer and surfactant self-assembly in aqueous solution attract interest due to influence of the components on a shape and a conformation of each other. In the case of addition of nonsoluble polymer the micellar chains can be transformed into more compact polymer/surfactant complex as we suggest on base of macroscopic rheological investigations, where gel-like state – liquid like state transition was observed. According to literature addition of nonsoluble polymers in a wormlike micelles solution may leads to phase separation or their transformation into spherical micelles.

Effect of nonsoluble polymer on the morphology of micellar chains was obtained. The results shown flexible cylindrical shape of the objects at saturated conditions, that indicates on wormlike micelles covered by polymer chains instead globule-like collapsed polymer chains stabilized by surfactant shell as might be proposed. Thus surfactant based nano-worms containing trapped nonsoluble polymer was observed. Such complex is promosing candidate for responsive hydrogel formation. Acknowledgement: the financial support of Russian Science Foundation (project №15-13-00114).