Block copolymer vesicles via liquid/liquid interface-mediated self-assembly

Self-assembly behavior of amphiphilic block copolymers has attracted much attention recently. In this paper, a novel liquid/liquid interface-mediated self-assembly behavior of block copolymer is reported. An aqueous solution of HAuCl4 and a chloroform solution of poly(2-vinylpyridine)-block-polycaprolactone (P2VP199-b-PCL22) are employed as the upper phase and the bottom phase, respectively. Structural transitions from toroids and plate like structures to vesicles and large compound vesicles are observed in the bottom phase by using transmission electron microscopy (TEM). It is proved that vesicles and large compound vesicles are formed through adsorption and desorption of copolymers at the liquid/liquid interface, molecular aggregation and microphase separation in the bottom phase due to the amphiphilic property of protonated P2VP199-b-PCL22. The well-dispersed Au nanoparticles are formed during the self-assembly process and embedded in the bilayers of the vesicles. The concentrations of HAuCl4 and P2VP199-b-PCL22 have an effect on the self-assembly behavior. A unique structure, “pearl necklace”, is obtained at higher concentrations. In addition, it was found that P2VP252-b-PCL44 also formed vesicles, while P2VP195-b-PCL75 and P2VP195-b-PCL307 formed spherical micelles in the bottom phase through the same approach. The dependence of the aggregate morphology and the molecular structure was discussed based on the critical packing parameter, p.