Co-assembly behaviour of Janus nanoparticles and amphiphilic block copolymers in dilute solution

Nanoparticles can co-assemble with amphiphilic block copolymers (ABPs) in solution to generate nanoaggregates with unique properties, yet the mechanism of such a co-assembly behaviour for Janus nanoparticles (JPs) and ABPs remains unclear. Here, the self-assembly behaviour of JP/ABP mixtures in dilute solution was studied via theoretical simulations. Two kinds of ABPs with different volume fractions f_A of hydrophilic blocks were considered: one is symmetric copolymers with f_A = 0.5, and the other is asymmetric ABPs with f_A = 0.3. In the first case, mixtures of spheres and rods, connected networks and vesicles were formed sequentially as the volume fraction c_JP of nanoparticles increases. In the second case, vesicles were constantly formed. For both cases, at lower c_JP values, the nanoparticles were located at the core-corona interfaces. By contrast, at higher particle loadings, a large number of particles were involved in clusters embedded in the vesicle walls. Based on the simulation results, a morphological diagram in the space of c_JP and f_A was constructed to indicate the stability regions of different nanostructures. Specifically, it was found that the vesicles formed by JPs and ABPs with short hydrophilic blocks are stimuli-responsive. By changing the interaction parameters between hydrophobic blocks, controllable pores in the vesicle walls could be created. Our findings not only provide insights into the co-assembly behaviour of Janus nanoparticles and amphiphilic block copolymers in solution, but also offer a novel strategy to prepare nanoreactors with permeable membranes.