Complexation Driven Assembly of Block Copolyelectrolytes into Spherical Micelles, Flower-like Micelles and Macro-Networks

Block copolymer amphiphiles, driven by solvophobic interactions, assemble into a range of micellar structures. Similar spherical micellar assemblies of block copolyelectrolytes can also be achieved by relying on electrostatic interactions between oppositely charged polyelectrolytes. These electrostatics driven assemblies, constituting of polyelectrolyte complex cores and neutral coronae, maintain a large fraction of water in their cores, thus making them particularly useful for encapsulation and delivery of charged therapeutics and nucleotides.

The generic micelle structures in complexation driven assemblies have been understood to be similar to those of amphiphilic micelles. However, recent investigations have unveiled salient differences between these solvophobicity and electrostatics driven assemblies. This presentation will highlight such differences by elaborating on both the typically acknowledged structure-defining contributions (via complexation) and additional structure-directing contributions (via intra-chain repulsion) of the charged blocks. Relying on extensive structural characterization from X-ray and neutron scattering experiments, specific examples of assembly of model oppositely charged diblock and triblock copolyelectrolytes that form spherical micelles and unique inter-connected networks of flower-like micelles, respectively, will be discussed. Further, the networks, at low polymer concentrations, phase separate from the solution, and our hypothesis on their structural features being primarily dictated by the conformations of the neutral block will be argued. In addition, conclusions from molecular dynamics simulations on the driving forces behind these unique assemblies and their direct comparisons with corresponding amphiphilic assemblies will be presented.