Modulating Water Distribution and the Intramicellar Assembly of Sequence-Defined Ionic Peptoid Block Copolymers by the Ionic Monomer Position

The intramicellar mass heterogeneity of a series of sequence-defined ionic peptoid block copolymers carrying a single charged monomer has been determined through contrast variation small-angle neutron scattering analysis. We observe that the internal micellar structure, namely, the number density radial distributions of invasive water and peptoid polymer, is significantly impacted by the location of the ionic monomer. By positioning the ionic monomer progressively closer to the hydrophilic/hydrophobic block junction, the micelles become less compact with increasing levels of chain folding and invasive water to accommodate electrostatic repulsion among the ionic monomers via solvation. This results in increasingly smaller micellar aggregates with aggregation numbers (N_agg) ranging from 15.6 to 44 and micellar radii (R_b) ranging from 61 to 94 Å. This study highlights the potential of using ionic monomer position as a design parameter to control the internal structures of nanoscale micellar assemblies.