Prediction of solvent-induced morphological changes of polyelectrolyte diblock copolymer micelles

Abstract

Self-assembly processes of polyelectrolyte block copolymers are ubiquitous in industrial and biological processes; understanding their physical properties can also provide insights into the design of polyelectrolyte materials with novel and tailored properties. Here, we report systematic analysis on how the ionic strength of the solvent and the length of the polyelectrolyte block affect the self-assembly and morphology of the polyelectrolyte block copolymer materials by constructing a salt-dependent morphological phase diagram using an implicit solvent ionic strength (ISIS) method for dissipative particle dynamics (DPD) simulations. This diagram permits the determination of the conditions for the morphological transition into a specific shape, namely vesicles or lamellar aggregates, wormlike/cylindrical micelles, and spherical micelles. The scaling behavior for the size of spherical micelles is predicted, in terms of radius of gyration (R_g,m) and thickness of corona (H_corona), as a function of solvent ionic strength (c_s) and polyelectrolyte length (N_A), which are R_g,m ∼ c_s^−0.06N_A^0.54 and H_corona ∼ c_s^−0.11N_A^0.75. The simulation results were corroborated through AFM and static light scattering measurements on the example of the self-assembly of monodisperse, single-stranded DNA block-copolynucleotides (polyT50-b-F-dUTP). Overall, we were able to predict the salt-responsive morphology of polyelectrolyte materials in aqueous solution and show that a spherical–cylindrical–lamellar change in morphology can be obtained through an increase in solvent ionic strength or a decrease of polyelectrolyte length.