Splitting of Surface-Immobilized Multicompartment Micelles into Clusters upon Charge Inversion

Abstract

We investigate a morphological transition of surface-immobilized triblock terpolymer micelles: the splitting into well-defined clusters of satellite micelles upon pH changes. The multicompartment micelles are formed in aqueous solution of ABC triblock terpolymers consisting of a hydrophobic polybutadiene block, a weak polyanionic poly(methacrylic acid) block, and a weak polycationic poly(2-(dimethylamino)ethyl methacrylate) block. They are subsequently immobilized on silicon wafer surfaces by dip-coating. The splitting process is triggered by a pH change to strongly basic pH, which goes along with a charge reversal of the micelles. We find that the aggregation number of the submicelles is well-defined and that larger micelles have a tendency to split into a larger number of submicelles. Furthermore, there is a clear preference for clusters consisting of doublets and triplets of submicelles. The morphology of surface-immobilized clusters can be "quenched" by returning to the original pH. Thus, such well-defined micellar clusters can be stabilized and are available as colloidal building blocks for the formation of hierarchical surface structures. We discuss the underlying physicochemical principles of the splitting process considering changes in charge and total free energy of the micelles upon pH change.

A mild and quantitative route towards well-defined strong anionic/hydrophobic diblock copolymers: synthesis and aqueous self-assembly

“…Examples of the most commonly employed weak electrolyte monomers include anionic (meth)acrylic acid [9][10][11] and cationic N,N-dimethylaminoethyl methacrylate, [12][13][14] with poly (acrylic acid) generally being synthesized from a tert-butyl-protected hydrophobic precursor. 15,16 While the weak ionic nature allows straightforward synthesis and characterization of amphiphilic block copolymers, it limits the applicable pH range if a high charge density is desired.…”

Cell Guidance on Nanostructured Metal Based Surfaces

“…Whereas pH changes can trigger charge reversal for the quaternized polymer, micelles from the non‐quaternized polymer are positively charged at all pHs, but can switch from crew‐cut micelles to spherical polyelectrolyte brushes. In the first case, pH changes can trigger a novel morphological transition, the splitting into clusters of submicelles . In the second case, no splitting occurs, but surface interactions are drastically altered.…”

Polymer-based drug delivery systems for cancer treatment

“…In addition to constructing NDDSs by using cationic or anionic polymers alone, complex NPs containing two pH‐responsive polymers with opposite charges have become a new research trend. Recently, Dewald et al fabricated a multicompartment micelle system, which was formed from a triblock terpolymer consisting of a hydrophobic polybutadiene block, a weak cationic poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) block, and a weak anionic poly(methacrylic acid) (PMAA) block . These micelles showed an irreversible structural transition on the surface when exposed to pH changes from pH 2 to 11 and returning to pH 2.…”