Balancing Segregation and Complexation in Amphiphilic Copolymers by Architecture and Confinement

Abstract

Segregation is a well-known principle for micellization, as solvophobic components try to minimize interactions with other entities (such as solvent) by self-assembly. An opposite principle is based on complexation (or coacervation), leading to the coassembly/association of different components. Most cases in the literature rely on only one of these modes, though the classical micellization scheme (such as spherical micelles, wormlike micelles, and vesicles) can be enriched by a subtle balance of segregation and complexation. Because of their counteraction, micellar constructs with unprecedented structure and behavior could be obtained. In this feature, systems are highlighted, which are between both mechanisms, and we study concentration, architecture, and confinement effects. Systems with inter- and intramolecular interactions are presented, and the effects of polymer topology and monomer sequence on the resulting structures are discussed. It is shown that complexation can lead to altered micellization behavior as the complex of one hydrophobic and one hydrophilic component can have a very low surface tension toward the solvent. Then, the more soluble component is enriched at the surface of the complex and acts as a microsurfactant. Although segregation dominates for amphiphilic copolymers in solution, the effect of the complexation can be enhanced by branching (change of architecture). Another possibility to enhance the complexation is by confining copolymers in a (pseudo-) 2D environment (like the one available at liquid-liquid interfaces). These observations show how new structural features can be achieved by tuning the subtle balance between segregation and complexation/solubilization.

Aggregation of Star Polymers: Complexation versus Segregation

“…As in our previous work, the star polymers were modeled with a simple bead spring model in which each effective monomer was described as a bead. The star polymers consist of three different types of beads: A, B, and C beads.…”

“…For bead type combinations of the type A‐B (or B‐A) the interaction parameter was set to . The value of was obtained from previous work where it was found that under these conditions a weak complex is formed. For all other bead combinations: . Bead Segregation : In this case, the B beads attract each other to segregate from the A beads.…”

“…Self‐assembly can be induced by various interactions like solvent‐specific interactions, interpolyelectrolyte complexation, and hydrogen bonding . Polymers which have effective attractive interactions between different monomeric units are called complex‐forming polymers …”

“…Recently, uncharged complex‐forming polymers were described, which show distinctively different behavior from ionic complexes due to the absence of long‐ranged interactions. It is assumed that such complex‐forming polymers form new structures, which would broaden the classical micellization scheme . To study the properties of such systems, we employed a generic model and performed simulations.…”

Stimulated Transitions of Directed Nonequilibrium Self‐Assemblies

“…Polymerizing NIPAM [22] in the presence of a soluble poly(dimethyl acrylamide) (PDMAM) macro-CTA, results in diblock copolymers which undergo spontaneous self-assembly due to the segregated [23] PNIPAM component (when synthesis conducted above LCST). [24] Unfortunately, these nano-objects could not conveniently be studied in a non-equilibrium state as the PNIPAM required crosslinking to avoid unimolecular dissolution at ambient temperature.…”