Aggregation behavior of rod-coil-rod triblock copolymers in a coil-selective solvent

Self-assembly of rod-coil-rod block copolymers in a coil-selective solvent: coarse-grained simulation results

The solution self-assembly of amphiphilic polymers provides a versatile approach to design novel nanostructured materials. Multiblock polymers, particularly those composed of liquid crystalline and coil blocks, are of significant interest due to the potential display of nematic ordering in liquid crystalline domains, offering intriguing optical and mechanical properties. In this study, dissipative particle dynamics is used to investigate the solution self-assembly of rod-coil-rod copolymers in a coil-selective solvent. Extensive molecular simulations were conducted to elucidate the impact of polymer composition, concentration and flexibility on the self-assembly behavior. A quantitative analysis was performed to investigate how polymer conformations varied with changes in composition, concentration, and rigidity. Simulation results show that, at small rod compositions, rod-coil-rod polymers self-assemble into micelles at low concentrations, transitioning to network formation as concentration increases. An increase in rod composition leads to the formation of larger aggregates, resulting in cylindrical micelles and membranes. The results reported here also offer insights into the role of flexibility in shaping the self-assembly behavior of rod-coil-rod triblocks in selective solvents, thus, contributing to a comprehensive understanding of the factors governing the formation of diverse structures in the solution self-assembly of triblock copolymers.

Liquid-Crystal Ordering and Microphase Separation in the Lamellar Phase of Rod-Coil-Rod Triblock Copolymers. Molecular Theory and Computer Simulations

A molecular model of the orientationally ordered lamellar phase exhibited by asymmetric rod-coil-rod triblock copolymers has been developed using the density-functional approach and generalizing the molecular-statistical theory of rod-coil diblock copolymers. An approximate expression for the free energy of the lamellar phase has been obtained in terms of the direct correlation functions of the system, the Flory-Huggins parameter and the Maier-Saupe orientational interaction potential between rods. A detailed derivation of several rod-rod and rod-coil density-density correlation functions required to evaluate the free energy is presented. The orientational and translational order parameters of rod and coil segments depending on the temperature and triblock asymmetry have been calculated numerically by direct minimization of the free energy. Different structure and ordering of the lamellar phase at high and low values of the triblock asymmetry is revealed and analyzed in detail. Asymmetric rod-coil-rod triblock copolymers have been simulated using the method of dissipative particle dynamics in the broad range of the Flory-Huggins parameter and for several values of the triblock asymmetry. It has been found that the lamellar phase appears to be the most stable one at strong segregation. The density distribution of the coil segments and the segments of the two different rods have been determined for different values of the segregation strength. The simulations confirm the existence of a weakly ordered lamellar phase predicted by the density-functional theory, in which the short rods separate from the long ones and are characterized by weak positional ordering.

Self-assembly and stimuli-responsive behaviours of side-chain liquid crystalline copolymers: a dissipative particle dynamics simulation approach

Side-chain liquid crystalline copolymers are able to self-assemble into various aggregates in selective solvents, in particular, deformed structures.

Polypeptide self-assemblies: nanostructures and bioapplications

Polypeptide copolymers can self-assemble into diverse aggregates. The morphology and structure of aggregates can be varied by changing molecular architectures, self-assembling conditions, and introducing secondary components such as polymers and nanoparticles. Polypeptide self-assemblies have gained significant attention because of their potential applications as delivery vehicles for therapeutic payloads and as additives in the biomimetic mineralization of inorganics. This review article provides an overview of recent advances in nanostructures and bioapplications related to polypeptide self-assemblies. We highlight recent contributions to developing strategies for the construction of polypeptide assemblies with increasing complexity and novel functionality that are suitable for bioapplications. The relationship between the structure and properties of the polypeptide aggregates is emphasized. Finally, we briefly outline our perspectives and discuss the challenges in the field.

An insight into non-emissive excited states in conjugated polymers

Conjugated polymers in the solid state usually exhibit low fluorescence quantum yields, which limit their applications in many areas such as light-emitting diodes. Despite considerable research efforts, the underlying mechanism still remains controversial and elusive. Here, the nature and properties of excited states in the archetypal polythiophene are investigated via aggregates suspended in solvents with different dielectric constants (ɛ). In relatively polar solvents (ɛ>∼ 3), the aggregates exhibit a low fluorescence quantum yield (QY) of 2–5%, similar to bulk films, however, in relatively nonpolar solvents (ɛ<∼ 3) they demonstrate much higher fluorescence QY up to 20–30%. A series of mixed quantum-classical atomistic simulations illustrate that dielectric induced stabilization of nonradiative charge-transfer (CT) type states can lead to similar drastic reduction in fluorescence QY as seen experimentally. Fluorescence lifetime measurement reveals that the CT-type states exist as a competitive channel of the formation of emissive exciton-type states.

Conjugated polymers in thin films exhibit low fluorescence quantum yields, but the mechanism is still unclear. Here, Hu et al. show the trade-off between charge transfer and emissive exciton states, whilst the former can be suppressed via dielectric-induced stabilization for large fluorescence quantum yields.