Effect of Chain Architecture on Self-Assembled Aggregates from Cyclic AB Diblock and Linear ABA Triblock Copolymers in Solution

Topology-controlled self-assembly of amphiphilic block copolymers

Contemporary synthetic chemistry approaches can be used to yield a range of distinct polymer topologies with precise control. The topology of a polymer strongly influences its self-assembly into complex nanostructures however a clear mechanistic understanding of the relationship between polymer topology and self-assembly has not yet been developed. In this work, we use atomistic molecular dynamics simulations to provide a nanoscale picture of the self-assembly of three poly(ethylene oxide)-poly(methyl acrylate) block copolymers with different topologies into micelles. We find that the topology affects the ability of the micelle to form a compact hydrophobic core, which directly affects its stability. Also, we apply unsupervised machine learning techniques to show that the topology of a polymer affects its ability to take a conformation in response to the local environment within the micelles. This work provides foundations for the rational design of polymer nanostructures based on their underlying topology.

Comparative Thermodynamic Studies of the Micellization of Amphiphilic Block Copolymers before and after Cyclization

The enthalpy and entropy of micellization in water, ΔH_mic and ΔS_mic, respectively, of three linear amphiphilic BAB block copolymers consisting of either poly(methyl acrylate) (M_n ∼ 1200 and 700 Da) or poly(ethyl acrylate) (M_n ∼ 800 Da) as hydrophobic (B) segments and poly(ethylene oxide) (PEO) as the hydrophilic (A, M_n ∼ 3000 Da) segment were determined by isothermal titration calorimetry (ITC). The ΔH_mic and ΔS_mic of the cyclic AB block copolymers obtained by cyclization of the linear triblock copolymers were determined under the same conditions. The ΔH_mic value of the cyclic copolymers was smaller than that of their linear precursors. The ΔS_mic value showed the same trend, but the relative difference between the cyclized and linear copolymers was less pronounced. The hydrodynamic diameter (D_h), critical micelle concentration (CMC), molecular weight (M_w-mic), and second virial coefficient (A₂) of the micelles were determined. The D_h value of the cyclic copolymer micelles was smaller than the linear counterpart. On the other hand, the CMC value became larger, whereas the A₂ value was comparable or increased by cyclization. Overall, the results suggest that, in the unimer state, the hydrophobic segments of the cyclized copolymers form a tightly coiled structure to minimize contact with water, resulting in the smaller ΔH_mic value. Contrary to the linear copolymer micelles, the cyclic copolymer micelles have no "dangling chains", which may explain the topology-driven slight difference in the ΔS_mic value.

Formation and Regulation of Multicompartment Vesicles from Cyclic Diblock Copolymer Solutions: A Simulation Study

The self-assembly of a cyclic AB copolymer system with relatively long A blocks and short B blocks in B-selective solvents is investigated using a simulated annealing method. By investigating the effect of the lengths and solubilities of A and B blocks (N A and N B, εAS and εBS), the incompatibility between A and B blocks (εAB), as well as the polymer concentration (C p) and the conditions for the formation of multicompartment vesicles in cyclic diblock copolymer solutions, is predicted. The phase diagrams in terms of N B, εAS, and C p are constructed. The mechanism of the morphological transition is elucidated. It is shown that for cyclic copolymers the change in the above factors relating to the polymer and solvent properties all can lead to the transition from simple vesicles to multicompartment vesicles, but two different transition mechanisms are revealed. In addition, our simulations demonstrate that the self-assembly of cyclic copolymers could provide a powerful strategy for regulating the compartment number and the wall thickness of the multicompartment vesicles by adjusting the block solubilities and block lengths, respectively. These findings will facilitate the application of multicompartment architectures in cell mimicry, drug delivery, and nanoreactors.

Micellization of Pluronic P123 in Water/Ethanol/Turpentine Oil Mixed Solvents: Hybrid Particle-Field Molecular Dynamic Simulation

The hybrid particle–field molecular dynamics simulation method (MD-SCF) was applied to study the self-assembly of Pluronic PEO₂₀-PPO₇₀-PEO₂₀ (P123) in water/ethanol/turpentine oil- mixed solvents. In particular, the micellization process of P123 at low concentration (less than 20%) in water/ethanol/turpentine oil-mixed solvents was investigated. The aggregation number, radius of gyration, and radial density profiles were calculated and compared with experimental data to characterize the structures of the micelles self-assembled from P123 in the mixed solvent. This study confirms that the larger-sized micelles are formed in the presence of ethanol, in addition to the turpentine oil-swollen micelles. Furthermore, the spherical micelles and vesicles were both observed in the self-assembly of P123 in the water/ethanol/turpentine oil-mixed solvent. The results of this work aid the understanding of the influence of ethanol and oil on P123 micellization, which will help with the design of effective copolymer-based formulations.

Versatile fabrication of patchy nanoparticles via patterning of grafted diblock copolymers on NP surface

Patchy nanoparticle formation via the patterning of grafted diblock copolymers on NP surface.