Study of Controllable Aggregation Morphology of ABA Amphiphilic Triblock Copolymer in Dilute Solution by Changing the Solvent Property

Mesoscopic study of the ternary phase diagram of the PS-PB-PtBMA triblock copolymer: modification of the phase structure by the composition effect

We explored in detail the ordered nanostructures and the ternary phase diagram of the polystyrene-polybutadiene-poly(tert-butyl methacrylate) (PS-PB-PtBMA) triblock copolymer via dissipative particle dynamics (DPD) simulations and coarse-grained models. The mesoscopic simulations show that the PS-PB-PtBMA copolymer in the bulk state can generate eight equilibrium phase regions with well-defined morphologies such as core-shell variations of spheres, cylinders, perforated layers, lamellar, gyroid, as well as cylinder-in-lamella, spheres-in-lamella, and cylinders in hexagonal lattice. The ordered phases exhibit high dependence on the chemical nature and volume fraction, thus portraying specific composition regions with high thermodynamic stability over a ternary phase diagram. The ternary phase diagram, including all equilibrium and metastable nanostructures detected, is described, and analysed in this work in detail. Finally, our dynamic simulation outcomes agree with experimental results. Our aim is to contribute to the understanding of the relationship between block volume fractions and bulk morphologies in ternary polymer systems.

Nano-porous structuresviaself-assembly of amphiphilic triblock copolymers: influence of solvent and molecular weight

Self-assembly of ABA triblock copolymer micelles into porous materials which are subsequently used as filtration membranes.

Self-Assembly and Critical Aggregation Concentration Measurements of ABA Triblock Copolymers with Varying B Block Types: Model Development, Prediction, and Validation

The dissipative particle dynamics (DPD) simulation technique is a coarse-grained (CG) molecular dynamics-based approach that can effectively capture the hydrodynamics of complex systems while retaining essential information about the structural properties of the molecular species. An advantageous feature of DPD is that it utilizes soft repulsive interactions between the beads, which are CG representation of groups of atoms or molecules. In this study, we used the DPD simulation technique to study the aggregation characteristics of ABA triblock copolymers in aqueous medium. Pluronic polymers (PEG-PPO-PEG) were modeled as two segments of hydrophilic beads and one segment of hydrophobic beads. Tyrosine-derived PEG5K-b-oligo(desaminotyrosyl tyrosine octyl ester-suberate)-b-PEG5K (PEG5K-oligo(DTO-SA)-PEG5K) block copolymers possess alternate rigid and flexible components along the hydrophobic oligo(DTO-SA) chain, and were modeled as two segments of hydrophilic beads and one segment of hydrophobic, alternate soft and hard beads. The formation, structure, and morphology of the initial aggregation of the polymer molecules in aqueous medium were investigated by following the aggregation dynamics. The dimensions of the aggregates predicted by the computational approach were in good agreement with corresponding results from experiments, for the Pluronic and PEG5K-oligo(DTO-SA)-PEG5K block copolymers. In addition, DPD simulations were utilized to determine the critical aggregation concentration (CAC), which was compared with corresponding results from an experimental approach. For Pluronic polymers F68, F88, F108, and F127, the computational results agreed well with experimental measurements of the CAC measurements. For PEG5K-b-oligo(DTO-SA)-b-PEG5K block polymers, the complexity in polymer structure made it difficult to directly determine their CAC values via the CG scheme. Therefore, we determined CAC values of a series of triblock copolymers with 3-8 DTO-SA units using DPD simulations, and used these results to predict the CAC values of triblock copolymers with higher molecular weights by extrapolation. In parallel, a PEG5K-b-oligo(DTO-SA)-b-PEG5K block copolymer was synthesized, and the CAC value was determined experimentally using the pyrene method. The experimental CAC value agreed well with the CAC value predicted by simulation. These results validate our CG models, and demonstrate an avenue to simulate and predict aggregation characteristics of ABA amphiphilic triblock copolymers with complex structures.

Effect of local chain deformability on the temperature-induced morphological transitions of polystyrene-b-poly(N-isopropylacrylamide) micelles in aqueous solution

The effect of temperature on the micellar morphology of two polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) diblock copolymers in an aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). At 25 °C, a mixture of vesicles and spheres are observed for the micelles of PS65-b-PNIPAM108, while PS65-b-PNIPAM360 exhibits mixed cylindrical and spherical micellar morphology. Upon increasing the temperature, the micellar morphology becomes spherical for PS65-b-PNIPAM108 at 60 °C and for PS65-b-PNIPAM360 at 40 °C. Such vesicle-to-sphere and cylinder-to-sphere transitions of micellar morphology are reversible when the micellar solutions are cooled back to 25 °C. However, these temperature-induced morphological transitions of the PS-b-PNIPAM micelles are contrary to the theoretical prediction. Qualitative analysis of the free energy shows that vesicular or cylindrical micelles tend to form at higher temperatures if only the overall volume change of the PNIPAM block is considered. The contradiction between the experimental results and theoretical prediction is interpreted in terms of the local deformability of the PNIPAM chains. At elevated temperatures, the collapsed PNIPAM globules are less deformable and must occupy larger areas at the micellar interface, although the overall volume is smaller at higher temperatures. This will lead to a larger repulsion between the PNIPAM globules and a remarkable increase in the free energy of the corona; thus, the formation of vesicles or cylinders at higher temperatures is prohibited.

Morphological transition difference of linear and cyclic block copolymer with polymer blending in a selective solvent by combining dissipative particle dynamics and all-atom molecular dynamics simulations based on the ABEEM polarizable force field

AAMD based on ABEEM PFF were performed to obtain reliable DPD parameters for morphological transition.

Complex micelles from self-assembly of ABA triblock copolymers in B-selective solvents

We report an extensive simulation study of the self-assembly of amphiphilic ABA triblock copolymers dissolved in solvents selective for the middle B-block. The effects of copolymer composition, copolymer concentration, and A-solvent interactions on the morphologies and morphological transitions of the aggregates are examined systematically. The simulations reveal that a rich variety of aggregates, ranging from spherical and rodlike micelles and vesicles to toroidal and net-cage micelles, can be formed spontaneously from a randomly generated initial state. Phase diagrams are constructed and rich morphological transitions are predicted. Chain packing in different micelles is investigated. The simulation results are compared with previous observations or predictions for related copolymer systems.

Self-assembly of hyperbranched multiarmed PEG-PEI-PLys(Z) copolymer into micelles, rings, and vesicles

Self-assembling of synthesized novel biodegradable hyperbranched amphiphilic poly(ethylene glycol)-polyethylenimine-poly(epsilon-benzyloxycarbonyl-l-lysine) (PEG-PEI-PLys(Z)) in aqueous media is studied. In aqueous media, PLys(Z) is the hydrophobic segment, with PEG and PEI as the hydrophilic segments. It will self-assemble into spherical shape when the selected solvent water is dropped into the common solvent tetrahydrofuran (THF). And when PEG-PEI-PLYS in common solvent is dropped into mixed solvent water and THF, rings will come into being. The spherical and rings are observed by environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM). It shows that the size of the sphere is about 100 nm, and the diameter of ring distributes from 400 nm to 10 microm and bigger with the time roll around. It also forms a large vesicle with a thick edge by another method, which is good for drug delivery.

Evolution of multicompartment micelles to mixed corona micelles using solvent mixtures

Miktoarm star triblock copolymers mu-[poly(ethylethylene)][poly(ethylene oxide)][poly(perfluoropropylene oxide)] self-assemble in dilute aqueous solution to give multicompartment micelles with the cores consisting of discrete poly(ethylethylene) and poly(perfluoropropylene oxide) domains. Tetrahydrofuran is a selective solvent for both the poly(ethylethylene) and poly(ethylene oxide) blocks, and thus in tetrahydrofuran mixed corona micelles are favored with poly(perfluoropropylene oxide) cores. The introduction of tetrahydrofuran into water induces an evolution from multicompartment micelles to mixed corona [poly(ethylethylene) + poly(ethylene oxide)] micelles, as verified by dynamic light scattering and nuclear magnetic resonance spectroscopy. A mixed solvent containing 60 wt % tetrahydrofuran corresponds to the transition point, as verified by analysis of a poly(ethylethylene)-poly(ethylene oxide) diblock copolymer in the same solvent mixtures. Furthermore, cryogenic transmission electron microscopy suggests that, as the poly(ethylethylene) block transitions from the core to the corona, the micelle morphologies evolve from disks to oblate ellipsoid micelles (with some vesicles), with worms and spheres evident at intermediate compositions.