Dissipative Particle Dynamics Study on Interfacial Properties of Symmetric Ternary Polymeric Blends

Investigation of morphology and structure of drug-loaded PLA-b-PEO-b-PLA polymeric micelle: A dissipative particle dynamics simulations study

The dissipative particle dynamics (DPD) simulation was used to study the morphologies and structures of the paclitaxel-loaded PLA-b-PEO-b-PLA polymeric micelle. We focused on the influences of PLA block length, PLA-b-PEO-b-PLA copolymer concentration, paclitaxel drug content on morphologies and structures of the micelle. Our simulations show that: (i) with the PLA block length increase, the self-assemble structure of PLA-b-PEO-b-PLA copolymers with paclitaxel vary between onion-like structure (core-middle layer-shell) to spherical core-shell structure. The PEO shell thins and the size of the PLA core increases. The onionlike structures are comprised of the PEO hydrophilic core, the PLA hydrophobic middle layer, and the PEO hydrophilic shell, the distribution of the paclitaxel drug predominantly occurs within the hydrophobic intermediate layer; (ii) The system forms a spherical core-shell structure when a small amount of the drug is added, and within a certain range, the size of the spherical structure increases as the drug amount increases. When the drug contents (volume fraction) cdrug = 10%, it can be observed that the PLA4-b-PEO19-b-PLA4 spherical structures connect to form rod-shaped structures. With the length of PLA block NPLA = 8, as the paclitaxel drug concentrations cdrug = 4%, PEO has been insufficient to completely encapsulate the PLA and paclitaxel drug beads. To enhance drug loading capacity while maintaining stability of the system in aqueous solution, the optimal composition for loading paclitaxel is PLA4-b-PEO19-b-PLA4; the drug content is not higher than 4%; (iii) The paclitaxel-loaded PLA4-b-PEO19-b-PLA4 micelle undergo the transition from onionlike (core-middle layer-shell) to spherical (core-shell) to rod-shaped and lamellar structure as the PLA4-b-PEO19-b-PLA4 copolymer concentration increases from ccp = 10% to 40%.

Effects of concentration and chain length of the sequence copolymer on interfacial properties of homopolymers/sequence copolymers ternary blends: A DPD simulation study

The effect of the concentration and chain length of the copolymer AB with sequence length τ = 8 on the interfacial properties of the ternary mixtures A₁₀/AB/B₁₀ are investigated by the dissipative particle dynamics (DPD) simulations. It is found that: i) As the copolymer concentration varies from 0.05 to 0.15, increasing the copolymer enrichment at the center of the interface enlarges the interface width ω and reduces the interfacial tension. However, as the concentration of the sequence copolymers further increases to 0.2, because the interface has formed micelles and the micellization could lower the efficiency of copolymers as a compatibilizer, the interfacial tension exhibits a slightly increase; ii) elevating the copolymer chain length, the copolymer volumes vary from a cylinder shape to a pancake shape. The blends of the copolymer with chain length N_cp = 24 exhibit a wider interfacial width w and a lower interfacial tension γ, which indicates that the sequenced copolymer N_cp = 24 exhibits a better performance as the compatibilizers. This study illustrates the correlations between the reduction in interfacial tension produced by the sequence copolymers and their molecular parameters, which guide a rational design of an efficient compatibilizer.

Linear, Graft, and Beyond: Multiblock Copolymers as Next-Generation Compatibilizers

Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technological breakthroughs on various fronts. Mechanical recycling of plastic waste into polymer blends is one method expected to contribute to a solution. Due to phase separation of individual components, mechanical recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further technical development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concentrations as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising solution to help close the loop on plastic waste. While a complete discussion of the implementation of this technology would entail infrastructural, policy, and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the technical advancements of block copolymer compatibilizers.

Effect of sequence distribution of block copolymers on the interfacial properties of ternary mixtures: a dissipative particle dynamics simulation

In this paper, the dissipative particle dynamics (DPD) simulations method is used to study the effect of sequence distribution of block copolymers on the interfacial properties between immiscible homopolymers. Five block copolymers with the same composition but different sequence lengths are utilized for simulation. The sequence distribution is varied from the alternating copolymer to the symmetric diblock copolymer. Our simulations show that the efficiency of the block copolymer in reducing the interfacial tension is highly dependent on both the degree of penetration of the copolymer chain into the homopolymer phase and the number of copolymers at the interface per area. The linear block copolymers AB with the sequence length of τ = 8 could both sufficiently extend into the homopolymer phases and exhibit a larger number of copolymers at the interface per area. Thereby the copolymer with the sequence length τ = 8 is more effective in reducing the interfacial tension compared to that of diblock copolymers and the alternating copolymers at the same concentration. This work offers useful tips for copolymer compatibilizer selection at the immiscible homopolymer mixture interfaces.

In this paper, the dissipative particle dynamics (DPD) simulations method is used to study the effect of sequence distribution of block copolymers on the interfacial properties between immiscible homopolymers.

DPD simulations on morphologies and structures of blank PLGA-b-PEG-b-PLGA polymeric micelles and docetaxel-loaded PLGA-b-PEG-b-PLGA polymeric micelles

Dissipative particle dynamics (DPD) simulation was used to study the morphologies and structures of blank (no drug) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PLGA-b-PEG-b-PLGA) polymeric micelles and the docetaxel (Dtx)-loaded PLGA-b-PEG-b-PLGA polymeric micelles. We focused on the influences of PLGA-b-PEG-b-PLGA copolymer concentration, composition, Dtx drug content and the shear rate on morphologies and structures of the micelles. Our simulations show that the PLGA-b-PEG-b-PLGA copolymers in the aqueous solutions could aggregate and form blank micelles while Dtx drug and PLGA-b-PEG-b-PLGA could aggregate and form drug-loaded micelles. Under different PLGA-b-PEG-b-PLGA concentrations and drug content, the blank and drug-loaded micelles are observed as spherical, onionlike, columnar, and lamellar structures. The onionlike structures are comprised of the PEG hydrophilic core, the PLGA hydrophobic middle layer, and the PEG hydrophilic shell. As the structure of micelles varies from a spherical core–shell structure to a core–middle layer–shell onionlike structure, the distribution of the Dtx drugs diffuses from the core to the PLGA middle layer of the aggregate. In addition, the drug release process of the Dtx-loaded micelles under shear flow is also simulated. And the results show that the spherical micelles turn into a columnar structure under a shear rate from 0.2 to 3.4. When the shear rate increases to 3.5, the Dtx drugs released gradually increase until all are released with time evolution. These findings illustrate the dependence of the structural morphologies on the detailed molecular parameters of PLGA-b-PEG-b-PLGA and Dtx.

Dissipative particle dynamics simulation was used to study the morphologies and structures of blank (no drug) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) polymeric micelles and the docetaxel-loaded polymeric micelles.

Phase behavior and interfacial tension of ternary polymer mixtures with block copolymers

The phase behavior and interfacial tension of ternary polymeric mixtures (polystyrene/polystyrene-b-poly(methyl methacrylate)/poly(methyl methacrylate), PS/PS-b-PMMA/PMMA) are investigated by dissipative particle dynamics (DPD) simulations. Our simulation results show that, as the PS-b-PMMA diblock copolymer concentration increases, the interfacial tension decreases due to the decayed correlations between homopolymers PS and PMMA. When the chain lengths of copolymers are fixed, with the increase of the chain lengths of PS and PMMA homopolymers the interfacial width becomes wider and the interfacial tension becomes smaller, due to the copolymers presenting more stretched and swollen structures in the mixtures with the short length of homopolymers. However, with simultaneously increasing chain lengths of both diblock copolymer and homopolymers with a fixed ratio, the interfacial tension increases because the copolymer chains with longer chain length penetrate more deeply into the homopolymer phase and the interactions between diblock copolymers become weaker. These results will provide a way to mix incompatible homopolymers to improve material performances.

DPD Study on the Interfacial Properties of PEO/PEO-PPO-PEO/PPO Ternary Blends: Effects of Pluronic Structure and Concentration

Using the method of dissipative particle dynamics (DPD) simulations, we investigated the interfacial properties of PEO/PEO-PPO-PEO/PPO ternary blends composed of the Pluronics L64(EO₁₃PO₃₀EO₁₃), F68(EO₇₆PO₂₉EO₇₆), F88(EO₁₀₄PO₃₉EO₁₀₄), or F127(EO₁₀₆PO₇₀EO₁₀₆) triblock copolymers. Our simulations show that: (i) The interfacial tensions (γ) of the ternary blends obey the relationship γF68 < γL64 < γF88 < γF127, which indicates that triblock copolymer F68 is most effective in reducing the interfacial tension, compared to L64, F88, and F127; (ii) For the blends of PEO/L64/PPO and the F64 copolymer concentration ranging from c_cp = 0.2 to 0.4, the interface exhibits a saturation state, which results in the aggregation and micelle formation of F64 copolymers added to the blends, and a lowered efficiency of the L64 copolymers as a compatibilizer, thus, the interfacial tension decreases slightly; (iii) For the blends of PEO/F68/PPO, elevating the Pluronic copolymer concentration can promote Pluronic copolymer enrichment at the interfaces without forming the micelles, which reduces the interfacial tension significantly. The interfacial properties of the blends contained the PEO-PPO-PEO triblock copolymer compatibilizers are, thus, controlled by the triblock copolymer structure and the concentration. This work provides important insights into the use of the PEO-PPO-PEO triblock copolymer as compatibilizers in the PEO and PPO homopolymer blend systems.

Effects of Repulsion Parameter and Chain Length of Homopolymers on Interfacial Properties of An/Ax/2BxAx/2/Bm Blends: A DPD Simulation Study

We explored the effects of the repulsion parameter (aAB) and chain length (N_HA or N_HB) of homopolymers on the interfacial properties of A_n/A_x/2B_xA_x/2/B_m ternary polymeric blends using dissipative particle dynamics (DPD) simulations. Our simulations show that: (i) The ternary blends exhibit the significant segregation at the repulsion parameter (aAB = 40). (ii) Both the interfacial tension and the density of triblock copolymer at the center of the interface increase to a plateau with increasing the homopolymer chain length, which indicates that the triblock copolymers with shorter chain length exhibit better performance as the compatibilizers for stabilizing the blends. (iii) For the case of N_HA = 4 (chain length of homopolymers A_n) and N_HB (chain length of homopolymers B_m) ranging from 16 to 64, the blends exhibit larger interfacial widths with a weakened correlation between bead A_n and B_m of homopolymers, which indicates that the triblock copolymer compatibilizers (A_x/2B_xA_x/2) show better performance in reducing the interfacial tension. The effectiveness of triblock copolymer compatibilizers is, thus, controlled by the regulation of repulsion parameters and the homopolymer chain length. This work raises important considerations concerning the use of the triblock copolymer as compatibilizers in the immiscible homopolymer blend systems.