Self-Organization Process of Ordered Structures in Linear and Star Poly(styrene)−Poly(isoprene) Block Copolymers: Gaussian Models and Mesoscopic Parameters of Polymeric Systems

Coarse-Grained Modeling of Ion-Containing Polymers

Ion-containing polymers have continued to be an important research focus for several decades due to their use as an electrolyte in energy storage and conversion devices. Elucidation of connections between the mesoscopic structure and multiscale dynamics of the ions and solvent remains incompletely understood. Coarse-grained modeling provides an efficient approach for exploring the structural and dynamical properties of these soft materials. The unique physicochemical properties of such polymers are of broad interest. In this review, we summarize the current development and understanding of the structure-property relationship of ion-containing polymers and provide insights into the design of such materials determined from coarse-grained modeling and simulations accompanying significant advances in experimental strategies. We specifically concentrate on three types of ion-containing polymers: proton exchange membranes (PEMs), anion exchange membranes (AEMs), and polymerized ionic liquids (polyILs). We posit that insight into the similarities and differences in these materials will lead to guidance in the rational design of high-performance novel materials with improved properties for various power source technologies.

Blending Linear and Cyclic Block Copolymers to Manipulate Nanolithographic Feature Dimensions

Block copolymers (BCPs) consist of two or more covalently bound chemically distinct homopolymer blocks. These macromolecules have emerging applications in photonics, membrane separations, and nanolithography stemming from their self-assembly into regular nanoscale structures. Theory suggests that cyclic BCPs should form features up to 40% smaller than their linear analogs while also exhibiting superior thin-film stability and assembly dynamics. However, the complex syntheses required to produce cyclic polymers mean that a need for pure cyclic BCPs would present a challenge to large-scale manufacturing. Here, we employ dissipative particle dynamics simulations to probe the self-assembly behavior of cyclic/linear BCP blends, focusing on nanofeature size and interfacial width as these qualities are critical to nanopatterning applications. We find that for mixtures of symmetric cyclic and linear polymers with equivalent lengths, up to 10% synthetic impurity has a minimal impact on cyclic BCP feature dimensions and interfacial roughness. On the other hand, blending with cyclic BCPs provides a route to "fine-tune" linear BCP feature sizes. We analyze simulated blend domain spacings within the context of strong segregation theory and find significant deviations between simulation and theory that arise from molecular-level packing motifs not included in theory. These insights into blend self-assembly will assist experimentalists in rationally designing BCP materials for advanced nanolithography applications.

Temperature-responsive morphology formation of a PS-b-PI copolymer: a dissipative particle dynamics simulation study

Self-assembly responsiveness to stimuli of polystyrene-block-polyisoprene (PS-b-PI) diblock copolymer materials is explored by means of classical molecular dynamics (MD) and dissipative particle dynamics (DPD) simulations. A concerted relationship between the parameters achieved from atomistic and DPD simulations is obtained for this molecular recognition as clearly pronounced in a phase transition. Effects of temperature, model size and composition on the morphological formation were systematically investigated for the diblock copolymeric system. Structural changes resulting in the evolution of rheology as well as an equilibrium ordered structure were analyzed in terms of order parameters and radial distribution functions. From our models, various morphologies were observed including discrete clusters (sphere-liked morphology), connected clusters (gyroid-liked morphology), hexagonally packed cylinders (HEX), connected cylinders, irregular cylinders, perfect lamellae, perforated lamellae and defected lamellae. Based on this finding, a bottom-up multi-scale simulation of the PS-b-PI diblock copolymer provides a link between equilibrium copolymeric morphologies and the crucial parameters.

Coarse-Grained Modelling and Temperature Effect on the Morphology of PS-b-PI Copolymer

Spontaneous spatial organization behavior and the aggregate morphology of polystyrene-block-polyisoprene (PS-b-PI) copolymer were investigated. Molecular dynamic (MD) and mesoscopic simulations using the dynamic of mean field density functional theory (DDF) were adopted to investigate the morphology changes exhibited by this block copolymer (BCP). In the mesoscopic simulations, several atoms in repeating units were grouped together into a bead representing styrene or isoprene segments as a coarse-grained model. Inter-bead interactions and essential parameters for mesoscopic models were optimized from MD simulations. Study indicated that morphology alternations can be induced in this system at annealing temperature of 393, 493, and 533 K. From our simulations, lamellar, bicontinuous, and hexagonally packed cylindrical equilibrium morphologies were achieved. Our simulated morphologies agree well with the reported experimental evidence at the selected temperature. The process of aggregate formation and morphology evolution were concretely clarified.

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.

Architectural evolution of phase domains in shape memory polyurethanes by dissipative particle dynamics simulations

The MDI phase in SMPUs develops a framework with netpoints evolving from spheres, to linked-spheres, linked-cylinders, and then to linked-bi-crossing-cylinders.

Revealing the morphological architecture of a shape memory polyurethane by simulation

The lack of specific knowledge of the network structure in shape memory polymers (SMPs) has prevented us from gaining an in-depth understanding of their mechanisms and limited the potential for materials innovation. This paper firstly reveals the unit-cell nanoscale morphological architecture of SMPs by simulation. The phase separated architecture of a segmented shape memory polyurethane (SMPU) with a 30 wt% hard segment content (HSC, 4,4’-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO)) showing good shape memory properties was investigated by dissipative particle dynamics (DPD) simulations. A linked-spherical netpoint-frame phase of MDI, a matrix-switch phase of polycaprolactone (PCL) and a connected-spider-like interphase for BDO were obtained for this SMPU. The BDO interphase can reinforce the MDI network. Based on these simulation results, a three-dimensional (3D) overall morphological architectural model of the SMPU can be established. This theoretical study has verified, enriched and integrated two existing schematic models: one being the morphological model deduced from experiments and the other the frame model for SMPs reported before. It can serve as a theoretical guide for smart polymeric materials design. This method for the simulation of polymer structure at the nanoscale can be extended to many areas such as photonic crystals where nanoscale self-assembly plays a vital role.

Chain stiffness regulates entropy-templated perfect mixing at single-nanoparticle level

The mixing on a single-particle level of chemically incompatible nanoparticles is an outstanding challenge for many applications. Burgeoning research activity suggests that entropic templating is a potential strategy to address this issue. Herein, using systematic computer simulations of model nanoparticle systems, we show that the entropy-templated interfacial organization of nanoparticles significantly depends on the stiffness of tethered chains. Unexpectedly, the optimal chain stiffness can be identified wherein a system exhibits the most perfect mixing for a certain compression ratio. Our simulations demonstrate that entropic templating regulated by chain stiffness precisely reflects various entropic repulsion states that arise from typical conformation regimes of semiflexible chains. The physical mechanism of the chain stiffness effect is revealed by analyzing the entropic repulsion states of tethered chains and quantitatively estimating the resulting entropy penalties, which provides direct evidence that supports the key role of entropic transition in the entropic templating strategy, as suggested in experiments. Moreover, the model nanoparticle systems are found to evolve into binary nanoparticle superlattices by remixing at extremely high stiffness. The findings facilitate the wide application of the entropic templating strategy in creating interfacially reactive nanomaterials with ordered structures on the single-nanoparticle level as well as mechanomutable responses.

Drug release from pH-sensitive polymeric micelles with different drug distributions: insight from coarse-grained simulations

How to control the release of drugs from pH-sensitive polymeric micelles is an issue of common concern, which is important to the effectiveness of the micelles. The components and properties of polymers can notably influence the drug distributions inside micelles which is a key factor that affects the drug release from the micelles. In this work, the dissipative particle dynamics simulation method is first used to study the structural transformation of micelles during the protonation process and the drug release process from micelles with different drug distributions. And then the effects of polymer structures, including different lengths of hydrophilic blocks, pH-sensitive blocks and hydrophobic blocks, on drug release are also studied. In the end, several corresponding design principles of pH-sensitive polymers for drug delivery are proposed according to the simulation results. This work is in favor of establishing qualitative rules for the design and optimization of congener polymers for desired drug delivery, which is of great significance to provide a potential approach for the development of new multiblock pH-sensitive polymeric micelles.

Molecular dynamics and dissipative particle dynamics simulations of the miscibility and mechanical properties of GAP/DIANP blending systems

Prediction of miscibility and mechanical properties of GAP/DIANP blends.

DISSIPATIVE PARTICLE DYNAMICS SIMULATION ON THE PREPARATION PROCESS OF MACROPOROUS STYRENE-DIVINYLBENZENE COPOLYMER

Dissipative particle dynamics (DPD) was carried out to study the copolymerization process of halogen-substituted styrene (ST-X), divinylbenzene (DVB), and dodecane (DO) in aqueous solution. The results showed that properly selecting the sizes of DO and water beads, and choosing the appropriate interaction parameters between beads are crucial in the simulation system. The influence of polymerization parameters, such as polymerization temperature, ST-X/DVB/DO/water ratio, and halogen substitution on ST on the copolymer morphology, were investigated in detail and confirmed that the simulation results can reproduce the macroscopic experimental phase separation. In addition, the pore volume of copolymers formed at different polymerization conditions is estimated, which consisted with the data measured in the experiments. Our work has demonstrated that DPD methods can be applied to study such copolymerization process.

STUDY ON HOMOGENEOUS PRECIPITATION OF CeO2 NANOPARTICLES BY DISSIPATIVE PARTICLE DYNAMICS SIMULATION

Dissipative particle dynamics (DPD) was carried out to study the nucleation and crystal growth process of cerium dioxide ( CeO 2) nanoparticles in alcohol/water mixed solvents by homogeneous precipitation method. The results showed that properly selecting the sizes of CeO 2 and water beads, and choosing the appropriate interaction parameters between beads are crucial in the simulation system. The nucleation and crystal growth process of CeO 2 can be classified into four stages: induction, nuclei growth, crystal forming, and crystal aggregation, which could be reproduced from different initial CeO 2 concentration and after different simulation time. The simulation results confirm that the effect of solvent on the nucleation and crystal growth of CeO 2 nanoparticles are different at four stages and cannot be simply described by Derjaguin–Landau–Verwey–Overbeek theory or nucleation thermodynamics theory as proposed in the published literatures. Our work demonstrated that DPD methods can be applied to study nanoparticle forming process.

Microphase separation of diblock copolymer poly(styrene-b-isoprene): A dissipative particle dynamics simulation study

Dissipative particle dynamics (DPD) simulations have been employed to study the microphase separation of the poly(styrene-b-isoprene) (PS-b-PI) diblock copolymer. The DPD model is constructed to match the physical description and structural properties of the PS-b-PI diblock copolymer. A coarse-grained force field has been developed for the diblock copolymer system in DPD simulations. The new force field contains bonded and nonbonded interaction terms, which are derived from atomistic molecular dynamics simulations and determined by fitting experimental data of the compressibility of water at room temperature and interfacial tension values, respectively. The morphologies of the PS-b-PI diblock copolymer system obtained from DPD simulations are in agreement with experimental observations as well as previous simulated results.