Dissipative particle dynamics studies on the interface of incompatible A/B homopolymer blends in the presence of nanorods

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.

Inhomogeneity of block copolymers at the interface of an immiscible polymer blend

We present the effects of structure and stiffness of block copolymers on the interfacial properties of an immiscible homopolymer blend. Diblock and two-arm grafted copolymers with variation in stiffness are modeled using coarse-grained molecular dynamics to compare the compatibilization efficiency, i.e., reduction of interfacial tension. Overall, grafted copolymers are located more compactly at the interface and show better compatibilization efficiency than diblock copolymers. In addition, an increase in the stiffness for one of the blocks of the diblock copolymers causes unusual inhomogeneous interfacial coverage due to bundle formation. However, an increase in the stiffness for one of blocks of the grafted copolymers prevents the bundle formation due to the branched chain. As a result, homogeneous interfacial coverage of homopolymer blends is realized with significant reduction of interfacial tension which makes grafted copolymer a better candidate for the compatibilizer of immiscible homopolymer blend.

Manipulating molecular order in nematic liquid crystal capillary bridgesviasurfactant adsorption: guiding principles from dissipative particle dynamics simulations

Effect of surfactant tail length on the orientation of liquid crystals is investigated with dissipative particle dynamics (DPD) simulations.

Phase transition of a symmetric diblock copolymer induced by nanorods with different surface chemistry

We investigate the phase transition of a symmetric diblock copolymer induced by nanorods with different surface chemistry. The results demonstrate that the system occurs the phase transition from a disordered structure to ordered parallel lamellae and then to the tilted layered structure as the number of rods increases. The dynamic evolution of the domain size and the order parameter of the microstructure are also examined. Furthermore, the influence of rod property, rod-phase interaction, rod-rod interaction, rod length, and polymerization degree on the behavior of the polymer system is also investigated systematically. Moreover, longer amphiphilic nanorods tend to make the polymer system form the hexagonal structure. It transforms into a perpendicular lamellar structure as the polymerization degree increases. Our simulations provide an efficient method for determining how to obtain the ordered structure on the nanometer scales and design the functional materials with optical, electronic, and magnetic properties.

Polymer-mediated nanorod self-assembly predicted by dissipative particle dynamics simulations

Self-assembly of nanoparticles in polymer matrices is an interesting and growing subject in the field of nanoscience and technology. We report herein on modelling studies of the self-assembly and phase behavior of nanorods in a homopolymer matrix, with the specific goal of evaluating the role of deterministic entropic and enthalpic factors that control the aggregation/dispersion in such systems. Grafting polymer brushes from the nanorods is one approach to control/impact their self-assembly capabilities within a polymer matrix. From an energetic point of view, miscible interactions between the brush and the matrix are required for achieving a better dispersibility; however, grafting density and brush length are the two important parameters in dictating the morphology. Unlike in previous computational studies, the present Dissipative Particle Dynamics (DPD) simulation framework is able to both predict dispersion or aggregation of nanorods and determine the self-assembled structure, allowing for the determination of a phase diagram, which takes all of these factors into account. Three types of morphologies are predicted: dispersion, aggregation and partial aggregation. Moreover, favorable enthalpic interactions between the brush and the matrix are found to be essential for expanding the window for achieving a well-dispersed morphology. A three-dimensional phase diagram is mapped on which all the afore-mentioned parameters are taken into account. Additionally, in the case of immiscibility between brushes and the matrix, simulations predict the formation of some new and tunable structures.

Dissipative particle dynamics simulations of the morphologies and dynamics of linear ABC triblock copolymers in solutions

Due to the great potential in the field of multifunctional nanoreactors and carriers, several previous works have shown the interesting morphologies of multicompartment micelles from simple linear ABC triblock copolymers in solutions.

Remarkable efficacy of graft block copolymers as surfactants for reducing interfacial tension

This work provides a standard model for experimental applications of graft copolymers as surfactants, especially for reducing the interfacial tension.

Architectural engineering of rod-coil compatibilizers for producing mechanically and thermally stable polymer solar cells

While most high-efficiency polymer solar cells (PSCs) are made of bulk heterojunction (BHJ) blends of conjugated polymers and fullerene derivatives, they have a significant morphological instability issue against mechanical and thermal stress. Herein, we developed an architecturally engineered compatibilizer, poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP), that effectively modifies the sharp interface of a BHJ layer composed of a P3HT donor and various fullerene acceptors, resulting in a dramatic enhancement of mechanical and thermal stabilities. We directly measured the mechanical properties of active layer thin films without a supporting substrate by floating a thin film on water, and the enhancement of mechanical stability without loss of the electronic functions of PSCs was successfully demonstrated. Supramolecular interactions between the P2VP of the P3HT-g-P2VP polymers and the fullerenes generated their universal use as compatibilizers regardless of the type of fullerene acceptors, including mono- and bis-adduct fullerenes, while maintaining their high device efficiency. Most importantly, the P3HT-g-P2VP copolymer had better compatibilizing efficiency than linear type P3HT-b-P2VP with much enhanced mechanical and thermal stabilities. The graft architecture promotes preferential segregation at the interface, resulting in broader interfacial width and lower interfacial tension as supported by molecular dynamics simulations.

Aspect-Ratio Effect of Nanorod Compatibilizers in Conducting Polymer Blends

Nanoparticles (NPs) at the interface between two different polymer blends or fluid mixtures can function as compatibilizers, thereby dramatically improving the interfacial properties of the blends or the fluid mixtures. Their compatibilizing ability is strongly dependent on their size, shape, and aspect ratios (ARs), which determines their adsorption energy to the interface as well as their entropic penalty when they are being strongly segregated at the interface. Herein, we investigated the effect of the ARs of nanorod surfactants on the conducting polymer blend of poly(triphenylamine) (PTPA) templated by polystyrene (PS) colloids. The lengths of the polymer-coated CuPt nanorods (CuPt NRs) were 5, 15, and 32 nm with a fixed width of 5 nm, thus producing three different AR values of 1, 3, and 6, respectively. For quantitative analysis, the morphological and electrical behaviors of the polymer blends were investigated in terms of the volume fraction and AR of the NRs. The dramatic change in the morphological and electrical properties of the blend film was observed for all three NR surfactants at the NR volume fraction of approximately 1 vol %. Therefore, NR surfactants with larger ARs had better compatibilizing power for a given number of NRs in the blends. Also, they exhibited a stronger tendency to be aligned parallel to the PS/PTPA interface. Also, we demonstrated the successful use of the NR surfactants in the fabrication of conducting polymer blend film that requires only minimal concentrations of conducting polymers. To the best of our knowledge, this is the first report of an experiment on the AR effect of NR compatibilizers in polymer blends.

A novel nanocage from the cooperative self-assembly of coil-rod-coil triblock copolymers and nanopartilces

Dissipative particle dynamics (DPD) simulations are performed to study the cooperative self-assembly of coil-rod-coil triblock copolymers and nanoparticles in solution. The results show that, when the nanoparticle concentration exceeds a given value, the ternary systems can form a novel nanocage composed of two-end coil-caps and middle rod-linkers. The novel nanocage is very similar to the real bird cage and the captured nanoparticles like the bird. It is the first nanocage from the self-assembly of coil-rod-coil triblock copolymers. This may be used for the release of drugs and fertilizers, or as nanoreactors.

Nanoparticle effects on the water-oil interfacial tension

Although it is well known that solid particles adsorb at interfaces, no consensus has been reached on whether the adsorbed nanoparticles affect interfacial tension. In this work the Wilhelmy plate method is implemented in mesoscale dissipative particle dynamics simulations to study the influence of nanoparticles on the water-oil interfacial tension. The results are compared with predictions that neglect nanoparticle-nanoparticle interactions at the interface. We find that the two estimates can differ significantly. In the regime where nanoparticle-nanoparticle repulsion is large, the Wilhelmy plate method suggests interfacial tension reduction, which appears to be a strong function of nanoparticle surface coverage. Some experimental data from the literature, in apparent disagreement, are reinterpreted based on this insight.