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Recent progress in producing short chain length diblock copolymers facilitates the fabrication of block copolymer nanostructures with extremely small feature sizes. In this work, phase diagrams for monodisperse, one-sided and two-sided polydisperse short diblock copolymer melts are constructed using dissipative particle dynamics (DPD) simulations. Detailed comparisons are carried out between these systems to elucidate the influence of chain length polydispersity on the phase behavior of short diblock copolymers. In particular, we find an unexpected stability of a bicontinuous structure over a wide composition range between 0.7

Block copolymers have the unique property to self-assemble into ordered microstructures with well-defined periodicity. Among the various attainable microdomain morphologies, complex morphologies with inherent structural connectivity are highly desirable. While such structures are difficult to obtain in monodisperse block copolymers, they may be stabilized by increasing block dispersity. In this study, we prepare poly (styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers where dispersity of both PS and PMMA blocks are varied independently. Morphology examination of the diblocks reveals that at fixed block composition, dispersity dictated phase transition is observed. In particular, in the case where dispersity of both blocks are high, the polymers are found to exhibit perforated lamellae and disordered bicontinuous morphologies. Dissipative particle dynamics (DPD) simulations are also carried out to confirm the stability of the observed morphologies. These results show that control of block dispersity can effectively stabilize energetically disfavored complex morphologies in block copolymers.

We present results of molecular dynamics simulations for coarse-grained polymers confined in nanopores in a wide temperature range to investigate the factors that affect the glass transition. We focus on the influences of interaction strength, confinement size and the mobility of boundary on the static and dynamic properties of confined polymers, and further study their influences on the glass transition temperature Tg and the fragility Df, which quantifies how rapidly relaxation times vary with temperature T. For the immobile nanopore boundary (i.e. the hard wall confinement model), strong attractive interaction between wall and polymer induces slow polymer dynamics near the wall, while the weak interaction gives rise to a relatively enhanced monomer mobility. The mobile nanopore boundary (i.e. the soft wall confinement model) has a great influence on the shift of Tg and Df: it accelerates the structural relaxation of nearby monomers and leads to a lower Tg and a larger Df. The soft confinement effect is more obvious for nanopores with strong interaction than those with weak interaction. In addition, smaller confinement size leads to lower Tg of confined polymers, except for those confined in hard nanopores with strong attractive interaction. Our analysis demonstrates the change of Tg of confined polymers is mainly controlled by the surface effects originated from the polymer–wall interaction and the mobility of nanopore boundary.

Comprehensive dissipative particle dynamics simulations are performed to investigate the effect of A-block polydispersity on the phase behavior of AB-diblock copolymers. The experimental results of Lynd and Hillmyer on polydispersity induced domain spacing expansion at different segregations (Macromolecules 2005, 38, 8803) are well reproduced and explained in terms of interfacial free energy and molecular stretching in domain center. Short block copolymers in polydisperse system are found to preferably accumulate at A/B interface as compatibilizers causing a reduction in interfacial free energy. At the same time, domain centers are found mainly occupied by long blocks which in turn determining the spacing of the corresponding domain. More importantly, increase in polydispersity will introduce more long blocks into system and therefore will enhance the molecular packing and stretching in the domain center. Such chain stretching in domain center and reduction in interfacial free energy are found to be more severe at stronger segregation, which will lead to more severe domain spacing expansion with increasing polydispersity.

Vesicles are membrane-enclosed capsules that can store or transport substances. Their structures and the corresponding structural transitions are important to fulfill specific functions. Using dissipative particle dynamics method, we study the complex structure transitions of vesicles that are spontaneously formed by A6(B2)3 type comb-like block copolymers. In the simulations, the interaction parameters between different components are tuned to mimic the variations of amphiphilicity of the block copolymers and the selectivity of the solvent which are experimentally tractable by, for example, a temperature quench. Complex vesicle structures are found in this research; their transitions, such as fission and reversal, are studied in detail with this dynamic simulation method. We find that the line tension plays a decisive role on the vesicle fission pathways. Moreover, the tube-like vesicles tend to transform to a special layered micelle structure, whereas the onion-shape vesicles tend to transform to reverse onion-shape vesicles when vesicle reversal takes place due to the variation of solvent selectivity.

We fabricated Layer-by-Layer (LbL) assemblies of poly(8-(4-carboxy-phenoxy)-octyl acrylate) (PCPOA) and poly(3-(4-pyridyl)-propyl acrylate) (PPyPA) in solvent mixtures of tetrahydrofuran (THF) and ethanol with different compositions. It was confirmed by FT-IR spectroscopy that the driving force for the assembly was mainly hydrogen bonding. Effect of solvent composition on the assembly was investigated using UV–vis spectroscopy. The amount of polymers in the film initially decreased with increase of THF content in solvent mixture, reaching a minimal value in the range between 45% and 70%, and then increased with increase of THF content. Combined with the polymer radius of gyration obtained from Dissipative Particle Dynamics simulation, we found that the adsorption amount of polymer is small when conformation of polymer is extended in a solution. We also investigated the effect of the number of methylene groups in polymer side chains on LbL assembly. When poly(2-(4-carboxy-phenoxy)-ethyl acrylate) (PCPEA) was used instead of PCPOA, we found that more polymers were adsorbed onto the substrate. In addition, we compared the normalized growth curves of both assemblies and found that the deviation of (PCPEA/PPyPA)n from linear growth was larger than that of (PCPOA/PPyPA)n.

By means of full atomistic molecular dynamics simulation, the solubility parameters for pure poly(3-hydroxybutyrate) and poly(ethylene oxide) are calculated and the results are in agreement with the literature values. Furthermore, in order to reveal the blend property, the volume–temperature curve of the PHB/PEO blend system (1:2 blends in terms of repeated units) is simulated by employing the united atom approximation to obtain the glass transition temperature. From the volume–temperature curve, the glass transition temperature is about 258 K, which is compared well with the experimental results. It should be pointed out that the two simulated solubility parameters are similar and there is only one glass transition of the blend system, these indicate that the studied blend system is miscible.