Flow‐Induced Morphologies of Diblock Copolymers in a Nanotube Studied by Dissipative Particle Dynamics Simulation

Morphology of lipid-like structured weak polyelectrolyte poly(ethylene oxide)-block-poly(methyl methacrylate) diblock copolymers induced by confinements

Combined with quantum calculations and mesoscale simulations, the self-assembly of twelve lipid-structured PEO-b-PMMA copolymers (BCPs) with six types of molecular topologies was investigated. The BCPs with MMA species as the connecting center of the other arms present ample mesoscale structures, such as micelles and lamellae or curved lamellar phases, and even macrophase separation occurs for the long-chained BCPs. The excluded volume effect of confinements helps form vesicle-like structures, which proved to be a possible method of confinement to regulate phase morphologies or segment distributions and, ultimately, the properties of materials. An analysis of the phase formation process of short-chained BCP with two hydrophilic EO segments and one hydrophobic MMA segment indicated that four stages were found in both neutral and non-neutral wall confinement, all of which present a hexagonal columnar phase. Surprisingly, when the repulsion effect of the wall to the EO segment is greater than that of the MMA segment, such BCP self assembles into a crossed columnar phase, and the intersection angle of the orientation of these two sets of cylinder arrays is 75 degrees, which can be used to produce heterogeneous nanotube arrays. For the short-chained BCP with four arms joined at MMA species and EO segments in the outer region, we found a novel method of exchanging the repulsive preference of the wall to the EO or MMA species that can control the adsorption or desorption of the lamellar phase with the interval of EO or MMA segments.

Soft confinement-induced morphologies of diblock copolymers

The self-assembly of diblock copolymers under soft confinement is studied systematically using a simulated annealing method applied to a lattice model of polymers. The soft confinement is realized by the formation of polymer droplets in a poor solvent environment. Multiple sequences of soft confinement-induced copolymer aggregates with different shapes and self-assembled internal morphologies are predicted as functions of solvent-polymer interaction and the monomer concentration. It is discovered that the self-assembled internal morphology of the aggregates is largely controlled by a competition between the bulk morphology of the copolymer and the solvent-polymer interaction, and the shape of the aggregates can be non-spherical when the internal morphology is anisotropic and the solvent-polymer interaction is weak. These results demonstrate that droplets of diblock copolymers formed in poor solvents can be used as a model system to study the self-assembly of copolymers under soft confinement.

Nanostructures self-assembled in polymer solutions confined in cylindrical nanopores

Polymer nanostructures self-assembled from solutions confined in cylindrical nanopores were investigated via Monte-Carlo simulations. The nanostructures, including some novel ones, were self-assembled under a wide range of conditions. It is shown that the interactions of the segments with the wall, reflecting the wetting/dewetting by the polymer segments of the wall, constitute a crucial factor in the nanostructure formation. When there are attractive interactions between the segments of a homopolymer or between one kind of segment of a copolymer and the wall, short nanorods, long nanorods, and long nanorods containing channels are generated, and the diameters of the nanostructures are close to the diameter of the cylindrical nanopores. When the above interactions are repulsive, nanospheres, short nanorods, nanocapsules, long nanorods, and nanocylindroids are formed, and generally, the diameter of the nanostructure is smaller than the diameter of the cylindrical nanopores because of the formation of a depletion layer near the wall of the cylindrical nanopores. Our results also indicate that nanostructures that occupy the entire height of the nanopores are more easily generated in nanopores with larger diameters. It should be noted that the nanostructures formed from solutions are usually irregular and cannot be characterized by a unique diameter.

Multiscale modeling of emergent materials: biological and soft matter

In this review, we focus on four current related issues in multiscale modeling of soft and biological matter. First, we discuss how to use structural information from detailed models (or experiments) to construct coarse-grained ones in a hierarchical and systematic way. This is discussed in the context of the so-called Henderson theorem and the inverse Monte Carlo method of Lyubartsev and Laaksonen. In the second part, we take a different look at coarse graining by analyzing conformations of molecules. This is done by the application of self-organizing maps, i.e., a neural network type approach. Such an approach can be used to guide the selection of the relevant degrees of freedom. Then, we discuss technical issues related to the popular dissipative particle dynamics (DPD) method. Importantly, the potentials derived using the inverse Monte Carlo method can be used together with the DPD thermostat. In the final part we focus on solvent-free modeling which offers a different route to coarse graining by integrating out the degrees of freedom associated with solvent.