Coarse-grained molecular dynamics simulation of a bead–spring polymer model has been conducted for polymer melt confined between two solid walls. The wall effect was studied by changing the distance between the walls and the wall–polymer interaction. It was observed that the polymers near the walls are compressed towards the walls: the component of the radius of gyration tensor perpendicular to the wall surfaces decreases in a layer near the walls. The thickness of this surface layer, estimated from the analysis of the static polymer structure, is about 1.0–1.5 times the radius of gyration $R_g$ in the bulk, and is independent of the distance between the walls and the wall–polymer interaction. The relaxation time of the polymers, obtained from the autocorrelation of normal modes, increases with increasing the strength of the wall–polymer interaction and with decreasing the distance between the walls. These wall effects are observed at a distance much larger than $R_g.$ This result is in agreement with the recent dielectric measurements of cis-polyisoprene confined between mica surfaces reported by Cho, Watanabe, and Granick [J. Chem. Phys. 110, 9688 (1999)]. The thickness of the surface layer was also estimated by the position dependence of the static and dynamic properties, and was found to agree with that estimated by the viscoelastic measurements.

The molecular mechanism of the strain–stress behavior of the ABA triblock copolymer is studied by combining self-consistent field (SCF) calculation and molecular dynamics (MD) simulation. First, the equilibrium structure was obtained by the SCF calculation. The bridge fraction ${\phi }_{\mathrm{bridge}}$ was found to be about 0.4, 0.6, and 0.8 for lamellar, cylindrical, and spherical phases, respectively. From the segment distribution calculated by the SCF, the equilibrium chain configuration was generated by the method reported previously [Aoyagi et al., Comput. Phys. Comm. 145, 267 (2002)]. The loading and unloading behavior was then studied by the MD simulation. The loading curve shows a strain-softening, and then a yielding at a strain of about 350%, where the breakup of microdomains takes place. The strain–stress curve in the second elongation-compression cycle is different from that of the first cycle. Such hysteresis effect is seen also for small elongation where the domain breakup does not take place.

Phase transition of anisotropic materials is ubiquitously observed in physics, biology, materials science, and engineering. Nevertheless, how anisotropy of constituent molecules affects the phase transition dynamics is still poorly understood. Here we investigate numerically the phase transition of a simple model system composed of anisotropic molecules, and report on our discovery of multistep nucleation of nuclei with layered positional ordering (smectic ordering), from a fluid-like nematic phase with orientational order only (no positional order). A trinity of molecular dynamics simulation, machine learning, and molecular cluster analysis yielding free energy landscapes unambiguously demonstrates the dynamics of multistep nucleation process involving characteristic metastable clusters that precede supercritical smectic nuclei and cannot be accounted for by the classical nucleation theory. Our work suggests that molecules of simple shape can exhibit rich and complex nucleation processes, and our numerical approach will provide deeper understanding of phase transitions and resulting structures in anisotropic materials such as biological systems and functional materials.