Molecular dynamics simulation in coarse-grained model of polyvinyl alcohol is made to get semicrystalline polymer from a molten state with slow cooling and partial crystallization.Evolution of static structure factor shows that intensity increasing in small-angle scattering appears before the Bragg peak in early crystallization,which is consistent with experimental observations with small/wide angle X-ray scattering.Simulated semicrystalline polymer shows a structure resembling Ying-shaped micro-beam model.Different cooling stages have different formation mechanisms with ordered structures.From crystallization to glass temperature in solidification process,stretching of molecular chain and arranging in parallel between straight molecular chains exist.Adjustment of straight chains in relative positions is only allowed by material activate.

A bridging domain method,in which molecular models and continuum models are coupled,is performed to study threedimensional contact of a rigid spherical tip and a smooth fiat substrate.It is compared with full-atom molecular simulations.We focus on relaxation behavior under a given load,continuity of displacement and stress at bridging domain,normal force and contact radius.It shows that the bridging domain method quickly reaches equilibrium and has weaker oscillations under a given external load.It has small relative errors as initial temperature of system is at 0 K.The bridging domain method can transmit continuously displacement and stress from molecular domain to continuum domain,and has goad coupling effect.Normal force-displacement and contact radius-displacement are nearly coincide with molecular simulations.Its computational accuracy is high.