Influence of hydrostatic pressure on water absorption of polyoxymethylene : experiment and molecular dynamics simulation

This work experimentally investigated the influence of hydrostatic pressure on the water absorption of polyoxymethylene, followed by analyzing its micro-mechanism via molecular dynamics simulation. Tests results show that the polyoxymethylene water absorption decreases with the increase in hydrostatic pressure when the latter is within 0–3.0 MPa; it subsequently increases with the increase in hydrostatic pressure in the range of 3.0–5.0 MPa. Simulation of water molecules diffusion on polyoxymethylene surface shows that water molecules diffuse into polyoxymethylene surface during an equilibration run, and water molecule displacement value of maximum relative concentration gives almost the same characteristics: firstly decreases and then increases with the increase of hydrostatic pressure. Simulation of water molecule diffusion inside polyoxymethylene suggests the following: (i) water molecules vibrate from the interior to the edge of polyoxymethylene cell during the equilibration run, and (ii) water diffusion coefficient in polyoxymethylene gives trend of firstly decreasing and then increasing with the increase of hydrostatic pressure. Copyright © 2016 John Wiley & Sons, Ltd.