Tsunetoshi Matsuda

A comparison of a united atom and an explicit atom model in simulations of polymethylene

We have carried out stochastic dynamics and molecular dynamics simulations of n‐tridecane (C13H28) as isolated chains, in bulk melts, and in confined melts between solid surfaces, employing both a united atom (UA) model and an explicit atom (EA) model, in order to compare chain conformations, packing, orientational correlations, and self‐diffusion predicted by the UA and EA models. The EA model, which explicitly takes into account all hydrogens, exhibits nearly identical results for chain conformations to those from the UA model. However, only the EA model, which shows considerably enhanced interchain packing and orientational correlations in the melts over those for the UA model, reproduces very closely the height and the width of the interchain peak in the experimental x‐ray scattering profile. Dynamically, inclusion of explicit hydrogens decreases the self‐diffusion constants in the melts by a factor of 6–8, resulting in reasonably good agreement with the experimental value. Moreover, in the melts conf...

Intrinsic Birefringence of γ‐Form Crystal of Nylon 6: Application to Orientation Development in High‐Speed Spun Fibers of Nylon 6

The intrinsic birefringences of the α- and the γ-form crystals of nylon 6 were calculated from the atomic coordinates and the bond polarizabilities using the Lorentz-Lorenz equation. The intrinsic birefringence of the γ-form crystal was found to be significantly smaller than that of the α-form crystal. Those values were applied to the evaluation of the orientation function of the amorphous phase of the nylon 6 fibers produced by the high-speed spinning process. The molecular orientation in the amorphous phase increased to the maximum point and then decreased with the spinning speed. These results suggested that an inhomogeneous structure in the fiber was formed for the higher take-up speed.