Static Properties of Homopolymer Melts in Confined Geometries Determined by Monte Carlo Simulation

Abstract

The static properties of a homopolymer melt between energetically neutral walls are studied as a function of the degree of confinement (plate spacing) and polymer molecular weight. The cooperative motion lattice model is used and allows all calculations to be performed at full occupancy (i.e., at a volume fraction of 1); chain lengths varying from 384 to 24 are examined. Properties investigated include the magnitude of the end-to-end vector, the radius of gyration, and components of the end-to-end vector. In addition, orientation effects and the distribution of chain ends are also calculated. As the chains are confined, the end-to-end vectors align parallel to the walls beginning at a value of about twice the unconstrained value of the radius of gyration, regardless of the molecular weight. For values less than this, chain conformations are distorted and the magnitude of the average end-to-end vector and radius of gyration increase. The components of the end-to-end vector parallel and perpendicular to the walls are considered; in the cases of confinement, it is seen that there is a universal scaling relationship between the parallel component of the end-to-end vector and the plate spacing. The parallel component increases with the decreasing plate spacing according to approximately a one-sixth power (〈r 2〉∥ 1/2 ∼ L -1/6). Chain ends are most likely to be in the vicinity of one of the walls due to entropic constraints.

Molecular-scale simulation of cross-flow migration in polymer melts

“…Unentangled polymer melts with N w = 64 and [30,31,35]. Results for the unentangled case closely parallel the results for the entangled case; one distinction is that for entangled chains wall slip provides a slight shear rate gradient near the wall which is absent in the unentangled case (see velocity profiles).…”

“…For the model applied to monodisperse linear chains it is found that the equilibrium ensemble averaged root mean squared end-to-end vector [32], R 2 1/2 , scales as: [35] …”

Monte Carlo simulation of homopolymer melts in plane Poiseuille flow

“…Further details of the algorithm are found in earlier works by Gauger et al, 23 Pakula, 24 and Pai-Panandiker and Dorgan. 25 The walls, located at xϭ0 and xϭL x , are impenetrable, neutrally energetic, purely reflective boundaries; periodic boundary conditions are imposed in the y and z-directions. Chain lengths and box dimensions are chosen in order to satisfy the condition of full occupancy.…”

Gaussian ellipsoid model for confined polymer systems

“…al. 20 examined orientational effects of the end-to-end vector in a Monte-Carlo Simulation of dense polymer films. They found an increasing alignment of the end-to-end vector with reducing L z , but averaged their quantities over the whole film.…”