Single chain structure in thin polymer films: Corrections to Flory's and Silberberg's hypotheses

Abstract

Conformational properties of polymer melts confined between two hard structureless walls are investigated by Monte Carlo simulation of the bond-fluctuation model. Parallel and perpendicular components of chain extension, bond-bond correlation function and structure factor are computed and compared with recent theoretical approaches attempting to go beyond Flory's and Silberberg's hypotheses. We demonstrate that for ultrathin films where the thickness, $H$, is smaller than the excluded volume screening length (blob size), $\xi$, the chain size parallel to the walls diverges logarithmically, $R^2/2N\approx b^2+c\log (N)$ with $c\sim 1/H$. The corresponding bond-bond correlation function decreases like a power law, $C(s)=d/s^{\omega }$ with $s$ being the curvilinear distance between bonds and $\omega =1$. % Upon increasing the film thickness, $H$, we find -- in contrast to Flory's hypothesis -- the bulk exponent $\omega =3/2$ and, more importantly, an {\em decreasing} $d(H)$ that gives direct evidence for an {\em enhanced} self-interaction of chain segments reflected at the walls. Systematic deviations from the Kratky plateau as a function of $H$ are found for the single chain form factor parallel to the walls in agreement with the {\em non-monotonous} behaviour predicted by theory. This structure in the Kratky plateau might give rise to an erroneous estimation of the chain extension from scattering experiments. For large $H$ the deviations are linear with the wave vector, $q$, but are very weak. In contrast, for ultrathin films, $H<\xi$, very strong corrections are found (albeit logarithmic in $q$) suggesting a possible experimental verification of our results.

16 pages, 7 figures. Dedicated to L. Schäfer on the occasion of his 60th birthday

References in corpus (1)

• Long Range Bond-Bond Correlations in Dense Polymer Solutions

Cited by in corpus (15)

• Molecular dynamics simulations of glassy polymers
• Intramolecular long-range correlations in polymer melts: The segmental size distribution and its moments
• Static Properties of Polymer Melts in Two Dimensions
• Intramolecular Form Factor in Dense Polymer Systems: Systematic Deviations from the Debye formula
• Entanglement reduction induced by geometrical confinement in polymer thin films
• Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model studies
• Spatial distribution of entanglements in thin free-standing films
• Scale-free center-of-mass displacement correlations in dense polymer solutions and melts without topological constraints and momentum conservation: A bond-fluctuation model study
• A finite excluded volume bond-fluctuation model: Static properties of dense polymer melts revisited
• Efficient equilibration of confined and free-standing films of highly entangled polymer melts
• Glass transition temperature of thin polymer films
• Are polymer melts "ideal"?
• Generating multi-chain configurations of an inhomogeneous melt from the knowledge of single-chain properties
• Surface segregation of conformationally asymmetric polymer blends
• Note: Scale-free center-of-mass displacement correlations in polymer films without topological constraints and momentum conservation