Structure and dynamics of polymer melt confined between two solid surfaces: A molecular dynamics study.

Area of Science:

• Polymer Physics
• Materials Science
• Surface Science

Background:

• Confined polymer melts exhibit unique properties influenced by interfaces.
• Surface roughness and substrate-polymer interactions are key factors in polymer behavior at interfaces.

Purpose of the Study:

• Investigate static and dynamic properties of linear polymer melts confined between solid surfaces.
• Analyze the impact of wall properties, including roughness, on polymer conformations and dynamics.
• Examine chain length dependence of melt pressure and surface tension.

Main Methods:

• Large-scale molecular dynamics simulations.
• Utilized repulsive and attractive walls with tunable roughness (pillars of varying grafting density).
• Analyzed polymer conformations, size distributions (trains, loops, tails), pressure, surface tension, and lateral dynamics.

Main Results:

• Polymer conformations at interfaces are independent of substrate interactions, matching single-chain critical adsorption.
• Melt pressure (PN) decreases with chain length (N) as PN - P∞ ∝ N⁻¹.
• Surface tension (γN) follows γN ∝ N⁻²/³.
• Lateral dynamics near rough surfaces decrease sharply when pillar separation is < 2Rg (bulk radius of gyration).

Conclusions:

• Silberberg's hypothesis on polymer conformations at interfaces is supported.
• Chain length significantly influences bulk and interfacial properties of confined polymer melts.
• Surface topography, specifically pillar spacing, critically impacts polymer dynamics near attractive surfaces.