Pressure Anisotropy in Polymer Brushes and Its Effects on Wetting

Area of Science:

• Materials Science
• Surface Chemistry
• Computational Chemistry

Background:

• Polymer brushes, dense macromolecule coatings, possess inherent lateral compressive pressure due to chain elasticity and excluded volume interactions.
• This pressure complicates defining interfacial properties and understanding brush wettability.
• The relationship between brush interfacial tension and wetting behavior requires clarification.

Purpose of the Study:

• To investigate the relationship between grafting-induced lateral pressure in polymer brushes, interfacial tension, and wettability.
• To analyze how lateral pressure influences the wetting behavior of polymer brushes.
• To clarify the role of interfacial tension in brush wettability.

Main Methods:

• Utilizing coarse-grained molecular dynamics simulations.
• Focusing on systems with grafting densities and polymer-liquid affinities preventing mixing.
• Analyzing the influence of grafting density on liquid contact angle and interfacial tension.

Main Results:

• The liquid contact angle of polymer brushes is independent of grafting density, indicating lateral pressure does not influence wettability.
• The difference in interfacial tension between wet and dry brushes is well-defined and accurately describes wettability via Young's law.
• A method was developed to isolate grafting-induced pressure, successfully disentangling interfacial and grafting effects except near the mixing point.

Conclusions:

• Grafting-induced lateral compressive pressure in polymer brushes does not directly impact their wettability.
• The difference in interfacial tension between wet and dry states provides an accurate measure of brush wettability.
• Interfacial and grafting effects can be effectively separated, offering insights into brush behavior, particularly concerning autophobic dewetting near mixing points.