Effect of molecular structure on liquid slip

Area of Science:

• Surface science
• Materials science
• Computational chemistry

Background:

• Understanding liquid-solid interface behavior is crucial for tribology and material design.
• Molecular structure plays a key role in interfacial phenomena like friction and slip.
• Previous models often simplified molecular complexity, limiting predictive power.

Purpose of the Study:

• To investigate how molecular shape and flexibility influence slip behavior at liquid-solid interfaces.
• To develop a model that captures the interplay between molecular structure and slip.
• To provide insights into the fundamental mechanisms governing liquid slip.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model three liquids with varying molecular architectures: linear (hexadecane), branched (pentaerythritol tetra), and ring-chain (polyphenylether).
• Reduced-order modeling, specifically a two-dimensional Frenkel-Kontorova model, was utilized to capture essential molecular features.
• An approximation to the Peierls-Nabarro energy was formulated, incorporating atomic positions and molecular flexibility.

Main Results:

• The study demonstrates that molecular structure directly affects liquid slip at the interface.
• Increased molecular flexibility allows liquids to conform more easily to the substrate, reducing slip.
• Less flexible molecules incur higher conformational energy penalties when interacting with the substrate, leading to increased slip.

Conclusions:

• Molecular flexibility is a critical determinant of slip behavior at liquid-solid interfaces.
• The developed model provides a framework for predicting slip based on molecular characteristics.
• These findings have implications for designing surfaces and lubricants with tailored frictional properties.