Basic requirements for potential differences across solid-fluid interfaces

Area of Science:

• Physical Chemistry
• Computational Materials Science

Background:

• Molecular ordering at interfaces influences electrostatic potential.
• Surface potential (χ) is a critical property at fluid-solid interfaces, previously measured at ~-0.5 V for water-vapor interfaces.

Purpose of the Study:

• To investigate the molecular origins of surface potential at model fluid-solid interfaces.
• To determine the molecular criteria for generating a non-zero surface potential.

Main Methods:

• Molecular dynamics simulations were employed.
• Model fluids composed of diatomic, dipolar molecules or single Lennard-Jones particles with dipole moments were simulated at a solid interface.

Main Results:

• Surface potential arises from molecular ordering and charge oscillations.
• A non-zero surface potential requires molecules with differing geometric and dipolar centers (asymmetry).
• Solid-fluid interaction strength impacts charge oscillation magnitude but not the potential drop (χ); steric effects, like atomic diameter, can alter the potential's sign.

Conclusions:

• The geometric and dipolar center displacement is a key criterion for fluid surface potential.
• Steric effects play a crucial role in determining the sign and magnitude of surface potential.
• Understanding these molecular factors is essential for controlling interfacial electrical properties.