Contact Angle and Adhesion Dynamics and Hysteresis on Molecularly Smooth Chemically Homogeneous Surfaces

Area of Science:

• Surface Science
• Physical Chemistry
• Materials Science

Background:

• Measuring equilibrium adhesion energies and contact angles is experimentally challenging due to slow required rates.
• Previous methods struggle to achieve the thermodynamic limit (zero velocity).

Purpose of the Study:

• To develop and validate experimental methods for measuring thermodynamic adhesion energies and contact angles.
• To unify kinetic theories of adhesion and contact angle hysteresis.

Main Methods:

• Measured dynamic adhesion energies and contact angles at velocities from 10 mm/s down to 1 nm/s.
• Applied Bell Theory (1978) to derive velocity-dependent expressions.
• Utilized Johnson-Kendall-Roberts (JKR, 1971) theory for adhesion and Blake & Haynes (1969) for contact angles.

Main Results:

• Advancing and receding adhesion energies/contact angles converged to thermodynamic values as velocity approached zero.
• Developed equations for dynamic contact angles that fit experimental data well.
• Demonstrated that kinetic effects, not hydrodynamic or inertial effects, dominate at studied interfacial velocities.

Conclusions:

• The proposed theoretical and experimental methods accurately determine thermodynamic adhesion and contact angle values.
• These methods unify previous kinetic theories and offer new ways to test them.
• Hydrodynamic and inertial effects are negligible in the studied velocity range for non-viscous liquids.