The temperature-dependence of the dynamic contact angle

Area of Science:

• Materials Science
• Physical Chemistry
• Surface Science

Background:

• Wetting phenomena are crucial in various applications, from industrial processes to biological systems.
• Understanding the molecular mechanisms governing dynamic wetting is essential for controlling surface interactions.
• The temperature dependence of dynamic contact angles provides insights into the underlying rate processes.

Purpose of the Study:

• To investigate the dynamic wetting of poly(ethylene terephthalate) (PET) tape by di-n-butyl phthalate (DBP) across a wide range of speeds and temperatures.
• To interpret the experimental data using the molecular-kinetic theory of dynamic wetting (MKT).
• To determine if dynamic wetting is a thermally-activated process and identify any changes in the wetting mechanism.

Main Methods:

• Dynamic contact angles were measured using the plunging-tape method and a low-powered microscope.
• Experiments were conducted on PET tape with di-n-butyl phthalate (DBP) over a speed range of 0.003–100 cm/s.
• Measurements were taken at five temperatures (15°C to 55°C) and analyzed using the molecular-kinetic theory (MKT).

Main Results:

• The MKT successfully explained the temperature dependence of dynamic contact angles, yielding parameters like activation free energy.
• Arrhenius-like behavior confirmed dynamic wetting as a thermally-activated process, independent of surface tension and viscosity effects.
• A discontinuity in dynamic contact angles (60°-90°) indicated a velocity-dependent shift in the wetting mechanism, attributed to PET surface heterogeneity.

Conclusions:

• Dynamic wetting of DBP on PET is a thermally-activated molecular rate process.
• The observed transition in wetting mechanism is linked to the chemical heterogeneity of the PET surface.
• The MKT provides a robust framework for understanding dynamic wetting phenomena and their temperature dependence.