Gd. Nadkarni et S. Garoff, REPRODUCIBILITY OF CONTACT LINE MOTION ON SURFACES EXHIBITING CONTACT-ANGLE HYSTERESIS, Langmuir, 10(5), 1994, pp. 1618-1623
We examine the quasi-static microscopic motion of the contact line on
an ambient surface which exhibits contact angle hysteresis. When the c
ontact line configuration is static or moving slowly, the microscopic
contact line configurations are highly reproducible between two cycles
of immersion of the surface. Mechanical vibrations produce a time jit
ter in the onset of reconfigurations of the contact line as it pulls f
ree from surface heterogeneities and moves rapidly across the surface.
This time jitter causes the contact line configurations to become irr
eproducible during the short times they are falling. As the contact li
ne repins on new defects, the contact line configurations again become
reproducible from one macroscopic cycle to the next. The observations
are explained by energy models used to describe wetting hysteresis. T
he presence of metastable states with temporally evolving energy barri
ers lead to the observed cyclical reproducibility/irreproducibility of
the microscopic contact line configurations. In view of the reproduci
bility of the microscopic contact line configurations, we suggest meth
ods of making reproducible macroscopic contact angle measurements on a
mbient surfaces.