Abstract
Many industrial processes depend on the wetting of liquids on various surfaces. Understanding the wetting effects due to ultrasonic vibration could provide a means for changing the behavior of liquids on any surface. In previous studies, low-frequency surface vibrations have been used to alter wetting states of droplets by exciting droplet volume modes. While high-frequency (>20 kHz) surface vibration can also cause droplets to wet or spread on a surface, this effect is relatively uncharacterized. In this study, droplets of various liquids with volumes ranging from 2 to 70 µL were vibrated on hydrophobic-coated (FluoroSyl) glass substrates fixed to a piezoelectric transducer at varying amplitudes and at a range of frequencies between 21 and 42 kHz. The conditions for contact line motion were evaluated, and the change in droplet diameter under vibration was measured. Droplets of all tested liquids initially begin to spread out at a similar surface acceleration level. The results show that the increase in diameter is proportional to the maximum acceleration of the surface. Finally, liquid properties and surface roughness may also produce some secondary effects, but droplet volume and excitation frequency do not significantly change the droplet spreading behavior within the parameter range studied.
Highlights
Manipulating droplet wetting can be useful for numerous tasks such as transporting or separating solid objects [1,2,3,4]
This work shows that ultrasonic vibration can be an effective way of controlling the spreading
This work shows that ultrasonic vibration can be an effective way of controlling the spreading droplets of a wide property range
Summary
Manipulating droplet wetting can be useful for numerous tasks such as transporting or separating solid objects [1,2,3,4]. Most coating and bonding processes depend on wetting conditions. Wetting conditions can be altered by many methods, including surface coatings [5], surfactants [6], and electric fields [7]. Many of these methods have been widely studied, and much scientific literature exists on each one. Vibration-driven wetting may be preferred as it does not alter the surface chemistry or require electrical connections, but the relationship between vibration conditions and wetting changes needs to be better understood
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