{"id":153,"date":"2017-07-31T12:20:39","date_gmt":"2017-07-31T16:20:39","guid":{"rendered":"https:\/\/cecas.clemson.edu\/~jbostwi\/?page_id=153"},"modified":"2021-06-19T12:32:11","modified_gmt":"2021-06-19T16:32:11","slug":"drops","status":"publish","type":"page","link":"https:\/\/cecas.clemson.edu\/~jbostwi\/research\/drops\/","title":{"rendered":"Drops"},"content":{"rendered":"\n
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Droplets are fundamental to fluid transport on solids.  Typical examples include 3D printing with relevance to rapid prototyping, self-cleansing surfaces for enhanced solar cell efficiency, microfluidics, spray cooling for high heat flux applications, drop atomization for drug delivery (aerosol) methods, and energy harvesting technologies, all of which involve the motion of droplets on scales where surface tension dominates.<\/p>\n\n\n\n

Constrained drops<\/h4>\n\n\n\n

A free drop will oscillate with characteristic frequency and mode shape predicted by Lord Rayleigh (1879). These predictions have been verified experimentally in both terrestrial and low-gravity situations. When the drop is constrained through contact with a solid surface, the frequency spectrum shifts and can `activate’ previously inaccessible low-frequency modes corresponding to motion of the drop’s center-of-mass, through a symmetry breaking mechanism. This can formalized mathematically via boundary homotopy into liquid bridges and impaled drops, as shown in the Figure on the right. Here the spectrum depends upon the dynamic wetting conditions through the static contact-angle and mobility of the three-phase contact-line. <\/p>\n<\/div>\n\n\n\n

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Spherical drop constrained by solid surface<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n

Sessile drops<\/h4>\n\n\n\n

The sessile drop is the canonical problem upon which many modern fluid transport applications are based. For the sessile drop, the spectrum depends upon both the wetting properties of the solid substrate and the mobility of the three-phase contact-line (spreading). Modal shapes can be distinguished by a polar k and azimuthal l wavenumber pair (k,l). In experiment, the sequence of modes observed during a frequency sweep can become distorted; i.e. the (8,8) mode has a lower resonance frequency than the (7,3) mode. This stands in contrast to the free drop (Rayleigh 1879), which preserves spectral ordering. The distorted spectrum can be understood by recasting the system in a symmetry-breaking framework organized by a `periodic table of droplet motions’. This classification is profound in implication and refreshing in originality. <\/p>\n\n\n\n