Microdroplet Evaporation with a Forced Pinned Contact Line

    Authors

    K. Gleason;S. A. Putnam

    Comments

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    Abbreviated Journal Title

    Langmuir

    Keywords

    DROPLET EVAPORATION; INTERFACIAL TEMPERATURE; SESSILE DROPLETS; WATER; DROPLET; TRIPLE LINE; THEORETICAL INVESTIGATIONS; HEATED SURFACE; SUBSTRATE; DYNAMICS; HYSTERESIS; Chemistry, Multidisciplinary; Chemistry, Physical; Materials Science, ; Multidisciplinary

    Abstract

    Experimental and numerical investigations of water microdroplet evaporation on heated, laser patterned polymer substrates are reported. The study is focused on both (i) controlling a droplet's contact line dynamics during evaporation to identifying how the contact line influences evaporative heat transfer and (ii) validating numerical simulations with experimental data. Droplets are formed on the polymer surface using a bottom-up methodology, where a computer-controlled syringe pump feeds water through a 200 pm diameter fluid channel within the heated polymer substrate. This methodology facilitates precise control of the droplet's growth rate, size, and inlet temperature. In addition to this microchannel supply line, the substrate surfaces are laser patterned with a moatlike trench around the fluid-channel outlet, adding additional control of the droplet's contact line motion, area, and contact angle. In comparison to evaporation on a nonpatterned polymer surface, the laser patterned trench increases contact line pinning time by similar to 60% of the droplet's lifetime. Numerical simulations of diffusion controlled evaporation are compared the experimental data with a pinned contact line. These diffusion based simulations consistently over predict the droplet's evaporation rate. In efforts to improve this model, a temperature distribution along the droplet's liquid-vapor interface is imposed to account for the concentration distribution of saturated vapor along the interface, which yields improved predictions within 2-4% of the experimental data throughout the droplet's lifetime on heated substrates.

    Journal Title

    Langmuir

    Volume

    30

    Issue/Number

    34

    Publication Date

    1-1-2014

    Document Type

    Article

    Language

    English

    First Page

    10548

    Last Page

    10555

    WOS Identifier

    WOS:000341230100048

    ISSN

    0743-7463

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