Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces
A droplet deposited on a rough, lyophilic surface satisfying the imbibition condition, results in complete wetting. However, in this work, we demonstrate that this behavior can be altered by superheating the substrate such that droplets can reside in a non-wetting Cassie state due to evaporation. Ph...
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ASME International
2019
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| Online Access: | http://hdl.handle.net/1721.1/120179 https://orcid.org/0000-0002-0258-0745 https://orcid.org/0000-0001-7045-1200 |
| _version_ | 1811078154623647744 |
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| author | Adera, Solomon Raj, Rishi Enright, Ryan Wang, Evelyn |
| author2 | Massachusetts Institute of Technology. Department of Mechanical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Mechanical Engineering Adera, Solomon Raj, Rishi Enright, Ryan Wang, Evelyn |
| author_sort | Adera, Solomon |
| collection | MIT |
| description | A droplet deposited on a rough, lyophilic surface satisfying the imbibition condition, results in complete wetting. However, in this work, we demonstrate that this behavior can be altered by superheating the substrate such that droplets can reside in a non-wetting Cassie state due to evaporation. Photolithography and deep reactive ion etching were used to fabricate a well-defined silicon micropillar array with diameter, height, and center-to-center spacings of 5.3, 21.7 and 27.5 μm, respectively. Water droplets placed on this microstructured surface at room temperature demonstrated superhydrophilic behavior with liquid filling the voids between pillars resulting in a vanishing contact angle. However, when the microstructured surface was superheated above a critical value, the superhydrophilicity was lost and non-wetting Cassie droplets were formed. The superheat required to deposit a Cassie droplet (>75°C) was found to be significantly higher than that required to sustain an already deposited Cassie droplet (<35°C). Interestingly, the superheat required to sustain a Cassie droplet after the initial deposition was found to decrease with the square of the droplet radius. These observations where an inherently superhydrophilic structured surface turns into superhydrophobic at nominal superheats has implications for phase change based heat transfer applications where the loss of contact between the substrate and the heat transfer fluid can be detrimental to the device performance. Topics: Drops, Evaporation |
| first_indexed | 2024-09-23T10:54:37Z |
| format | Article |
| id | mit-1721.1/120179 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T10:54:37Z |
| publishDate | 2019 |
| publisher | ASME International |
| record_format | dspace |
| spelling | mit-1721.1/1201792022-09-27T15:53:16Z Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces Adera, Solomon Raj, Rishi Enright, Ryan Wang, Evelyn Massachusetts Institute of Technology. Department of Mechanical Engineering Adera, Solomon Raj, Rishi Enright, Ryan Wang, Evelyn A droplet deposited on a rough, lyophilic surface satisfying the imbibition condition, results in complete wetting. However, in this work, we demonstrate that this behavior can be altered by superheating the substrate such that droplets can reside in a non-wetting Cassie state due to evaporation. Photolithography and deep reactive ion etching were used to fabricate a well-defined silicon micropillar array with diameter, height, and center-to-center spacings of 5.3, 21.7 and 27.5 μm, respectively. Water droplets placed on this microstructured surface at room temperature demonstrated superhydrophilic behavior with liquid filling the voids between pillars resulting in a vanishing contact angle. However, when the microstructured surface was superheated above a critical value, the superhydrophilicity was lost and non-wetting Cassie droplets were formed. The superheat required to deposit a Cassie droplet (>75°C) was found to be significantly higher than that required to sustain an already deposited Cassie droplet (<35°C). Interestingly, the superheat required to sustain a Cassie droplet after the initial deposition was found to decrease with the square of the droplet radius. These observations where an inherently superhydrophilic structured surface turns into superhydrophobic at nominal superheats has implications for phase change based heat transfer applications where the loss of contact between the substrate and the heat transfer fluid can be detrimental to the device performance. Topics: Drops, Evaporation United States. Office of Naval Research 2019-02-04T19:18:38Z 2019-02-04T19:18:38Z 2012-07 2019-01-09T17:40:55Z Article http://purl.org/eprint/type/ConferencePaper 978-0-7918-4479-3 http://hdl.handle.net/1721.1/120179 Adera, Solomon, Rishi Raj, Ryan Enright, and Evelyn N. Wang. “Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces.” ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels, July 8-12, 2012, Rio Grande, Puerto Rico, USA, ASME, 2012. © 2012 ASME https://orcid.org/0000-0002-0258-0745 https://orcid.org/0000-0001-7045-1200 http://dx.doi.org/10.1115/ICNMM2012-73224 ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf ASME International ASME |
| spellingShingle | Adera, Solomon Raj, Rishi Enright, Ryan Wang, Evelyn Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces |
| title | Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces |
| title_full | Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces |
| title_fullStr | Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces |
| title_full_unstemmed | Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces |
| title_short | Evaporation-Induced Cassie Droplets on Superhydrophilic Microstructured Surfaces |
| title_sort | evaporation induced cassie droplets on superhydrophilic microstructured surfaces |
| url | http://hdl.handle.net/1721.1/120179 https://orcid.org/0000-0002-0258-0745 https://orcid.org/0000-0001-7045-1200 |
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