Humidity-Dependent Wetting Properties of High Hysteresis Surfaces
Abstract
The advancing contact angle (θ_(adv)) of water on thin films (∼1 μm) of poly(ethylene glycol) (PEG) with fluoroalkyl endgroups (6 kg/mol PEG with 10-carbon fluoroalkyl, denoted 6KC10) changes strongly with relative humidity (RH). Films of 6KC10 on silicon wafers pretreated with a fluorinated alkylsilane (TFOS) display θadv increasing from 75° at 12% RH to 95° at 94% RH. The surprising transition to nonwetting character at high humidity is attributed to fluoroalkyl groups ordering at the air−hydrogel interface when they are liberated by dissolution of PEG crystallites above 85% RH. When water is withdrawn from a drop on 6KC10, the contact line does not recede. This extreme hysteresis is attributed to restructuring of the gel to bury the fluoroalkyl groups when in contact with water.
Additional Information
© 2007 American Chemical Society. Received 20 June 2006. Published online 9 November 2006. Published in print 1 January 2007. We thank Jeffrey A. Hubbell for inspiration. Sandra M. Troian assisted us with two especially valuable conversations during the early stages of this project. 6KC10 was synthesized by Giyoong Tae. Ellipsometry was performed at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. M.J.M. was supported in part by a NSF Graduate Student Fellowship.Additional details
- Eprint ID
- 79317
- Resolver ID
- CaltechAUTHORS:20170725-072343555
- NSF Graduate Research Fellowship
- Created
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2017-07-25Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field