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Science 7 January 1994:
Vol. 263. no. 5143, pp. 60 - 62
DOI: 10.1126/science.263.5143.60
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Articles

Patterned Condensation Figures as Optical Diffraction Gratings

Amit Kumar 1 and George M. Whitesides 1

1 Department of Chemistry, Harvard University, Cambridge, MA 02138

Heterogeneous, patterned surfaces comprising well-defined hydrophobic and hydrophilic regions and having micrometer-scale periodicities were prepared by patterning the adsorption of ohgr-functionalized alkanethiolates in self-assembled monolayers (SAMs) on gold. Condensation of water on such surfaces resulted in drops that followed the patterns in the SAMs. These patterned condensation figures (CFs) acted as optical diffraction gratings for reflected (or transmitted) light from a helium-neon laser (wavelength of 632.8 nanometers). Under an atmosphere of constant relative humidity, the development of the condensation figure was monitored quantitatively, as the temperature of the surface was lowered, by following the change in intensity of a first-order diffraction spot. This experimental technique may be useful in the development of new types of optical sensors that respond to their environment by changing the reflectivity of patterned regions and for studying phenomena such as drop nucleation, contact angle hysteresis, and spontaneous dewetting and break-up of thin liquid films.

Submitted on September 23, 1993
Accepted on November 8, 1993

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Science. ISSN 0036-8075 (print), 1095-9203 (online)