The wetting property and evaporation behavior of ethanol-water mixtures of various concentrations on gold surfaces modified with 1-decanethiolate self-assembled monolayers (SAMs) were studied by digital contact angle analysis. It has been shown that the initial contact angle decreases monotonically with increased concentration of ethanol in the mixture. Evaporation studies revealed a general trend with a preliminary increase in contact angle accompanied with a decrease in contact area, then a constant contact angle accompanied with a slower, linear decrease in contact area. At the very beginning of the evaporation process, the contact angles showed a rapid decrease for the microdroplets of a binary mixture with equal volume fractions (i.e., 50% ethanol). Three distinct stages of the evaporation profile for the ethanol-water mixtures were observed, which differ from the inclusive "pinning" and "shrinking" behavior observed for the pure liquid case. Ultimately, the study makes possible the use of an evaporation profile to monitor the change in concentration of a binary system and allows a better understanding of the interactions between liquid microdroplets with solid substrates.

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The evaporation of water microdroplets from solid surfaces was studied using digital contact angle analysis techniques. An inclusive trend for the evaporation process, that is, a switch from the initial constant contact area to the subsequent constant contact angle mode was observed for all surfaces examined, including mixed self-assembled monolayers (SAMs) on gold and "conventional" surfaces such as silicon wafers, polycarbonate, and Teflon. More importantly, it has been shown that the change in contact angle during the evaporation process (i.e., evaporation hysteresis, delta theta(evap), the difference between the initial and "equilibrated" contact angle) correlates well with the wetting hysteresis determined directly (i.e., measuring the advancing and receding contact angles on these surfaces by changing the drop volume). The comparison between mixed SAM surfaces and conventional solids revealed that the evaporation/wetting hysteresis is dominated by the roughness (from nanometer to micrometer scale) rather than the chemical heterogeneity of the surface. The evaporation rates of water microdroplets on these surfaces were also monitored and modeled.

In this paper we describe the general role that surface morphology and chemical nature play in guiding the cathodic deposition of oxide thin films onto electrode surfaces. By use of a "featureless" stamp for microcontact printing (µCP), the pregrooved microfeatures ("mountains" and "valleys" representing the track trails) of recordable compact disc (CD-R) gold substrates can be selectively modified with OH-or CH 3 -terminated self-assembled monolayers (SAMs). For comparison, "flat" gold substrates were patterned with the above SAMs in parallel "microstrips" that are analogous to the CD-R substrate (but no height differences). Electrochemical deposition of zirconia thin films showed that, on the CD-R substrates, surface morphology (height difference) dominates over the blocking effects of the SAMs; that is, deposition occurred primarily on the mountains despite these sites being modified with organic monolayers. For flat gold substrates it was found that n-alkanethiolate SAMs block deposition in modified areas while directing the deposition to regions of the bare surface. When flat gold substrates were modified with CH 3 -and OH-terminated SAMs in alternating microstrips, deposition was confined to "narrower" regions that are different from the periodicity on the stamp. The type of microstructures and feature sizes of the zirconia thin film were dependent on scan rate, number of cycles, and terminal groups of the SAM to a lesser extent.

We have explored how surface morphology and structure affect wetting properties of electrodeposited oxide thin films notwithstanding chemical modifications. Microstripes of self-assembled monolayers (SAMs) on gold were prepared using a microcontact printing (μCP) technique, which served as molecular templates to guide the electrochemical deposition of zirconia in aqueous solution. The wetting properties of the thus-prepared zirconia oxide thin films are shown to be tunable; i.e., a wide range of wettabilities from hydrophilic to superhydrophobic can be obtained by simply varying the SAM template and the electrodeposition conditions (potential scan rate and number of cycles). In particular, a "two-tier" micro/nanoscale roughness was achieved on the gold substrate patterned with alternating stripes of 1octadecanethiol and 6-mercapto-1-hexanol SAMs, which leads to a superhydrophobic surface (water contact angle ∼150°). Of great significance is the demonstrated ability herein to convert an intrinsically hydrophilic into a hydrophobic surface by changing the conditions for materials fabrication, which does not involve any chemical modifications.