The overall objective of this Ph.D. thesis is to control the wetting behavior of surfaces by exploring the effects of topography on wettability, and ultimately make ultrahydrophobic surfaces. Three different approaches were taken in preparing rough surfaces with controlled wettability. The first approach involved the use of photolithography that resulted in a series of silicon surfaces with different post size, shape and separation (Chapter 2). The second approach was the surface modification of low density polyethylene (Chapter 3). The last one was to adsorb polystyrene colloids with different diameters onto polyelectrolyte multilayers (Chapter 4). The wettability of the patterned silicon surfaces prepared by photolithography and hydrophobized using reactive silane chemistry was explored. Surfaces containing square posts with X-Y dimensions of 2 μm-32 μm exhibited ultrahydrophobic behavior with high advancing and receding contact angles. The contact angles were independent of the post height and surface chemistry. Surfaces with larger posts were not ultrahydrophobic-water droplets pinned on these surfaces. Increasing the separation between the posts caused increases in receding contact angles up to the point that water intruded between the posts. Changing the shape of the posts also increased the receding contact angles due to the more contorted contact lines. The oxidative etching of low density polyethylene films followed by uniaxial or biaxial tension resulted in the formation of micron size fragments. 5 minutes oxidized films had smaller islands than the 15 minutes oxidized ones. The fragments became smaller and more distant from each other with increase in strain that affected the wettability of the surfaces. At 400%, the films exhibited ultrahydrophobic behavior. At a higher strain, the islands were very small and apart from each other, the receding contact angle dropped significantly. Submicron and micron scale rough surfaces were prepared by adsorbing polystyrene colloids onto polyelectrolyte multilayers. The negatively charged colloids were efficiently adsorbed onto the outermost cationic polyelectrolyte surface, showing no aggregation. The advancing water contact angle increased and the receding contact angle decreased as the surface coverage increased, resulting in a remarkable hysteresis of ∼122°. Thus, hydrophobic surfaces could not be achieved by making rough surfaces by colloidal adsorption.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-3574 |
| Date | 01 January 2001 |
| Creators | Oner, Didem |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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