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Applicability of liquid-like nano polydimethylsiloxane from 1,3-dichlorotetramethyldisiloxane to the wetting of rough surfaces

University of British Columbia

Surface roughness plays an important role in wetting phenomena. For a certain intrinsic material chemistry, the addition of roughness can provide different wetting states. Liquid-like polydimethylsiloxane coatings fabricated using 1,3-dichlorotetramethyldisiloxane are nanoscale, transparent, and show excellent repellency for both low and high surface tension liquids, i.e. low contact angle hysteresis, on flat surfaces. However, the applicability of this coating system to rough surfaces has not been explored. This thesis aimed at investigating the applicability of 1,3-dichlorotetramethyldisiloxane to rough surfaces including textiles, paper, and sandpapers. Textile did not show much promise as 1,3-dichlorotetramethyldisiloxane did not react very well with the surface, and only hydrophobicity was achieved. For papers, a reduction of roughness was necessary to achieve repellency to various liquids. Finally, we investigated whether prior theories for understanding wettability of idealized textures may be extended to randomly rough surfaces. Fewer works have investigated the wettability of randomly textured surfaces, although they are much more similar to scalable and bio-inspired surfaces. Sandpapers of varying grit size, when hydrophobized using 1,3-dichlorotetramethyldisiloxane, served as model randomly-rough surfaces. Two analyses were conducted. In the first, termed the non-statistical approach, direct imaging of the surfaces was used to extract an effective texture size and spacing, based on particle analysis and Delaunay triangulation. In the second, termed the statistical approach, two metrology parameters, sample autocorrelation length and mean periodicity, served as the effective texture size and spacing. Overall, the statistical method predicted water contact angles better than the non-statistical approach, especially for surfaces in the fully-wetted Wenzel state or fully-non-wetted Cassie state. For surfaces exhibiting a mixed Cassie state of wetting, neither approach was able to predict the apparent contact angles well, likely due to the propagation of wetting in three dimensions, as two-dimensional analysis was used to derive the theories of wetting investigated. Estimates on the pressure stability of the non-wetted states were underpredicted when using the statistical parameters. In summation, when randomly rough surfaces exhibit a distribution of texture sizes and spacings, current theories of wettability cannot be directly implemented by a simple mapping using statistical parameters.

Text

2020-11-05

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/76460

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/