Spontaneous pattern formation as a route to droplet motion

Langley, K. (2012) Spontaneous pattern formation as a route to droplet motion. PhD thesis, University of Nottingham.

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Abstract

Two important areas of physics are spontaneous pattern formation and droplet motion on surfaces. These two areas can be brought together since the texture of a surface can influence its wetting properties. Therefore by controlling the factors that determine the length scales of the patterns during spontaneous pattern formation, it is possible to design surfaces with very specific wetting properties. This was used to create surfaces that could direct the motion of sessile water droplets.

Patterned surfaces with micro-wrinkled surface structures were prepared by thermally evaporating thin Aluminium (50−500nm thick) (Al) layers on to thick pre-strained layers of a silicone elastomer and subsequently releasing the strain. This resulted in the formation of sinusoidal periodic surface wrinkles with characteristic wavelengths in the 3 − 45μm range and amplitudes as large as 3.6μm. The Al thickness dependence of the wrinkle wavelengths and amplitudes were determined for different values of the applied pre-strain and compared to a selection of wrinkle formation theories.

Samples with spatial gradients in wrinkle wavelength were also produced by applying mechanical strain gradients to the silicone elastomer layers prior to deposition of the Al capping layers. Sessile water droplets that were placed on these surfaces were found to have contact angles that were dependent upon their position. When vibrated close to their resonant frequency, these water droplets were observed to move from regions of short wrinkle wavelength to regions of large wrinkle wavelength. These samples are therefore viable candidates for the production of low cost gradient energy surfaces.

Item Type:Thesis (PhD)
Supervisors:Sharp, J.S.
Mellor, C.J.
Faculties/Schools:UK Campuses > Faculty of Science > School of Physics and Astronomy
ID Code:2335
Deposited By:Mr K Langley
Deposited On:09 Oct 2012 11:22
Last Modified:09 Oct 2012 11:22

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