Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635142
Title: Capillarity in lithographically patterned micro channels
Author: Javed, H.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2013
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Abstract:
The spontaneous capillary-driven filling of micro channels is important for a wide range of applications. Reporting for the first time for vertically mounted open top channels, in this work the theory for capillary rise in channels of rectangular cross-section has been tested and verified, taking into account the effects of surface topography assuming a Wenzel state. The theory has been tested via capillary rise experiments using polydimethylsiloxane oils of viscosity 96.0, 48.0, 19.2 and 4.8 mPa s within the 400μm and 600μm closed square glass tubes and SU8 open top smooth walled rectangular cross-section channels having width 400μm and 600μm and depth 135μm. It has been shown that capillary rise heights in plane open top walled channels (with roughness factor of 1) can be fitted using the exact numerical solution and that these are similar to fits using the analytical visco-gravitational solution. The viscous friction contribution was found to be higher than predicted by theory assuming a non-rigidified liquid–air boundary, but far below that for a rigidified boundary, which is recently reported for imbibition into horizontally mounted open micro channels. It has also been observed that fingers of liquid spreading along the internal edges of the smooth walled channels in advance of the main body of liquid consistent with wetting expectations. These fingers were observed to be thicker and larger in size for wider and shallower channels. The data from the experiments in which prominent liquid fingers were observed was fitted using the visco-gravitational approximation and it was found that the rise heights were far less than the expected heights especially in wider and shallower channels. In SU8 open top channels, Wenzel roughness was introduced on the walls in the form of triangular steps to provide additional surface area to rising liquid. The experiments were performed with 300-350μm deep open top rough walled SU8 channels of width 400μm and 600μm using PDMS oils of viscosity 19.2, 48 and 96 mPas. The equilibrium height was observed to be increased in channels with greater roughness. The data was fitted using the visco-gravitational solution and the fitted height was found to be increased with roughness but not as much as expected from a Wenzel consideration. This deviation of fitted height from its predicted value was found to be more in the channels with greater roughness factors. The stick-slip behaviour of the liquid fingers was observed along the roughness steps.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.635142  DOI: Not available
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