Date of Award

5-2001

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

Douglas W. Bousfield

Second Committee Member

Adriaan R.P. van Heiningen

Third Committee Member

Yang Xiang

Abstract

Non-uniform porosity of paper and coated paper is important in printing and paper making industries. Current porosity measurements give results averaged over a large area. A new method is developed to determine local variations in porosity and surface chemistry. A measured volume of a probe liquid is applied to a hemispherical glass probe. The substrate of interest is brought into contact with the fluid drop. The resulting liquid bridge exerts a force on the probe due to surface tension forces. A video camera is used to visually correlate the physical phenomena with the force-time data. The force-time data is recorded for substrates in four main groups: 1) non-porous, 2) model porous, 3) swellable substrates, and 4) real substrates. The force is found to be a function of the minimum fluid column radius and the surface tension of the fluid for nonporous substrates. For porous samples, the force rapidly increases to a value and is followed by a decrease. For porous samples, this decrease is related to the radial spreading of the fluid into the porous substrate and is related to the local rate of fluid uptake. A theoretical model is proposed that describes the results on porous substrates. The model describes the shape of the force-time curves as well as the slope for a range of substrate and probe fluids. For swellable samples, the force slowly increases to a maximum and then decreases. This behavior is linked to the spreading of the fluid on the surface and the wetting delay. Real paper surface are some combination of the two behaviors.

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