Characterization of porous media by dynamic wicking combined with image analysis

Dynamic wicking is a well-known technique for the determination of contact angles between porous media (or powders) and liquids, the determination of surface properties and pore sizes. Wicking data have the form of weight or optical measurements. Acquiring and analysing weight data is easy and appropriate instruments can be found in the market. On the other hand, optical data carry a lot of information that cannot be retrieved by weight measurements. The optical observation of the wicking phenomenon can reveal heterogeneities in the material under investigation related to its pore structure and/or surface properties. This information can be of significant technological importance for several applications such as yarns and textiles, porous food systems, and powders. Unfortunately, to our knowledge, no commercial instrument providing analysis of optical data of dynamic wicking exists. The aim of this work was to develop an algorithm, program and user-friendly software for the analysis of dynamic wicking images and explore its capabilities. The application refers to wicking experiments where the wicking front propagates towards one direction. In order to cover a wide range of possible cases we performed numerous wicking experiments. In the experiments, porous materials having different properties (surface roughness, pore sizes and pore size distribution, transparency, ability to reflect light) were used. In addition, during the wicking tests we caused several lighting disturbances (uneven lighting, lighting that changes over time, etc.) aiming to best simulate actual experimental conditions and further stress the capabilities of the algorithm. Results of the developed application are compared with results analysed without it. Finally, we performed wicking tests on two biological materials and local analysis of the wicking data was applied. The technological significance of these results is discussed. The program can provide global and local information of the wicking phenomenon giving as an output the distance vs time data. These data can be used for the determination of contact angles, surface properties and effective mean pore radii of the material. The application can be used as stand-alone as well as a module of already existing axisymmetric drop shape analysis instruments. (C) 2012 Elsevier B.V. All rights reserved,