Spreading of droplets of different liquids on specially structured papers

The spreading kinetics of drops of different liquids (water, glycerol and ethylene glycol) on different types of model papers have been investigated. In the first part of the investigation single ply and two-ply papers, made from pulps with different degrees of beating, were investigated. The results show that is very common the surface layer of the paper had a much larger influence on the spreading than the bottom ply. By normalising the data showing the drop radius as a function of time with the viscosity and surface tension of the liquids all data collapse onto a master curve. The results from the first part of the investigation also show that in order to determine a contact angle between the liquid and the paper the drop volume should remain constant and the contact angle should be determined when the drop has reached its equilibrium volume. In the second part of the investigation the influence of surface topography and surface energy of the papers on the spreading kinetics was determined. The results show that when the pattern of use, the avails on the surface creates fine capillaries the contact angle is decreased compared to the situation with a flat surface. For papers with a higher roughness the uneven structure creates barriers against the spreading which increases the contact angle compared to the situation with a flat surface. A simple attempt to fit the data to a power law based on a hydrodynamic approach was also conducted. The results from this treatment show that it is possible to get a good match for the sheets with virtually only surface spreading. The constants achieved in this treatment can be used to rationalise the spreading data to be compared with other investigations.