Penetration of Aqueous Solutions into Models for Coating Layers, 1995 Coating Fundamentals Symposium Proceedings
The printing process involves a number of different liquid-solid interactions e.G. Wetting, spreading and penetration. The aim of this work has been to gain basic knowledge relevant to the printing process about the spontaneous penetration of aqueous solutions into porous sheets which serve as coating layers. Special emphasis is placed on the effect of liquid surface tension, solid surface free energy and pore size. The work includes the preparation and characterization of model materials as well as penetration and spreading studies of droplets using the dynamic absorption tester. Materials with 30% porosity and pore diameters of 0.1 µM and 0.25 µM, as well as non-porous reference materials have been produced. The surface composition, and thus the surface free energy, was modified by silanization. Liquids used in this study were aqueous solutions of isopropanol and of a non-ionic surfactant. It is shown that the wetting process can be divided into different steps. The initial stage includes the initial spreading and initial penetration. This takes place within 60 ms and for some systems this can be the main part of the process. The second stage is much slower and involves mainly penetration. In this stage, the penetration rate, if the volumes are normalized with respect to the wetted area, is proportional to the square root of the penetration time. The data for the surfactant solutions deviate slightly from this relationship. Key words wetting, penetration, absorption, porous substrates, surface free energy, aqueous solutions, solid-liquid interaction, printing, fountain solution.