(59b) Dynamic Wetting of Multicomponent Particle Systems
We studied wettability in terms of the content and the contact angle of hydrophobic material within a single pore as well as in a powder mixture. In a first step, cleaned and silanized glass was used as hydrophilic and hydrophobic model material, respectively, in order to focus on the wetting step in avoidance of swelling or dissolution of components. Secondly, the hydrophilic and hydrophobic glass materials were replaced by food components in order to progress towards real systems leading to changing solid and liquid properties during the wetting process. A two-wall setup was developed to study the capillary rise in a single gap containing walls of two materials with different wetting properties. Therefore, two slides were fixed around a spacer, which is changeable and determines the gap width. The dynamic rise was captured using a high speed camera (NX-S2, Imaging Solutions GmbH, Germany). Additionally, a Washburn setup (Washburn tool of the K100 tensiometer from Krüss, Germany) was used to determine penetration rates of water into powder beds. The experiment was performed with two particle fractions of different sizes in order to investigate the impact of pore size on the dynamic wetting as well. There was a significant deceleration of penetration rate observable into the powder mixture if hydrophobic surfaces are involved. Already low quantities of hydrophobic material within the powder mixture cause a significant change in wetting behaviour. Furthermore, a model equation was used to calculate theoretical penetration rates into pore networks with hydrophilic and hydrophobic walls. The results of the experimentally determined and calculated penetration rates showed a good accordance.
 Charles-Williams, H., Wengeler, R., Flore, K., Feise, H., Hounslow, M.J., Salman, A.D., 2013. Granulation behaviour of increasingly hydrophobic mixtures. Powder Technology 238, 64â76. 10.1016/j.powtec.2012.06.009.
 Nguyen, T., Shen, W., Hapgood, K., 2009. Drop penetration time in heterogeneous powder beds. Chemical Engineering Science 64 (24), 5210â5221. 10.1016/j.ces.2009.08.038.
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