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摘要
One of the most widely used techniques for evaluating the wettability of powdered foods is the capillary rise method, in which the contact angle is usually estimated using the classical Washburn model. However, this model does not take into account the effect of the dissolution of the particle bed in the rising process, which is an important limitation for its application to many powdered foods. This work presents a new mathematical model for the analysis of capillary rise data considering the partial dissolution of the particle bed. As in the case of the classical Washburn model, the proposed model, designated Dissolution-Modified Washburn Model (DM-Washburn), was obtained by the integration of the Navier-Stokes equation, but introducing a dependency of the capillary diameter as a function of meniscus position and time as a strategy to quantify the dissolution effects. The comparison between the DM-Washburn and the classical Washburn models in terms of quality of fit was performed using experimental data of capillary rise in D-(+)-glucose and lactose using as wetting liquids pure water and aqueous solutions of these two materials with concentrations up to saturation. The DM-Washburn model provided better fit to the height versus time data, with mean relative deviation (MRD) values lower than 5% for all tested conditions. Further, the estimates of contact angle obtained with the DM-Washburn model showed to be independent of the carbohydrate concentration in the wetting liquid, differently from what Was observed using the classical Washburn model. Additionally, tests with microcrystalline cellulose (MCC), a water insoluble material, showed the consistency of the DM-Washburn model in conventional capillary experiments, i.e., without significant dissolution of the particle bed. The obtained results indicate that the model has great potential for evaluating the wettability of soluble materials.
- 出版日期2018-2-1
