A new model to determine contact angles on swelling polymer particles by the column wicking method

The contact angle determination on swelling polymer particles by the Washbu rn equation using column wicking measurements may be problematic because sw elling occurs during the wicking process. The objective of this research wa s to develop a new model to more accurately determine contact angles for po lymer particles that undergo solvent swelling during the column wicking pro cess. Two phenomena were observed related to the swelling effect during the wicking process: (1) a temperature rise was detected during the wicking pr ocess when the swelling polymer particles interacted with polar liquids, an d (2) a smaller average capillary radius (r) was obtained when using methan ol (polar liquid) compared to using hexane (non-polar liquid). The particle swelling will induce both particle geometry changes and energy loss which will influence the capillary rise rate. The model developed in this study c onsidered the average pore radius change and the energy loss due to the pol ymer swelling effect. Contact angle comparisons were conducted on wood with formamide, ethylene glycol, and water as test liquids, determined by both the new model and the Washburn equation. It was shown that the contact angl es determined by the new model were about 4-37 degrees lower than those det ermined by the Washburn equation for water, formamide, and ethylene glycol. To determine whether the polymer particles are swelling, two low surface t ension liquids, one polar (methanol) and the other non-polar (hexane), can be used to determine the average pore radius (r values) using the Washbum e quation. If the same r values are obtained for the two liquids, no swelling occurs, and the Washburn equation can be used for the contact angle calcul ation. Otherwise, the model established in this study should be used for co ntact angle determination.