Experimental Study on Wetting of Fibers with Non-Newtonian Liquids

Parameters of wetting dry fibers with non-Newtonian liquids are studied experimentally. Rheological tests show that seven of the 13 test liquids adhere to Newtonian behavior with a wide range of viscosities 3 < μ < 30,000 mPa · s. The other six liquids show shear-thinning behavior with different flow indices. Some of the liquids exhibited viscoelastic behavior. Diameters of the fibers are in the range 0.033 < D < 0.071 cm. Experimental measurements cover contact angles, interfacial depths and diameters, as well as the critical wetting speed of entraining visible small air bubbles in the liquid volume. Dynamic contact angles are strong functions of the apparent viscosity of the liquid at the particular wetting speed regardless of whether the liquid is Newtonian or non-Newtonian. Higher values of contact angles correspond to wetting of fiber with larger diameter for less viscous liquids. Critical capillary numbers of air entrainment for shear thinning liquids are generally higher than those for Newtonian liquids. Depressions created in the surface of different test liquids can be classified into three different scales, corresponding to three scales of liquid viscosities.