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Water Potential and Aggregate Size Effects on Contact Angle and Surface Energy

^a Institute of Soil Science, Univ. of Hannover, Herrenhaeuser Str. 2, 30419 Hannover, Germany
^b Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

View larger version (60K): [in a new window]   Fig. 1. Experimental setup of the capillary rise method.

View larger version (20K): [in a new window]   Fig. 2. Evaluation of the capillary rise measurement for water and n-hexane (1- to 2-mm Al aggregates, ignited); the contact angle of the outer aggregate surface is calculated from the slope of Stage 2; Stages 1 and 3 are not considered.

View larger version (36K): [in a new window]   Fig. 3. Contact angles of different size fractions as a function of soil water potential; the gravimetric water contents (WC) are given at the upper axes.

View larger version (52K): [in a new window]   Fig. 4. Contact angles of the ignited homogenized fractions after equilibration at 99.9% relative humidity.

View larger version (85K): [in a new window]   Fig. 5. Contact angles as a function of soil water potential and aggregate size; darker coloring indicates wettability, lighter coloring indicates increasing water repellency.

View larger version (20K): [in a new window]   Fig. 6. Contact angle differences between aggregates and homogenized material (<1- and 2- to 4-mm fractions).

View larger version (31K): [in a new window]   Fig. 7. Determination of polar and dispersion components of surface free energy for the Ap material; the squared slope m is the polar component and the squared intercept b is the dispersion component of the solid surface free energy.