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Measurement of Initial Soil‐Water Contact Angle of Water Repellent Soils
Author(s) -
Carrillo M. L. K.,
Yates S. R.,
Letey J.
Publication year - 1999
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1999.03615995006300030002x
Subject(s) - contact angle , soil water , surface tension , infiltration (hvac) , penetration (warfare) , soil science , chemistry , drop (telecommunication) , water repellent , environmental science , materials science , thermodynamics , composite material , mathematics , physics , telecommunications , operations research , computer science
Water repellent soils are common throughout the world. Water repellency significantly affects infiltration, evaporation, and other water‐soil interactions. Various indices, such as the water‐solid contact angle (θ), water drop penetration time (WDPT), and 90° surface tension (γ ND ), have been proposed to characterize the degree of water repellency. The water repellency of many soils is not stable, but changes with time after contact with water. No method is available to measure the initial soil‐water contact angle. The purpose of this study was to establish a technique to measure the initial soil‐water contact angle. We combined previously published theoretical relationships to develop the equations cosθ = [(γ ND /γ w ) 1/2 − 1] and h p = 2[(γ w γ ND ) 1/2 − γ w ]/ r ρ g , where γ w is the water surface tension, h p is the breakthrough pressure head, r is the pore radius, ρ is the water density, and g is the gravitational constant. The validity of these relationships was established by treating two sand materials with octadecylamine or solvent extracts from peat moss to create various levels of water repellency. An instrument was developed to measure h p . A linear relationship was found between h p and γ 1/2 ND , as specified by the equation. The value of r was computed from the slope h p vs. γ 1/2 ND curve, and this r value was combined with h p in the capillary rise equation to compute cosθ. Good agreement was found between measured and predicted relationships between cosθ and γ 1/2 ND . The major conclusion is that the value of θ can be determined by measuring γ ND , which is easily done in the field or laboratory.