MEASUREMENT OF CONTACT ANGLE, WATER DROP PENETRATION TIME, AND CRITICAL SURFACE TENSION

 LETEY, J

PARTIALLY SUPPORTED BY U.S. DEPARTMENT OF AGRICULTURE, FOREST SERVICE, GRANT NO. 4000. IN: SYMPOSIUM ON WATER-REPELLENT SOILS, PROCEEDINGS, MAY 6-10, 1968, UNIVERSITY OF CALIFORNIA, RIVERSIDE, P 43-47, MARCH 1969. 1 FIG, 3 REF.



THE LIQUID-SOLID CONTACT ANGLE HAS BEEN ONE METHOD OF CHARACTERIZING WATER REPELLENCY ON PLANE SURFACES, BUT IT CANNOT BE MEASURED WITHIN A SOIL SYSTEM. THE HEIGHT OF CAPILLARY RISE IS A FUNCTION OF THE LIQUID-SOLID CONTACT ANGLE. IT IS ALSO A FUNCTION OF PORE RADIUS, WHICH IS DIFFICULT TO MEASURE. HOWEVER, BY USING ETHANOL, WHICH HAS A CONTACT ANGLE OF 0, THE PORE RADIUS CAN BE DETERMINED AND USED TO CALCULATE THE WATER CONTACT ANGLE. THE WATER DROP PENETRATION METHOD IS BASED ON THE ASSUMPTION THAT THE CONTACT ANGLE MUST BE GREATER THAN 90 DEGREES ON REPELLENT SUBSTANCES. IT IS A DIFFICULT METHOD TO USE BECAUSE THE CONTACT ANGLE CHANGES WITH TIME. THE CONTACT ANGLE IS ALSO DEPENDENT ON THE LIQUID SURFACE TENSION AND IN GENERAL DECREASES AS SURFACE TENSION DECREASES. CRITICAL SURFACE TENSION IS A PROPERTY OF THE SOLID, AND THE HIGHER IT IS, THE LESS WATER REPELLENT THE MATERIAL IS. CRITICAL SURFACE TENSION MEASUREMENTS OF SOILS MAY LEAD TO A SIMPLE EFFICIENT REPELLENCY INDICATOR, BUT MORE RESEARCH IS NEEDED. (CASEY-ARIZONA)



Descriptors: *WETTABILITY | *SOIL PHYSICS | *SURFACE TENSION | *CAPILLARY ACTION | PORES | INFILTRATION | REPELLENTS | *LIQUID-SOLID CONTACT ANGLE | *CRITICAL SURFACE TENSION | *WATER-REPELLENT SOILS | ETHANOL | EFFECTIVE PORE RADIUS

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