TY - JOUR

T1 - The capillary action of water as a function of meniscus length and wetting angle

AU - Hartge, K. H.

AU - Bachmann, J.

N1 - Copyright: Copyright 2017 Elsevier B.V., All rights reserved.

PY - 2000

Y1 - 2000

N2 - Soil physics literature contains various expressions for the contracting force of menisci between solid soil particles. To find the most suitable expression, we measured the interaction of water and glass when one or more drops of water resided between two parallel glass plates separated by varying distances within a range of a few millimeters. Several equations were used to quantify the contracting force associated with the surface tension of water. To assess the impact of meniscus length and contact angle, we compared the force exerted by the number of individual menisci with the force exerted by the same volume of water unified in a single meniscus. Results showed that the compression of several menisci into a single meniscus reduced the contracting force. It was observed further that the attraction during the lifting phase (receding contact angle) exceeded the corresponding forces during lowering (advancing contact angle). The difference in contracting force caused by increasing meniscus length was of the same order of magnitude as the difference induced by increasing or decreasing the distance of the plates corresponding to receding or advancing contact angles. The pressure predicted, with the classical capillary equation for curved interfaces multiplied with the contact area and a modified equation, including the contact angle at the three phase line of contact, described the measured data better than the equations of either Kezdi or Bernatzik. However, in most cases, the calculated contracting force exceeded the measured values considerably. Nonlinear regression analysis showed that the closest fits were obtained when the advancing angle of about 20°, measured on smooth glass plates, was adjusted to values of about 40 to 90°. This result supports the hyphothesis that either contact angle hysteresis or the meniscus length have a considerable impact on capillary pressure and attractive forces in partly saturated capillaries.

AB - Soil physics literature contains various expressions for the contracting force of menisci between solid soil particles. To find the most suitable expression, we measured the interaction of water and glass when one or more drops of water resided between two parallel glass plates separated by varying distances within a range of a few millimeters. Several equations were used to quantify the contracting force associated with the surface tension of water. To assess the impact of meniscus length and contact angle, we compared the force exerted by the number of individual menisci with the force exerted by the same volume of water unified in a single meniscus. Results showed that the compression of several menisci into a single meniscus reduced the contracting force. It was observed further that the attraction during the lifting phase (receding contact angle) exceeded the corresponding forces during lowering (advancing contact angle). The difference in contracting force caused by increasing meniscus length was of the same order of magnitude as the difference induced by increasing or decreasing the distance of the plates corresponding to receding or advancing contact angles. The pressure predicted, with the classical capillary equation for curved interfaces multiplied with the contact area and a modified equation, including the contact angle at the three phase line of contact, described the measured data better than the equations of either Kezdi or Bernatzik. However, in most cases, the calculated contracting force exceeded the measured values considerably. Nonlinear regression analysis showed that the closest fits were obtained when the advancing angle of about 20°, measured on smooth glass plates, was adjusted to values of about 40 to 90°. This result supports the hyphothesis that either contact angle hysteresis or the meniscus length have a considerable impact on capillary pressure and attractive forces in partly saturated capillaries.

KW - Capillary force

KW - Contact angle

KW - Meniscus length

UR - http://www.scopus.com/inward/record.url?scp=0033711386&partnerID=8YFLogxK

U2 - 10.1097/00010694-200010000-00001

DO - 10.1097/00010694-200010000-00001

M3 - Article

AN - SCOPUS:0033711386

VL - 165

SP - 759

EP - 767

JO - Soil Science

JF - Soil Science

SN - 0038-075X

IS - 10

ER -