NDLI: Understanding and explaining surface tension and capillarity: an introduction to fundamental physics for water professionals

Content Provider	Springer Nature Link
Author	Sophocleous, Marios
Copyright Year	2009
Abstract	Understanding and explaining surface tension and capillarity are not easy tasks. In this manuscript, an attempt is made to explain such phenomena for the generally educated professional. Following a conceptual explanation of the molecular basis of surface tension, it is shown that the true force exerted by the solid walls of a capillary tube on the liquid causing capillary rise is the difference in the surface tensions of the solid-liquid and solid–vapor interfaces leading to free surface energy reduction on wetting the solid walls of the capillary bore, and not the pressure drop at the curved interface. It is also shown that the water in the capillary tube is suspended from the meniscus and is under tension, rather than being pushed up the capillary from below. The energy necessary for capillary rise, being derived from the diminution of surface energy that accompanies the movement of liquid in the capillary, emphasizes the important role of wetting in characterizing surface phenomena. A recommended explanation of capillary rise incorporates the reduction in free surface energy on wetting the inside walls of the capillary bore, where the opposition offered to spreading by the weight of the raised liquid is smaller (because of the narrowness of the bore) than that of the outside walls.Comprendre et expliquer la tension de surface et la capillarité n’est pas une chose facile. Ce manuscript tente d’expliquer ces phénomènes aux professionnels. Suivant une explication conceptuelle de la base moléculaire de la surface de tension, il est montré que la vraie force exercée par les parois solides d’un tube capillaire sur le liquide provoquant une ascension capillaire est la différence entre les tensions de surface des interfaces solide–liquide et solide-vapeur amenant à une réduction de l’énergie libre de surface par mouillage des parois solides du tube capillaire, et non pas une chute de pression à l’interface courbe. Il est également montré que l’eau dans le tube capillaire est suspendue en ménisque et est sous tension et non pas poussée depuis le bas par capillarité. L’énergie nécessaire à l’ascension capillaire, dérivée de la diminution de l’énergie de surface qui accompagne le mouvement du liquide dans le capillaire, souligne le rôle important du mouillage dans la caractérisation des phénomènes de surface. Une explication préconisée pour expliquer l’ascension par capillarité intègre la diminution de l’énergie libre de surface par mouillage des parois intérieures du forage capillaire, alors que l’opposition à la propagation exercée par le poids du liquide surélevé est plus petite (due à l’étroitesse du forage) que celle des parois extérieures.La compresión y explicación de la tensión superficial y de la capilaridad no son tareas fáciles. En este manuscrito, se intenta explicar tales fenómenos para el profesional con una educación general. Tras una explicación conceptual de la base molecular de la tensión superficial, se demuestra que la verdadera fuerza ejercida por las paredes sólidas de un tubo capilar sobre el líquido que causa el ascenso capilar es la diferencia entre las tensiones superficiales de las interfases sólidos, líquidos y sólidos–vapor que conducen a una reducción de la energía de la superficie libre al mojado con las paredes sólidas del orificio capilar, y no la caída de presión en la interfase curva. También se muestra que el agua en el tubo capilar está suspendida del menisco y está bajo tensión, más bien que siendo empujada hacia arriba por el capilar desde abajo. La energía necesaria para el ascenso capilar, puesto que proviene de la disminución de la energía superficial que acompaña al movimiento del líquido en el capilar, enfatiza el rol importante del mojado en la caracterización de los fenómenos de superficie. Una explicación recomendada del ascenso capilar, incorpora la reducción de la energía libre de la superficie al mojar las paredes interiores del tubo capilar, donde la oposición presentada a la dispersión por el peso del líquido ascendido es más pequeña (debido a la estrechez del orificio) que aquellas la de las paredes exteriores.摘要 : 理解和解释表面张力与毛细力并非易事。本文尝试向普通专业人士解释这些现象。通过在分子层次上对表面张力进行概念性解释, 揭示了毛细管中固体内壁施加的引起液体毛细上升的力, 实际上是润湿毛细管固体内壁时固-液和固-气界面间表面张力之差所造成的表面自由能的降低, 而非弯曲界面的压力降低。还揭示了毛细管中的水系受到张力作用而悬挂于弯液面, 并非自毛细管下部推升。毛细上升所需的能量, 源于与毛细管中液体运动伴生的表面能降低, 突出了润湿作用在表面现象中的重要作用。对毛细上升的解释包括了润湿发生时毛细管内壁表面自由能的降低, 内壁处上升液体的重力造成的阻碍液体传播的反向力小于 (由于管道狭窄) 外壁。Entender e explicar os conceitos de tensão superficial e capilaridade não são tarefas fáceis. Neste documento é feito um esforço para explicar estes fenómenos aos profissionais com educação genérica. Depois de uma explicação conceptual sobre a base molecular da tensão superficial, demonstra-se que a verdadeira força exercida pelas paredes sólidas de um tubo capilar sobre o líquido, que causa a ascensão capilar, corresponde à diferença das tensões de superfície das interfaces sólido–líquido e sólido–vapor, levando a uma redução da energia livre da superfície durante o humedecimento das paredes sólidas do tubo capilar, e não à descida de pressão na interface curva. Também é demonstrado que a água no tubo capilar está suspensa a partir do menisco e está sob tensão, em vez de ser empurrada de baixo para cima ao longo do capilar. A energia necessária para a ascensão capilar, induzida pela diminuição da energia superficial que acompanha o movimento do líquido no capilar, realça o papel importante do humedecimento na caracterização de fenómenos de superfície. Uma explicação recomendada para a subida capilar contempla a redução da energia livre da superfície durante o humedecimento das paredes internas do tubo capilar, onde a oposição oferecida ao espalhamento devido ao peso do líquido em ascensão é menor (devido à estreiteza do tubo) do que a oferecida pelas paredes externas.
Starting Page	811
Ending Page	821
Page Count	11
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	18
Issue Number	4
e-ISSN	14350157
Language	Portuguese
Publisher	Springer-Verlag
Publisher Date	2010-01-15
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Capillary rise Unsaturated zone Wetting phenomena Young's equation Interfacial energy Waste Water Technology Water Pollution Control Water Management Aquatic Pollution Geology Hydrogeology
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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