山东大学：《物理化学》课程教学资源（讲义资料）8.1 Surface tension

Chapter 8 Surface phenomena and dispersion system 8. 1 Surface tension Levine, p 384-387 13. 1 The interphase region

Chapter 8 Surface phenomena and dispersion system 8.1 Surface tension Levine, p. 384-387 13.1 The interphase region

8.1 surface tension 1. 1 Some important concepts and phenomena (1) Surface and Interface Surface: The boundary between non-gaseous phases and vacuum The boundary between liquid or solid phase and their vapors can be approximated as Surface In other cases, the boundary is interface So far, we have only considered bulk properties of materials. In this section, the surface interface properties of pure liquid/vapor, solution surface and solid gas interface will be treated

Surface: The boundary between non-gaseous phases and vacuum. The boundary between liquid or solid phase and their vapors can be approximated as Surface. In other cases, the boundary is interface. 1.1 Some important concepts and phenomena (1) Surface and Interface So far, we have only considered bulk properties of materials. In this section, the surface / interface properties of pure liquid/vapor, solution surface and solid / gas interface will be treated. 8.1 surface tension

8.1 surface tension (2) Some important surface phenomena 手U想拍围

(2) Some important surface phenomena 8.1 surface tension

8.1 surface tension (2) Some important surface phenomena 独竹 终=点 5is HUAN等写 People in Zunyi city cross Xiangjiang river on a piece of bamboo Damo crossed Changjiang river on a reed

Damo crossed Changjiang river on a reed. People in Zunyi city cross Xiangjiang river on a piece of bamboo. 8.1 surface tension (2) Some important surface phenomena

8.1 surface tension (2)Some important surface phenomena water strider水黾

water strider 水黾 8.1 surface tension (2) Some important surface phenomena

8.1 surface tension (2) Some important surface phenomena 25328 a nickel floating on water surface Buoyancy Once immersed in water. the nickel would sink at once

A nickel floating on water surface Once immersed in water, the nickel would sink at once. ? Buoyancy Gravity 8.1 surface tension (2) Some important surface phenomena

8.1 surface tension 1.2 Micro-mechanism of surface tension Unbalanced force and surface tension a net attractive force exists for molecules at the surface

1.2 Micro-mechanism of surface tension A net attractive force exists for molecules at the surface. Unbalanced force and surface tension 8.1 surface tension

8.1 surface tension 1.2 Micro-mechanism of surface tension o move molecules toward the surface, i.e., enlarge the surface area, energy must be expended o∝dA Surface area enlargement SW= odA The energy of a molecule at the surface is higher than that in the interior

The energy of a molecule at the surface is higher than that in the interior Surface area enlargement To move molecules toward the surface, i.e., enlarge the surface area, energy must be expended. −W' dA −W' = dA 1.2 Micro-mechanism of surface tension 8.1 surface tension

8.1 surface tension 1. 3 Theoretical definition of the surface tension W∝dA-oW=lA dw= odA is another kind of useful energy d=d7+++∑dhn For reversible process: B Sn=dG G At constant temperature and pressure T aA T dG=odA o is the excess energy per m possessed by the surface specific surface energy The energy of the surface increases Its unit is J m-2=NmI. which can be taken with the enlargement of the surface as the force exerted on unit length. surface area tension

1. 3 Theoretical definition of the surface tension −W' dA −W' = dA For reversible process: , ' W dGT p − =  T p, G A     =       is the excess energy per m2 possessed by the surface. specific surface energy. Its unit is J m-2 = N m-1 , which can be taken as the force exerted on unit length. surface tension dG =dA The energy of the surface increases with the enlargement of the surface area. At constant temperature and pressure: -W = dA is another kind of useful energy. 8.1 surface tension B B B dG S T V p dA n = + + + - d d d   

8.1 surface tension 1. 4 Measurement of surface tension: Slide l I. capillary rise I 2. maximum bubble pressure Soap film 3. ring method A=2ldx 4. drop weight method 5. Wilhelmy slide method 6. the shape of drops or bubbles 7. flow method 8. capillary waves method, etc. W=oA=2oldx W= fdx 2l

1. capillary rise 2. maximum bubble pressure 3. ring method 4. drop weight method 5. Wilhelmy slide method 6. the shape of drops or bubbles 7. flow method 8. capillary waves method, etc. 1.4 Measurement of surface tension: Slide l Soap film A = 2ldx −W =A = 2ldx W = Fdx l F 2  = 8.1 surface tension