第二章表面與界面現(xiàn)象

1、第二章表面及界面現(xiàn)象 2.1表面及界面現(xiàn)象 2.2吸附、潤濕、乳化、增溶及相關(guān)應(yīng)用 2.3界面雙電層Interface and surface An interface is the physical boundary between two adjacent bulk phases.界面是兩個相鄰主體相的物理邊界。In some cases it may extend over several molecular thicknesses.We use the word surface in order to define the physical boundary of only one o

2、f these phases, such as solid surface and liquid surface etc.Interface and surface當(dāng)我們用“表面”這個詞的時候，是用來指某個“單相”的物理邊界，比如固體表面和液體表面等。Interface and surfaceIn reality, we deal with an interface in all cases other than absolute vacuum conditions for solids, since every single phase is in contact with another

3、phase such as solidair,liquidair contacts.實際上，除了絕對真空條件下的固體以外，在所有情況下我們處理的都是界面，因為每個“單一相”都與其他“相”相接觸，如Interface and surfaceIn many standard physical chemistry, surface chemistry and surface physics textbooks, the words surface and interface are used interchangeably because the authors neglect the small

4、differences between the air phase and absolute vacuum conditions.在物理化學(xué)、表面化學(xué)和表面物理的教材在物理化學(xué)、表面化學(xué)和表面物理的教材中，表面和界面可以互換使用。中，表面和界面可以互換使用。 solidgas solidliquid solid1-solid2 liquidgas liquid1liquid2Interface and surface The molecules that are located at the phase boundaries (that is between solidgas,solidliq

5、uid, liquidgas and liquid1liquid2) behave differently to those in the bulk phase.Interface and surfaceThis rule generally does not apply for solidsolid and gasgas interfaces.where atomic and molecular bonding in the solid structure restrict the reorientation of interfacial molecules for the former,

6、and the ease of miscibility of different gas molecules in free space does not allow any interface formation for the latter.Interface and surface表面和界面(surface and interface)常見的界面有：1.氣-液界面表面和界面(surface and interface)2.氣-固界面表面和界面(surface and interface)3.液-液界面表面和界面(surface and interface)4.液-固界面表面和界面(sur

7、face and interface)5.固-固界面properties of liquid surface Elasticity: Liquid surfaces tend to contract to the smallest possible surface area Violent agitation: water molecules on surface jump in and out of the surface very rapidly Adsorption: concentration difference between surface and bulk in solutio

8、n Surface tension: is the force that operates inwards from the boundaries of its surface perpendicularly, tending to contract and minimize the area of the surface. Capillary action:is a physical effect caused by the interactions of a liquid with the walls of a thin tube. properties of liquid surface

9、 Impurity:A solid surface is mostly contaminated with foreign matter as a thin layer above thetopmost surface molecules (or atoms), unless very special precautions are perties of solid surface surface roughness: uneven Surface roughness is defined as the ratio of real surface area to the pl

10、an area, and it is larger than 1 for all practical perties of solid surface chemically heterogeneous: due to the presence of different chemical groups, impurities or crystals at the perties of solid surface The chemical heterogeneity of a surface is an important property in in

11、dustry affecting catalysis, adhesion, adsorption, wettability, biocompatibility, printability and lubrication behavior of a surface, and it must be determined analytically when perties of solid surface it has become possible to image surface atoms with the advent of scanning probe micros

12、copy techniques, such as atomic force microscopy (AFM), and scanning tunneling microscopy (STM).properties of solid surfaceproperties of solid surface At the atomic level, solid surfaces have been found to consist of a mixture of flat regions, called terraces, and defects, steps, kinks and point def

13、ectsScanning tunneling microscopeThe silicon atoms on the surface of a crystal of silicon carbide (SiC). Image obtained using an STM Image of reconstruction on a clean Gold (100) surfaceAn STM image of a single-walled carbon nanotubeScanning tunneling microscopeadsorption Adsorption is the adhesion

14、of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.This process creates a film of the adsorbate on the surface of the adsorbent. Adsorption and absorption This process differs from absorption, in which a fluid (the absorbate) permeates or is dissolved by a liquid or sol

15、id (the absorbent).Adsorption is a surface-based process while absorption involves the whole volume of the material. The term sorption encompasses both processes(adsorption and absorption), while desorption is the reverse of it. Adsorption is a surface phenomenon.Adsorption and absorptionwetting Wet

16、ting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. Wettability and repellencyWater droplet i

17、mmersed in oil and resting on a brass surfaceSame fluids as above, but resting on a glass surfaceWettability and repellencyWetting of different fluids: A shows a fluid with very little wetting, while C shows a fluid with more wetting. A has a large contact angle, and C has a small contact angle emul

18、sion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable). In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). The word emulsion comes from the Latin word for to milk, as milk is an emulsion of fat and

19、water, among other components.emulsion Emulsions are not a human invention. In living nature they play an especially important role in the absorption of fats with nutrients. The earliest known use of an emulsion by humans is certainly the exploitation of milk and milk products such as cream, butter

20、and cheese for nutritional purposes.emulsion The most familiar types are oil-in-water emulsions (O/W emulsions), which consist of colloidal or microscopic oil droplets in water, and water-in-oil (W/O emulsion), where an aqueous solution is emulsified in an outer oil phaseemulsionSolubilization Solub

21、ilization, according to an IUPAC definition,is a short form for micellar solubilization, a term used in colloidal and surface chemistry. Solubilization is the process of incorporating the solubilizate (the component that undergoes solublization) into or onto the micelles. Schematic of micellar solub

22、ilization of fatty substance in water with the use of a dispersant.SolubilizationIUPAC definitionFluid system in which liquid droplets are dispersed in a liquid.Note 1: The definition is based on the definition in ref.1Note 2: The droplets may be amorphous, liquid-crystalline, or anymixture thereof.

23、Note 3: The diameters of the droplets constituting the dispersed phaseusually range from approximately 10 nm to 100 m; i.e., the dropletsmay exceed the usual size limits for colloidal particles.Note 4: An emulsion is termed an oil/water (o/w) emulsion if thedispersed phase is an organic material and

24、 the continuous phase iswater or an aqueous solution and is termed water/oil (w/o) if the dispersedphase is water or an aqueous solution and the continuous phase is anorganic liquid (an oil).Note 5: A w/o emulsion is sometimes called an inverse emulsion.The term inverse emulsion is misleading, sugge

25、sting incorrectly thatthe emulsion has properties that are the opposite of those of an emulsion.Its use is, therefore, not recommended.emulsion比表面（specific surface area） 比表面通常用來表示物質(zhì)分散的程度，有兩種常用的表示方法：一種是單位質(zhì)量的固體所具有的表面積；另一種是單位體積固體所具有的表面積。即：/ /mVAA mAA V或式中，m和V分別為固體的質(zhì)量和體積，A為其表面積。目前常用的測定表面積的方法有BET法和色譜法。分散

26、度與比表面 把物質(zhì)分散成細(xì)小微粒的程度稱為分散度。把一定大小的物質(zhì)分割得越小，則分散度越高，比表面也越大。 例如，把邊長為1cm的立方體1cm3逐漸分割成小立方體時，比表面增長情況列于下表：邊長l/m 立方體數(shù) 比表面Av/（m2/m3）110-2 1 6 102 110-3 103 6 103 110-5 109 6 105 110-7 1015 6 107 110-9 1021 6 109 分散度與比表面 從表上可以看出，當(dāng)將邊長為10-2m的立方體分割成10-9m的小立方體時，比表面增長了一千萬倍。 可見達(dá)到nm級的超細(xì)微粒具有巨大的比表面積，因而具有許多獨特的表面效應(yīng)，成為新材料和多相

27、催化方面的研究熱點。如鉑黑電極及多孔電極由于其表面積較大，電流密度小，因而極化??；再如，由超細(xì)微粒制備的催化劑由于具有很高的比表面因而催化活性較普通催化劑高；此外，將藥物磨成細(xì)粉以提高藥效、將金屬做成超細(xì)微粒以降低熔點都說明了超細(xì)微粒具有獨特的表面效應(yīng)。 薄膜：film 色譜柱:chromatographic column Scanning probe microscopy Atomic force microscopy Coating 拒水拒油整理:water and oil repellentWater beads on a fabric that has been made nonwet

28、ting by chemical treatmentHelmholtz and GouyChapman model of the electric double layer.detailed illustration of interfacial DL The diffuse layer, or at least part of it, can move under the influence of tangential stress. There is a conventionally introduced slipping plane that separates mobile fluid

29、 from fluid that remains attached to the surface. Electric potential at this plane is called electrokinetic potential or zeta potential (also denoted as -potential). Zeta potential can be measured using electrophoresis, electroacoustic phenomena, streaming potential, and electroosmotic flow . Simplified illustration of the potential developmen