第二章表面与界面现象

Adsorption and absorption
The term sorption encompasses both processes(adsorption and absorption), while desorption is the reverse of it. Adsorption is a surface phenomenon.
properties of solid surface
• chemically heterogeneous: due to the presence of different chemical groups, impurities or crystals at the surface.
properties of solid surface
wetting
• Wetting 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 repellency
Water droplet immersed in oil and resting on a brass surface
Same fluids as above, but resting on a glass surface
Wettability and repellency
properties of liquid surface
• 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.
当我们用“表面”这个词的时候，是用来指某个“单相”的物理边界， 比如固体表面和液体表面等。
Interface and surface
In 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 phase such as solid–air,liquid–air contacts.
Image of reconstruction on a clean Gold (100) surface
An STM image of a single-walled carbon nanotube
adsorption
• Adsorption is the adhesion 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.
表面和界面(surface and interface)
5.固-源自文库界面
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 solution
properties of solid surface
• 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 taken.
Wetting 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
properties of solid surface
it has become possible to image surface atoms with the advent of scanning probe microscopy techniques, such as atomic force microscopy (AFM), and scanning tunneling microscopy (STM)..
properties of solid surface
• surface roughness: uneven Surface roughness is defined as the ratio of real surface area to the plan area, and it is larger than 1 for all practical surfaces.
This rule generally does not apply for solid–solid and gas–gas interfaces.
Interface and surface
where atomic and molecular bonding in the solid structure restrict the reorientation of interfacial molecules for the former, and the ease of miscibility of different gas molecules in free space does not allow any interface formation for the latter.
Adsorption and absorption
• This process differs from absorption, in which a fluid (the absorbate) permeates or is dissolved by a liquid or solid (the absorbent). Adsorption is a surface-based process while absorption involves the whole volume of the material.
第二章表面及界面现象
• 2.1表面及界面现象 • 2.2吸附、润湿、乳化、增溶及相关应用 • 2.3界面双电层
Interface and surface
• An interface is the physical boundary between two adjacent bulk phases.
Interface and surface
• • • • • solid–gas solid–liquid solid1-solid2 liquid–gas liquid1–liquid2
Interface and surface
• The molecules that are located at the phase boundaries (that is between solid– gas,solid–liquid, liquid–gas and liquid1– liquid2) behave differently to those in the bulk phase.
Scanning tunneling microscope
The silicon atoms on the surface of a crystal of silicon carbide (SiC). Image obtained using an STM
Scanning tunneling microscope
表面和界面(surface and interface)
常见的界面有： 1.气-液界面
表面和界面(surface and interface)
2.气-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
界面是两个相邻主体相的物理边界。
In some cases it may extend over several molecular thicknesses.
Interface and surface
We use the word surface in order to define the physical boundary of only one of these phases, such as solid surface and liquid surface etc.
properties 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 defects
• The chemical heterogeneity of a surface is an important property in industry affecting catalysis, adhesion, adsorption, wettability, biocompatibility, printability and lubrication behavior of a surface, and it must be determined analytically when required.
实际上，除了绝对真空条件下的固体以外，在所有情况下我们处 理的都是界面，因为每个“单一相”都与其他“相”相接触， 如……
Interface and surface
在物理化学、表面化学和表面物理的教材 中，表面和界面可以互换使用。 In many standard physical chemistry, surface chemistry and surface physics textbooks, the words surface and interface are used interchangeably because the authors neglect the small differences between the air phase and absolute vacuum conditions.