01 / 87Chapter Twelve Colloidal System and Surface Phenomena
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Chapter Twelve Colloidal System and Surface Phenomena
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12-1 Colloidal Dispersions 12-2 Formation of Colloidal Particles 12-3 Properties of Colloidal Dispersions 12-4 Surface Tension
12-1 Colloidal Dispersions • the average diameter of particle • 1nm < 1~100nm < 100nm • Solution Colloidal suspension • Hydrophilic Hydrophobic • ColloidsColloids • (very large molecules) (mass molecules)
Definitions • Sol • general term used primarily for dispersions of solids in liquids, but also for dispersions in solid or gaseous media • hydrosol - dispersion in water • alcosol - dispersion in alcohol • aerosol - dispersion in air
Gel • a colloidal system which under a set of conditions of concentration and temperature, "sets" into a solid or semisolid • the rigidity of a gel is due to an intertwining network which traps the dispersion medium
Table 12-1: The type of dispersion system Solution colloidal dispersion suspension one phase present two phases present two phases present homogeneous borderline /or not heterogeneous does notdoes not separates separate on standing separate on standing on standing can pass through can not pass throughcan not pass through semipermeable membrane Transparent（透明）borderline not transparent
Types of Colloidal Systems Table 12-2: Colloidal dispersions disperseddispersingtype examples phasemediumname gasliquidfoam 泡沫beer froth, soap suds gassolidsolid foam Polyurethane (聚氨酯) foam liquidgasliquid aerosol fog, clouds liquidliquid emulsion mayonnaise（蛋黄酱）, milk liquidsolidsolid emulsion cheese solid gassolid aerosol smokes, dust solidliquidsol most paints, starch dispersed in water, solidsolidsolid sol many alloys, black diamonds, ruby glass (gold in glass)
12-2 Formation of Colloidal Particles • Dispersion methods: in which large pieces of the substance are broken up into particles of colloidal size. • Condensation methods: in which molecules or ions or atoms are made to cluster together to form particles of the desired size.
§12－2 溶胶的制备 离子、分子 粗粒子 (分散法) (凝聚法) 1～100nm 凝 聚 (有新相生成) 分 散 (比表面增加) 一、溶胶制备的一般条件： ① 分散相在介质中溶解度须极小，且反应物浓度很稀，生 成物的难溶晶体很小，又无长大条件； ② 必须有稳定剂存在。
Dispersion Method of Forming Colloids Larger pieces of matter can often be reduced in size by grinding, stirring, beating, or whipping. Example: Ag sol preparation by thearc method,
Condensation Method of Forming Colloids • Molecules or ions or atoms are made to cluster together to form particles of the desired size. Example: the formation of fog and clouds by the clustering together of water molecules has already been mentioned.
There is some methods： 1). Double-replacement method: AgNO3 + NaCl → AgCl↓ + NaNO3 As2O3 + 3H2S → As2S3 ↓ + 3H2O 2). Reductive method 2HAuCl4+3H2O2 →8HCl+3O2+2Au At the same time, added a littleNaOH: HAuCl4+5NaOH → 4NaCl+3H2O + Na+AuO2- Steady reagent
3). Hydrolysis method FeCl3 + 3H2O(aq) → Fe(OH)3 ↓+ 3HCl Fe(OH)3 + 3HCl → FeO+Cl- + 2H2O Steady reagent 4). Method of changing solvent e.g. Sulfur sol
二、溶胶的净化 Dialysis(透析，分离 ) • The separation of ions from colloids by diffusion through a semipermeable membrane is called dialysis.
二、 Brownian Movement • Random motion of colloidal particles in a dispersing medium is called Brownian movement
The action of the Brownian Movement • 1. Diffusion effect: have coagulation聚结stability and keep sedimentation 沉降 equilibrium • 2. Sedimentation effect: forms the ladder of concentration 胶体体系动力稳定的因素之一 胶体体系动力不稳定的因素之一
三、Electrophoresis（电泳） • The charged, dispersed particles in a colloidal system moves toward the electrode that has the opposite charge. This movement is called electrophoresis. • Almost all colloidal particles have an electrical charge-either positive or negative. • Why?
1. Adsorption • Sol: has a tremendous amount of surface. It is that the most important properties of colloidal matter are those which are dependent on surface interactions such as adsorption. total area • Surface have • tendency to • decrease E specific surface energy Surface energy 比表面能是使其表面增加单位面积所需要的能量
四、Coagulation(聚沉) of ColloidalDispersions • It is often desirable during chemical operations to coagulate colloidal dispersions. Several methods of bringing about the coagulation: 1. In many cases, heating is all that is necessary. 2. The most effective way of coagulating colloidal dispersions of the sol and emulsion type is by adding an electrolyte
Two rules of coagulation 1) The effective coagulating electrolytes are opposite ions. 2) The coagulating ability of ions with identical charges are the same approximately; the coagulating ability of ions increase remarkably with increasing of electrolyte ion charges (exponentially).
12-4 Surface Tension • problem: Why, doeswater bead up on a newly waxed car instead of forming a sheet over it? • solution: • in intermolecular forces.
surface tension (r): ——The surface tension of a liquid is the amount of energy required to stretch or increase the surface by unit area. 比表面能：是增加单位面积所需要的能量 On number
一、 Adsorption • Adsorption ,in (Chemistry) is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase gas, liquid or solid. adsorbent:liquid, gas,and solid adsorbate: atoms, molecules, or ions
adsorption isotherm linear（中文 p287） • Only at very low concentrations is the adsorption isotherm linear. 固-液界面吸附最主要的应用之一是色谱法(或称层析法)。 色谱法是利用粉状吸附剂对混合液中各组分的吸附能力不同使吸附质彼此分离的一种方法。
Emulsions • The chemical definition of an emulsion is a • stable mixture of two or more immiscible(不能混合的) liquids where one liquid (in the form of droplets or globules) is dispersed in the other.
Emulsions Shakeplaced 2. Addedassociation colloid 1.temporaryemulsion oil water Not stability system
