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Chapter Twelve Colloidal System and Surface Phenomena

Chapter Twelve Colloidal System and Surface Phenomena. <1nm. Dispersed phase (NaCl) Dispersing phase (medium) (water). Solution Colloid Suspension. Dispersed System. 1~100nm. >100nm. 12-1 Colloidal Dispersions 12-2 Formation of Colloidal Particles

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Chapter Twelve Colloidal System and Surface Phenomena

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  1. Chapter TwelveColloidal System and Surface Phenomena <1nm Dispersed phase (NaCl) Dispersing phase(medium) (water) Solution Colloid Suspension Dispersed System 1~100nm >100nm

  2. 12-1 Colloidal Dispersions 12-2 Formation of Colloidal Particles 12-3 Properties of Colloidal Dispersions 12-4 Surface Tension

  3. 12-1 Colloidal Dispersions • the average diameter of particle • 1nm < 1~100nm < 100nm • Solution Colloidal suspension • Hydrophilic Hydrophobic • ColloidsColloids • (very large molecules) (mass molecules)

  4. 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

  5. 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

  6. 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

  7. 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)

  8. 分散体系分类（按聚集状态分类）

  9. 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.

  10. §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。

  11. 机械法：胶体磨气流粉碎机 分 散 法 电弧法 超声波法 胶溶法 冷 却 蒸汽状态 溶解状态 胶态 物理法 的物质 改变溶剂 凝 聚 法 还原法（金属溶胶） 氧化法 化学法 复分解反应（盐类溶胶 ） 水解 （金属氧化物溶胶 ） 溶胶 净化 过滤、沉降或离心 除去溶胶中的粗粒子 渗析 ∕电渗析 除去多余的电解质

  12. 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,

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. Dialysis

  18. 生命体的净化举例

  19. 12-3 Properties of Colloidal Dispersions • Tyndall Effect ——Optical Properties • Brownian Movement • Electrophoresis • Adsorption • Coagulation of Colloidal Dispersions

  20. 一、Optical Properties Tyndall Effect --the scatting of light bycolloidal particales.

  21. Tyndall效应产生的原因？

  22. 二、 Brownian Movement • Random motion of colloidal particles in a dispersing medium is called Brownian movement

  23. 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

  24. 沉降与沉降平衡 沉降:粒子在重力场的作用下有向下沉降的 趋势,结果是底部粒子浓度大于上部, 造成 区域间的浓度差. 扩散:由于浓差的存在, 在扩散驱动力的 作用下, 扩散又使浓度趋于均一. 沉降平衡:沉降作用与扩散作用两相处于平衡状态时, 各一定高度上的粒子浓度不再随时间而变, 这种状态称为“沉降平衡” (如图).

  25. 密度及沉降特性 密度： RNA>双链DNA； 环状DNA >开环、线状DNA 单链DNA >双链DNA 沉降速度： RNA >环状DNA>开环、线状DNA

  26. 沉降分析法

  27. 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?

  28. 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

  29. adsorption 1. 胶核界面的选择性吸附： 胶粒中的胶核（原子、离子、分子的聚集体）常选择性地吸附电解质中与其组成类似的离子作为稳定剂，并使其界面带有一定的电荷。 2. 选择性吸附与反应物浓度有关： 改变两种反应物的用量,可使制备的溶胶带有不同符号的电荷 3. 若无相同离子，则首先吸附水化能力较弱的负离子，所以自然界中的胶粒大多带负电，如泥浆水、豆浆等都是负溶胶。

  30. [(AgI)m n I – (n-x)K+]x– xK+ |________________________| |________________________________| negative colloid [(AgI)m n Ag+ (n-x)NO3–]x+ xNO3– |______________________________| |_______________________________________| positive colloid 例1：AgNO3 +KI(过量)→KNO3 + AgI↓ 例2：AgNO3(过量)+ KI→KNO3 + AgI↓ 胶团的结构表达式 ：

  31. 水 水 Fe(OH)3溶胶 Sb2S3溶胶 电泳 带电胶粒或大分子在外加电场的作用下向带相反 电荷的电极作定向移动的现象

  32. 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

  33. ζ Electrokinetic potential 当胶粒移动时，其表面上的水合膜层（即吸附层）以及在此层里的离子都随之移动： 滑动面——吸附层移动时与扩散层分开的界面， ζ电势——是滑动面与均匀液相之间的电势差 + - + + - - - + + - - - + - - + - + + + 无论是正电溶胶还是负电溶胶： 胶粒带电荷越多，δ电势绝对值越大，水化双电层越厚， 胶粒越不易合并变大，溶胶就越稳定。

  34. 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).

  35. 不同电解质的聚沉值（mmol·dm-3） 电解质 AgI 电解质 Al2O3 （负溶胶） （正溶胶） NaNO3 140 NaCl 43.5 Ca(NO3)2 2.40 K2SO4 0.30 Al(NO3)3 0.067 K3[Fe(CN)6] 0.08 聚沉值： 是在一定条件下刚刚足够引起某种溶胶聚沉的 电解质浓度，一般以毫摩/升表示。

  36. 不同胶体的相互作用 与加入电解质情况不同的是： 当两种溶胶的用量恰能使其所带电荷的量相等时， 才会完全聚沉，否则会不完全聚沉，甚至不聚沉。

  37. 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.

  38. Molecules within a liquid are pulled in all directions; there is no tendency for them to be pulled in any one way. • However, molecules at the surface are pulled only downward and sideways but not upward

  39. 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

  40. 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

  41. 固体表面上吸附的应用： • 1g活性炭的总表面面积可达100m2。表面突出的原子处于价的不饱和状态，具有吸引其它分子的能力。 • 将活性炭少许加入盛有溴蒸气（红色）的容器中，密塞后震荡活性炭，则可观察到红色逐渐消失。这是由于Br2分子被活性炭吸附到它的表面上。 • 在氢电极铂片上镀铂黑以吸附氢气，就是由于光亮平板状的铂片无吸附性能，而镀上一层疏松的铂原子，总的表面面积大大增加，并且表面突出的原子多，利用突出原子的余价以吸附氢气。 • 医药上常用活性炭来脱色、吸附微量杂质和热原。例如制备葡萄糖液体时，先配成叫浓溶液，加活性炭振荡后过滤，再冲稀到欲配浓度。

  42. 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。

  43. 二、 Another way that surface tension 润湿现象　当液体和固体接触时界面出现的现象： 同一种液体，对不同的固体来说，它可以是润湿的， 也可以是不润湿的。

  44. 润湿和不润湿可以用其分子间相互作用力的大小来解释。 内聚力（cohesion）——液体分子之间的吸引力； 附着力(adhesion)——液体分子和固体分子之间的吸引力。 若 内聚力〈 附着力，固体就被润湿 —— 润湿现象。 若 内聚力 〉附着力，固体上的液滴不会展开 ——无不润湿现象。

  45. Adhesion > cohesion, concave Adhesion < cohesion, convex

  46. 三、液体表面的吸附和表面活性物质 1. 液体表面上的吸附 在一定温度下， 纯水中加入不同种类的溶质: σ （肥皂）小于σ（水） 肥皂分子可以部分的代替 水分子聚集在溶液表面，使 σ（水）降低。 研究发现：溶质在水溶液中的 分布是不均匀的； c表面（肥皂）＞c内部（肥皂） 以肥皂（脂肪酸钠）为例 正吸附

  47. 反之为负吸附 无机盐类，糖类，淀粉 类等多羟基有机物， σ 大于σ（水） c表面＜c内部 • 反之，若加入的溶质将增高溶剂的表面张力，则溶液表面层将排斥溶质分子(或离子)，使其尽可能进入溶液内部，此时溶液表面层的浓度小于其内部浓度，这种吸附称为负吸附。

  48. 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.

  49. Emulsions Shakeplaced 2. Addedassociation colloid 1.temporaryemulsion oil water Not stability system

  50. Oil can not dissolve in water no mater how drastically you stirred. • Surface active agent (small σ) • Adsorption

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