Chapter 1 intro to surface chemistry

1、表表 界界 面面 化化 学学surface & interface chemistry授课人授课人 陈晓龙陈晓龙 Purpose of the course1、grasp basal content & principal of surface science, like surface tension、surface free energy、 Gibbs-Maranon effect 、Curved interface phenomenon 、Yang Laplasse equation 、adsorption phenomenon、Focus Equation、Kelvin

2、 Equation、wetting and contact angle in common liquid-liquid interface、liquid-gas interface、solid-gas interface、solid-liquid interface，surfactant chemistry，and so on.2、use knowledge learned in class to explain some phenomenon concerned with surface chemistry in our daily life or in mineral processing

3、 field.3、use classical formula to do calculation in surface chemistry . features of the course 1、Not hard， but eye opening 2、Popular science & interest 3、Rich in content ，near to daily life & our major 4、coupled with classical Chinese and English textbook ExperimentalExperimentalExperimental

4、Dip into the keroseneExperimentalWater drop on keroseneExperimentalWater drop on modified & unmodified calcium carbonate “Yesterday, I could not define surface chemistry; Today, I am doing it.” This variation of an old quip could apply to many recent chemistry and engineering graduate on enterin

5、g employment in the “ real world”. Two facts underline this situation. First, Surface science , although traditional part of physical chemistry, have largely disappeared from introductory physical chemistry course. Second, in research, technology, and manufacturing, countless problems are encountere

6、d that fall squarely within the purview of surface science. Paul C Introduction 表界面化学是研究与化学有关的表界面现象的科学，是研究表面热力学、表面动力学和表面结构，包括表面的组成，结构和化学反应的学科。如颗粒或微粒表面物理化学特性表征、表面富集，吸附，粘附，多相反应及催化、表面活性剂作用及胶体化学等。 界面是指两相接触的约几个分子厚度的过渡区，若其中一相为气体，这种界面通常称为表面。严格讲表面应是液体和固体与其饱和蒸气之间的界面，但习惯上把液体或固体与空气的界面称为液体或固体的表面。实际上，表面和界面是统一的。自

7、然界中不存在脱离界面而存在的表面，（真空环境除外）。 常见的界面有：气-液界面，气-固界面，液-液界面，液-固界面，固-固界面。表界面概念与表界面化学的内容1.气-液界面常见界面 常见界面2.气-固界面 3.液-液界面常见界面4.液-固界面常见界面 5.固-固界面常见界面 Chapter Introduction to Surface chemistrySmall puddles of water on a smooth clean surface have perceptible thickness Water adheres weakly to wax and strongly to it

8、self, so water clusters into drops. Surface tension gives them their near-spherical shape, because a sphere has the smallest possible surface area to volume ratio. Beading of rain water on the surface of a waxy surface, such as an automobile.Water beading on a leaf nap Surface tension is responsible

9、 for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer.In the absence of other forces, including gravity, drops of virtually all liquids would be perfectly spherical. The spherical shape mini

10、mizes the necessary wall tension of the surface layer according to Laplaces law.Water beading on a leaf nap Another way to view it is in terms of energy. A molecule in contact with a neighbor is in a lower state of energy than if it were alone (not in contact with a neighbor). The interior molecules

11、 have as many neighbors as they can possibly have, but the boundary molecules are missing neighbors and therefore have a higher energy.For the liquid to minimize its energy state, the number of higher energy boundary molecules must be minimized. The minimized quantity of boundary molecules results i

12、n a minimized surface area.Water dripping from a tap Formation of drops occurs when a mass of liquid is stretched. The animation shows water adhering to the faucet gaining mass until it is stretched to a point where the surface tension can no longer bind it to the faucet. It then separates and surfa

13、ce tension forms the drop into a sphere. If a stream of water were running from the faucet, the stream would break up into drops during its fall. Gravity stretches the stream, then surface tension pinches it into spheres.Water striders stay atop the liquid because of surface tension Flotation of obj

14、ects denser than water occurs when the object is non-wettable and its weight is small enough to be borne by the forces arising from surface tension. Water striders use surface tension to walk on the surface of a pond. The surface of the water behaves like an elastic film: the insects feet cause inde

15、ntations in the waters surface, increasing its surface area. Lava lamp with interaction between dissimilar liquids; water and liquid wax Separation of oil and water is caused by a tension in the surface between dissimilar liquids. This type of surface tension is called interface tension, but its phy

16、sics are the same.Mechanism of lava lamp?Photo showing the tears of wine phenomenon. Gibbs-Maranon effect 吉布斯-马兰戈尼效应，表面张力梯度驱动下的液体流动。 1、what makes the phenomenon happen?2、describe the whole process ?3、What are the factors which may affect this phenomenon？Photo of flowing water adhering to a hand. Sur

17、face tension creates the sheet of water between the flow and the hand.Gallery of surface tension effectA metal paper clip floats on water. Several can usually be carefully added without overflow of water. An aluminium coin floats on the surface of the water at 10 C. Any extra weight would drop the c

18、oin to the bottom.Gallery of surface tension effectThe entirety of the flower lies below the level of the free surface. The water rises smoothly around its edge. Wall tension prevents water filling the air between the petals and possibly submerging the flower. A soap bubble balances surface tension

19、forces against internal pneumatic pressure.Gallery of surface tension effect孙子兵法云：备周则孙子兵法云：备周则怠，常见则不疑。怠，常见则不疑。肥皂泡不破的奥秘何在？肥皂泡不破的奥秘何在？一 些 让 人 费 解 的 解 释肥皂泡不破的原因探究弯曲界面现象曲面附加压力弯曲界面为了缩小表面积，就有拉平趋势，即从凸方拉向凹方的作用，平衡时，单位面积上所受内外两向压力之差称为曲面附加压力。 P曲 = P内 P外杨拉普拉斯方程P大气 + P 曲 = P内Surface chemistry in environmental sci

20、enceSurface chemistry in life science表面现象的原因 The cohesive forces among the liquid molecules are responsible for this phenomenon of surface tension. In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, resulting in a net force of zero. The mol

21、ecules at the surface do not have other molecules on all sides of them and therefore are pulled inwards. This creates some internal pressure and forces liquid surfaces to contract to the minimal area.物体内部分子所受周围分子的引力平均来说在各方面相等，相互抵消。物体表面层的分子则不然，由于内外两相分子的种类和浓度不同，所受内部分子的引力常比所受外界分子的引力强些，表面分子就有向内钻的趋势，形成表面

22、分子的特性。通常物体的比表面积不大，表面分子数的比值就不大，表面特征就不明显，可以忽略。但对于高分散度或者多孔固体，表面特征就非常重要了。表界面化学的概念 表界面化学是研究与化学有关的表界面现象的科学，是研究表面化学热力学、化学动力学和表面结构化学，包括表面富集、吸附、粘附、多相反应及催化、表面活性剂作用、颗粒或微粒特征及胶体化学等。 表界面化学研究液液、液气、固固、固气、固液界面的物理化学问题，其基本内容是研究表面能，主要表现为润湿、吸附、粘附、表面活性剂作用、多相催化、烧结作用及分散体系性能等。与表界面化学相关的过程 examples of process rely heavily on

23、the application of surface phenomena Adhesion （粘附）； ore flotation（矿物浮选）； wetting （润湿） ；detergency（洗涤过程）； Electrophoretic deposition（电泳沉积） ；chromatography（色层分析法）； emulsion polymerization（乳液聚合） Precipitation （沉淀）；food processing（食品加工） grinding（研磨） lubrication （润滑）； heterogeneous catalysis（多相催化）； road

24、surfacing （路面处理）；sewage disposal （污水处理）； soil conditioning（土壤改良） ion exchange（离子交换）；sugar refining（食糖精制）water clarification（水净化）；water repellency （疏水处理） oil-well drilling （油井钻探） ；water evaporation control（水蒸发控制）Grinding Firstly, let us take grinding for example. Energy is putting into the crushing a

25、nd grinding process, which breaks particles into smaller ones. The result is that the chemical bonding is broken and new surfaces are created. New surfaces lead to huge surface energy, which put the fines together to form fake particles. To talk about the energy, the data is as followed. As someone

26、calculated, when silicon of 1Kg whose grain size is 1cm is made into fines of 1nm grain size, the total surface and total surface energy will increase by 107times. Such amount of energy can increase the temperature of the 650Kg water by 4 centigrade. Small dimensional effectthe importance of the sur

27、face for small particlesconsider a spherical particle of some unspecified material in which the sphere has a convenient radius of , say, 1.0cm. Let us reapportion this fixed quantity of material by subdividing it repeatedly into arrays of spheres, each with a radius half that of the original sphere.

28、Calculation?Small dimensional effectincrease in surface area and energy with decrease in sizewe can learn two lessons of importance. The first one is that the properties of a material can be sensitive to the amount of samples under consideration. To see this point, assume that material from which th

29、ese spheres are made is water at density of, say, 1.0 g/cm3. Using this we can convert the particle volume in last Table into the number of water molecules per sphere after each cut as shown in this table corresponding to the cuts used before. It is evident that by the time we reach spheres of radiu

30、s 10-8cm(i.e. , typical atomic dimensions), we have begun chopping up water molecules. We reach one water molecule per sphere after 25.62 halving of all spheres, starting from one sphere of Rs=1cm. This corresponds to a radius of 0.193 nm for water molecules. Actually, the radius of water molecule e

31、stimated from the value of van der waals coefficient b is about 0.145nm.( more precise) the substantial discrepancy arises when a bulk property such as density is applied all the way down to molecular dimensions. A property such as density depends not only on the mass and volume of the molecule, but

32、 also on their packing in a bulk sample.The second one we learn from this exercise is concerned with the extent of increase in surface area and surface energy as we go to smaller and smaller particles. Let us first calculate the average number of water molecules that reside at the surface of spheres

33、 by assuming that the area occupied by each molecule at the surface is about 0.1nm2. Using this estimate and total area at various stage of subdivision, we obtain an estimate of number of molecule in the surface.Now let us consider the last column. In the column the total surface energy of the array of sphere water droplet is reported at each stage of the process. The surface tension of a substance is the ener