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Chapter V Surface & Interface of solids

Chapter V Surface & Interface of solids. 5.1 Solid surface 5.2 Solid interface 5.3   Behavior of the interface 5.4 Clay － water system. 5.3   Behavior of the interface. 5.3.1 Curved surface effect 5.3.2 Adsorption and solid surface modification 5.3.3 Wetting and adhesion.

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Chapter V Surface & Interface of solids

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  1. Chapter V Surface & Interface of solids 5.1 Solid surface 5.2 Solid interface 5.3   Behavior of the interface 5.4 Clay－water system

  2. 5.3   Behavior of the interface 5.3.1 Curved surface effect 5.3.2 Adsorption and solid surface modification 5.3.3 Wetting and adhesion

  3. 5.3.1 Curved surface effect 1. additional pressure(△P) convex surface —— ris positive , △P is positive ； concave surface —— ris negative , △P is negative .

  4. aspheric surface： γ —— surface tension； rl, r2 ——two main radius of curvature. spherical surface： rl＝r2＝r ,

  5. 2 . Capillarity(毛细现象） 指液体能在毛细管中自动上升或下降的现象, 由弯曲液面附加压力产生, 此附加压力称为毛细管力（Capillary force）.

  6. （1）Wetting（润湿）：contact angleθ < 90o, concave surface , △P is negative , 液面沿管壁上升——capillary force； • （2）Nonwetting（不润湿）：contact angleθ > 90o, convex surface , △P is positive , 液面沿管壁下降.

  7. pressure difference of curved surface

  8. i.e. ρ —— density； h —— height of a liquid column； g ——gravitational field strength； R —— radius of curvature； r —— radius of capillary tube.

  9. 3. Saturated vapor pressureon the surface Saturated vapour pressure of particles is greater than plane saturated vapour pressure at the same temperature. Kelvinformula（开尔文公式）： P —— Saturated vapor pressure on the curve surface； P0 —— Saturated vapor pressureon the surface； r —— radius of spherical particle； r1, r2 —— two main radius of curvature； ρ —— density of particle； M —— molar mass； R —— gas constant. or：

  10. For liquid wetting capillary, Kelvinformula： r —— radius of capillary tube. if θ≈0:

  11. If r < 0：P < P0, then at a given temperature and the ambient steam pressure is P0, P0 is not up to saturated on plane liquid , while supersaturation to the liquid in capillmp, steam will be condensed into a liquid in a capillary——Capillary condensation.

  12. 4. Solubility and melting point of microcrystalline Kelvinformula ： γLS —— Solid-liquid interface tension； C ——Solubility of small crystal with r radius； C0 ——Solubility of large crystal ； d —— density.

  13. 4. melting point of microcrystalline γSV —— surface tension of solid； T——melting point of small crystal with r radius； T0 ——melting point of large crystal ； △H —— melting heat.

  14. 5. excess vacancy concentrationof curved surface C——vacancy concentration of holes； C0——vacancy concentration on the pore surface； γ —— surface tension； a0—— particle diameter； k —— Boltzmann constant； T —— absolute temperature.

  15. 5.3.2 Adsorption and modification of solid surface Adsorption is the adhesion of atoms or molecules (adsorbate)  of gas, liquid, or dissolved solids to a surface (adsorbent). 1. Adsorption essence Results of interaction between force field of solid surface and molecular. divided into： physical adsorption—— intermolecular attraction chemisorption—— chemical force

  16. Adsorption curve（a）and Adsorption characteristics（b） • physical adsorption：q is smaller, r0 is larger（Apoint）； • chemisorption：q is larger, r0 is smaller, （Cpoint）. q－吸附热；r0－平衡距离 B——化学吸附活化能

  17. Example：The adsorption ofO2on the W surface

  18. 2, Adsorption theory • 吸附过程中, 固, 液两相经过充分的接触后, 最终将达到吸附与脱附的动态平衡 将平衡吸附量qe与相应的平衡浓度ce作图得吸附等温线（adsorption isotherm）

  19. 朗格缪尔吸附 Langmuir isothermal qe-equilibriumadsorption quantity ce-liquid phase equilibrium concentration a-constant； b-constant.

  20. Brunaner-Emmert-Teller (B.E.T.) isothermal cs—the saturation concentration of adsorbate； B—constant

  21. 3. Influence of adsorptionon the solid surface The solid surface of silicate is always covered by adsorbed water film ： chemisorptionHydrogen bonding adsorption

  22. (1) Reduce surface energy wetting：An interface behavior of solid-liquid. Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together.

  23. (2) Reduce mechanical strength Ideally, Fracture formula σ ——surface energy a0 ——atomic distance E —— modulus of elasticity microcrack, actual strength C —— microcrack lengths then：adsorbed film formation→σ↓, R ↓

  24. (3) Change the metal work function（φ） Work function（φ）：minimum energy  needed to remove an electron from a solid to a point immediately outside the solid surface. Ionization energy : the energy needed to remove electrons from an atom. Electron affinity : the energy change when an electron is added to the neutral atom to form a negative ion

  25. Reactive metal： Non-metal atom :

  26. (4) Deterioration ofwetting and adhesion (5) Adjusting the friction and lubrication of solids Friction coefficient of graphite： in a vacuumf=0.80 no wetting effect； in airf=0.18 γ↓, surface adhesion reduced. So：Graphite can be used as solid lubricant

  27. 4. Surface modification of solid • Surface modification(表面改性)：利用固体表面吸附特性通过各种表面处理改变固体表面的结构和性质, 以适应各种预期的要求. • 实质：改变固体表面结构状态和官能团. • Methods：最常用的是采用各种有机表面活性剂. • Surfactant（表面活性剂）：能够显著降低体系的表面（或界面）张力的物质, 如润湿剂, 乳化剂, 分散剂, 塑化剂, 减水剂, 去污剂等.

  28. Molecular structure of surfactant • lyophilic radical——－OH, －COOH, －SO3H, －SO3Na, －NH； • lyophobic radical——alkanes, aromatic hydrocarbon. the longer hydrophobic groupand the higher molecular weight, the worse water-solubility. hydrophobicity order： aliphatic hydrocarbon（paraffin hydrocarbon＞olefin）＞branched chain aromatic hydrocarbon＞ aromatic hydrocarbon＞with weak hydrophilic group（ricinoleic acid（－OH）).

  29. Classification • Ionic（Anionic, Cationic, Zwitterionic） • Nonionic • Mechanism orientation arrange of hydrophobic groups and hydrophilic groups on the solid surface： • Polar group toward the polar solid surface, nonpolar group toward the medium • Nonpolar grouptoward the nonpolar solid surface, Polar group toward the medium.

  30. Samples* • Ceramic industry → Increase the liquidityand suspension stabilityof mud • Al2O3(high-temperature structural ceramics ) Al2O3powder（hydrophilic surface）＋paraffin（lipophilic）→mud surfactant： ：oleic acid Al2O3hydrophilicity → lipophilicity

  31. CaTiO3-High frequency ceramic capacitor CaTiO3powder（hydrophobic surface）＋water→ mud surfactant：sodium alkyl benzene sulfonate CaTiO3lipophilicity → hydrophilicity

  32. Cement indestry →Increase the suspension stabilityandworkability of mortar surfactant：water reducer ——anionic surfactant Mechanism of water reducer

  33. Grinding process→grinding aids, improving the cement grinding efficiency mechanism： • 吸附膜对微细裂纹的“劈裂作用” ； • 助磨剂分子吸附于颗粒表面形成一层均匀的吸附膜, 使裂纹内部表面能降低而不易愈合并对尖端又有其挤压作用； • 吸附膜的润滑作用； • 使颗粒均匀分分散于研磨体中, 阻止细粉聚集, 提高粉磨效率.

  34. 5.3.3    Wetting and adhesion • 1. wetting type • （1） wet粘湿 （2） permeate浸湿 （3）spread 铺展 • 2. Contact angle andYoungEquation • 3. Influence factors • （1）Interfacial tension • （2）roughnessof surface • （3）组合表面与chemical composition • 4. the method to find solid surface tension • 5. adhesion and chemical condition

  35. 1. Wetting type 润湿：一种流体从固体表面置换另一种流体, 使体系的Gibbs自由能降低的过程. 最常见的润湿现象是一种液体从固体表面置换空气, 如水在玻璃表面置换空气而展开. 1930年Osterhof和Bartell把润湿现象分成沾湿, 浸湿和铺展三种类型.

  36. （1）沾湿（附着润湿） 沾湿引起体系自由能变化为： 式中, γLV, γSV和γSL分别为单位面积固－液, 固－气和液－气的界面自由能. Essence：是液体在固体表面上的粘附. Adhesion work： 式中, Wa为将单位面积液－固界面拉开所作的功.

  37. Analysis： The smaller of γSL, the larger of Wa, 液体越易沾湿固体. 若Wa≥0, 则（ΔG）T, P≤0, 沾湿过程可自发进行. 固－液界面张力总是小于它们各自的表面张力之和, 表明固－液接触时, 其粘附功总大于零. 则对任何液体和固体, 其沾湿过程总可自发进行.

  38. L v S 沾湿过程

  39. （2）浸湿（浸渍润湿） changes of Gibbs free energy： immersion work： If Wi≥0, then ΔG≤0, process occur spontaneous. Attention：only when γSV>γSL, the process can occur spontaneously.

  40. V S L 浸湿过程

  41. （3）铺展（铺展润湿） 铺展：恒温恒压下, 液滴在固体表面上自动展开形成液膜的过程. changes of Gibbs free energy：

  42. If S≥0, then ΔG≤0, liquid can be automatically spreaded  on solid surfaces. spreading coefficients： Wc: cohesive work of liquid. Just Wa> Wc, liquid will be automatically spreaded  on solid surfaces.

  43. L V S The spreading of liquid on the solid surface

  44. 2. Contact Angle and YoungEquation liqudi（L）on a ideal surface（S）, and one phase is a gas. The contact angle is the angle at which a liquid/vapor interface meets a solid surface. YoungEquation（1805）：

  45. V γLV L θ γSV S γSL Contact Angle: a liquid interface meets the soiled surface

  46. 粘湿： 浸湿： 铺展： θ=0或不存在, S≥0 .

  47. θ＞90º θ＜90º θ＝0º nonwetting wetting completely wetting 浸湿过程润湿判断条件determining conditions

  48. S S V 沾湿 浸湿 L 铺展 固体进入液体的三个过程

  49. 3. influencing factors （1）interfacial tension： γSL γLV good wettability: θ↓, cosθ↑ 1） Solid-Liquid composition and structure is similar, γSL decreased

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