8.2 Surface phenomena of liquid. Out-class reading: Levine p Curved interfaces

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1 Out-class reading: Levine p Curved interfaces

2 8.2.1 Some interesting phenomena Evolution of bubbles on porous surface.

3 8.2.1 Some interesting phenomena Addition of a seed in Supersaturated solution.

4 8.2.1 Some interesting phenomena Provided by Prof. Yu-Peng GUO of Jilin University Instantaneous freezing of supercooled water.

5 8.2.2 Curved surface and additional pressure 1. Curved liquid surface Drop/droplet Convex surface Bubble Concave surface In graduated cylinder

6 8.2.2 Curved surface and additional pressure Convex surface Concave surface p ex p p p in ex p p p in ex p additional pressure For convex surface: p>0 For concave surface: p < 0

7 8.2.2 Curved surface and additional pressure To increase the volume (dv) of liquid at p ex = p + dp p in p p Δp in ex p ex ( p dp) dv da pdv da da p V dv 8 rdr 2 p 2 4 r dr r 4 r A 4r 2 p r Laplace equation

2 p r For convex surface, r > 0, p > 0, point to liquid; For concave

8 8.2.2 Curved surface and additional pressure For curved surface: 1 1 p r1 r2 Laplace-Young equation r is the radius of curvature. 2 p r For convex surface, r > 0, p > 0, point to liquid; For concave surface, r<0, p < 0, point to gaseous phase; For plane surface, r, p 0, p ex = p in, For bubble

9 8.2.3 Vapor pressure under curved surface Δ r Vmdp VmΔp For liquid with plane surface: RT ln p For liquid in droplet: * r RT ln p r The droplets gradually disappear and the water level in the beaker increases. For droplet or bubble pr M 2 Δ RT ln V Δ * m p p r Kelvin equation ln p p r * 2M RT r

10 8.2.3 Vapor pressure under curved surface ln p p r * 2M RT r r / m p r / p * P r / P * x x x x x x10-8 The change in vapor pressure is not large enough to be of any concern in the case of macroscopic systems, such as d > 10-7 m, or 0.1 m. r / m

11 8.2.3 Vapor pressure under curved surface

12 (1) supersaturated vapor / supercooling Vapor pressure under curved surface If a vapor is cooled or compressed to a pressure equal to the vapor pressure of the bulk liquid, condensation should occur. The difficulty is that the first few molecules condensing can only form a minute drop and the vapor pressure of such a drop will be much higher than the regular vapor pressure. p r = 2.95p * p = p *

13 8.2.3 Vapor pressure under curved surface Artificial rainfall 1) Depress temperature using dry ice ln p vap RT Hm k 2) Increase the initial radius of the embryo: dust, AgCl particles

14 8.2.3 Vapor pressure under curved surface Droplet can not form from the pure saturated vapor spontaneously. Therefore, in clean systems, large degrees of supersaturation or super-cooling are possible. fluctuation

15 8.2.3 Vapor pressure under curved surface 2) superheated liquid: p ex Δ p p p p in ex l p l r 0,Δp p in p When temperature is over boiling point, liquid does not boil. 1 1 R 2 ln 1 T T0 vap H m rp0 For water with air bubble with diameter of 10-6 meter as seed, it boils at 123 o C.

16 8.2.3 Vapor pressure under curved surface 2) Supersaturation Evolution of bubbles on porous surface.

17 8.2.3 Vapor pressure under curved surface Once the bubble of relative large diameter formed, the evaporation would proceed in an explosion manner.

18 8.2.3 Vapor pressure under curved surface 3) condensation in capillary: ln When liquid forms concave surface in capillary, r < 0 p p r * 2M RT r p r < p *, it is easy for vapor to condense in capillary. Constant-temperature evaporation

19 8.2.3 Vapor pressure under curved surface 沐雾甲虫 (Onymacris unguicularis), Water uptake from saturated or subsaturated air, demonstrated for a few arthropod species

8.2.3 Vapor pressure under curved surface 3) supersaturated solution and ageing of crystal ln S r S 2M RTr Decrease in diameter of solid will increase surface area and thus specific surface energy of

20 8.2.3 Vapor pressure under curved surface 3) supersaturated solution and ageing of crystal ln S r S 2M RTr Decrease in diameter of solid will increase surface area and thus specific surface energy of the system and lower melting point, increase solubility of the solid. The melting point of ultrafine powder may be only 2/3 of its normal one. Thermal plating ageing of crystal

21 8.2.4 Capillarity Capillary rise / depression

22 8.2.4 Capillarity r cos R h 2 cos ( 1 2 ) gr p p l 2 r h( ) g 1 2 h 2 ( 1 2 ) gr Discussion

23 8.2.4 Capillarity 2 cos h ( 1 2 ) gr Measurement of porosity distribution: p Mercury method This relation can be used to determine the surface tension of liquids capillary rise method

24 8.2.5 Interaction between two phases--wetting and spreading Superhydrophobic, superhydrobicity

25 8.2.5 Interaction between two phases--wetting and spreading

26 Work of Adhesion Work of immersion Interaction between two phases--wetting and spreading (1) Adhesion (2) Immersion g S l g-l + g-s s-l G = s-l ( g-l + g-s ) = -W a W a > 0 g-s s-l G = s-l - g-s = -W i

27 8.2.5 Interaction between two phases--wetting and spreading (3) Spreading g-s s-l + l-g G = s-l + l-g - s-g = -S spreading coefficient

28 8.2.5 Interaction between two phases--wetting and spreading (4) Contact angle () cos g-s s-l g-l The contact angle () is the angle measured through the liquid, where a liquid/vapor interface meets a solid surface The direction of surface tension sg gl ls When : g-s - s-l = g-l, cos =1, = 0 o, Complete wettable. When : g-s - s-l < g-l, 0<cos <1, <90 o, wettable. Under equilibrium: g-l cos + s-l = g-s Young equation When : g-s < s-l, cos < 0, > 90 o, nonwettable.

29 8.2.5 Interaction between two phases--wetting and spreading (5) Lyophobic and lyophilic solids g-l g-s s-l The greater the specific energy, the easier the spreading of liquid over solid.

30 8.2.5 Interaction between two phases--wetting and spreading goniometer Hydrophobicity of conversion layer on Mg alloy

31 8.2.5 Interaction between two phases--wetting and spreading (5) Lyophobic and lyophilic solids Nonstick cooker g-s < 100 mn m -1, low-energy surface: organic solids, polymers. PTFE: g-s 18 mn m -1 g-s > 100 mn m -1, high-energy surface: Metals, oxides, chlorides, inorganic salts. g-s 500 ~ 5000 mn m -1

32 8.2.5 Interaction between two phases--wetting and spreading (5) Lyophobic and lyophilic solids How can we judge the cleanness of the glass surface?

33 8.2.5 Interaction between two phases--wetting and spreading (6) Spreading over liquid Liquids Iso-C 5 H 12 O C 6 H 6 C 6 H 12 CS 2 CH 2 I 2 S O/W S O/W = - G = W - O - W/O S O/W > 0, oil can spread over water S O/W < 0, oil floats in shape of lens.

34 8.2.5 Interaction between two phases--wetting and spreading (6) Spreading over liquid wreck of a tanker Spreading of oil over seawater

35 8.2.5 Interaction between two phases--wetting and spreading (6) Spreading over liquid 2010 年 5 月 5 日, 美国墨西哥湾原油泄漏事件

36 8.2.5 Interaction between two phases--wetting and spreading (6) Spreading over liquid Clapham Common (2000 m 2 ) 1774 Benjamin Franklin (2.4 nm) The film formed over water is of one molecule thick. (proved by Pockels and Rayleigh): Unimolecular film, monolayer, Insolvable film

8.2 Surface phenomenon of liquid. Out-class reading: Levine p Curved interfaces

8.2 Surface phenomenon of liquid. Out-class reading: Levine p Curved interfaces Out-class reading: Levine p. 387-390 13.2 Curved interfaces https://news.cnblogs.com/n/559867/ 8.2.1 Some interesting phenomena 8.2.1 Some interesting phenomena Provided by Prof. Yu-Peng GUO of Jilin