－ Traube rule (特劳贝规则) ：
（1） o ac
（2）
n 1 3.2 n
1.4.3 Adsorption
superheated liquid:
pex pl pin
p
pin pex pl Δp
3. Supersaturated solution (过饱和溶液)
• Under some circumstances it is possible to prepare a solution which behaves anomalously and contains more solute than a saturated solution. Such a solution is said to be supersaturated.
✓ When the force of Adhesion is greater than the cohesion, the liquid is said to wet the capillary wall, spreading over it, and rising in the tube.
2、Maximum bubble pressure method
Ⅰ：无机酸、碱、盐—— 溶液的表面张力升高 Ⅱ：醇、酮、醛、酸、酯 ——表面张力降低 Ⅲ：肥皂、洗涤剂类物质 ——显著降低水的表面张 力，达一定浓度后不再改 变
o ac
溶液表面张力与 溶质浓度的关系
1.4.2 Surface tension & concentration
• 有机物质水溶液的表面张力呈现一定的规 律性。属于同系的有机物 R(CH2)nX〔例如 脂肪醇 R(CH2)nOH〕，每增加一个-CH2 基 使其在稀溶液中降低同样表面张力所需浓
1.3 Measurement of surface tension
(表面张力的测量)
1、Capillary rise method
❖When a capillary tube is placed in a liquid, it rises up the tube a certain distance. By measuring this rise, it is possible to determine the surface tension of the liquid. It is not possible, to obtain interfacial tensions using the capillary rise method. ❖ Cohesive force is the force existing between like molecules in the surface of a liquid ❖Adhesive force is the force existing between unlike molecules, such as that between a liquid and the wall of a glass capillary tube
度约减小了 3 倍，即 (dγ/dc)c→o 值增加了 3 倍。这一近似规律常称为“特劳贝（Traube） 规则”。293K 时一些脂肪醇水溶液的表面 张力随浓度变化关系如图所示。
Surface tension of aqueous solutions of alcohols at 293K
γ与c关系的两个经验规则
1.4.1 Surface tension of solution
溶液至少由两种分子组成。由于溶质分子与 溶剂分子之间的作用力与纯液体不同，因此，溶 液的表面张力除与温度、压力、溶剂的性质有关 外，还与溶质的性质和浓度有关。实验表明，水 溶液表面张力随浓度变化规律大致有三种类型。
图中 γ0为纯水在测定温度下的表面张力。
(最大气泡压力法)
气泡形成过程示意图
装置图：1-减压装置；2-样品管； 3.毛细管；4-恒温加套；5-压力计； 6、7、8-活塞
测定原理
最大附加压力
ps,m
2
r
ghm
整理可得
1 2
r
g
hm
K hm
式中 K 1 r g 称为仪器常数
2
若以水为标准，则
K 水
h m
,水
待测液体的表面张力为
1.4 Surface tension of solution and adsorption (溶液的表面张力与表面吸附)
2. Superheated liquid (过热液体)
sure increases until the vapor pressure equals the pressure of the gas above it.
• A liquid boils at a temperature at which its vapor pressure is equal to the pressure of the gas above it.
RT ln cr 2 slM
c0
r
Supersaturated solution and ageing of crystal
• 在结晶过程中，如果溶液的过饱和程度太 大，会生成大量过于细小的晶体颗粒，给 过滤和洗涤带来困难，并影响产品质量。 在实际操作中，常常向饱和溶液中投入小 晶体作为新相的种子，防止溶液的过饱和 程度过高，并获得较大颗粒的晶体。
➢ Bubbles of vaporized liquid (i.e., gas) form within the bulk liquid and then rise to the surface where they burst and release the gas. (At the boiling temperature the vapor inside a bubble has enough pressure to keep the bubble from collapsing.)