Surface Tension

Surface tension is caused by the inward attraction of molecules at a boundary.

Surface tension is the energy required to stretch a unit change of surface area - and the surface tension will form a drop of liquid to a sphere since the sphere offers the smallest area for a definite volume.

Surface tension can be defined as

σ = F_s / l                                                  (1)

where

σ = surface tension (N/m)

F_s =  stretching force (N)

l = unit length (m)

Alternative Units

Alternatively, surface tension is typically measured in dynes/cm, which is

• the force in dynes required to break a film of length 1 cm

or as surface energy J/m² or alternatively ergs per square centimeter.

• 1 dynes/cm (dyn/cm) = 0.001 N/m = 0.0000685 lb_f/ft = 0.571×10^-5 lb_f/in = 0.0022 poundal/ft = 0.00018 poundal/in = 1.0 mN/m = 0.001 J/m² = 1.0 erg/cm² = 0.00010197 kg_f/m

Common Imperial units used are lb/ft and lb/in.

Surface Tension of Water

Surface tension of water at some temperatures:

Surface Tension Common Fluids

Surface tension of fluids at 25 ^oC (77 ^oF).

Common Fluids - Surface Tension

Fluid	Surface Tension (N/m)
Acetaldehyde	0.021
Acetic acid, Ethanoic acid	0.027
Acetic anhydride, Acetyl acetat	0.032
Acetone, 2-Propanone	0.024
Acetonitrile, Methyl cyanide	0.287
Allyl alcohol	0.025
Ammonia, R-717	0.021
Aniline, Benzenamine	0.042
Anisole, Methoxybenzene	0.035
Benzene, Annulene	0.028
Benzonitrile, Phenyl cyanide	0.039
Benzylamine	0.039
Bromine	0.041
Bromobenzene	0.035
Bromoethane	0.024
n-Butane	0.023
1-Butanol, Butyl alcohol	0.025
Butyl acetat	0.025
Butylamine	0.023
Diethyl ether	0.017
Carbon dioxide	0.00056
Carbon disulfide	0.032
Carbon tetrachloride	0.027
Clorobenzene, Phenyl chloride	0.033
Chlorodifluoromethane, HCFC-22	0.008
Chloroform	0.0271
1-Chlorohexane, Hexyl chloride	0.026
1-Chloropentane	0.024
p-Cresol	0.035
Cyclohexane	0.024
Cyclohexanol	0.033
Cyclohexene	0.026
Cyclopentane	0.022
Decane	0.024
Dibutylamine	0.024
Dichlorodifluoromethane, CFC-12	0.0086
Diethylene glycol	0.045
Diethyl ether, Ethyl ether	0.017
Diethyl sulfide, Ethyl sulfide	0.025
Ethane	0.00048
Ethanol, Ethyl Alcohol, Pure Alcohol, Grain Alcohol, Drinking Alcohol	0.022
Ethanolamine, glycinol	0.048
Ethyl acetate	0.024
Ethylamine, Ethanamine	0.019
Ethylbenzene, Phenylethane	0.029
Ethyl benzoate	0.035
Ethyl bromide	0.025
Ethyl mercaptan	0.024
Ethylene glycol	0.0477
Formamide	0.057
Formixc acis, Methanoic acid	0.037
Furfural	0.043
n-Heptane	0.020
Heptanoic acid, Enanthic acid	0.028
Hexadekane, Cetane	0.027
n-Hexane	0.018
Hexanenitrile, Capronitrile	0.027
1-Hexanol, Caproyl alcohol	0.026
1-Hexene	0.018
Hydrazine	0.066
Glycerol	0.064
Isobenzene, Phenyl iodide	0.039
Isobutane, 2-Methylpropane	0.010
Isobutyl acetat. 2-Methylpropyl acetat	0.023
Isobutyric acid	0.025
Isopropanol, 2-propanol, Isopropyl Alcohol, Rubbing Alcohol, Sec-propyl Alcohol, s-Propanol	0.022
Mercury, Quicksilver	0.485
Methanol, Methyl alcohol	0.022
Methyl acetat	0.025
Methyl formate	0.025
Nitrobenzene (50 oC)	0.041
Nitromethane, Nitrocarbol	0.036
Nonane	0.022
Octane	0.021
Pentane	0.015
Pentyl acetat	0.025
Propane, LPG	0.007
1-Propanol, Propyl alcohol	0.023
n-Propyl alcohol	0.024
n-Propyl benzene	0.030
Pyridine	0.037
Trichloromethane, Chloroform	0.023
Toluene, Methylbenzene	0.028
Trifluormethane, Fluoroform	0.00003
Undecane, Hendecane	0.025
Water at 20 oC	0.072
Water, soapy at 20 oC	0.0250 - 0.0450
Water-d2, Heavy Water	0.071
Xenon (10 oC)	0.00044
o-Xylene	0.029
m-Xylene	0.028
p-Xylene	0.028

Surface Active Agents

Soaps, detergents or surfactants - also called surface-active agents - added to to water even in small substances decreases the surface tension of water to a considerable extent. Due to decreased surface tension water with soap can remove oil or grease where clean water can not.