INDUSTRIAL AND ENGINEERING CHEMISTRY
902
-OH
or -COOH, are present. The energy in water, a polar liquid, is still higher. (3) Extremely small quantities of water in benzene increase the energy of immersion of these oxides to about three times the value for pure benzene, while a very small amount of butyric acid in the benzene may nearly double the value.
Vol. 22, No. 8
(4) The work of adhesion is equal to the sum of the free energies of the two surfaces (solid and liquid, for example) which disappear when the two surfaces meet minus the free energy of the interface which appears. Wa =
- AY =
yI
f
yi
-
ys,z
(Duprk’s equation)
A similar equation for the total surface energy of adhesion (ha) is ha = - A h
ha
+ hi - h,,i
( 5 ) The spreading coefficient S A I Efor the spreading of the liquid A over the solid or liquid B is equal to the work of adhesion between the two minus the work of cohesion of A . S A / E=
-W
~ = A YE
-
(YA
+
YA,B)
The spreading coefficient may be either the initial coefficient S, or the final coefficient S’. Spreading occurs if S or S’ is positive, and does not occur if S or S’ is negative. The
----_--_-----
_-__--_-
Figure 11-Orientation of Molecules of a n Alcohol or an Acid a t Interface with a Solid Oxide
(4) These facts indicate that if the oxide powder is immersed in butyric acid or alcohol, or in other similar organic liquids of the polar-non-polar type, the molecules of the liquid a t the interface orient themselves in such a way that the polar group is toward the surface of the solid and the nonpolar group toward the oil. (5) The evidence indicates that in benzene or any other hydrocarbon oil an immersed surface of a solid oxide becomes covered with an adsorbed monomolecular film of water, of butyric acid, or of any similar substance, whose molecules contain a polar group, if these are present in solution. The adsorption is much greater than that at the interface between oil and water. (6) Titanic oxide, stannic oxide, and zinc oxide act in an entirely similar way with respect to their surface energy relations. The only specific difference is that the chemical action of acids ‘is more marked with zinc oxide than with the others. (7) Soaps are highly adsorbed from solutions in hydrocarbon oils by any of these oxides. Collected Equations
The energy quantities listed in this summary relate to 1 sq. cm. of area: (1) The total energy, h, of a surface or interface is equal to its free energy, y, plus its latent heat, 1. h = y + l
(2) The energy of immersion of a powder is equal to the surface energy of the solid powder minus the interfacial energy of the liquid. This is true of either the free energy of immersion, fL,or of the total energy of immersion, h,.
f, =
y*
h, = ha
- YaJ - h,,i
(3) The energy of cohesion is equal to twice the free surface energy of the substance. wc = 27
----___-
--A/cohd--_-- - - - --- -_ - _Figure 12-Orientation Where a Column of Alcohol or Acid Is Broken Apart
initial coefficient is valid for the spreading of a pure liquid over the clean surface of a solid (or liquid). The final coefficient is valid for the spreading of a liquid over a solid (or liquid) already coated by a film of the liquid and in equilibrium with it. (6) The “final” energy of immersion of a powder f’ or h’ is the energy change when a solid, coated with a film in equilibrium with the saturated vapor of the liquid, is immersed in the liquid.
X’ = h,‘ f,’ =
- Yd’ - h,,i y l COS e Ys’
ha’
if e is the angle of contact between the liquid and the solid. The final free energy of immersion is often considered from the viewpoint of a force and the magnitude is called the “adhesion tension,” but it is more properly an “immersion tension,” since it refers directly neither to adhesion nor to spreading, though it is obvious that it is indirectly related to both.
Correction In the introductory paragraph of “High-Boiling Solvents from Natural-Gas Pentanes,” by Lee H. Clark, IND.ENG.CHEM., 22, 439 (1930), an obviously inaccurate statement appears to the effect that the operations of the Sharples Solvents Corporation represent “the first commercial venture in the use of petroleum hydrocarbons as the raw material for organic synthesis.” Mr. Clark is not responsible for this inadvertence. Operations such as those of the Carbide and Carbon Chemicals Corporation based on ethylene antedate the industrial utilization of the pentanes as developed by the Sharples Solvents Corporation. E. P. PARTRIDGE
