1064
MARIANNE K. BERNETTAND
w.A. ZISMAN
Surface Chemical Displacement of Organic Liquids from Solid Surfaces1
by Marianne K. Bernett and W. A. Zisman U.S. Naval Research Laboratory, Washington, D . C . 20390 (Received September 7 , 1965)
An investigation has been made of the various factors operative in the displacement by organic liquid compounds of a bulk layer of any nonaqueous liquid from a solid surface. Although solid surfaces used in the experiments were SAE 1020 steel and borosilicate glass, the results are readily extended to other solids. The nonaqueous pure liquids displaced were selected so as to cover a wide surface-tension range and included n-hexadecane, ardibromoethylbenzene, tricresyl phosphate, and propylene carbonate. A large number of well-defined displacing agents were investigated, of which the most efficient proved to be those for which an optimum balance could be achieved between low surface tension, high equilibrium spreading pressure, and good solubility with respect to the organic substrate to be removed. Agents which were particularly effective for long-lasting or permanent displacement were certain classes of highly fluorinated organic compounds and low-molecular weight dimethyl silicones. Low surface tension polar hydrocarbon derivatives, such as the 1-alkanols, were effective for temporary displacement. The several mechanisms operative in liquid-liquid displacement from solid surfaces have been investigated and are discussed. It is shown that these results and generalizations include earlier results on water-displacing agents as a special (and extreme) case.
Introduction Comparatively little has been published on the spreading of liquids over solid surfaces previously coated with a thin layer of a different liquid. Baker and Zisman2 studied many solid hydrophilic surfaces coated with a thin layer of water and found that certain types of pure organic liquids were able not only to spread rapidly on the water but also to displace it from the solid. I n each instance the organic liquid had a hydrophobic-hydrophilic (or amphipathic) molecular structure. The most effective compounds were somewhat soluble in water and had large initial spreading coefficients on water (or high equilibrium spreading pressures). When a drop of such an organic liquid was placed gently on the surface of the water-coated solid surface, it spread rapidly on the water surface, a hole formed in the water layer, and it grew in diameter while exposing a dry surface of area 2 . Ultimately 2 attained a maximum value ,,Z, which was a function of the mass and constitution of the drop of the waterdisplacing liquid. It was shown that some waterdisplacing liquids deposited a hydrophobic film on the exposed solid surface such that after the water layer The Journal of Physical ChemiStTy
had been displaced it would not respread. By the addition of a suitable solute, any water-displacing liquid could be made to behave in that way. Bakers-5 subsequently prepared emulsions of hydrocarbon solvents in water which were effective in displacing thin layers of oils from solid surfaces. By the successive applications of oil and water-displacing agents, Baker, Singleterry, and Z i ~ m a n ~ developed -~ the theory and practice for an economic and efficient proc(1) Presented before the Colloid and Surface Chemistry Division at the 150th National Meeting of the American Chemical Society in Atlantic City, N. J., Sept 16, 1965. (2) (a) H. R. Baker and W. A. Zisman, “Water Displacing Fluids and Their Application to Reconditioning and Protecting Equipment,” U. S. Naval Research Laboratory Report C-3364, Oct 4, 1948, Washington, D. C.; (b) H. R. Baker and W. A. Zisman, U. S. Patent 2,647,839 (1953). (3) H. R. Baker and P. B. Leach, “Salvage of Flooded Electrical Equipment,” U. S.Naval Research Laboratory Report 5316, June 16, 1959, Washington, D. C. (4) H. R. Baker, U. S.Patent 3,078,189 (1963). (5) H. R. Baker, U. S.Patent 3,167,514 (1965). (6) H. R. Baker, P. B. Leach, C . R. Singleterry, and W. A. Zisman, “Surface Chemical Methods of Displacing Water and/or Oils and Salvaging Flooded Equipment,” Part I, U. S. Naval Research Laboratory Report 5606, Feb 23, 1961, Washington, D. C.
SURFACE CHEMICAL DISPLACEMENT OF ORGANIC LIQUIDSFROM SOLIDSURFACES
1065
ess for salvaging equipment previously damaged by after to liquid b as the oil-displacing “agent” and to water and/or smoke. liquid a as the displaced “oil.” I n the past decade investigations of surface activity Experimental Conditions, Materials, and Techniques in nonaqueous liquid systems and of the surface chemistry of fluorocarbon derivatives have established I n the experiments described here, the approach was that (a) surfaces of close-packed adsorbed perfluoroessentially the same as that used to observe the watermethyl groups have the lowest surface energies known displacing properties of organic comp0unds.2-~ We a t ordinary ternperatures1°-15 and (b) suitably constifirst investigated the ability of many pure compounds tuted fluorocarbon derivatives are the most effective to displace each of a selected group of pure organic compounds for depressing the surface tensions of any liquids from clean, smooth, horizontal plates of steel nonfluorocarbon liquids a t such temperatures.16-23 and glass; however, as we will show later, the results This report will present our recent work using the can be extended readily to other solids. I n order to above-mentiont:d concepts to demonstrate the existensure solid surfaces free from chemisorbed organic ence of agents capable of displacing a great variety matter, panels of SAE 1020 cold-rolled steel 15.0 cm of organic liquids from solid surfaces. long and 7.5 cm wide were polished with No. 4/0 For the effective displacement of water from solid sandpaper and then rinsed repeatedly with ACS grade surfaces, Baker, Singleterry, and Z i ~ m a n ~found ~~~~**~ that the essential properties were some solubility of the (7) H. R. Baker, P. B. Leach, and C. R. Singleterry, “Surface agent in water and a large value of either the Harkins Chemical Methods of Displacing Water and/or Oils and Salvaging Flooded Equipment,” Part 11, U. S. Naval Research Laboratory initial spreading coefficient, S b j a 2 4 ’ 2 5 Report 5680, Sept 19, 1961, Washington, D. C. kqbia
=
Ya
-
(Yb
+
Yb’a’)
(1)
or the equilibrium spreading pressure, F b l a , 2 6 where F b / a = ?’a
-
Tat
(2)
Here, ya and Yb are the surface tensions of the liquid a to be displaced and the displacing liquid b, respectively, and Yb’a’ is the interfacial tension of b and a, the prime superscripts indicating that a is saturated with b and vice versa. Therefore, we sought at first to find a somewhat soluble pure liquid compound b which when placed on the surface of the organic liquid a to be displaced would exhibit the largest possible values of S b j s (or F b / s ) . Inspection of eq 1 reveals that if liquid b is to be effective in displacing liquid a it should have a surface tension (Yb) as much below Y~as possible. This is obvious when a and b are such that the interfacial tension (Ya’b’) is small when compared with either ya or Yb. Where a and b are somewhat soluble, Pound’s interfacial tension rule2’ 28 reveals that Ya’b’ will be small or negligible. Equation 2 shows that F b I a will be greater, the smaller the value of i.e., the greater the surface tension depressant ability of b when dissolved in a. Since certain types of fluorocarbon derivatives are now known to be the most, efficient surface tension depressant^,^^,^^,!^,^^ any liquid member of such a homologous family of compounds was assumed to be suitable as the displacing liquid b. However, the maximum spreading pressure of b on a and the optimum liquid-displacing effect would be determined by some upper and lower limits to the allowable solubility of b in a. For the sake of brevity, we will refer here-
(8) H. R. Baker, C. R. Singleterry, and W. A. Zisman, “Surface Chemical Displacement of Water and/or Oils from Solid Surfaces and Application t o Salvaging Equipment after Flood or Fire,” to be published. (9) H. R. Baker, C. R. Singleterry, and W. A. Zisman, “Factors Affecting Surface-Chemical Displacement of Bulk Water from Solid Surfaces,” presented to the Division of Colloid and Surface Chemistry, 150th National Meeting of the American Chemical Society, Atlantic City, N. J., Sept 16, 1965. (10) H. W.Fox, E. F. Hare, and W.A. Zisman, J . Colloid Sci., 8, 194 (1953). (11) F. Schulman and W. ,4. Zisman, J . Am. Chem. Soc., 74, 2123 (1952). (12) E. F. Hare and W. A. Zisman, J . Phys. Chem., 59, 335 (1955). (13) H. W. Fox, E. F. Hare, and W. A. Zisman, abid., 59, 1097 (1955). (14) E. G. Shafrin and W. A. Zisman, ibid., 64, 519 (1960). (15) W. A. Zisman, Advances in Chemistry Series, No. 43, American Chemical Society, Washington, D. C., 1964, p 1. (16) H. M. Scholberg, R. A. Guenthner, and R. I. Coon, J . Phys.
Chem., 57, 923 (1953). (17) G. B. Blake, A. H. Albrecht, and H. G. Bryce, American Chemical Society Division of Petroleum Chemistry, General Papers, NO. 32, 1954, pp 131-142. (18) A. H. Ellison and W. A . Zisman, J . Phys. Chem., 63, 1121 (1959). (19) N.L. Jarvis and W.A. Zisman, ibid., 64, 150 (1960). (20) N. L. Jarvis and W. A. Zisman, ibid., 64, 157 (1960). (21) M. K. Bernett, N. L. Jarvis, and W. A. Zisman, ibid., 66, 328 (1962). (22) M.K. Bernett and W. A. Zisman, ibid., 65, 448 (1961). (23) N. L. Jarvis and W. A. Zisman, “Encyclopedia of Technology,”
Kirk-Othmer, Interscience Division, John Wiley and Sons, New York, N. Y., in press. (24) W. D. Harkins and A. Feldman, J . Am. Chem. Soc., 44, 2665 (1922). (25) W. D. Harkins, Chem. Rev., 29, 385 (1941). (26) A. Cary and E. K. Rideal, Proc. Roy. SOC.(London), A109, 328 (1928). (27) J. R. Pound, J . Phys. Chem., 30, 791 (1926). (28) D. J. Donahue and F. E. Bartell, ibid., 56, 480 (1952).
V o l u m e 70, N u m b e r 4
April 1966
MARIANNE K. BERNETT AND W. A. ZISMAN
1066
~~~
Table I: Behavior of Oil-Displacing Agents on Steel Substrates a t 25' Agent Y,
Compound
Perfluorooctyl ethanesulfonate Hexyl perfluorobutyrate Bis(perfluoroocty1)-0-n-dodecenyl succinate Bis(perfluoroocty1) 3-methylglutarate Bis(perfluorohexy1) 3-methylglutarate 1,2,3-Trimethylolpropanetris(perfluor0butyrate) Bis(w-hydrogen perfluoroheptyl) 3methylglutarate Bis(w-hydrogen perfluoroheptyl) phenylsuccinate Bis(w-hydrogen perfluoroheptyl) phenylglutarate w-Hydrogen perfluoroheptyl hydrogen3-methylglutarate
dynes/ cm
d,
BP,
g/ml
"C (mm)
19.1 19.2 19.4
Fluorinated Esters 1.709 100 ( 2 . 8 ) 1.231 74 (20) 1.484 185 ( 0 . 3 )
Good Excellent
19.5 19.7 21.4
1.689 1.539 1.614
145 ( 0 . 5 ) 115 ( 0 . 5 ) 120 ( 0 . 2 )
Good Good Fair
25.6
1.648
147 (0.5)
25.9
1.640
26.2 26.4
Good Excellent Good
Good Good Fair
Good Good Good
Good Good Good
Poor
Poor
Good
Good
165 (0.25)
Inactive
Poor
Fair
Fair
1.654
180 ( 0 . 5 )
Inactive
Poor
Fair
Fair
1.557
143 (0.5)
Inactive
Poor
Fair
Fair
Fair
Good
Good
Good
Good Good
Good Fair
Good Fair
+
a
dec.
y
Viscous
...
18.4 20.8
Silicones 1.525 108(0.3) 1.474 125 ( 0 . 3 )
Good Good
15.9 17.4 18.0 18.7 19.2 25.7
0.761 0.818 0.853 0.873 0,900 1.24
Fair" Fair" Fair* Fair" Good Inactive
15.1 16.3 17.8 18.5 20.2
Fluorocarbons 1.915 134 1.992 115(98) ... 143(95) 1.996 127 (10) 1.996
'
100 152 192 230 70-100 ( 0 . 5 )
...
I
.
.
Excellent Excellent
Fair Fair Fair Poor Poor
.
benzene. The borosilicate (Pyrex) plates of the same dimensions were soaked for 1 hr in a hot sulfuric acidnitric acid (ratio 1:2) bath and then were rinsed repeatedly with distilled water. All specimens were dried in a clean oven at 100" for several hours. Each test plate was mounted on a leveling table with the plane face horizontal and then covered to a depth of 0.2 mm f 1.0% with the oil or organic liquid to be displaced. Unless stated otherwise, a 0.01-ml f 1.0% drop of the oil-displacing agent was delivered gently to the wet surface from a freshly flamed platinum wire tip, and the speed, extent, and mode of spreading and oil displacement were observed where necessary through
I
.
...
... ... ...
...
...
...
... ...
Good Poor
Poor
...
Poor
...
Fair Fair
... ...
...
Fair
y 38.2 dynes/cm, d 1.738 g/ml, and bp -260'. 27.0 dynes/cm, d 0.775 g/ml, and bp 287'. e Area recovered after 15 min. y 41.4 dynes/cm, d 1.198 g/ml, and bg -240'.
The Journal of Physical Chemistry
Propylene carbonated
Good Excellent Good
.'. 1.5 C?F,~CONH(CH,)~N(CH~)~(CH~)ZCOOBis(t-butoxy )bis(perfluorooctoxy )silane Bis( t-butoxy )-bis( w-hydrogen perfluoroheptoxy )silane Silicone DC 200, 0.65 poise Silicone DC 200, 1.0 poise Silicone DC 200, 1.5 poises Silicone DC 200, 2.0 poises Silicone DC 200, 3.0 poises Fluorosilicone QF 1-0065
Behavior on displacement of oil arDibromoethylTricresyl HexadecaneO benzeneb phosphateC
Fair y
Fair Fair Fair Fair Fair Poor Fair Good Good ... Inactive
40.4 dynes/cm and bp -410'
a low-power lens. During these observations each panel was completely enclosed and observed through a glass cover plate to avoid disturbances by dust or air currents. This precaution was helpful also in observing the behavior of the more volatile oil-displacing agents. Unless indicated otherwise, all experiments were conducted at 25" and 50% relative humidity. Organic liquids displaced from the panels are listed in the first row of Table I, and the pure liquid compounds used to displace them are given in the first column. The former liquids were selected to cover a wide range in surface tensions at 25" and a promising variety of chemical compositions. Each organic liquid
SURFACE CHEMICAL
~~~~
DISPLACEMENT OF ORGANIC
1067
LIQUIDS FROM S O L I D S U R F A C E S
~
Table 11: Behavior of Aliphatic 1-Alkanols as Oil-Displacing Agents at 25’ Agent
Hexadecane@--
Compound
Ethanol
dynes/ cm
d, dml
22.3
0.785
Butanol-1
23.9
0.810
Pent anol- 1
24.9
0.814
Hexanol-1
24.9
0.819
Heptanol-1
26.2
0,822
Octanol-1
26.9
0,825
Nonanol-1
27.4
0.827
Decanol-1
27.4
0.833
Undecanol-1
28.1
0.833
Dodecanol-1
28.7
0.831
a
-Propylene
Emaxjmole,
Ybi
ys 27.0 dynes/cm and d 0.775 g/ml.
Substrate
Steel Pyrex Steel Pyrex Steel Pyrex Steel Pyrex Steel (4/Od) Steel (400Ad) Nickel (4/Od) Nickel ( C Y A1203d) Soda-lime glass Pyrex Steel Pyrex Steel Pyrex Steel Pyrex Steel Pyrex Steel Pyrex
*
cm* X 10 - 4
1.5 1.5 2.8 0.9 2.7 4.9 1.0 7.3 1.1 0.7 1.3 6.2 6.5
carbonateb----
Emaximoler
Area condition
tmsx,
min
ImmC Imm Imm Imm 1 1 Imm 1 1 1 1 5
...
...
... ... Dry Center drop
... Dry Moist
tmax,
10 - 4
min
4.2 3.7 6.5 2.8 4.5 11.6 1.5 5.2 2.8
ImmC Imm Imm 1 1 1 2 1 3
...
...
...
...
... Dry
... ... , . .
... ... . . ... ... ...
...
41.1 dynes/cm and d 1.198 g/ml.
Immediate.
Area condition
...
... Moist Dry Moist center Moist center Center drop Center drop Center drop
... ...
...
5
7.6 5 Inactive Inactive Inactive Inactive Inactive Inactive Inactive Inactive Inactive Inactive
cm2 X
...
... 2.8 0.8 0.8 1.4 0.2 2.3 0.4 1.7 1.7 1.8 1.8
1 5 1 10 1 15 5 30 5 60 5
Center drop Large drop Large drop Large drop All drop Large drop All drop Large drop Large drop Large drop Large drop
Surface finish.
or oil-displacing agent, however previously prepared and purified, was finally purified by being percolated slowly at room temperature through an adsorbent column of activated alumina and Florisil just prior to each experiment in order to remove any traces of polar adsorbable impurities. Surface tensions were measured by the ring method with a du Nouy tensiometer (6-cm circumference platinum ring), using the corrections of Harkins and Jordanz9 for conventional liquids and the corrections of Fox and Chrisman30 for liquids of high density and low surface tension, The solubility of an oil-displacing agent in an oil was obtained by measuring the surface tension of a progressively more concentrated solution and by finding that point in the surface tension us. concentration curve at which an additional quantity of solute did not further depress the surface tension. The equilibrium spreading pressure (Fbia) was calculated from eq 2.
panels revealed distinctive patterns of oil-displacemen t behavior which were dependent upon several parameters. Baker, Singleterry, and Z i ~ m a n ~had - ~ observed that maximum water displacement was a function of the solubility of the agent in water, the initial spreading coefficient (or else the equilibrium spreading pressure) on water, and the speed of spreading. The present investigation showed that displacement of the oil by the agent was determined by its solubility in the oil, the difference ( Y ~- -yb) in the surface tension of the agent and the oil, and the volatility of the agent. Table I lists the fluorinated esters, silicon-containing compounds, and halogenated hydrocarbons examined as oildisplacing agents, along with selected physical constants and a qualitative statement of the oil-displacement characteristics observed. Table I reveals that the most efficient oil-displacing liquids had an appreciably smaller surface tension ( ~ b )than that of the
General Conditions for “Oil” Displacement from Metal Substrates Observations made of the various materials on steel
(29) W. D. Harkins and H. F. Jordan, J . Am. Chem. Soc., 52, 1751 (1930). (30) H. W. Fox and C. H. Chrisman, Jr., J . P h y s . Chem., 56, 284
~~
(1952).
Volume 70,Number .I April 1966
MARIANNE K. BERNETT AND W. A. ZISMAN
1068
Table 111: Behavior of Fluorinated 1-Alkanols as Oil-Displacing Agents a t 25’ -Agent
Compound
dynes/ cm
Sub-
d, dml
strate
19.5
1.374
Perfiuorobutanol-1
17.2
1.600
Perfluorohexanol-1
17.4
1.686
Perfluorooctanol-1
17.0
1.734
a
Ya
26.0
1.485
23.5
1.665
22.7
1.753
27.0 dynes/cm and d 0.775 g/ml.
Steel Pyrex Steel Pyrex Steel Pyrex Steel Pyrex Steel Pyrex Steel Pyrex Steel Pyrex
carbonate*---
cm* X 10-4
tmsx,
Area condition
cm2 X 10 - 4
tmax,
min
0.6 0.6 2.1 1.5 1.4 6.7
1 1 1 1 5 1 30 1 5 5 5 5 5 5
Small drop Small drop Small drop Small diop Large drop Small drop Large drop Large drop Large drop Large drop Large drop Large drop Large drop Large drop
9.1 3.4 29.5 19.6 83.8 17.0 152.0 21.9 11.2 6.7 30.6 26.2 107.0 107.9
ImmC Imm 1 Imm 2 1 5 1 20 Imm 30 5 60 60
5.3 10.4 0.2 0.2 0.3 1.1 1.0 1.0
41.1 dynes/cm and d 1.198 g/ml.
oil displaced (ra); however, solubility in the oil as well as other physical properties were also involved. Furthermore, it was observed that oil displacement proceeded at various speeds, and the resulting cleared area could be (a) perfectly dry and clean, (b) covered with a thin layer of oil, or (c) showing a combination of both properties in various proportions.
Oil Displacement by Agents Having Polar Functional Groups E$ect of Homology and Molecular Weight of Displacing Agent. In Tables I1 and I11 are given the observations made on the homologous series of liquid 1alkanols, perfluoro-1-alkanols, and w-monohydrogen perfluoroalkanols when a drop of each is placed on a 0.2mm layer of hexadecane or propylene carbonate covering a steel or Pyrex panel. In these experiments certain spreading properties were measured with a precision of &2%. These are Lax, the maximum value of the approximately circular area of oil displaced by 0.01 ml of displacing agent, and t,,,, the time required to attain .,,Z, For more meaningful comparison of the was calculated in terms of area various agents, ,,Z, displaced by 1 mole of the agent; this value was designated as Llmaximole and is used in the tables and figures. In addition, a brief remark was added to describe the ultimate condition of the cleared solid surface. When the molecular weights ( M ) in the homologous series of perfluoro alcohols were plotted against Zmax/mole (as represented in Figure 1 for propylene carbonate), it was found that Llmaxjmole increased with M , the slope becoming steeper with higher values of M . The The Journal of Physical Chemiatry
-Propylene &“/mole,
&n”/rnolel
Perfluoroet hanol
a-Hydrogen perfluoropropanol-1 a-Hydrogen perfluoropentanol-1 w-Hydrogen perfluoroheptanol-1
Hexadecanea-
r
Ybv
min
Area condition
Dry D rY Droplets Dry Droplets Center drop Droplets Center drop Droplets rY Droplets Dry Dry Dry
Immediate,
family of o-hydrogen perfluoroalkanols behaves similarly at high values of M , but the lower members were not as efficient as the lower perfluoroalkanols in displacing the propylene carbonate. In contrast to the fluorinated alcohols, the lower 1-alkanols were less effective in displacing propylene carbonate, and when M exceeded 100, became essentially ineffective. Whereas the surface tensions of the perfluoroalkanols decrease with increased molecular weight, the opposite occurs in the family of 1-alkanols (see Figure 2). Hence, Z:max/mole can be directly related to ya - Yb, the difference in surface tension of the oil and the displacing agent. The interfacial tension Yb’a’ is smaller than the surface tension (ra)of the organic liquid; it decreases as the solubility of the agent increases, and it approaches zero at infinite solubility. Thus, the value of Yb’a’ can be neglected in eq 1, so that (ya - 71,)becomes and also equal to the initial spreading coefficient a&/, approximates the spreading pressure F b / a . Plots of LlmaxJmole against (Ya - Yb) are given in Figure 3 for each of the three homologous series of alcohols when placed on specimens coated with propylene carbonate or with n-hexadecane. For comparison purposes, results obtained on specimens coated with water are also included. Displacement of propylene carbonate or of hexadecane by the same agent made it evident that greater oil-displacing ability was observed the higher the surface tension of the oil. I t was also evident that the fluoro alcohols were more effective in displacing liquids than were the 1-alkanols. Another measure of the efficiency of the oil-displacing agent is t,, which is plotted in Figure 4 against
SURFACE CHEMICAL DISPLACEMENT OF ORGANICLIQUIDS FROM SOLIDSURFACES
160,
1069
160
1
e -
'I 120
P AO-HICH&CH2 HlCF2)NCH20H OH CARBONATE
0- FICF2)NCHZOH
7 o - n (DYNE5KMI
Figure 3. Effect of surface tension difference of liquid and agent on maximum area displaced of liquid (substrate steel).
Figure 1. Effect of molecular weight of oil-displacing agent on maximum area displaced of propylene carbonate (substrate steel).
-
28
-
26
-
-
5 24 -
I
z w
-
d
n
22-
x
I40 180 BOILING POINT ( " C )
20 -
18
16
0
I
2 4 6 8 1 0 1 2 1 4 NUMBER OF CARBON ATOMS IN ALCOHOL MOLECULE
Figure 2. Surface tensions of 1-alkanols a t 25".
the boiling point of the agent. As in any homologous series, an increase in the molecular weight raises the boiling point and lowers the vapor pressure. The inof Figure 4 may be regarded as the result crease in t, of the decrease in the vapor pressure of the agent or a lower rate of agent diffusion in the oil. Eflect of Solubility of Displacing Agent in Oil. The effectiveness of water-displacing agents was found by Baker, Singleterry, and Z i ~ m a n ~to- ~be roughly proportional to the solubility in water. This is reasonable because in each homologous series of such agents, higher water solubilities correspond to lower molecular weights, higher volatilities, higher rates of spreading, and higher equilibrium spreading pressures. In order to observe the effect of agent solubility in oil-displacing mechanisms, we examined several agents having large
220 ~~.
-
3
3
Figure 4. Effect of boiling point on time necessary to reach maximum area when 1-alkanols are spread on propylene carbonate (substrate steel).
differences in solubility in oils of nearly equal surface tensions. ar-Dibromoethylbenzene (Alkazene 42) and propylene carbonate, which have surface tensions a t 25" of 38.2 and 41.1 dynes/cm, respectively, are two such oils. Here, the value of ya - Y b of the oil-displacing agent with respect to each oil is nearly the same and, therefore, of negligible influence. Any difference in oil-displacing properties must then necessarily be due to solubility properties only. Table IV summarizes the results obtained with these oils. For purposes of comparison, the results observed on displacing hexadecane (ra = 27.0 dynes/cm) are also given in Table IV. Where the solubility of the agent (for example, that of any fluorinated alcohol) is greater in propylene carbonate than in ar-dibromoethylbensene, the value of &,,ax/mo~e is always greater; where the agent solubility is in reverse order (1-decanol or the methyl silicones are examples), 2max/mole is always Volume YO, Number
4 April
1966
1070
MARIANNE K. BERNETT AND W. A. ZISMAN
Table IV : Effect of Solubility, Spreading Pressure, and Surface Tension Difference on Behavior of Oil-Displacing Agents
Agent
Perfluorobutanol-1
Perfluorooctanol-1
Oil"
P B H P B
o-Hydrogen perfluoroheptanol Butanol-1
H P B
H P B H
Decanol-1
P B
Dimethyl silicone ( D C 200, 0.65 poise) Dimethyl silicone ( D C 200, 3.0 poises)
a
dry.
P = propylene carbonate; B
H P H P
Solubility, moles/l.
ya
- yb,
dynes/cm
~m,lmols#
Fbts
dyneidom
om' X 10 -4
tmsm
min
>2 Insol 1 Insol
