104 LETTERS TO THE EDITOR
a= cosh-1 [1 + (h-t-b b - - ) 1" [3B]
It may be shown (4) that
lim h), h~0y =1
so that in the limit  and  become identical. As illustrated in Fig. 1, the previously reported (1) experimental values
of the approach velocity which agree with  at low values of h (1) agree with  over the entire range, thus confirming Brenner's theory.
1. MACKAY, G. :D. M., riND MASON, S. G., J. Colloid Sci. 16, 632-635 (1961). 2. CHARLES, G. E., aND MASON, S. G., J. Colloid Sci. 15, 105 (1960). 3. BRENNEr, HOWAI~D, Chem. Eng. Sci. 16, 242 (1961). 4. MacKaY, G. D. M., Ph.D. Thesis, McGill University, 1962.
Pulp and Paper Research Institute of Canada, and Depart- G.D.M. MacKAY ment of Chemistry, McGill University, Montreal, Canada M. Suzvx~ October 3, 1962 S.G. Mason
MAKING AND TESTING REPRODUCIBLE W/O EMULSIONS
Lack of methods for producing reproducible emulsions has long slowed the development of the laws governing their behavior (1). Usually the average size of the droplets has not been controlled and the size distribution curve is wide. In speeiM cases, fairly good monodisperse O/W emulsion preparations have been made (2, 3), and recently tedious methods of manu- facture based on the accumulation of closely monodisperse aerosols into water solutions of emulsifying agents have been devised (4, 1). The present communication describes a simple method of manufacture of reproducible W/O emulsions and a shear method for rating stabilities.
The emulsions are prepared on a co-planar three-roll system called a Pope and Gray Litho-Break Tester (5). The top roll is a vibrating 1~ inch di- ameter roll to distribute and to keep distributed the oil phase which is ap- plied to the lower two rolls, one 3 inches and the other 4 inches in diameter. The two larger rolls are geared so that each has a peripheral speed of 32 em./sec. The oil phase is applied to the vibrating roll with an ink pipet. After distribution is achieved, a curved pan containing the water or solution of suffactant is slipped under the bottom roll so that the roll dips into the water.
LETTERS TO THE EDITOR 105
The water phase is carried on the oily film on the lowest roll to the lower nip between the two larger rolls, the excess water is rejected, and that carried through the nip implodes into the cavities formed during the film splitting at the exit side of the nip. The cavitation process has been studied by Myers, Miller, and Zettlemoyer (6). As the roll speed is increased, a narrower size distribution of the cavities develops (7). Above 32 cm./sec., a more closely monodisperse W/O emulsion should be formed; emulsion formation at increased speeds and actual distributions of droplet sizes need to be carefully investigated.
The emulsification machine is run for about 20 min. until a steady state is reached. Then, the emulsion is scraped off the central steel roll and ex- amined in two ways: for the watercontent by a vacuum desiccation at 50C. after reaction with 2,2-dimethoxypropane (8) and for stability by meas- uring the shear rate required for breakdown in a band viscometer (9). Break- down is indicated by beads of water ejected at the entrance nip and/or
TABLE I W/O Emulsions
Water Content and Breakdown Shear Range at 25C
Emulsion Breakdown Water content Oil phase plastic viscosity shear range (poises) (g. tt20/g, oil) (sec.-~)
A. Water Polybutene H-50 76
#0 Trans. Litho 13 Varnish 1
~4 R.eg. Litho 72 Varnish I
B. Rutile Pigment in Oil Phase Polybutene H-50; 30% TiO~ 125 #0 Trans. Litho; 67% TiO~ 133
#4 Reg. Litho; 10% TiO~ 143
0.11 630-811 0.12 753-849 0.11 610-750 0.10 367-399 0.11 291-382 0.40 390-410
0.18 375-439 0.13 98-139 0.14 87-103 0.37 290-339 0.35 230-293
C. Stabilizer Added Polybutane H-50; Gum Arabic Soln. ~ 97 0.17 #0 Trans. Litho; G.A. Soln. 2 27 0.09 #4 Reg. Litho; G.A. Soln. 2 96 0.36 Polybutene H-50; (30% TiO2) G.A. Soln.3 __ 0.20 #4 Reg. Litho (10%); G.A. Soln. 2 148 0.30 #4 Reg. Litho (0.35% A1 Stearate) - - 0.55
1216-1372 713-1244 877-1010 754-800 500-575 12,000
1 Heat bodied linseed oils. 2 Aqueous solution containing 0.22% gum arabic, 0.08M H3PO~, 0.003M Zn(NO3),,
and 0.0007M (NH4)~ Cr~O~.
106 LETTERS TO THE EDITOR
formed on the Mylar band as it passes from the viscometer. In all the meas- urements reported here, gap width in the viscometer was 7 mils and the selected Mylar film thickness was 1 mil; temperature was 25C. Advantages of the band viscometer are that it is simple to operate and perfect laminar shear is produced.
Tw o important findings have emerged from the scores of W/O emulsions prepared and studied in the manner described. In the first place, the water content is readily reproduced within 2 % or better. In the second place, the shear rate required for breakdown is closely reproduced. Because of the lack of a large supply of any given emulsion, a stability range only is es- tablished; that is, at the lower rate, breakdown did not occur, and at the higher rate, it did occur. Further measurements enable the range to be narrowed. Several studies have been made to show that the same break- down range is established either by repeat runs at higher shear rates or by a shear measurement on a fresh supply of emulsion at the breakdown shear rate.
Table I lists typical results obtained. The reproducibility as to water uptake and shear stability is evident.
Detailed studies of the effect of composition on water uptake and stability are proceeding in several directions. Methods are also being sought for the direct measurement of droplet size distributions. It seems likely that repro- ducible O/W emulsion could slso be produced on a roll system, but the band viscometer seems to hold little promise in the study of their stability.
Surface Chemistry Laboratory, A.C. ZETTLEMOYEI~ Lehigh University, JEAN S. BUCKINGHAM Bethlehem, Pennsylvania W.D. SCHAEFFER
Received November 16, 1962
1. WACHTEL, R. E., AND LAMER, V. K., J. Colloid Sci. 17,531 (1962). 2. WILLIAMS, R. C., ANn BACKVS, R. C., J. Appl. Phys. 20,224 (1949). 3. BowCoTT, J. E., AND SCHULMAN, J. H., Z. Elektrochem. 59,282 (1955). 4. NAWAB, M. A., ANn MASON, S. G., J. Colloid Sci. 13, 179 (1958). 5. Am. Ink Maker 37, 50 (March 1959). 6. MYERS, R. R., MILLER, J. C., AND ZETTLEMOYER, A. C., J . Colloid Sci. 14, 287
(1959). 7. MILLER, J. C., PH.D. Dissertation, p. 92. Lehigh University, Bethlehem, Pennsyl-
vania, 1956. 8. BOaCHERS, C. H., Private correspondence. 9. TAYLOR, J. H., ANn COZZENS, S. L., Am. Ink Maker 39, 62 (May 1961) ; WACHHOLTZ,
F. V., AND ASBECK, W. D., Kolloid-Z. 93,280 (1940).