JOURNAL OF COLLOID SCIENCE 12, 5 2 3 - 5 2 5 (1957)

LETTER TO THE EDITOR

HENRYgS LAW CONSTANTS OF BUTADIENE IN AQUEOUS SOLUTIONS OF A CATIONIC SURFACTANT

The solubilization of organic vapors by aqueous solutions of surfactants has been studied by McBain and co-workers (1-3). Although results for a large number of cationic, anionic, and nonionic surfactants have been re- ported, no single agent has been investigated sufficiently to obtain the variation of the Henry's law constant for the solubility of the gas as a function of the concentration of the surfactant. We report herein the Henry's law constants for butadiene in water and in aqueous solutions of a cationic surfactant, Hyamine 1622, at 25.0°C.

The materials used were: Matheson Company's C.P. grade, 99.0 % pure, 1,3-butadiene, freed from traces of air by freezing and pumping at liquid nitrogen temperature; Hyamine 1622 (Rohm and Haas Co.), 98.8 % p-diiso- butylphenoxyethoxyethyldimethyl-benzylammonium chloride monohy- drate.

The apparatus used was essentially a volumetric adsorption system with a mercury manometer, which was read to the nearest 0.05 ram. by means of a cathetometer. The amount of gas solubilized was calculated from pressure measurements before and after admitting gas to the solution, the necessary corrections being made for the presence of water vapor and changes in total volume of the system. The temperature of the solution was kept constant by circulating water from a thermostat at 25°C. through the jacketed sample holder. The solution was stirred with a magnetic stirrer, to reach equilibrium sooner.

The isotherms for pure water and for three concentrations of Hyamine 1622 are given in Fig. 1. In each solution the solubility of butadiene in- creased linearly with the equilibrium pressure. Henry's law constants from these data are as follows: Concentration ofsurfactant (wt. %): 0.00 1.00 2.00 4.00 k X 10 -6 in mm./mole gas/mole soln.: 2.96 2.04 1.62 1.24

The Henry's law constant of butadiene in pure water compares favorably with the value of 2.72 X 106 mm./mole gas/mole soln., which can be calcu- lated from the data reported by McBain and O'Connor (1).

The regular decrease of the Henry's law constant is found to be linear with the logarithm of the surfactant concentration, as shown in Fig. 2. Extrapolating the experimental straight line to the concentration of sur-

523

3t I i 30 HYAMINE 1622

E 1622

~ NE 1622

°2 O IOO 2 0 0 3 0 0 4 0 ~ ~ ' ~ ' 0

Pressure in ram.

FI~. 1. Mole f rac t ion of bu tad iene dissolved in pure wate r and in solut ions of Hyamine 1622 as a funct ion of the equi l ibr ium par t ia l pressure of butadiene .

v

o

4.00

2 .00

1,00

0.,5(

0.2!

0.19

\ \

\ \

\ \

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\ \1

I

Henry ' s law cons tan t X 10 - s

FIG. 2. Var ia t ion of the Henry ' s law cons tan t for the solubi l i ty of bu tad iene in aqueous solut ions of Hyamine 1622 wi th the concen t ra t ion of the solut ion.

LETTER TO THE EDITOR 525

factant corresponding to a Henry's law constant of 2.96 X 106 would presumably yield a minimum concentration of surfactant below which no solubilization occurs. In terms of present-day theory, solubilization results from the presence of association micelles in solution; the existence of a minimum concentration below which solubilization does not occur is evi- dence of a critical micelle concentration. The value for the minimum con- centration obtained from Fig. 2 is 0.19% Hyamine 1622. The critical micelle concentration of Hyamine 1622 as determined by conductivity measurements by T. H. Bramfitt in this laboratory, is 0.16 %. The role of micelles in solubilization is thus unequivocally shown.

REFERENCES

1. McBxIN, J. W., XND O'CONNOR, J. J., J. Am. Chem. Soc. 63, 875 (1941). 2. McBAIN, J. W., AND SOLDA~E, A. M., J. Am. Chem. Soc. 64, 1556 (1942). 3. McBAIN, J. W., Advances in Colloid Sci., Vol. 1, p. 116 (1942).

Department of Chemistry, SYDNEY Ross Rensselaer Polytechnic Institute, JOHN B. HUDSON Troy, New York

Received September 16, 1957