Communicationsto the Editor
as8 (2)0. Arfken. "Mathematical M B W Sfw PhysicisW. Academic R e s . New York. N.Y.. 1966: ret 32 in ret 1.
Department of Chemistry
The University of Gtiteborgand Chaimers University of Technology Gothenberg, Sweden
E. A. 0. Anlan.lon* S. N. Wall
Received November 11. 1974
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Rate of Phase Separation in Liquid Mixtures Studied by T-Jump Experiments under Pressure Publrcatnn cam assisted by Verbandder Cbmiscbn Wustrie e. V.. Fonds der Chemischen Industr&
Sir: In this paper some preliminary results for the time de-
pendence of the phase separation into two liquid phases of homogeneous mixtures of pyridine, water, and potassium chloride under pressure are reported. In recent years the pressure dependence of immiscibility phenomena in liquid mixtures has been extensively investigated, and demixing phenomena in aqueous solutions of nonelectrolytes were also studied as a function of pressure, temperature, concentration, and content of added salts. Figure 1 shows a plot of demixing temperatures as a function of vressure for vvridine-water mixtures with various amounts of potassium chloride added, according to measurements by Russo and Schneider;' regions where two liquid phases coexist are indicated by hatching. Starting from conditions of temperature and pressure in the homogeneous region just below the curves plotted, heterogeneous states can be reached rapidly by a relatively small temperature jump. By measuring the degree of turbidity as a function of time some knowledge can be obtained for the time dependence of demixing phenomena in these mixtures. Measurements were made in a temperature jump apparatus that has been developed for the investigation of fast reactions in solutions under high pressure. Here the temperature jump is generated by decharging a high voltage capacitor. The measuring cell with optical windows for spectroscopic measurements is mounted in a high-pressure autoclave. Details of the experimental device have been reported elsewhere.2 With only slight modifications this apparatus was used for the measurements of this paper. T h e system was pressurized and temperature jumps between 2.4 and 5.4O were created within 3.5 psec. Turbidity was observed by measnring the change of optical transmissioR; the wavelength used was 560 nm. T h e current of the photomultiplier was recorded on a storage oscilloscope. Figure 2 shows a typical trace of the oscilloscope for a pyridine-water mixture (wt % pyridine/wt % water = 35/65) with KCI added (14.6 g of KCI in 100 g of H20)starting from 85 bar and 58.2'. The vertical scale is in arbitrary units of decreasing optical transmission (according to increasing turbidity); the horizontal scale is 200 psec per large scale division. After the temperature jump is initiated at t = 0. the transmission first remains nearly constant for approximately 80 psec.
The JOurnaiolPhySlCal Chernbhy, Vol. 79. No. 8, 1975
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2000
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Fbum 1. Liquid-liquid phase separation temperatures for the system pWine-water-KCI as a function of pressure (wt % pyridinelwt % H20 = 35/65; salt concentration in g of KC11100 g of H 2 0 twophase regions are indicated by hatching).
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Fbure 2. Typical temperature jump trace for the phase separation in
a pyridine-water-KCI mixture (wt % pyridinelwt % H20 = 35/65; 14.6 g of KClllOO g of H20: starting condnions p = 85 bar, T = 58.P. A T = 5.4'.
X 560 nm).
Then the transmission decreases rapidly until finally an approximately constant yalue is reached after about 1 msec. Experiments with a shorter wavelength show that in this case the decrease of the transmission starts earlier after the temperature jump. Assuming a diffusion-controlled growth of the turbidity creating droplets a time of approximately 100 psec can be calculated considering a mean diffusion coefficient of D iz cm2 sec-l until the droplets reach a diameter on the order of the wavelength used. It follows from the above experiments that the growth of the droplets will probably start immediately after the temperature jump without considerable supersaturation. References and Notes (11 0. M. Schnelder and C. RUSSO.8% Bunsenges. Phys. Chem.. 70, 1008 (1988). (2)A. Jost. Be,. BunrenQes.phvs Chem.. 78.300 (1974).
Department of Chernktry University of Bochum 4630 Bcchum
German Federa1,Republic Received aeCember 2. 1974
A. JOSI G. M. Schneider'
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