CHEMICAL OSCILLATIONS AND INSTABILITIES .94. THRESHOLDS FOR NUCLEATION OF BUBBLES OF N2 IN VARIOUS SOLVENTS

We have used procedures developed previously to measure maximum attainable concentrations of N2 in various supersaturated solutions. We are convinced that these concentrations are identical with the thresholds for nucleation of bubbles in the same solutions. The threshold in water is virtually constant between 15 and 35-degrees-C, implying that the entropy of activation for forming an unstable nuclear bubble is quite negative or else that such a bubble contains more gas molecules at 35 than at 15-degrees-C. Increase of ionic strength reduces the threshold for nucleation in water. Surfactants greatly reduce surface tensions of aqueous solutions but have rather little effect on thresholds for homogeneous nucleation in bulk solution. Nucleation thresholds in various solvents show little correlation with either surface tensions or viscosities. Addition of glycerol or ethylene glycol to water decreases the concentrations at which bubbles of N2 are nucleated. However, nucleation thresholds in many organic solvents are 4-6 times greater than those in water and indicate that nucleation is more difficult in these nonaqueous solvents. Nucleation thresholds in aqueous solutions are about 100 times solubilities at 1 atm, while in many organic solvents and in aqueous glycerol thresholds are only about 30-50 times solubilities. We believe that techniques other than chemical reactions could be developed to measure nucleation thresholds in important systems which could not be studied by procedures employed in this paper.