A Dielectric-Constant Method for Following the Non-Stationary State of Radical Reactions

Abstract

MUCH of the recent development in the kinetics of chemical reactions has been concerned with the absolute evaluation of rate constants for the elementary reactions comprising a complex process. This has been carried out mainly indirectly in photo-reactions, using intermittent radiation to determine the life of the radical or chain concerned in the rate-controlling step. It would, however, be much more desirable in such reactions to be able to determine these life-times directly, by delineating the rise in concentration of a radical following the commencement of irradiation and the corresponding decay when irradiation is stopped. This can be done in principle, given a method of detecting reaction which is both highly sensitive and also very rapid in response, since life-times may be as short as 10−3 sec. These stringent requirements have now been met in the case of the liquid-phase polymerization of vinyl compounds by the construction of an instrument for following the change in dielectric constant which accompanies the reaction. This instrument has a sensitivity of 1 part in 108 of dielectric constant and a response time of 10−4 sec.; the frequency of operation is 50 Mc./s. We are indebted for the design of the instrument to Dr. C. M. Burrell, of the Radar Research and Development Establishment, and to the Ministry of Supply for invaluable help in its construction.

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References

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    Symposium on Combustion and Explosion, Wisconsin (1947).

  2. 2

    Burnett, G. M., Valentine, L., and Melville, H. W., Trans. Farad. Soc., 45, 960 (1949).

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MELVILLE, H., MAJURY, T. A Dielectric-Constant Method for Following the Non-Stationary State of Radical Reactions. Nature 165, 642 (1950) doi:10.1038/165642a0

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