Critical slowing of chemical reactions

Procaccia and Gitterman have suggested that the reaction rates of chemically reacting binary mixtures are drastically reduced near their thermodynamic critical points and that this reduction is responsible for anomalies observed in a series of experiments performed more than 15 years ago. A more detailed analysis shows that this suggestion is untenable, that spatially uniform composition fluctuations are not drastically retarded at thermodynamic critical points, and that spatially varying composition fluctuations are at best slowed down over a small range of wavenumbers that will be difficult to detect experimentally. A qualitative picture is provided by mean-field and Van Hove theory. Quantitative corrections are obtained with use of renormalization-group techniques. At small and large wavenumbers, the hydrodynamic modes most affected near the critical point are, respectively, thermal and particle diffusion. The mode-couplings relevant in these regimes differ from the mode couplings relevant at intermediate wavelengths where the critical slowing of a reaction might be observable.