Critical phenomena and renormalization-group theory

After a review of the history and an assessment of the current status of the subject, we present light-scattering data to determine the critical correlation-function exponents for an aqueous electrolyte solution yielding the experimental values γ=1.238±0.012, ν=0.629±0.003, η=0.032±0.013. We conclude the paper with some comments concerning the temperature dependence of non-asymptotic effective critical-exponent values of fluids.

Experimental Critical-Exponent Values for Fluids

The static and dynamic critical properties of a nonionic amphiphile aqueous solution showing a lower consolution point are investigated by laser-light scattering. The osmotic isothermal compressibility and the correlation length of the concentration fluctuations diverge with mean-field-theory critical exponents. The behavior of the mass diffusion constant in the hydrodynamic region is in good agreement with the predictions of the mode-mode-coupling theory.

Critical Behavior of a Micellar Solution

We report turbidity measurements of a nonaqueous ionic solution of triethyl n‐hexylammonium triethyl n‐hexylboride in diphenyl ether. A classical susceptibility critical exponent γ=1.01±0.01 is obtained over the reduced temperature range 10−4≤ t≤10−1. The best fits of the sample transmission had a standard deviation of 0.39% over this range. Ising and spherical model critical exponents are firmly excluded. The correlation length amplitude ξ0 from fitting is 1.0±0.2 nm which is much larger than values found in neutral fluids and some aqueous binary mixtures.

The susceptibility critical exponent for a nonaqueous ionic binary mixture near a consolute point

The critical behavior of turbidity for an array of ionic fluids is reported. The ionic fluid is comprised of a low melting organic salt in an organic solvent, and the critical temperature (Tc) refers to the liquid–liquid coexistence. The phase separation is driven, predominantly, by Coulombic interactions in the low dielectric constant (e) solvents and, primarily, by solvophobic effects in the high e solvents. For the moderately Coulombic case, the critical exponents of osmotic compressibility and correlation length (γ and ν, respectively), which are deduced from turbidity, exhibit a crossover from their Ising to mean‐field values when moved away from the Tc. The crossover region moves closer to Tc as the effective e of the solvent is decreased. For the solvophobic case, the critical behavior of turbidity can be adequately described by Ising critical exponents without correction‐to‐scaling terms. In addition, several specific features of this class of ionic fluids are presented. Some potential factors that influence the values of the critical exponents are also discussed.

Critical phenomena in ionic fluids : a systematic investigation of the crossover behavior

Turbidity Measurements in S F 6 Near Its Critical Point

We have measured the linewidth of light Brillouin scattered from C${\mathrm{O}}_{2}$ for $0.015l~T\ensuremath{-}{T}_{c}l~15$ \ifmmode^\circ\else\textdegree\fi{}C. As ${T}_{c}$ is approached from high temperature, the linewidth increases rapidly but then saturates at $T\ensuremath{-}{T}_{c}\ensuremath{\approx}1$ \ifmmode^\circ\else\textdegree\fi{}C and remains roughly constant to $T\ensuremath{-}{T}_{C}=0.015$ \ifmmode^\circ\else\textdegree\fi{}C. These results are discussed in the light of the dynamic scaling laws.

N. C. Ford

Papers

Turbidity Measurements in S F 6 Near Its Critical Point

Brillouin Linewidths in C O 2 Near the Critical Point