Critical behavior of a ternary microemulsion studied by turbidity, density, and refractive index.

Abstract

A detailed study of turbidity, density, and refractive index in the critical region of two samples of a water in an oil ternary microemulsion system, water plus benzene plus benzyl hexadecyl dimethylammonium chloride (BHDC), is presented. Special care is taken to determine the criticality of the samples. The critical point is approached from the homogeneous phase by varying the temperature at fixed concentrations of the components. Along this path Fisher-renormalized Ising exponents are expected. The critical exponents for the correlation length (\ensuremath{\nu}) and osmotic susceptibility (\ensuremath{\gamma}) are determined through the turbidity. The critical exponent \ensuremath{\alpha} can be deduced from the (1-\ensuremath{\alpha}) behavior of the density and the refractive index. From mere numerical analysis alone turbidity behavior cannot be distinguished between Ising and Fisher-renormalized Ising exponents. However, physical arguments suggest the latter values for the exponents \ensuremath{\nu} and \ensuremath{\gamma}. We do not see any anomaly in the density within a resolution of \ifmmode\pm\else\textpm\fi{}3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$. This is consistent with the renormalization of \ensuremath{\alpha} [${\mathrm{\ensuremath{\alpha}}}^{\mathrm{*}}$=-\ensuremath{\alpha}/(1-\ensuremath{\alpha})]. A very weak anomaly in the refractive index is detected which is better described by a function of the exponential type, which has been discussed for a quaternary microemulsion near the critical end point, than the (1-\ensuremath{\alpha}) power behavior.