Critical Exponents near the Lower Consolute Point of Nonionic Micellar Solutions
Abstract
New and accurate light-scattering measurements near the critical point of the nonionic micellar solution $n$-dodecyl octaoxyethylene glycol monoether in ${\mathrm{H}}_{2}$O in the reduced temperature range $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}<\ensuremath{\epsilon}<2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ confirm that this binary system presents anomalous critical exponents $\ensuremath{\gamma}$ and $\ensuremath{\nu}$. The values obtained are $\ensuremath{\gamma}=0.88\ifmmode\pm\else\textpm\fi{}0.03$ and $\ensuremath{\nu}=0.43\ifmmode\pm\else\textpm\fi{}0.03$. The substitution of ${\mathrm{D}}_{2}$O for ${\mathrm{H}}_{2}$O changes the exponents to $\ensuremath{\gamma}=1.20\ifmmode\pm\else\textpm\fi{}0.03$ and $\ensuremath{\nu}=0.59\ifmmode\pm\else\textpm\fi{}0.03$. Intermediate exponents are obtained by use of a mixture of ${\mathrm{H}}_{2}$O and ${\mathrm{D}}_{2}$O as the solvent. Both the osmotic compressibility and the correlation range closely follow a power-law behavior as function of $\ensuremath{\epsilon}$ without showing any crossover effect or correction-to-scaling contribution.