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 $6\times {10}^{-5\mathrm{}}<\epsilon <2\mathrm{}\times {10}^{-2\mathrm{}}$ confirm that this binary system presents anomalous critical exponents $\gamma$ and $\nu$. The values obtained are $\gamma =0.88\mathrm{}\pm 0.03$ and $\nu =0.43\mathrm{}\pm 0.03$. The substitution of ${\mathrm{D}}_2$O for ${\mathrm{H}}_2$O changes the exponents to $\gamma =1.20\mathrm{}\pm 0.03$ and $\nu =0.59\mathrm{}\pm 0.03$. 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 $\epsilon$ without showing any crossover effect or correction-to-scaling contribution.