Angular distribution of light scattered from critically quenched liquid mixtures

Light scattering was used to determine the structure factor $S(k,\tau )$ of two binary mixtures which were quenched through the critical point. The experiments, which were carried out in isobutyric acid-water and 2,6-lutidine-water, show that the normalized structure factor has the scaling form $\overline{S}(k,\tau )=K^{-3\mathrm{}}F\left(\frac{k}{K}\right)$ where $K^{-1\mathrm{}}$ is the size of a growing domain and $F\left(x\right)\mathrm{}$ is time independent. Our findings are in approximate agreement with those of Marro et al., who obtained $\overline{S}(k,\tau )$ from a computer simulation of a quenched $A-B$ Ising lattice. The computer experiments yield an initial time dependence in $F\left(x\right)\mathrm{}$, whereas the light-scattering measurements reveal no evidence of this transient effect over the (dimensionless) time interval $6\lesssim \tau \lesssim 1000$. The experiments spanned the temperature range $3\times {10}^{-6\mathrm{}}\le \epsilon \le 2\times {10}^{-5\mathrm{}}$, where $\epsilon \equiv |\frac{T_f}{T_c}-1|$. In this interval the integrated scattering cross section at every instant of time is proportional to ${\epsilon }^{2\lambda }$ with $0.22\le \lambda \le 0.33$.