Neutron Scattering Experiments with a Binary Critical Mixture for the Determination of the Critical Exponent ζ

Abstract

AbstractSmall angle neutron scattering experiments are carried out with an isobutyric acid (COOD)/deuterium oxide mixture of critical composition. The scattering patterns are measured at small temperature differences (T ‐ Tc) ≦ 1.0 K above the critical temperature Tc. In his temperature range and for scattering vectors larger than 0.03 Å−1 the critical scattering was found to be independent of temperaure. From these data the experimental correlation scaling function gexp(x) is constructed for values of the scaling variable x in the range 4 < x < 540. The Fisher‐Langer approximation of the correlation scaling function and its asymptotic form for large values of x are fitted to gexp(x). In this way a value of the critical exponent η of η = 0.039 ± 0.009 is obtained. It is based on the analysis of the experimental correlation scaling function composed of five scattering patterns obtained at five different temperature differences (ΔT ≤ 1.0 K). The analysis of 4 individual scattering patterns (ΔT ≤ 0.08 K) gives η = 0.037 ± 0.006.