Discrepancies in turbidity measurements in the ionic binary mixture triethyl n-hexyl ammonium triethyl n-hexyl boride in diphenyl ether

Abstract

We have repeated and extended turbidity measurements on a new sample of the ionic mixture triethyl n-hexyl ammonium triethyl n-hexyl boride (N2226B2226) in diphenyl ether in a temperature range above its consolute point. Previous measurements on this system by some of us indicated mean-field critical behavior over the range of reduced temperatures 10−4<t<10−1. Our new measurements do not reproduce those reported before. The transmission of the new sample is substantially lower, and the turbidities up to a factor of 3 higher than those of the sample used in the previous work. The correlation-length amplitude is approximately 40% larger than that found for the previous sample. Unlike the earlier results, the new data do not display a substantial range of mean-field critical behavior. In our investigation of this irreproducibility, we have carefully reviewed the earlier experiment, and we report here an effect not previously noted: a time dependence of the turbidity of the earlier sample. It is likely that the discrepancy is due to impurity effects, but we do not understand their origin.