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

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. (C) 1997 American Institute of Physics.