Small-angle neutron scattering study of D ₂ O–alcohol solutions

Small-angle neutron scattering (SANS) measurements have been carried out on heavy water solutions of ethanol, isopropyl alcohol, n-propyl alcohol, t-butyl alcohol and butoxyethanol between 5 and 37 °C at the concentrations where ultrasonic attenuation exhibits peak values. The wavevector dependence and the absolute intensity of the scattered intensities were analysed according to a microscopic model of the solutions in terms of aggregated complexes. The results indicate that at 25 °C there exist either alcohol ‘micelle-like’ structures or alcohol–heavy water complexes which increase on going from the lower to higher alcohol solutions. As temperature increases from 25 to 37 °C a higher aggregation is observed in butyl alcohol and butoxyethanol solutions. This behaviour is attributed to the demixing tendency of these systems at high temperatures. On going from 25 to 5 °C the aggregation increases again. This trend is associated with the anomalous behaviour of the specific heat and ultrasonic attenuation of these systems. The occurrence of a low-temperature phase transition suggested by these anomalies is supported by our results.