Raman spectra in the O–H stretching band in normal and supercooled water have been investigated. Spectra are taken as a function of temperature in the range +95 to −24°C. Absolute Raman cross sections corrected for instrumental and physical factors are obtained. It is shown that the isotropic O–H stretching bands in the range +20 to +95 °C are due to the contribution of ’’open’’ (or tetrahedrically bonded) and ’’closed’’ water that are temperature independent. The percentage of open water α(T) is connected and interpreted in the frame of the Stanley site percolation model. As a consequence, the isobestic point is obtained. In the supercooled region, a third spectral contribution arises, which is centered near the main peak of the isotropic O–H band of ice. Such a contribution is tentatively explained as the presence in supercooled water of true ice, as a heterophase fluctuation.

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 t h e 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 t h e 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 t h e 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 t h e demixing tendency of these systems at high temperatures. On going from 25 to 5°C the aggregation increases again. This trend is associated with t h e 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.

Ultrasonic velocity measurements in ethanol aqueous solutions from +30 to −40 °C over the entire composition range and in the frequency range 10–70 MHz are presented. The results, in combination with previous determinations up to +80 °C, allow us to follow the peculiar behavior of the adiabatic compressibility of this system in a very large temperature range extending from a region where the anomalies of pure water tend to disappear, down to the supercooled region where these anomalies are noticeably enhanced. A ‘‘normal’’ and an ‘‘anomalous’’ contribution to the isothermal compressibility of water, as derived from these data, is compared with previous evaluations and discussed in the framework of the existing theoretical models. The compressibility of the diluted solutions is interpreted in terms of stabilization of water into ordered, less dense, and more rigid structures around the solute. We show that a simple two-state model based on this concept and on the hypothesis of a structural breakdown at the concentration of maximum sound absorption can explain the main experimental features of the volumetric properties of these solutions.

We present small angle neutron scattering measurements on binary aqueous solutions of some short-chain amphiphiles (diols, triols, glycols and diglycols) at room temperature. The spectra were analysed in terms of the Teubner-Strey phenomenological formula which allows to obtain a measure for the amphiphilicity strength of each system (amphiphilicity factor fa). In some systems, however, other models, valid for micellar solutions, give also a good representation of the spectra. As a result, we find that, independently of the type of hydrophilic group side (oxydrilic or oxirane), these systems cover the entire accessible amphiphilicity scale ( -1 < fa < 1). Some disordered systems (fa > 1) presumably are able to form micelle-like aggregates.

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