F. Wanderlingh

Raman scattering and structure of normal and supercooled water

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.

Raman spectroscopy and local order in aqueous solutions of strong II–I electrolytes

We report polarized Raman spectra for aqueous solutions of NiCl2, CdCl2, ZnCl2, CuCl2, Cu(NO3)2, and SrCl2. Our analysis of the Raman data provides an interpretation for the diffuse low frequency Raman scattering in transition metal halide–water solutions in terms of a vibrational density of states. Such a density corresponds to collective vibrational modes in a solute‐connected middle range lattice. The results are also discussed on the basis of recent measurements of viscosity, thermodynamic quantities, and EXAFS.

Vibrational dynamics of glassy and molten ZnCl2

Polarized Raman spectra of ZnCl2 were obtained in the liquid phase near the melting point (T = 598 K), and in the glassy phase (T = 293 K). Measurements were performed down to a very low frequency shift (2 cm−1) from the exciting line. Our analysis of the Raman data provides an interpretation of the collision‐like contribution in terms of a structural relaxation time in the picosecond range, while the phonon‐like contribution gives an effective Raman density of states. These results are also discussed in terms of existing structureal models.

Structural properties of macromolecular solutions

We report measurements of viscosity and light scattering in an aqueous solution of BSA. Like the lysozyme solutions, previously investigated, the BSA solutions show thixotropic properties. Optical measurements of both elastic and inelastic light scattering indicate the existence of a structure in which the BSA molecule tends to clusterize, each cluster being correlated to the others. A k‐dependent diffusion coefficient D(k) is found. The static structure factor deduced from the values of DL(k) agrees well with the indications given by the elastically scattered intensity J(k). Also, the statical properties of scattered light appear to be consistent with the proposed model. A qualitative explanation, in terms of a dominant component in the fluctuations of concentration, is briefly sketched.

Collective vibrational modes in strong electrolyte solutions at high concentrations

Abstract We report evidence for the existence of solute related collective vibrational modes in strong II-I electrolyte solutions at high concentrations both in H2O and D2O. The evidence was obtained by studying the polarized Raman spectra of solutions of CdCl2 and NiCl2 Checks were also performed by taking the Raman spectra of the relative hydrated salts. Our results are explained in terms of vibrational densities of states corresponding to collective vibrational modes in a solute connected middle range lattice.

Dynamical Behaviour of Structured Macromolecular Solutions

Abstract A large number of experimental results have shown that macromolelcules in solution give rise to ordered (thyxotropic) structures, a noticeable role being played by a dynamic correlation. In the present paper we develop a semi-phenomenological model that can be solved analytically. The model is able to describe in a quantitative way both structural and dynamical properties of a thyxotropic solution. A careful experimental investigation is also carried out and the experimental results are compared to the theoretical prediction. In such a way the relevant parameters implied in the structure can be evaluated. Some implications concerning energy exchanges between proteins and the thermal bath are discussed.

Viscosity measurements and structural properties in aqueous NiCl2 solutions

We measured viscosity as a function of concentration in an aqueous solution of NiCl2. We also measured compressibility and density in the same system. The data are discussed in the frame of existing phenomenological theories. In all cases it appears that some structural changes take place at a given concentration. We also propose a new phenomenological equation that describes the viscosity in terms of a function of the concentration, that turns out to have a rather universal character being able to describe also the behavior of other properties such as compressibility and density. The building up of some sort of structure can easily be revealed by such a treatment, also in comparison with other experimental results.

Incoherent quasielastic neutron scattering from H2O and aqueous ZnCl2 solutions

A study of the diffusive motions of the protons in pure water and ZnCl2 aqueous solutions has been performed, using incoherent quasielastic neutron scattering. It is shown that it is essential to take into account the rotational motion of the water molecules. The translational linewidth is conveniently fitted over the whole Q-range, using the Random Jump Diffusion model for which the jump length turns out to be roughly the same for pure H2O and the saturated solution, fairly close to the distance between protons in the water molecule.

Depolarized Raman scattering in normal and supercooled antimony trichloride

Depolarized low frequency Raman spectra obtained for molten antimony trichloride are discussed. Measurement has also been performed on the supercooled liquid down to 53.2° below the melting point (tm = 73.4 °C. The experimental results indicate that the spectral contributions, in the range 2–100 cm−1 of Stokes shift from the exciting line are due to: (1) a central Lorentzian line, whose width and intensity are connected to the dynamics of the break‐up of intermolecular chlorine bridges; and (2) a solidlike contribution that furnishes an effective density of states, which corresponds to a convolution of ’’acoustical’’ and ’’optical’’ modes in a coupled linear chain structure with middle range order.

Structure of Water in Microemulsions Investigated by Raman Scattering

Abstract Measurements of Raman intensity of the O—H stretching band in microemulsions give experimental evidence of the existence of a layer of water whose structural properties differ from those of bulk water. The measurements are performed with an isotopic substitution method, which allows a careful evaluation of various contributions. The depth of the layer can be evaluated, and the structural situation of water is discussed in the frame of the current theories.