Density fluctuations of water–glucose mixtures studied by inelastic ultra-violet scattering

Hydration properties and water structure in aqueous solutions of native and modified cyclodextrins by UV Raman and Brillouin scattering

“…As a consequence, the plateau value of E app provides a reasonable estimate of the activation energy E A associated to the relaxation process. Figure b shows that the results for all the samples investigated are close to that of pure water, suggesting that the thermally activated relaxation that we probe is connected with fast density fluctuations mainly related to the breaking/reforming process of water H‐bonds. We also note that the value of E A of this process is a little higher than the value of ΔH derived from the van't Hoff treatment of Raman data.…”

“…In fact, Raman spectroscopy is sensitive to localized molecular vibrations, whereas Brillouin spectroscopy with ultraviolet excitation allows us to probe the collective dynamics of density fluctuations on a mesoscopic length scale. The advantage of using UV‐BS with respect to the more traditional visible‐light Brillouin scattering is in the higher value of the wavevector exchanged in the phonon–photon scattering process (q ≈ 0.06–0.07 nm −1 ), which allows to reveal acoustic modes with a higher frequency (about twice in our case) and then to probe more efficiently the structural relaxation process in water‐based systems . New and existing UV‐BS data of water‐glucose solutions have been taken as a basis for comparison.…”

“…At all concentrations, we focus on the temperature behavior of the Brillouin linewidth Γ B obtained by fitting the spectra with Equation . This quantity is directly related to the acoustic attenuation of the system and, for aqueous solutions at sufficiently high temperatures, acts as an indirect probe of the collective molecular rearrangement occurring at a picosecond time scale via H‐bond breaking and reforming processes. Indeed, when T is sufficiently high the Brillouin peaks are located at frequencies much lower than the rate of such molecular rearrangement (ω B «1/τ, with τ the average relaxation time ranging from fractions to few picoseconds), and the system is in a completely relaxed (liquid‐like) regime.…”

“…(b) Activation energy E A derived from the high‐temperature value of E app ( T ), for SBE‐β‐CD and glucose aqueous solutions as a function of concentration. Data for glucose obtained from measurements with incident wavelength of 244 nm (Gallina et al) are also reported for comparison…”

Brownian motion of single glycerol molecules in an aqueous solution as studied by dynamic light scattering

“…However, it is also evident that liquids in general and mixtures of liquids, i.e., solutions, in particular may exhibit at least one relaxation process on a time scale much slower than the α relaxation. Such an ultraslow relaxation process has been observed by a wide range of different experimental techniques, such as dynamic light scattering (DLS) [3][4][5][6][7], dielectric spectroscopy [8][9][10][11][12], and Brillouin ultraviolet scattering [13]. Generally, it is acknowledged to be caused by long-range density fluctuations on a length-scale of 100-300 nm [14] or concentration fluctuations in the case of solutions [15], since its relaxation time usually exhibits a 1/q 2 dependence (where q is the momentum transfer of the scattering event), as typical for long-range diffusion.…”