It was observed that when polarized by an intense electric field, water is able to self-arrange into macroscopic cylindrical wires that can hang up and remain floating against gravity. This phenomenon is now known as a ‘water bridge’. Several attempts have been made to give an explanation of this apparently unusual behaviour of water. A number of experiments have been performed with the aim of probing any possible structural change of bulk water, after application of the electric field. None of the available findings appear conclusive at the moment.Here we report the results of the first Raman scattering experiment on floating water bridges. The inter-molecular OH-stretching band has been investigated and the results have been compared with those from bulk water. Some changes in the scattering profiles after application of the electric field are shown to have a structural origin. The bridges have been obtained, for the first time, in a vertical geometry and under application of an alternating field. The adopted geometry has allowed us to reveal a clear asymmetry between opposite direct current biasing, which can be related to the nature of the charge carriers.

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Recent phenomenological studies have drawn attention to an appealing effect, observed for the first time in 1893, today known as water-bridge. The phenomenon has been ascribed to unknown properties of water. We report some experimental results showing that, contrary to a widely common belief, the phenomenon is not to be related with water neither with a property of hydrogen bonded networks. Using a very simple model, we show that the liquid bridge phenomenon is originated by electrostatic effects and can be reproduced in any dense fluid with no respect of its peculiar molecular properties. This basic approach is able to reproduce many of the experimentally observed features of the bridge formation. In perspective of future investigations, the possible phenomena responsible of the bridge stability, after its formation, are briefly discussed.

The investigation of the structural relaxation properties of poly(ethylene glycol) methacrylates are of practical interest, due to their ability to work as the inert backbone to which poly(ethylene oxide) oligomers can be attached to obtain highly amorphous polymeric matrices.Two poly(ethylene glycol) methacrylate, PEGMA, macromonomers, with different side chain lengths, are investigated by the dielectric technique, in the frequency range 0.3-300 kHz, and by Brillouin scattering. The analysis of the Brillouin spectra gives evidence for the existence of a relaxation process in both the systems. Furthermore, a comparison of the normalized absorption data with their corresponding classical values (deduced from the shear viscosity data) suggests that what the Brillouin scattering experiment detects is a dissipative relaxational process in which the shear viscosity plays the main role. The comparison of the Brillouin scattering results with the dielectric data shows that what we are observing, in both the systems, is a single relaxation process. The temperature dependences of the relaxation times, observed on more than 10 decades, fail to follow simple Arrhenian behaviours. Both the systems can be interpreted as intermediate between strong and fragile liquids, following the Angell classification, and appear characterized by the existence of a wide variety of local structural environments, triggered by some relaxation process. Such a situation is more clearly evidenced by the macromonomer with longer chain. From the whole body of experimental data, it can be deduced that shorter-sidechain PEGMA macromonomers are better candidates for the formation of highly amorphous comb-branched polymers.

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In this paper we present some results from Brillouin scattering measurements on lecithin-based gels. The normalized hypersound absorption data give clear evidence of the establishement of an extended network at temperatures lower than 25 O C , when the micelle size reaches a threshold value. The transition between the two regions is interpreted as originated by a delicate balance between the breaking and re-forming mechanisms of the micelles and the system polydispersivity on which the collisional effects play the main role. General ConsiderationsSoybean lecithin is able to act as a surfactant giving rise to the formation of micellar solutions in the lecithin/organic solvent/ water system. Very recently, a growing interest has been devoted to the study of the static and dynamical properties of this system, as a result of the discovery of a gellike phase in the reverse micellar solution.I4 It was hypothesized that the addition of very small quantities of water induces the one-dimensional growth of giant reverse cylindrical micelles, whose length reaches a maximum value at a critical concentration w0,,, (w, = number of water molecules per lecithin molecule) whose value depends on the solvent under consideration. It is to be stressed that the value of w,,,, seems to be quite independent on the lecithin concentration2 4. Above a crossover lecithin volume fraction 4* the entanglement of micelles becomes highly favorable with the subsequent formation of a transient network very similar to that observed in semidilute polymer solutions. As a consequence a hierarchy of structures can be hypothesized, each one contributing to a relaxation spectrum5where Go is the characteristic modulus of the fully cross-linked network and T~~~ represents the cutoff in the relaxation time spectrum due to the existence of a maximum correlation length.The structural model was successively confirmed for the lecithin/isooctane solutions by means of small angle neutron scattering (SANS): quasi-elastic light scattering (QLS),'I and rheological measurements.2v6 In particular, a deviation from the expectation for a polymer-like model is observed in therelationship between qs and concentration. The divergence can be imputed to the fact that micelles are dynamical entities whose breaking and re-forming mechanisms give additional contributions to the stress relaxation.Later we also investigated the same system by means of depolarized Rayleigh scattering (DRS)7,9 measurements, ultrasonic technique,7s9 and dielectric measurement^.^^^ The resulting data are consistent with a situation which looks very similar to that observed for a nearly critical gel and agree with the existence of the hypothesized local structure. Structures with different 0022-3654/93/2097-6541504.00/0 400 I 1 -8 -4 0 4 8 u * 400 z c 2 . I c ZOO aoow Z . . . 100 U d) 0 -L Y U 0 a 0 cn ?. 0 ' I -8 -4 0 4 8 w (GHz) Figure 1. Brillouin spectra from the system lccithin/cyclohexane/water at fued volume fraction #I = 0.142 and different water contents w,: wo = 0 (a); w, = 3 (b); w, = 8 (c)...

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