Interfacial water network

In the following, the application of this method of analysis will be illustrated for the case of Pt(l 11) in 0.1 M HCIO4 solutiom First, the evaluation of the entropies of formation of the interphase, double-layer and the interfacial water network will be described in Sections IV. 1, IV.2 and IV.3, respectively. Then, these results will be employed to evaluate the absolute molar entropy of adsorbed hydrogen and OH on Pt(lll), in Section IV.4. Finally, these results will be critically compared with those obtained with a generalized isotherm in Section IV.5. 

Entropy of Formation of the Interfacial Water Network on Pt(lll) in 0.1 M HCIO4 Solution... 

Figure 10 plots the results of AS, AS and ASdi, against the free charge density. It is observed that the difference between ASJ and ASdi is relatively small, thus supporting the qnalitative interpretation of ASdi in terms of the state of disorder of the interfacial water network (Sections IV.2 and V.2). Similarly, the present result also gives support to the interpretation of... 

Figure 10. Entropies of formation of the double layer, ASdi, the inner double-layer, AS, and the interfacial water network,, plotted against the free charge density, for Pt(l 11) in 0.1 M HCIO4 solution at 298 2 K. Adapted from Ref. 18.

In conclusion, the present results show that the entropy of the interfacial water network on Pt(lll) is nearly dominated by the free charge density. The state of maximum disorder corresponds to Om 0, i iipzfc. Then, at om < 0, the entropy of the interfacial water network decreases, due to the fact that the interfacial water molecules achieve a net polarization with the hydrogen end towards the metal. Conversely, at om > 0, the orientation with the oxygen end towards the metal becomes the most favorable. Noteworthy, the fact that water reorientation on Pt(l 11) takes at om 0, E evidences that specific interactions between water molecules and the Pt(l 11) surface play a minor role on the orientational behavior of the interfacial water network. That is, water stmctures with net orientations with the hydrogen and with the oxygen towards the metal seem to experience similar specific interactions with the Pt(lll) surface. These conclusions will be discussed in more detail in Section V.3. 

The behavior of interfacial water on the three platinum basal planes, under electrochemical conditions, has been studied, for the first time, by means of the laser-induced temperature jump method. Moreover, the comparison of these results with charge density data has contributed to the understanding of the electrostatic and chemical interactions governing the reorientation of the interfacial water network on platinum electrodes. Below we provide a brief summary of the main results of this study. 

The Chapter by N. Garcia, V. Climent and J. Feliu provides a lucid and authoritative overview of the use of laser-pulsed induced temperature variations at the platinum single-ciystal/aqueous solution interphases and of the rigorous analysis of these experiments via Gibbs thermodynamics to extract new and very valuable information on the stracture and reactivity of the metal/solution interphase. The authors show how some key interfacial properties can be evaluated directly via this elegant analysis, such as the entropy of charge-transfer adsoibed species, the entropy of formation of the interfacial water network and the potential of water reorientation. 

These facts support the existence of three water states water in glycerol FI-bond networks (H20(gw ). water in ice structure (H20(ice)) and interfacial water (H20(interface)). Let us discuss a possible kinetic mechanism of the broad melting behavior. The relations between the three states of water can be described by... 

Simulation. In this study, VSFS and molecular dynamics calculations were employed to examine the structure and dynamics of the hydrogen bonding network of water at the hexane/water, heptane/water and octane/water interfaces in detail [66]. The complementary nature of the approaches has allowed a more detailed understanding of the interface. The calculations provide information not available in the spectroscopic studies, namely the interactions between interfacial water molecules that are isotropically oriented. The direct and iterative comparison of experiment with theory allows for the improvement of the models used to describe water-water and water-solute interactions. 

Pair correlation functions can also be used to show differences in structure between the bulk PEM and interfacial regions. Figure 13 shows the difference in the water network in the aqueous domain of bulk membrane of Nafion to those adsorbed on to a catalyst surface through the Oh o Oh o POF at all the water con-... 

Results relative to a 25% hydrated Vycor sample indicates that at room temperature interfacial water has a structure similar to that of bulk supercooled water at a temperature of about 0°C, which corresponds to a shift of about 25 K [40]. The structure of interfacial water is characterized by an increase of the long-range correlations, which corresponds to the building of the H-bond network as it appears in low-density amorphous ice [41 ]. There is no evidence of ice formation when the sample is cooled from room temperature down to -196°C (liquid nitrogen temperature). 

D. E. Khoshtariya, E. Hansen, R. Leecharoen, and G. C. Walker, Probing protein hydration by the difference 0-H (O-D) vibrational spectroscopy Interfacial percolation network involving highly polarizable water-water hydrogen bonds. J. Mol. Liq., 105 (2003), 13-36. 

The proximity of this liquid-liquid transition to the protein-glass transition temperature is suggestive. Clearly, at temperatures below 220 K or so, the dynamics of water and protein are highly coupled. A recent computer simulation study has shown that the stmctural relaxation of protein requires relaxation of the water HB network and translational displacement of interfacial water molecules. It is, therefore, clear that the dynamics of water at the interface can play an important role. This is an interesting problem that deserves further investigation. 

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