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Dipole moments water adsorbed

Figure A2.4.10. Orientational distribution of the water dipole moment in the adsorbate layer for tlu-ee... Figure A2.4.10. Orientational distribution of the water dipole moment in the adsorbate layer for tlu-ee...
For a polar surface and molecules with permanent dipole moments, attraction is strong, as for water adsorption on a hydrophilic adsorbent. Similarly, for a polar surface, a molecule with a permanent quadrupole moment vidll be attracted more strongly than a similar molecule with a weaker moment for example, nitrogen is adsorbed more strongly than oxygen on zeolites (Sherman and Yon, gen. refs.). [Pg.1503]

As a rule, no information is available on the local value of 8, which constitutes the main obstacle to an a priori calculation of A )(. In the fields of physics and surface chemistry, an assumption is often made that 8 =1 either because the molecules are treated as isolated entities or there is lack of a better value. It is known that p values derived from experimental Ay data (e.g., for insoluble monolayers) with the assumption 8 = 1 are substantially different from the dipole moment for the same molecule in the bulk of the solution.4 The reasons offered to explain this difference are manifold, e.g., (1) inappropriate value of 8, (2) reorientation of water molecules around the adsorbate, or (3) lateral interaction between adsorbed molecules in the monolayer. [Pg.38]

The physical meaning of the g (ion) potential depends on the accepted model of an ionic double layer. The proposed models correspond to the Gouy-Chapman diffuse layer, with or without allowance for the Stem modification and/or the penetration of small counter-ions above the plane of the ionic heads of the adsorbed large ions. " The experimental data obtained for the adsorption of dodecyl trimethylammonium bromide and sodium dodecyl sulfate strongly support the Haydon and Taylor mode According to this model, there is a considerable space between the ionic heads and the surface boundary between, for instance, water and heptane. The presence in this space of small inorganic ions forms an additional diffuse layer that partly compensates for the diffuse layer potential between the ionic heads and the bulk solution. Thus, the Eq. (31) may be considered as a linear combination of two linear functions, one of which [A% - g (dip)] crosses the zero point of the coordinates (A% and 1/A are equal to zero), and the other has an intercept on the potential axis. This, of course, implies that the orientation of the apparent dipole moments of the long-chain ions is independent of A. [Pg.41]

The dipole moment of the adsorbed water molecules is estimated to be = 0.22 D (unit of D = 3.36 x 10 ° C m) from the slope of the observed curves shown in Fig. 5-25. Since this dipole moment is nearly one tenth of the dipole moment of gaseous water molecules (m = 1.84 D), the dipole of the adsorbed water molecules on the silver surface is suggested to be aligned almost parallel to the metal surface by forming hydrogen-bonded two-dimensional clusters of water molecules. On the other hand, bromine molecules are in the state of dissociative adsorption on the silver surface, producing adsorbed bromine atoms which receive electrons... [Pg.151]

It is important to emphasize that in the present model one assumes that the interaction of the hydration sheaths of the adsorbed ions with the neighboring free water molecules outside the bilayer of charge produces changes in the N molecules but no change in the S water molecules. Denoting by jra the z component of the total dipole moment of the three water molecules of the N region and by a the number of hydrated ions adsorbed per unit area, we can write that ... [Pg.467]

When adsorbed (from ambient air), water molecules might act as plasticizers and alter the dynamics of polymers. Moreover, water has a strong dipole moment and, consequently, dielectric active relaxation processes, which could partially occlude significant parts of the dielectric spectra of interest. Special attention to this effect has to be paid when the dynamics of thin polymer films is investigated, for example in relation to phenomena like the glass transition, dewetting, pattern formation, surface mobility etc. [Pg.36]

With the only exception of thiourea, all aliphatic compounds are characterized by positive dl/dE values.54 Within the limits in which we can exclude an appreciable reorientation of the aliphatic molecules with a change in the applied potential E, the increase of l with an increase in E is to be ascribed to a gradual reorientation of the adsorbed water molecules. Water molecules have a particularly high dipole moment per unit volume, and are known to be readily orientable under the influence of an electric field. A progressive shift of E towards more positive values causes to pass gradually from negative to positive values. Consequently, the contribution to aM required to keep E constant upon removing v adsorbed water molecules by one... [Pg.340]

The solvent also acts as a dielectric medium, which determines the field diji/dx and the energy of Interaction between charges. Now, the dielectric constant e depends on the inherent properties of the molecules (mainly their permanent dipole moment and polarizability) and on the structure of the solvent as a whole. Water is unique in this sense. It is highly associated in the liquid phase and so has a dielectric constant of 78 (at 25 C), which is much higher than that expected from the properties of the individual molecules. When it is adsorbed on the surface of an electrode, inside the compact double layer, the structure of bulk water is destroyed and the molecules are essentially immobilized... [Pg.425]

An additional unique feature of electrosorption is that the coverage is a function of potential, at constant concentration in solution. Thus, we can discuss two types of isotherms those yielding 0 as a function of C and those describing the dependence of 0 on E. This is not a result of faradaic charge transfer. Neither is it due to electrostatic interactions of the adsorbed species with the field inside Ihc compact part of the double layer, since a potential dependence is observed even for neutral organic species having no permanent dipole moment. As we shall see, it turns out that the potential dependence of 0 is due to the dependence of the free energy of adsorption of water molecules on potential. [Pg.477]


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