Repulsion lateral

This destabilization of surface Rh oxide formation with increasing catalyst potential or work function has been shown to be due to strong lateral repulsive interactions of the backpspillover O2 species and normally chemisorbed oxygen33 which causes a pronounced, up to leV, decrease in the chemisorptive bond strength of normally chemisorbed o.35,36... 

There is a negligible effect of adsorbate-adsorbate interaction on step surfaces. Some lateral repulsion of hydrogen adsorbed on Pt(lll) could be inferred. A strong adsorption of bisulphate and sulphate anions on the (111) oriented terraces and step sites considerably affects both reactions. These data show that each crystallographic orientation of the electrode surfaces gives a different electrochemical entity. 

Voltammetry curves for all three low-index surfaces are given in Fig. 1. Hydrogen adsorption at Pt(lll), the process at -0.25 < E < -0.05 V in Fig. 1, is not affected by the nature of the anion (such as SO 2-, CIO.- or F-) (12). The lack of a well defined peak, in the drawn-out curve of Fig. 1 clearly indicates a strong lateral repulsion between adsorbed hydrogen adatoms. This is probably a consequence of a partially charge on the adsorbed hydrogen adatoms which, in turn, does not allow the... 

Fig. 6.106. The lateral-repulsion model for the explanation of the capacity-potential curve.

After this decrease in capacity, the attracting forces between the metal charge and the ion charge overcome the lateral repulsion forces. The rate of adsorption increases and the capacity also increases after passing through a minimum after the hump. This lateral-repulsion model is able, then, to explain and reproduce the maximum (the hump) and the minimum in the C-qM curve (Table 6.14). 

It appears from eqns. (175) and (176) that the free energy of adsorption increases with increase in coverage when g is negative (lateral repulsions) and, conversely, decreases for positive g (attractive interactions). 

More elaborate treatments consider the lateral repulsion between reactant and adsorbate [120—123]. Parsons used a generalized version of the Frumkin isotherm, obtaining for the rate coefficient in the presence of adsorbed substance [124]... 

It is also easily understood why in the case of hafnium the surface coverage increases as the pH becomes higher. Under these conditions the adsorbate consists only of neutral hafnium species. Since there is no lateral repulsion between them, the uncharged Hf(OH)4 can adsorb until a close packed monolayer is formed. The experiments indicate no evidence of multilayer adsorption. Once saturation is reached the adsorbed amount remains constant regardless of the equilibration time or the concentration of the hafnium salt in solution. 

Type B is very common. It is concave with respect to the abscissa. Most surfaces are heterogeneous. There are adsorption sites, which have a high affinity, and regions, which have a low affinity. The high affinity sites are occupied first, which accounts for the steep increase at low pressure. Another reason is sometimes a lateral repulsion between adsorbed molecules. This type of adsorption isotherm is described by the Freundlich1 adsorption isotherm equation [366] ... 

Micelles are not completely hydrophilic on their surface. The lateral repulsion between the head groups is usually so strong that, in between, some hydrophobic inner part of the micelle... 

For ionic surfactants another effect often dominates and usually salt tends to stabilize emulsions. Reason without salt the distance between surfactants in the interface is large because the molecules electrostatically repel each other. This prevents a high surface excess. The addition of salt reduces this lateral repulsion and more surfactant molecules can adsorb at the interface. Then, according to the Gibbs adsorption isotherm Eq. (3.52), the surface tension is reduced and the emulsion is stabilized. 

The adsorbed CO molecules are under strong lateral repulsion, in particular, adsorption of these molecules on the Ru(001) face leads to an appearance of the R( /3 x /3) ordered structures in LEED patterns [153]. This means absence of an uniform occupation of every adsoprtion site by the CO molecules the CO molecules are accommodated in the different sublattices non-uniformly, and this is the typical case when lateral interactions are responsible for a non-uniform adspecies distribution on a homogenous surface. Splitting of the experimental spectra is a signal of the... 

Thus, were the xanthate ion itself to adsorb and retain its charge, lateral repulsion would make it impossible for the surface coverage on the mineral to be a high one, and the desired hydrophobicity of the surface would not be achieved. In the electrochemical mechanism described by Salami and Nixon, the adsorption can become a charge-transfer reaction, continuing by the participation of oxygen until the surface is fully covered with dixanthate (and hence wettable). The mechanism is thus an electrochemical oxidation. 

According to the polyelectrolyte character of ODNs, the effect of salt concentration on adsorption should be considered. Indeed, the ionic strength affects (i) the electrostatic interactions between the ODN and the adsorbent and (ii) the lateral repulsive electrostatic interactions between adsorbed ODNs. 

Forr, = 70, 100, 150, and 200 pm, the calculated coordination numbers obtained on such a basis are shown in Tables 2.21 and 2.22. Real values should be less, because of lateral repulsion of molecules. 

In Fig. 31 we show positive as well as negative values of the parameter r. What is the physical meaning of r < 0, namely of an increase in the absolute value of the standard free energy of adsorption with coverage We have seen that a positive value of r can be due either to a surface inhomogeneity or to lateral repulsion interactions. A negative value of the same parameter hence must correspond to lateral attraction interactions, which lead to an increase of the equilibrium... 

A final remark concerns the effect of interfacial curvature. Above we have considered the surface to be flat, i.e., its radius of curvature is supposed to be large with respect to the thickness of the adsorbed layer. Some adsorption studies, however, deal with colloidal particles which are too small to fulfil this condition. Intuitively, one would expect different adsorbed amounts on a strongly convex surface, since the curvature changes the lateral repulsion. Others have argued that also the thickness could be different. Very few studies have dealt explicitly with these effects -2 3 4)... 

The existence of a curved conformation associated with the action potential is supported by the fact that the ion influx at the spike will induce an increased average wedge-shape of the molecules, due to electrostatic screening of the lateral repulsion of phosphatidylserine molecules. Furthermore a conformation associated with the spike would directly relate action potential propagation to the mass-cooperative vesicular fusion, involved in the chemical signal transfer by transmitter molecules at the pre-synaptic membrane. Experimental support for this concept has been recently reported [39]. This well-controlled fusion process of numerous "vesicles" with the presynaptic membrane must take place as a phase transition. The... 

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