Surface charge regulation

Beyond this, the inclusion of the competition for surface sites of different competing species (e.g. H vs. Na" ") gives rise to the further problem of surface charge regulation [22, 27-30], with a concomitant appearance of a so-called "secondary hydration force". Surface localised dipole-dipole correlations give rise to a further force [31, 32], and much of what was confused falls into place. These developments represent a first conceptual step forward on the way to a more complete and necessary stage of... 

Behrens SH, Brakovec M (1999) Electric double layer interaction of ionizable surfaces charge regulation for arbitrary potentials. J Chem Phys 111 382-385... 

Li J, et al. Surface charge regulation of osteogenic differentiation of mesenchymal stem cell on polarized ferroelectric crystal substrate. Adv Healthc Mater 2015 4(7) 998-1003. 

S. H. Behrens and M. Borkovec, J. Chem. Phys., Ill, 382 (1999). Electric Double Layer Interaction of lonizable Surfaces Charge Regulation for Arbitrary Potential. 

The second important difference is that the interface potential is present at the (outer) Helmholtz layer of the semiconductor/soiution interface. The interface potential is produced by surface dipoles of surface bonds as well as surface charges due to ionic adsorption equilibria between the semiconductor surface and the solution. If the interface potential can be regulated by a change in the chemical structure of the semiconductor surface, then the semiconductor band energies can be shifted to match the energy levels of the solution species (oxidant or reductant). This is another advantage of the semiconductor system because this enables improvement of the electron transfer rate at the semiconductor/soiution interface and the energy conversion efficiency. 

In addition to the constant potential and surface charge density boundary conditions, a third condition has been proposed [18,19] that is essentially a linear combination of the other two. This linearized regulation boundary condition takes the form... 

It is possible to calculate Vr as a function of separation exactly using numerical techniques. The method of Chan et al. 145] may be used for this purpose. Interested readers are referred to Ref. 45 for further information about these calculations. It is also possible to calculate the interaction for the charge regulation case where knowledge of the surface density of acid groups and their dissociation constants is required. 

If the dissociation of the ionizable groups on the particle surface is not complete, or the configurational entropy Sc of adsorbed potential-determining ions depends on N, then neither of ij/o nor of cr remain constant during interaction. This type of double--layer interaction is called charge regulation model. In this model, we should use Eqs. (8.35) and (5.44) for the double-layer free energy [ 11-13]. 

Comparison is made with the results for the two conventional models for hard plates given by Honig and Mul [11]. We see that the values of the interaction energy calculated on the basis of the Donnan potential regulation model lie between those calculated from the conventional interaction models (i.e., the constant surface potential model and the constant surface charge density model) and are close to the results obtained the linear superposition approximation. 

Most materials discussed in this book are electrical insulators, and their surface charge is regulated by sorption processes. However, a few oxides show sufficient degree of electronic conductivity that makes it possible to polarize the surface using an external battery. For example, the charging curves of IrOj can be plotted as a function of pH (when the oxide is polarized to constant potential) or as a function of polarizing potential at constant pH [5], Properties and preparation of oxide electrodes (often termed DSA, dimensionally stable anodes) were reviewed by Trasatti [6], Also adsorption properties of some sulfides, e.g. natural chalcocite [7] can be modified by polarization by external electric potentials. 

Zhmud, B.V. and Sonnefeld, J., Charge regulation at the surface of porous silica,... 

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