I am working on graphene nanocomposite electrochemistry. I want know about relation between capacitance and zeta potential?
I would like to help you , but you must first tell me what you mean by zeta potential.
regards
Petr
Have a look at the following ref.
http://dx.doi.org/10.1016/j.jcis.2006.12.075
Dear Thankavel,
thanks to Gustav, I now know what is meant by zeta potential. And it is what I have been fearing, a rather ill-defined quantity that in the colloidal science is considered rather important, but is very difficult to measure, despite the apparent various electro-acoustic methods. There are two cases to consider and I guess yours is the case n.2 :
1.Case 1- colloidal particle. If the particle(usually large compared to other electrically active spieces in the solution/electrolyte) is electrically polarisable, then in principle (energy considerations) , ions of a particular charge will get stuck to it's surface and thus become immobile (the effective size of a particle "increases"). A charge dipole is thus formed across the particle-immobile ion interface. It is postulated that another layer, adjacent to the first immobile ion layer, might be formed by solvated/hydrated ions of the opposite charge, which will be(by the same argument) quasi-immobile. Further away then is the rest of electrolyte with mobile ions(possibly solvated/hydrated), where the region of non-zero total charge is called (in my view rather incorrectly) a diffuse layer(the transport in this region IS NOT governed by diffusion, but rather by diffusion and drift !!). The non-zero charge density in the region where the charges are immobile then determines the electrical field and potential(~zeta potential) that gives rise to your capacitance you are after. It is approximately geometrical capacitance of this region with modified dielectric constant (somewhat different from the solute dielectric constant). The only problem is that you will never be able to measure it, since you can not put your external measuring potential in the middle of your colloidal particle. So, in my view, the only way how to determine properly this layer, is through measurement of the overall colloidal particle effective mobility, assuming the validity of Stoke's law. We were able to measure the absolute hydrated ion mobilities in this way, using Electrical Impedance Spectroscopy. I would not trust other methods, but then I do not know enough about them.
2. Case2 - metal electrode surface. The same arguments apply here, only now the situation is "easier", because the electrode surface is charged, not just polarisable and the whole problem is well defined. Everything can be calculated and checked experimentally since the calculated capacitances are MEASURABLE directly ! But even here the situation is quite non-trivial because what you measure is various capacitances(shorted by corresponding dc currents-resistors) in series. At high frequencies you will measure the electrolyte bulk geometrical capacitance (not a problem). However, going down in frequencies, there will be 2 to 3 contributions to the measured capacitance. In increasing order (decreasing thickness) they are "diffusion layer" capacitance, Double layer capacitance and possible contribution from "universal dielectric response" very often seen in electrolytes in this interfacial region.
In conclusion then, the relation you seek between the so called zeta potential and capacitance is the relation/correlation between the potential from the electrode surface to the "slipping plane"(demarcation line-ill defined !!, between the immobile and mobile charges near metal electrode-solute interface) and corresponding geometrical capacitance of that spatial region.
I hope this will help you on the way
With best regards
Petr
As soon as a double layer forms a capacitor is formed but if there exists a flowing solution along the surface then some of the charge will be carried away by the solution.Here comes the zeta potential into play. Capacitance depends on the two charged surfaces while the flowing electrolyte's concentration creates a zeta potential which is due to the compression of the double layer
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