I wonder some principles to tell the zeta potential of a material such as glass, cotton, paper or plastic. Are they positively or negatively charged in water? Why ?
Do you mean a nature of zeta potential of these materials? The matter of the question's not clear
Yes, Michael. You are right. That is the new field to me. I just what to know whether a material has positive or negative charge.
You name only non-conducting materials. But these have certain conductivities as well, even if the values are very low. In addition they will have quite different surface topographies and /or dissolvable functional groups. All these parameters determine the amount of surface charge that will adsorb to the surface in a fluid and may result in quite different zeta potentials.
Zeta potential is dependent on the nature of charge (positive or negative) as well as on the charge density. The latter is also influenced by the swellability of the material eventually leading to a reduced charge density (reduced potential height) which can be expected e.g. for the cotton fibre.
Zeta potential is essential to know if charged species will be attracted toward, or repulsed from, the surface of your material. Therefore such kind of measurement, which most of times depend on the pH, is of key importance for many applications: adsorption, dying, ...
Alain
Notice, that both parameters are not similar. Comparing pHPZC, when point of charge = 0, with the isoelectric point (pHIEP, zeta potential = 0) you should keep in mind two different mechanisms of these phenomena. PZC is provoked by the absence of any ions on the interface. Contrastingly, the isoelectic point is a result of the presence of potential-determining ions of the surface compensated by counterions found in liquid phase. You see?
In this paper you can find the determination of the pzc of several industrially used catalytic supports (SiO2, TiO2, gamma-Al2O3 and MgO).
Potentiometric mass titrations: a quick scan for determining the point of zero charge
John Vakros, Christos Kordulisab and Alexis Lycourghiotis
CHEM. COMMUN. , 2002, 1980–1981
It is measure of potential from the plane of shear, plane of shear is an imginary plane (viscosity drastic change indicator) sometimes it is treated as OHP. sign of the zeta potential values depends on the charge on the material if matrials bear positive charge zeta potential is positive and viz viz
For the materials you mentioned I would expect negative zeta potentials. Glass and cotton bear OH-groups which can be deprotonated with increasing pH. I would expect this also for paper based on cellulosic fibres. However, I don't know what additives are used in papermaking which might influence the type of surface charge.
In case of polymers you also can expect more or less negative charges. For example PP is very sensitive towards oxidation (due to its tertiary carbon) leading to more or less amounts of carboylic groups in the material surface.
Hello Daniel,
I also new in this but it may be helpful the following way:
The Origin of Charges in Polar Media
All materials spontaneously acquire a surface electrical charge when brought into contact with a polar medium (i.e., water). Generally an interface in deionized water is negatively charged, but there are materials that can be positively charged. Some charging mechanisms are:
1. Electron affinity differences of two phases
2. Ionization of surface groups
3. Differential ion adsorption from electrolyte solution
4. Differential ion dissolution from a crystal lattice
5. Surface anisotropy
6.Isomorphous substitution
More details are given in the attached file from some pharmaceutical company.
The best review about different approaches describing zeta potential of various fumed oxides is attached. It's written by my supervisor. The approaches are good for all types of materials. So, our topicstarter's getting pretty tired of plenty of information. He's proposed to be left for a while for trying to find the sense of all written stuff here. )))
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