I realise that this is an old question and hope Sayed found an answer elsewhere, but for the benefit of anyone else stumbling across this question and looking for a similar answer.

A common reason for measuring zeta potential is to infer something about the conditions in which a dispersed material is stable, assuming that electrostatic interactions are the mode of stability, and not steric stabilisation.

You will often read apparent universal rules of > +/- 30mV indicates stability, but this is misquoted from literature and is an arbitrary assessment for a particular system.

That said, the greater the magnitude of zeta potential, the stronger the electrostatic interactions which may give better stability.

That assumes that other factors such as sedimentation are not dominant.

In terms of what can we predict from a zeta potential of -100mV, the short answer is nothing without more information about the system in question and the conditions of the measurement.

Alexander Malm 's last sentence - Yes!

Another important factor that modern science (last 20 years) has forgotten or just is too lazy to read about is that particles like this are hydrophilic colloids. The concepts of stability as usually applied (DLVO theory etc) - do NOT apply.

Further, the particles are porous and allow fluid to flow inside the particle. This means the usual equations linking electrophoretic mobility (the thing Zetasizers etc measure) and zeta potential (that is calculated) are INVALID.

In fact, the "soft" nature of a particle such as this even means the concept of zeta potential is meaningless.

So...the usual concepts for stability and zeta potential are unlikely to apply.

Hermans, J. J. Sedimentation and Electrophoresis of Porous Spheres. J. Polym. Sci. 1955, 18 (90), 527–534. https://doi.org/10.1002/pol.1955.120189008.

Ohshima, H. Electrophoretic Mobility of Soft Particles. Electrophoresis 1995, 16 (1), 1360–1363. https://doi.org/10.1002/elps.11501601224.

Hill, R. J.; Saville, D. A.; Russel, W. B. Electrophoresis of Spherical Polymer-Coated Colloidal Particles. Journal of Colloid and Interface Science 2003, 258 (1), 56–74. https://doi.org/10.1016/S0021-9797(02)00043-7.

Duval, J. F. L.; Ohshima, H. Electrophoresis of Diffuse Soft Particles. Langmuir 2006, 22 (8), 3533–3546. https://doi.org/10.1021/la0528293.

Hsu, H.-P.; Lee, E. Electrophoresis of a Single Charged Porous Sphere in an Infinite Medium of Electrolyte Solution. Journal of Colloid and Interface Science 2013, 390 (1), 85–95. https://doi.org/10.1016/j.jcis.2012.09.036.

Verwey, E. J. W. Theory of the Stability of Lyophobic Colloids. J. Phys. Chem. 1947, 51 (3), 631–636. https://doi.org/10.1021/j150453a001.

I say zeta potential is invalid because it implies a rigid surface. The concept of a potential does apply to soft particles but it's definition is different. If you are using light scattering to measure zeta potential then you are actually measuring electrophoretic mobility. The instrument then applies a calculation that assumes that the concept of zeta potential applies (usually one of three models - Huckel, Smoluchowski or Henry). The challenge is finding the correct electrokinetic theory to relate your particle charge to the electrophoretic mobility. There are many including some that allow for the flow of liquid through all or part of the particle. This effects a number of things such as the viscous drag of the particle when moving in the electric field. I didn't intend to imply zeta potential isn't appropriate for sedimenting particles. I meant that the the viscous drag is different for a porous particle than a solid one. Thus there is a parallel between the theories for sedimentation and electrophoresis for porous particles. Both involve an external force field to make the particles move in a viscous medium.

I'm currently writing a paper that is very relevant to this. It shows with experimental titration and electrophoresis data of proteins the importance of selecting the right electrokinetic model and also making measurements at multiple salt concentrations. The paper also shows the weaknesses of the current generation of electrophoretic light scattering instruments when it comes to making reliable enough measurements at the conditions needed to identify the correct electrokinetic model.

Thanks a lot Sir.