Measuring zeta potential - origin of zeta potential

This is a recording of a webinar I gave on How To Measure Zeta Potential More Confidently.
I show you how you can maximize the confidence in your measurements - and their interpretation - needed for robust decision making.
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TRANSCRIPT
What happens when a charged particle is immersed in a liquid such as an aqueous electrolyte solution? In this case, there's a positively-charged particle surface and somewhere there has to be a balancing negative charge.
Typically, that will be in the form of ions adsorbed onto the surface of the particle. You can consider this to be a fixed or rigid layer of charged material.
With an electrolyte solution, there's a uniform distribution of anions and cations in the bulk.
Near the particle, anions (shown in yellow) will be attracted towards the particle leading to a higher concentration of anions.
And, similarly, repulsion of cations (shown in blue) will result in a lower concentration of cations.
This region is a diffuse layer of ions balancing the charge on the particle. So, we have a rigid layer associated with the particle surface and tightly bound material, and then a diffuse layer.
Combined, we get the diffuse electrical double layer.
There's a transition from the diffuse layer with an excess of counterions to the bulk solution with a uniform concentration of ions.
Very close to the particle, material is either adsorbed or strongly associated with the particle such that it remains with the particle when it moves relative to the bulk liquid. The transition point between bound and free liquid is called the shear or slipping plane. But what does this say about the magnitude of the electrostatic repulsion between particles? If we have two such particles approaching, we know intuitively that there'll be electrostatic repulsion. But how is that quantified? And how does it look spatially as you go away from the particle?