Zeta potential in present context for determining stability for nano-emulsion systems is hugely dependent on the kind of surfactants which are being employed for fabrication. It gains prominence, when the surfactant in question is either anionic or cationic. Quite a few literature are available on it:

http://ac.els-cdn.com/S1359029405000348/1-s2.0-S1359029405000348-main.pdf?_tid=cb0f4c3c-fead-11e4-8535-00000aab0f26&acdnat=1432098491_c0d255ed9c7735e42bf9aad8b3d3e758

Dear Usama,

I would say that if tour zeta potential value is higher or lower than +20mV, -20mV respectively, it should ensure you good stability of the nano-emulsion  by electrostatic repulsion. With non-ionic/polymeric surfactant you should also obtained stable nano-emulsion with almost zero zeta potential, in this case the droplets are stabilized by steric repulsions.

Dear jeremie Nestor,

Can you explain how does the nanoemulsion prepared using non ionic surfactants with almost zero zeta potential are stabilized by stearic repulsions?? can you provide any refernce for the same.

Dear Usama Ahmad, it is equally important to note that zeta potential is quite different from viscosity, the zeta potential is measured in mV while the viscosity is in cps.The zeta potential measures surface charge on the droplets.

Regards.

 Dear Atit, 

You can have a look to some reviews of Tharwat Tadros that describe very in detail steric stabilization. Best regards  

Dear Pandey

I prepared nanoemulsions using self-emulsifying non ionic surfactants. zeta potential measured for different formulas always so close to zero. when it is away from zero (like in one case it was +19 & -19, the report will read (poor quality).