see the following link may be help you

http://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.6b01116?journalCode=enfuem

Write correctly pH!  The concept of pH is designed for aqueous solutions. In organic media (acids, amines), it is also sometimes used.

Https://www.iupac.org/publications/pac/1985/pdf/5703x0531.pdf

Vegetable oils are characterized by an acid number. This indicator indicates the amount of free acids in the oil. They are few, but they are in every oil. Higher fatty acids can react with aluminum oxide to form salts. They increase the viscosity of the dispersion and stabilize it. 

i am not sure the details but higher pH often gives the particles more negative surface charge, which increases colloids stability   

Can you measure the Zeta potential? 

@ Robert Is your comment 'tongue in cheek'?!  The zeta potential can be derived from a mobility measurement of a particle in an electrical field. Conductivity is needed for such mobility and I'm unsure of whether there's enough ionic content in coconut oil to permit this.  Certainly ions will be tightly bound to the alumina and the concept of a slipping plane may be difficult to understand in such a non-aqueous system (and pH is also something that's inappropriate for such systems as Yuri has correctly pointed out above). Zeta potential is most often used in aqueous systems where it can be used as a marker of stability for charge-stabilized systems (as opposed to sterically stabilized systems).

I have used Zeta potential to determine emulsion stability. It does work with lipophilic systems. And coconut oil doesn't oxidize alumina oxide. I know this from formulating this and similar systems in sunscreens.