Sana Mirza Research and Google 'zeta potential' and read any books by Robert Hunter... For example, Zeta Potential in Colloid Science

Robert J Hunter Elsevier Ltd (1981) ISBN: 978-0-12-361961-7. You should be able to get this book in your university library or (at worst) by inter-library loan. See the Loan Arranger. Good luck with your research.

I would add to Alan F Rawle 's helpful answer that it also depends on the type of colloid. There are two broad classes: lyophilic and lyophobic. They behave very differently in response to pH and ionic strength. Very few books bother to discuss lyophilic colloids which can lead to confusion when a real world colloid doesn't behave the way the (wrong) theory suggests. A classic example is aqueous protein dispersions.

Hi,

Role of ionic strength in colloids

The ions have an electrical charge that can attract or repel each other. Furthermore, this attraction and repulsion has direct influence in the stability of the colloidal solution.

The higher the repulsion, the higher the stability of the colloidal solution ie) it helps the colloidal solution to stay without combining, with the zeta potential value we can understand this.

There are literatures that say zetapotential value of colloids above +30mV (like +40, +50) or below -30mV (like -40,-50) are said to be more stable.

Role of pH strength in colloids

Increasing the pH increases the negative charge on the colloidal particles and thereby increases the surface potential

The isoelectric point of a colloid is a pH at which net charge on colloidal particles is zero. Above this pH, the particles are negatively charged and below this pH, particles are positively charged

Literature for ref

https://doi.org/10.1021/acs.langmuir.5b01857

10.1016/j.carbpol.2015.07.050

Article Formulation of a stable biocosmetic nanoemulsion using a Bac...

https://thefactfactor.com/facts/pure_science/chemistry/physical-chemistry/charge-on-colloidal-particles/11893/#:~:text=The%20isoelectric%20point%20of%20a,pH%2C%20particles%20are%20positively%20charged.

Hope this helps!!