You can use the nanoparticles adsorbed on a certain support that can reduce the agglomeration tendency as well as facilitate convenient separation of nanoparticles after treatment.

Kindly refer the attached link for detailed procedure.

https://www.sciencedirect.com/science/article/pii/S0925346717305505

The greater the Gibbs surface energy of the disperse system, the stronger the particles aggregate. The change in the Gibbs surface energy in the process of aggregation is equal to the multiplication of the change in the specific energy (surface tension) by changes in the surface. This is a theory. Surface tension is changed by surfactants, high-molecular substances, electrolytes. Change in the surface is achieved by changing the particle size. Therefore, the micro-particles will aggregate less than nanoparticles.

If you're starting with a powder then you'll have a fused set of sub- and post-micron sized particles caused by solid-solid diffusion. Aggregation is irreversible (agglomerates can be separated by sonication). Aggregates cannot be separated into their 'primary particles'. Van der Waals forces are always attractive and thus the system can only be effectively preserved by 2 routes:

• A bottom-up process keeping the particles discrete and stable (e.g in colloidal suspension or atomized form). This can be a charge stabilized (optimum concentration of phosphate for metal oxides) or steric stabilization (an absorbed polymer, say a 50 kDa PEG or PEI)
• A bottom- up process generating one particle on another thus sterically separating them as Rohini suggests above. Supported metal catalysts are one example. Salbutamol on lactose is another.

See, for example (open in IE):

Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge

November 3rd, 2015 Adhesion and cohesion http://tinyurl.com/zwb2wlh

Thank you for all of your answers.

My simple contribution though. Raising the pH of colloidal nano particles increases the density of negative charges on their surface. Hence, the electrostatic repulsion between nano particles are increased, reducing aggregation. So, simply dissolving (colloidal) nano particles in water and tuning the pH can be an effective way to tune colloidal dispersion. Thank you.

Dear Stephen,

pH is the negative logarithm of the activity of hydrogen ions. There can not be a pH of the colloidal nano particles. Maybe the pH of the solution. When dissolving colloidal nanoparticles, they will not. You meant the distribution of nanoparticles in water. The expert should not make such mistakes.

Thanks for your correction Professor Yuri. Actually, I meant the pH of the solution in which the nanoparticles will be dissolved. Definitely, the distribution of nanoparticles in water for the case presented, where the pH and zeta potential can be correlated. I speak of pH-dependent surface charging of nanoparticles. For example, silica nanoparticles with silanol (Si-OH) groups on their surface. Dispersion of the said nanoparticles in water influences the overall pH measured. Let's say a certain weight fraction of silica nanoparticles in water (at a pH of 3) aggregates, and you observe white cloudiness. When you add some base, say NaOH, and after stirring for some time, you can observe the disappearance of the white cloudiness. Excess OH(-) in solution, as made available by the NaOH, results in the dissociation of Si-OH into Si-O(-). Afterwards, a high density coverage of negatively charged groups on the nanoparticles causes electrostatic repulsion which counters the aggregation, at least to a large extent.

Try to cover the surface of your nanoparticles with hydrophillic ligand. It will help your particles to get nicely dispersed in the water.

The particles aggregate may be reduced either by adding surfactants or increasing nanoparticle's dia. or both.