thermodynamics - Estimating maximum size of magnetite particles in this Nile Red ferrofluid video?

In the Nile Red video Making ferrofluid from scratch a suspension of small magnetite ($\ce{Fe^{2+}Fe_2^{3+}O_4^{2−}}$) particles is produced from a combination of ferrous chloride and ferric chloride.

The nanoparticles are then given a coating of oleic acid ($\ce{CH3(CH2)7CH=CH(CH2)7COOH}$) to provide steric stabilization to prevent aggregation, then dissolved in kerosene.

After about 23:20:

…the magnetite isn’t truly dissolving, it’s going into suspension. This is because the nanoparticles aren’t soluble in the solvent, but they’re small enough that they can still easily get dispersed.

The oleic acid coating that helps with this, by preventing two particles from coming too close together, and by also allowing them to interact with the non-polar solvent. The result of this is a stable suspension known as a colloid, where it’s almost like the magnetite being dissolved.

As an exercise I'd like to estimate the maximum size of the oleic acid-coated magnetite particles that can be stable in this solution. Some considerations are:

1. 
   

   While the magnetite particles themselves have a high density (over 5 g/cm³), the oleic acid molecules might be arranged radially making the volume of the complete particle much larger than the magnetite core.

   
   


2. 
   

   While large magnetite particles would sink quickly to the bottom due to gravity, the thermal agitation (Brownian motion) at room temperature is sufficient to keep these in colloidal suspension if they are small enough. This suggest that there might be some ratio of $k_B T$ with some expression of gravitational potential energy.

   
   

Question: How would I go about estimating the maximum size of the magnetite nanoparticles that could remain in stable suspension in this case?

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