If you want to make chemistry modification, you can use a hydrophobic subsbtances. Another option is embedded the particles with hydrophobic liquid (this is not the best method).

You can modify surface of NP with hydrophobic material like; Organo Silane material, fluoroniate  material and other to have hydrophobic surface and low surface energy.  

Check this, however, this mostly applies only metal oxide nanoparticles

https://www.researchgate.net/publication/261101583_Smoothly_Tunable_Surface_Properties_of_Aluminum_Oxide_Core-Shell_Nanoparticles_By_A_Mixed-Ligand_Approach

And this:

https://www.researchgate.net/publication/281056317_Very_Facile_Polarity_Umpolung_and_Noncovalent_Functionalization_of_Inorganic_Nanoparticles_A_Tool_Kit_for_Supramolecular_Materials_Chemistry

Can anyone let me know how to make the TiO2 nanoparticle surface hydrophobic by chemical functionalization? - ResearchGate. Available from: https://www.researchgate.net/post/Can_anyone_let_me_know_how_to_make_the_TiO2_nanoparticle_surface_hydrophobic_by_chemical_functionalization [accessed May 4, 2016].

Article Smoothly Tunable Surface Properties of Aluminum Oxide Core-S...

Article Very Facile Polarity Umpolung and Noncovalent Functionalizat...

if the particles were in microns, you could have modify the surface and make it hydrophilic to solve the issue, for nano particles, however, I believe huge surface energy will not be surpassed. well I may be wrong though...

generally speaking, any linear molecule that includes a CH or n-CH termination on one side and a thiolated or carboxili or amined termination on the other side can be used to make the oxide (or oxidized) nanoparticle surface hydrofobic. The trick is applying the right bath chemical reaction to favor the second termination (thiolated or else) grafting onto the nanoparticle size via a relatively strong bond, so to form a sort of properly aligned crown of such linear molecules around the particle. To process this encapsulation would require proper environment (and water is not aleays the case), sometimes using catalyzers or physical solicitations like UV irradiation or simply heat.

A case study is n-thioles grafted on Gold NPs (e.g. dodecanthiole on NP).

If the molecules you select possess also the right structure, with some reactive side termination, lateral polimerization or reticulation can be activated (usually through physical solicitations) after grafting, which ends up into a sort of quasi-compact coating of the nanoparticle that keeps the CH-structured external termination and hence the hydrophobic behaviour.

You can use various low surface energy carboxylic acids to modify the nanoparticle surfaces. 

Article Branched Hydrocarbon Low Surface Energy Materials (LSEMs) fo...

I am very thankful and really pleased to see so nice and prompt replies. I am very impressed!