Normally silica is hydrophilic. If your silica is hydrophobic, that means some functional groups attach on the surface of the silica. You can remove the functional groups by high temperature annealing first and then disperse the treated silica in alcohol.

Or you can try to disperse the hydrophobic silica in non-polar solvent like toluene by probe sonication.

Instead of alcohol and water try dispensing your hydrophobic particles in analytical or semiconductor grade kerosene, toluene, benzene, MEK, tetrahydrofuran, n-hexane - something should wet them. If for some you have to dispense in water/alcohol mix then try adding tiny quantity of surfactant, either amonium laurate or sodium dodecyl sulfate could often work to wet powders. Good luck!

Thanks so much guys for the suggestion. I will try them

Try cyclohexane since your NPs is hydrophobic

I don't recommend you to heat your system. Silica particles morphology are dependant on the temperature, heating them makes them loose surface area by viscous sintering, if they are amorphous. I also advise for cyclohexane and them using ultrasonic bath.