Correlation of Solvent Contact Angle and Nanoparticle Dispersibility Due to Surface Grafting

The dispersion of inorganic nanoparticles in resin, monomer or their compatible solvent is the first step in thepreparation of organic/inorganic nanocomposite for applications such as high refractive index opticalmaterials and photoresist for next-generation photolithography. For the dispersion in high dielectric polarsolvents, the surface charge on nanoparticles, thus the electrostatic repulsion between them, is the majorfactor. However, for dispersion in a low dielectric nonpolar solvent, the electrostatic force no longerdominant. The inorganic nanoparticles must be modified with a ligand that interacts favorably with thedispersing solvent. The compatibility between ligand and solvent may be analyzed based on their Hansensolubility parameters (HSP), which is available for the most solvents. The parameters for the attached ligand,on the other hand, must be found by the direct observation of compatibility, i.e., whether the modifiedparticles disperse in the solvent. Not only is this process circular-riddle, but the surface modificationprocedure may also affect the ligand loading density on the surface, thus leading uncertainty to the result. Itis known that the interaction between the attached ligand and the solvent also manifest as the interfacialtension, thus the contact angle, of a solvent droplet on a self-assemble-monolayer (SAM) of the ligand on asubstrate. The SAM can be prepared with better confidence and the measurement of the contact angle aroutine. Therefore, we propose to study the compatibility between ligand and solvent by contact anglemeasurement and confirm the results with the dispersion of ligand modified nanoparticles. We expect toestablish a correlation between the HSP and the contact angles, which will be useful for future dispersionstudies.