Interactions between nanofluids and solid substrate: Role of pH and nanofluid particle concentration on the three -phase-contact angle

We investigated the effect of pH on the interactions between a silica slurry and a silica wafer substrate (TEOS) made by the chemical vapor deposition of tetraethylorthosilicate gas in order to understand the optimization of the Chemical Mechanical Polishing (CMP) process and develop a high-performance silica slurry. The nature of the interactions is probed by the solid-liquid interfacial energy and the electrostatic surface potential at the solid surface.;The surface potential and surface charge density at the silica/water surface are calculated by a model based on the Young-Lippmann equation in conjunction with the Gouy-Chapman model for the electric double layer. In order to evaluate the model, a galvanic mica cell was made of a mica sheet and the surface potential was measured directly at the mica/water interface. The model results are validated by the experimental data from the literature, as well as the results obtained by the potentiometric titration method and the electro-kinetic measurements.;The interactions between the nanofluid (liquids contain nanoparticles) and solid surface are explored by measurements of three-phase contact angle of the nanofluid on a silica substrate. The results show that the contact angle decreases as the volume fraction increases due to the formation of particle layers on the solid surface. We conclude that it is driven by the depletion attraction between the nanoparticles and a solid surface. We found that the strong repulsive force (hydration force) at a short distance (less than 2 nm) gives rise to enough energy to change the three-phase contact angle.