Fine-tuning of surface properties of dual-size TiO2 nanoparticle coatings

In this work, we focus on wetting and morphology properties of fluoroalkylsilane modified TiO2 (FAS-TiO2) and as-received TiO2 nanoparticle coatings. TiO2 nanoparticles of two sizes (30 nm and 300 nm) were spin coated onto steel substrate covered with 300 nm layer of epoxy via layer-by-layer (LbL) deposition until the desired wetting characteristics were achieved. Static water contact angles, advancing and receding contact angles and contact angle hysteresis were measured to evaluate the wetting properties of FAS-TiO2 and as-received TiO2 nanoparticle coatings. The morphology of coatings was analyzed with average surface roughness (Sa) measurements and SEM imaging. We have presented a simple step-like procedure to fabricate TiO2 nanoparticle coatings with target wetting properties, either (super)hydrophobic or (super)hydrophilic. Order of the LbL deposition of dual-size nanoparticles for the fabrication of superhydrophobic/superhydrophilic coatings was found to be an important factor influencing on surface roughness and hence wettability. SEM images revealed a typical morphology and Sa difference between FAS-TiO2 and as-received TiO2 nanoparticle coatings reflected in the discrepancy of the average size of the agglomerates that are coating the substrate. Based on these results we can fine-tune the surface roughness and wettability by controlling the LbL deposition of dual-size FAS-TiO2 and as-received TiO2 nanoparticles.