Sol-gel hybrid fluorinated coatings : preparation, characterisation and correlation with human perceived sensorial properties

The aim of the project was to develop and characterise transparent sol-gel hybrid fluorinated coatings with high mechanical properties, and also to correlate human perceived sensorial properties with coatings physical properties. Sol-gel hybrids containing either silica or a mixture of silica and zirconia were formulated and compared. Five different compositions were selected in order to observe the change in properties caused by inorganic-to-organic weight ratios and by different zirconia-to-silica ratios. The coatings were deposited by spin coating on glass, aluminium and polycarbonate substrates. Chemistry of the reaction was evaluated with infra-red spectroscopy. Thermogravimetric analysis was used to estimate the crosslinking degree. Surface chemical composition was studied with X-ray photoelectron spectroscopy. Optical contact angle measurements were performed to evaluate wettability. Atomic Force Microscopy (AFM) was used to measure Young’s modulus with nanoindentation tests. AFM imaging was also performed to investigate surface morphology and phase homogeneity. Nanoscratch hardness was evaluated by performing lithography on the samples with a diamond tip. Young’s moduli up to 31GPa and scratch hardness up to 3GPa were obtained. Solvent and thermal resistance, weatherability and pencil hardness tests confirmed the high performance and durability of the hybrid coatings in many application fields. In particular, it was found that the sol-gel coatings enhanced the scratch resistance of polycarbonate after accelerated solar light degradation. Eventually, different coatings, including one of the hybrids, were deposited on aluminium panels with different finishes. Volunteers were asked to rate their perceptions regarding slipperiness, roughness and brilliance of this set of samples. Physical properties such as coefficient of friction, gloss, surface free energy and roughness were measured. The influence of the coatings on the subjective perceptions was investigated with ANOVA tests. Coatings had a significant effect on the perception of roughness, slipperiness and brilliance. Correlations were found between some physical properties and subjective ratings.