Preparation of Superhydrophilic TiO2 Multilayer Coatings via Dip Coating for Improved Tribological Performance
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Superhydrophilic titanium dioxide (TiO2 ) coatings were fabricated on glass substrates using dip coat ing to improve the tribological performance of mold applications. Coating solutions containing 3 wt% TiO2 nanoparticles, a 1 wt% silane coupling agent (A174), and 1 wt% tetraethyl orthosilicate (TEOS) in ethanol were prepared and applied through repeated dip-coating cycles at a withdrawal speed of 0.3 mm/s. The surfaces with one or multiple coating layers (1-5) were characterized for surface morphology, roughness, wettability, and tri bological properties. Single-layer coatings exhibited incomplete surface coverage with scattered islands of the coating material, whereas coatings with four or more layers exhibited complete surface coverage. The surface roughness increased from 0.01 (bare glass) to 0.14 μm (5 layers), with a plateau occurring after three layers. After applying four and five coating layers, the water contact angle of the surfaces significantly decreased from 91.53° (bare glass) to 2.43° (5 layers), resulting in superhydrophilic behavior. Tribological tests conducted on the sur faces under dry conditions revealed that the friction coefficient decreased from 1.45 (bare glass) to 0.82 (four layers), with multilayer coatings forming compacted particle layers. With underwater lubrication, the supe rhydrophilic surfaces demonstrated outstanding performance, with a low friction coefficient of 0.54 (4 layers), which can be attributed to the formation of a stable water film. The four-layer coating, with superhydrophilicity and enhanced tribological performance, is the optimal configuration, which can replace the expensive titanium based molds in manufacturing applications.
Abstract
Superhydrophilic titanium dioxide (TiO2 ) coatings were fabricated on glass substrates using dip coat ing to improve the tribological performance of mold applications. Coating solutions containing 3 wt% TiO2 nanoparticles, a 1 wt% silane coupling agent (A174), and 1 wt% tetraethyl orthosilicate (TEOS) in ethanol were prepared and applied through repeated dip-coating cycles at a withdrawal speed of 0.3 mm/s. The surfaces with one or multiple coating layers (1-5) were characterized for surface morphology, roughness, wettability, and tri bological properties. Single-layer coatings exhibited incomplete surface coverage with scattered islands of the coating material, whereas coatings with four or more layers exhibited complete surface coverage. The surface roughness increased from 0.01 (bare glass) to 0.14 μm (5 layers), with a plateau occurring after three layers. After applying four and five coating layers, the water contact angle of the surfaces significantly decreased from 91.53° (bare glass) to 2.43° (5 layers), resulting in superhydrophilic behavior. Tribological tests conducted on the sur faces under dry conditions revealed that the friction coefficient decreased from 1.45 (bare glass) to 0.82 (four layers), with multilayer coatings forming compacted particle layers. With underwater lubrication, the supe rhydrophilic surfaces demonstrated outstanding performance, with a low friction coefficient of 0.54 (4 layers), which can be attributed to the formation of a stable water film. The four-layer coating, with superhydrophilicity and enhanced tribological performance, is the optimal configuration, which can replace the expensive titanium based molds in manufacturing applications.