Photo- and Thermoresponsive Reversible Wettability and Corrosion Protection of Electrophoretically Deposited TiO2/Pectin Composite Coatings.

Stimuli-responsive coatings with reversible wettability hold substantial promise for biomedical, environmental, and industrial applications. Among these, titanium dioxide (TiO2)-based coatings are widely studied for their unique photoresponsivity and high refractive index; however, they often rely on complex and resource-intensive production processes, raising environmental and economic concerns. This study introduces a sustainable alternative with a TiO2-pectin composite coating on stainless steel fabricated via a simple electrophoretic deposition process. Pectin, a renewable hydrophilic polysaccharide, was incorporated specifically to optimize the coating wettability. Here, we show that TiO2-pectin composite coatings exhibit reversible wettability, transitioning from superhydrophobic (154°) to hydrophilic (57.46°) under UV irradiation, with complete recovery through thermal treatment at 80 °C. Fourier-transform infrared and X-ray photoelectron spectroscopy before and after UV exposure confirm the composites' chemical and structural morphology, with pectin concentration playing a key role in modulating this reversible behavior. Mechanistically, pectin's functional groups synergize with TiO2's surface properties to enhance responsive water adsorption and enable switchable wettability. Potentiodynamic polarization tests reveal mixed-type inhibition behavior, with corrosion current densities of 180 and 221.3 nA/cm2 after 1 and 7 days of NaCl solution immersion, respectively, demonstrating sustained corrosion resistance under saline conditions. These eco-friendly TiO2-pectin composite coatings offer a multifunctional solution combining sustainable design with reversible wettability and corrosion resistance.