In the last 50 years, there has been a significant increase in the use of synthetic paints for indoor and outdoor applications, mainly due to its wide range of available colors and easy usage. Acrylic/resin-based paints contain several types of heavy metals, volatile organic compounds (VOCs), non-degradable biocides and additives for microbial, physical and chemical protection that affect human health and the environment.  Although traditional lime-based paints have emerged as an alternative due to their low cost and antibacterial character, there are some concerns related to their low durability, affecting its commercial feasibility. Currently, water repellency or self-cleaning properties of plant leaves have inspired the extensive development of anti-wetting surfaces for different applications. Engineered self-cleaning coatings require static contact angles (CA) higher than 150° and sliding angles (SA) lower than 10° to allow liquid droplets to pick up and remove dust, viruses, and bacteria during bouncing and rolling contact with the surface. Hence, the following study aims to evaluate the development of nano-paints based on the incorporation of S80APT, S80SY, MgO, CaCO3 , and CNTs (Carbon nanotubes) nanoparticles (NP) and a commercial fluorocarbon surfactant (named as SY) in lime-based paints for the development of self-cleaning paints in order to improve its resistance and durability for commercial applications. Nanoparticles characterization was performed by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR) and surface area (SBET). Static contact angles and sliding angle measurements were performed in order to evaluate the self-cleaning capacity of the obtained nano paints. Surface free energy (SFE) of the nano-paint was estimated by the Wu model, using three pure liquid compounds such as water (W), ethylene glycol (EG) and n-undecane (UD). The results reveal that polar/non-polar liquids repellence capacity depends on the SY dosage and the nanoparticles nature as agents for chemical modification and nano-roughness enhance. Liquid CA and SFE values for the prepared nano paints exhibit the following tendency: 5%wt SY (UD:106.5°, EG: 145.6°, W: 154.6°, SFE: 13.7 mJ/m2) > SY + MgO (UD:115.2°, EG: 148.7°, W: 138.8°, SFE: 9.7 mJ/m2) > SY + CaCO3 (UD:118.6°, EG: 164.4°, W: 165.3°, SFE: 7.7 mJ/m2) > SY + S80APT (UD:138.2°, EG: 156.1°, W: 159.7°, SFE: 7.4 mJ/m2)  >  SY + NTC (UD:128.2°, EG: 167.6°, W: 165.5°, SFE: 7.2 mJ/m2) > SY + S80APT (UD:138.2°, EG: 156.1°, W: 159.7°, SFE:  mJ/m2). The synergy between SY and the proposed nanomaterials allows SA values lower than 10°, which proves that a dual-scale micro/nanostructure and low surface energy in the coating, enhance the liquid repellence capacity, resistance, and durability of traditional lime-based paints. This development opens a landscape for the application of self-cleaning paint as protective and high durable coatings for several indoor and outdoor surfaces.

Lime based Nanopaints for polar/non-polar liquid repellence: Self-cleaning approach

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