Controlling the wettability of plastic by thermally embedding coated aluminium oxide nanoparticles into the surface

Nanoparticle embedding into the surface of plastics provides an effective anchor that improves the durability of coatings formed from functionalized nanoparticles. Coatings formed from thermally embedded particles show superior wear resistance relative to coatings formed from non-embedded particles. As a consequence of this, embedded nanoparticles functionalized with hydrophilic and hydrophobic carboxylates are better suited for controlling the wettability of plastics than when the nanoparticles are deposited onto the plastic under ambient conditions.

Carboxylate-functionalized Al₂O₃ nanoparticles were embedded into ethylene vinyl acetate through spray coating the particles onto the substrate during heating. Sonication was used to remove excess particles that did not become embedded into the material. Coatings formed from the embedded particles were characterized through scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The wettability of the coatings was characterized using static and dynamic contact angle (CA) measurements to measure the apparent water contact angles, and sliding angle measurements, whilst the durability of the coatings was studied using scratch testing, tape peel tests, and abrasion tests. The build-up of fog on the substrates was also studied through exposing the surfaces to water vapour.

Thermal embedding of the particles into the surface of the plastic was observed to occur when the material was heated to temperatures around its melting temperature. AFM and SEM showed that plastic embedded with the nanoparticles possessed a morphology that was substantially rougher than the untreated plastic. CA measurements showed that plastic embedded with hydrophobic isostearate functionalized nanoparticles was highly hydrophobic and displayed a CA of approximately 152°. Dynamic CA measurements and sliding angle measurements revealed that plastic embedded with the isostearate functionalized nanoparticles showed petal-like wetting behavior. Furthermore, it was observed that the CA of the plastic could be varied from highly hydrophobic to highly hydrophilic through embedding varying amounts of isostearate and hydrophilic 2-[2-(2-methoxyethoxy)ethoxy]acetate functionalized Al₂O₃ nanoparticles into the surface of the material. Scratch testing showed that thermally embedding the nanoparticles into the plastic substantially improved their abrasion resistance, relative to when the nanoparticles are deposited onto the non-heated material. This methodology indicates that embedding nanoparticles into plastics creates durable coatings that can display variable wettability. Consequently, this methodology could be useful in applications where it is desirable to keep plastics dry, such as for food packaging or medical devices.