Independent Two Way Switching of the Wetting Behavior of Cellulose-Derived Nanoparticle Surface Coatings by Light and by Temperature

Recently, donor acceptor Stenhouse adducts (DASAs) have received interest as photoresponsive polarity switches. In this work, a range of DASAs are synthesized and combined with nanoparticles from hydroxypropyl cellulose stearic acid ester to yield a photoresponsive composite material. This composite is spray-coated onto porous paper substrates, forming an interface that is initially superhydrophobic and can be switched by a visible light trigger to become hydrophilic. Subsequently, this hydrophilic state can be switched back to regain a hydrophobic surface by heating above the T-m of the polymer, creating a system that can exist in three stable states, which can be triggered by independent (i.e., light/heat) stimuli. If such coatings are being applied onto porous paper substrates, using such independent stimuli, water drops placed on top of the paper can be submerged (i.e., wicked) into the paper by simple illumination with light, and the surface can be reclosed by subsequent heating of the paper. The latter may become promising for paper-based fluid timers, e.g., in diagnostic applications.