Optical Patterning in Photoresponsive Azobenzene-Based Waterborne Coatings

Reversible photoresponsive waterborne dispersions can be directly applied in the paint and printing industry and have several potential applications such as in rewritable optical patterns, security labeling, and sensing. However, the synthesis of such dispersions and application as waterborne coatings has rarely been reported. In this work, photoresponsive polymer dispersions containing light-responsive azobenzene were prepared by resin-stabilized emulsion polymerization. The aqueous dispersions consist of core/shell type polymer particles, where the resin forms the shell around the polymer core. The photoresponsive azobenzene was incorporated into the resin shell (azo-in-shell) or polymer core (azo-in-core). Waterborne coatings were easily prepared by applying the dispersions on glass or paperboard. The photoresponsive behavior of the azobenzene in the dispersions and coatings shows fast and reversible isomerization and a similar half-life of the cis-azobenzene regardless of its surrounding matrix in the coating, dispersion, or solution. Optical patterns were reversibly imprinted in the coatings on paperboard, which remain visible for several hours at room temperature and several weeks when stored in the freezer. The water barrier properties of the azobenzene-containing coatings on paperboard were unaffected by the addition of the azobenzene moieties and isomerization state. Our results reveal a class of photoresponsive azobenzene waterborne coatings that can be easily applied on different substrates.