Synthesis and photosensitivity of azobenzene functionalized hydroxypropylcellulose

Azobenzene functionalized hydroxypropyl cellulose derivatives (azo-HPCs) with different degrees of substitution with azobenzene moieties were synthesized and characterized. The degree of substitution with the azobenzene moieties (DSazo) can be adjusted by changing the feed ratio in the reaction mixture. The photosensitivity of the azo-HPCs in both solution and solution film was investigated. The azobenzene moieties of the azo-HPCs exhibited a reversible cis-to-trans isomerization transition upon irradiation with UV and visible light in both solution and the solid state. The reversible trans-to-cis photoisomerization led to a change of the wettability of the azo-HPC films. Surface energy estimations suggest that the tunable film wettability was attributed to the change of the dipole moment of the azobenzene moieties in the film surface. The variation of the contact angle depends on the DSazo of the azo-HPC derivatives. A higher DSazo corresponds to a larger variation of water contact angle upon UV irradiation under the same conditions. This work offers a versatile method to manipulate the surface properties of the eco-friendly cellulose derivatives.