Cellulose substance with reversible photo-responsive wettability by surface modification

Cellulose materials with photo-reversible wettability were prepared by self-assembling of 7-[(trifluoromethoxyphenylazo)-phenoxy] pentanoic acid (CF3AZO) monolayer onto titania ultrathin film pre-coated nanofibre surfaces of commercial laboratory filter paper. The as-prepared CF3AZO monolayer modified filter paper approached superhydrophobicity, and it transited to extremely hydrophilic state after being exposed to UV light (lambda = 365 nm) irradiation, and the original surface wettability recovered after dark storage. The conformational transformation of the photo-sensitive CF3AZO molecules during UV irradiation and dark storage was related to the reversible wettability. A titania gel layer deposited on the nanofibre surfaces of filter paper, compared with silica gel layer, was more active for assembly of CF3AZO molecules, and the hydroxyl moieties implanted on the surface of titania gel layer during UV irradiation and their substitution by oxygen in the dark demonstrated a synergic effect on tailoring surface wettability.