title: Photoresponsive wettability in monolayer films from sinapinic acid.
abstract: Sinapinic acid is an interesting material because it is both antioxidant and antibacterial agent. In addition, when illuminated with ultraviolet light, it can exhibit the so-called photodimerization process. In this paper, we report on the investigation of monolayer films from 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SinA) deposited onto poly(allylamine hydrochloride), PAH, films. SinA monolayers were prepared by using the layer-by-layer (LbL) self-assembly technique. Adsorption kinetics curves were well fitted by a biexponential function suggesting that the adsorption process is determined by two mechanisms: nucleation and growth of aggregates. By using wetting contact angle analysis, we have found that SinA monolayers exhibit photoresponsive wettability under UV irradiation (365 nm); that is, wettability decreases with increasing UV irradiation time. The photoresponse of wettability was attributed to photodimerization process. This hypothesis was supported by the dependence of surface morphological structure and absorption on UV irradiation time. The mechanism found in the well-known transcinnamic acid crystals is used to explain the photodimerization process in SinA monolayers.
authors.affiliation: Grupo de Materiais Nanoestruturados, Universidade Federal de Mato Grosso, 78600-000 Barra do Garças, MT, Brazil.
authors.forename: Cleverson A S
authors.initials: CA
authors.lastname: Moura
authors.forename: Douglas J C
authors.initials: DJ
authors.lastname: Gomes
authors.forename: Nara C
authors.initials: NC
authors.lastname: de Souza
authors.forename: Josmary R
authors.initials: JR
authors.lastname: Silva
mesh_terms: D000327:Adsorption; D003373:Coumaric Acids / Q000737:chemistry*; D019281:Dimerization; D007700:Kinetics; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D055668:Photochemical Processes; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013499:Surface Properties; D017155:Wettability
chemical_list: D003373:Coumaric Acids; D011084:Polycyclic Aromatic Hydrocarbons; C073734:sinapinic acid