title: Spontaneous formation of photochromic coatings made of reversible microfibrils and nanofibrils on an elastomer substrate.
abstract: We report the spontaneous formation of photochromic microcrystalline and nanocrystalline fibrils forming dense coatings of cactuslike supramolecular structures on the surface of a soft poly(dimethylsiloxane) (PDMS) elastomer. The initial deposition of the photochromic molecules of diarylethenes on the elastomer is done by dip adsorption, a process that permits the homogeneous distribution of the molecules not only on the surface but also in the inner part of the polymer. Detailed thermal and microscopy studies reveal that the growth process of the fibrils is initiated by the formation of crystal seeds of the diarylethene in the proximity of the elastomer's surface empty voids and progresses toward the elastomer-air interface as a result of the high mobility of the molecules at room temperature. Fibril formation is possible only when the molecules are in the open form because the UV irradiation responsible for their transformation to the close isomeric form immediately after deposition totally prohibits the crystals' formation. Furthermore, the UV irradiation of the grown supramolecular assemblies provokes their destruction, but when the irradiated samples are left to recover under ambient conditions, they form new assemblies of fibrils in a faster and more efficient way. The resulting systems exhibit superhydrophobic to slightly hydrophobic properties with differences of almost 80° in water contact angles upon dark storage-UV irradiation cycles. The proposed systems can be an alternative to the facile formation of reversible photochromic fibrils on soft polymer surfaces for utilization on diverse soft devices, where controlled surface morphology and wettability are desired.
authors.affiliation: Smart Materials, Nanophysics, Istituto Italiano di Tecnologia , via Morego 30, 16163 Genova, Italy.
authors.forename: Reinier
authors.initials: R
authors.lastname: Oropesa-Nuñez
authors.forename: Despina
authors.initials: D
authors.lastname: Fragouli
authors.forename: Francesca
authors.initials: F
authors.lastname: Pignatelli
authors.forename: Alice
authors.initials: A
authors.lastname: Scarpellini
authors.forename: Efisio
authors.initials: E
authors.lastname: Gigliotti
authors.forename: Elena
authors.initials: E
authors.lastname: Samoylova
authors.forename: Athanassia
authors.initials: A
authors.lastname: Athanassiou
mesh_terms: D000388:Air; D004129:Dimethylpolysiloxanes / Q000737:chemistry; D020724:Elastomers / Q000737:chemistry*; D008027:Light; D057139:Nanofibers / Q000737:chemistry*; D013696:Temperature; D017155:Wettability
chemical_list: D004129:Dimethylpolysiloxanes; D020724:Elastomers; C013830:baysilon