Complex light-induced surface structuring of azopolymer films

Il giorno 1 luglio 2019, ore 14.30, nelle aule 2G26 e 2G27,
il Dr Stefano Luigi Oscurato -assegnista di tipologia A- terrà un seminario sull'attività svolta a conclusione della sua annualità.
"Complex light-induced surface structuring of azopolymer films"
Films of azobenzene-containing polymers develop surface reliefs as consequence of illumination with spatially structured Uv/visible light. The surface deformation is the manifestation of a series of light-driven complex microscopic motions which, originated by the photo-isomerizing azobenzene molecules and their interactions with the host material at molecular level, propagate up to macroscopic scales. The exact nature of the microscopic processes driving this macroscopic material transport is still to be fully unveiled, but its phenomenology, and the general rules governing the resulting surface deformation, are well-established. Superficial structuration is obtained only in the illuminated areas of the film. It is reversible and high directional, with a peculiar dependence on the intensity distribution; on the polarization state; and, in some cases, even on the wavefront of the irradiating light beam [1]. Because of this variegate response to the irradiated optical field distribution, the mass migration can be successfully used to realize complex superficial textures, sometimes not even achievable with standard photoresists that only respond to light intensity patterns.  
The vectorial response of the azomaterials can be included in a phenomenological model that describes the surface structuration as dependent on the full vectorial optical field and its spatial derivatives. Although missing the details of the process at the microscopic level, the model allows to qualitatively, but precisely, predict the final surface structuration of the film on the basis of the knowledge of characteristic empirical material responses to simple illumination configurations and the actual spatial distribution of the optical field vector inside the irradiated film. This empirical approach can be particularly relevant for the applications of the light-structured azomaterial films in photonics, surface science and biology, where the precise control on the illumination schemes and spatial field distributions can be used to accurately design complex surface morphologies with specific functionalities [2].
In this talk, I will present  the recent advances in the realization of deterministic light-induced complex reliefs on the surface of the azopolymer films obtained in several illumination schemes. These include: multiple and sequential film exposure; direct laser writing; light-induced reconfiguration of properly pre-patterned surfaces and irradiation with spatially structured fields realized by means of digital holography [3].
1. S. L. Oscurato, M. Salvatore, P. Maddalena, and A. Ambrosio, "From nanoscopic to macroscopic photo-driven motion in azobenzene-containing materials," Nanophotonics 7, 1387–1422 (2018).
2. S. L. Oscurato, F. Borbone, P. Maddalena, and A. Ambrosio, "Light-Driven Wettability Tailoring of Azopolymer Surfaces with Reconfigured Three-Dimensional Posts," ACS Appl. Mater. Interfaces 9, 30133–30142 (2017).
3. S. L. Oscurato, M. Salvatore, F. Borbone, P. Maddalena, and A. Ambrosio, "Computer-generated holograms for complex surface reliefs on azopolymer films," Sci. Rep. 9, 6775 (2019).
Data: 01/07/2019