Modeling of azopolymer surface restructuring under complex irradiation patterns

• Applicant: Privatdozentin Dr. Marina Grenzer
• Subject Area: Experimental and Theoretical Physics of Polymers ; Polymer Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 526190489

Polymers that can change their molecular architecture under such an external stimulus as light have attracted great attention in the scientific community. Particularly known are photosensitive azopolymers, which have many applications in different fields due to their high versatility. In modern engineering, a special interest has been evoked by a unique opportunity to control the deformations of thin azopolymer films depending on the light irradiation pattern. The topographical restructuring has been used to produce the surfaces with light-controlled wettability, templates for living cells in biotechnology, large-scale multiplexed gratings for photonic applications. Multiple theoretical interpretations have been developed to explain the appearance of surface reliefs (SR), but only a few of them consider the features of underlying molecular architecture. We have been also working on this problem by pursuing the orientation approach, which establishes a clear relation between the light characteristics and the molecular properties of azo-containing materials. Recently we provided a couple of decisive proofs that reorientation of polymer backbones along the light polarization direction should be the main reason of photoinduced deformations in azopolymer films. The ultimate objective of this project is to develop the viscoplastic modeling approach for complex irradiation patterns. To reach this objective, two limiting cases of linearly and circularly polarized beams should be extended to a general case of elliptical polarization. The model will be refined by comparing its predictions with appearance of SRs inscribed by the interference patterns of spatially varying elliptical polarization. Then we concentrate on the understanding of the spiral surface reliefs and the wavefront sensitivity of photodeformations. The spiral reliefs are inscribed by irradiating a surface of azopolymer sample with tightly focused helical beams. Such beams can be produced by modern optical elements, which significantly extends the possibilities offered by azopolymer-based nanolithography. The optical field of a helical beam is rather complex. We intend to model the appearance of spiral reliefs under action of such a field, to test the validity of orientation approach at extreme irradiation conditions. Underlying molecular parameters will be provided by atomistic modeling of the side-chain azopolymers used in the experiments. When we succeed, not only an ultimate solution of a long-standing mystery of SRs inscription will be provided but also a versatile modeling approach will be developed for practical applications in modern optics and photonics.

• DFG Programme: Research Grants