Local Direction of Optomechanical Stress in Azobenzene Containing Polymers During Surface Relief Grating Formation

Abstract

In this work, it is revealed how the photoinduced deformation of azobenzene containing polymers relates to the local direction of optomechanical stresses generated during irradiation with interference patterns (IPs). It can be substantiated by the modeling approach proposed by Saphiannikova et al., which describes the directional photodeformations in glassy side-chain azobenzene polymers, and proves that these deformations arise from the reorientation of rigid backbone segments along the light polarization direction. In experiments and modeling, surface relief gratings in pre-elongated photosensitive colloids of few micrometers length are inscribed using different IPs such as SS, PP, ±45, SP, RL, and LR. The deformation of colloidal particles is studied in situ, whereby the local variation of polymer topography is assigned to the local distribution of the electrical field vector for all IPs. Experimentally observed shapes are reproduced exactly with modeling azopolymer samples as visco-plastic bodies in the finite element software ANSYS. Orientation approach correctly predicts local variations of the main axis of light-induced stress in each interference pattern for both initially isotropic and highly oriented materials. With this work, it is suggested that the orientation approach implements a self-sufficient and convincing mechanism to describe photoinduced deformation in azopolymer films that in principle does not require auxiliary assumptions.

Photomotion of Hydrogels with Covalently Attached Azo Dye Moieties—Thermoresponsive and Non-Thermoresponsive Gels

“…Under these conditions, only a few reported models may be suitable as reference. These are the orientation model [ 33 , 34 , 35 ], the gradient force model [ 8 , 36 , 37 , 38 , 39 , 40 ], and the mean field model [ 41 , 42 ]. These models have in common that they assume reorientation of the chromophore during irradiation in the material by trans-cis-trans isomerisation cycles and alignment of the chromophores in the optically induced electric field.…”

Viscoplastic Modeling of Surface Relief Grating Growth on Isotropic and Preoriented Azopolymer Films

“…The diagonal components of can be calculated as follows: where and are components of the orientation tensor parallel and orthogonal to the electric field vector E . In our latest paper [ 43 ], Equation (2) is solved for different IPs, starting from isotropic and anisotropic initial states. The parameter defines the reduced strength of the effective orientation potential, which acts on the polymer backbones during illumination [ 41 ].…”

“…In RL and LR polarization patterns, the light has constant intensity , and its linear polarization rotates along the grating period. Therefore, the coordinate system of each finite element is rotated in respect to the laboratory system, as described elsewhere [ 43 ].…”

“…Both processes can be described with the help of effective orientation potentials [ 35 , 41 ]. The local ordering of the polymer backbones within thin film generates corresponding mechanical stress that causes plastic deformations in the glassy polymer, with the appearance of different grating structures determined by the light intensity and polarization distribution [ 42 , 43 ].…”

“…In the previous study, we successfully implemented the orientation approach to model the inscription of SRGs in the pre-elongated photosensitive colloids under irradiation with SS and PP intensity interference patterns (IIPs), as well as the restructuring of film edges by RL and LR polarization interference patterns (PIPs) [ 43 ]. A striking resemblance between the experimentally recorded and modeled structures was established.…”