Probing Opto-Mechanical Stresses within Azobenzene-Containing Photosensitive Polymer Films by a Thin Metal Film Placed Above

Azo-modified photosensitive polymers offer the interesting possibility to reshape bulk polymers and thin films by UV-irradiation while being in the solid glassy state. The polymer undergoes considerable mass transport under irradiation with a light interference pattern resulting in the formation of surface relief grating (SRG). The forces inscribing this SRG pattern into a thin film are hard to assess experimentally directly. In the current study, we are proposing a method to probe opto-mechanical stresses within polymer films by characterizing the mechanical response of thin metal films (10 nm) deposited on the photosensitive polymer. During irradiation, the metal film not only deforms along with the SRG formation but ruptures in a regular and complex manner. The morphology of the cracks differs strongly depending on the electrical field distribution in the interference pattern, even when the magnitude and the kinetics of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. In addition, the neutron reflectivity measurements of the metal/polymer interface indicate the penetration of a metal layer within the polymer, resulting in a formation of a bonding layer that confirms the transduction of light-induced stresses in the polymer layer to a metal film

Motion of Adsorbed Nano-Particles on Azobenzene Containing Polymer Films

We demonstrate in situ recorded motion of nano-objects adsorbed on a photosensitive polymer film. The motion is induced by a mass transport of the underlying photoresponsive polymer material occurring during irradiation with interference pattern. The polymer film contains azobenzene molecules that undergo reversible photoisomerization reaction from trans- to cis-conformation. Through a multi-scale chain of physico-chemical processes, this finally results in the macro-deformations of the film due to the changing elastic properties of polymer. The topographical deformation of the polymer surface is sensitive to a local distribution of the electrical field vector that allows for the generation of dynamic changes in the surface topography during irradiation with different light interference patterns. Polymer film deformation together with the motion of the adsorbed nano-particles are recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the surface deformation. The particles undergo either translational or rotational motion. The direction of particle motion is towards the topography minima and opposite to the mass transport within the polymer film. The ability to relocate particles by photo-induced dynamic topography fluctuation offers a way for a non-contact simultaneous manipulation of a large number of adsorbed particles just in air at ambient conditions

Mapping a Plasmonic Hologram with Photosensitive Polymer Films: Standing versus Propagating Waves

We use a photosensitive layer containing azobenzene moieties to map near-field intensity patterns in the vicinity of nanogrids fabricated within a thin silver layer. It is known that azobenzene containing films deform permanently during irradiation, following the pattern of the field intensity. The photosensitive material reacts only to stationary waves whose intensity patterns do not change in time. In this study, we have found a periodic deformation above the silver film outside the nanostructure, even if the latter consists of just one groove. This is in contradiction to the widely accepted viewpoint that propagating surface plasmon modes dominate outside nanogrids. We explain our observation based on an electromagnetic hologram formed by the constructive interference between a propagating surface plasmon wave and the incident light. This hologram contains a stationary intensity and polarization grating that even appears in the absence of the polymer layer

Mid‐infrared dual‐comb polarimetry of anisotropic samples

Abstract The mid‐infrared (mid‐IR) anisotropic optical response of a material probes vibrational fingerprints and absorption bands sensitive to order, structure, and direction‐dependent stimuli. Such anisotropic properties play a fundamental role in catalysis, optoelectronic, photonic, polymer and biomedical research and applications. Infrared dual‐comb polarimetry (IR‐DCP) is introduced as a powerful new spectroscopic method for the analysis of complex dielectric functions and anisotropic samples in the mid‐IR range. IR‐DCP enables novel hyperspectral and time‐resolved applications far beyond the technical possibilities of classical Fourier‐transform IR approaches. The method unravels structure–spectra relations at high spectral bandwidth up to 90 cm−1 and short integration times of 65 μs, with previously unattainable time resolutions for spectral IR polarimetric measurements for potential studies of noncyclic and irreversible processes. The polarimetric capabilities of IR‐DCP are demonstrated by investigating an anisotropic inhomogeneous freestanding nanofiber scaffold for neural tissue applications. Polarization sensitive multi‐angle dual‐comb transmission amplitude and absolute phase measurements (separately for ss‐, pp‐, ps‐, and sp‐polarized light) allow the in‐depth probing of the samples’ orientation‐dependent vibrational absorption properties. Mid‐IR anisotropies can quickly be identified by cross‐polarized IR‐DCP polarimetry. Key points A novel dual‐comb laser‐based technique is established for polarization‐dependent mid‐infrared spectroscopy. Independent measurements of spectral s‐ and p‐polarized transmission amplitudes and phases in the μs range. Visualization of the anisotropy of nanofiber scaffolds as used for neural tissue applications

Probing Opto-Mechanical Stresses within Azobenzene-Containing Photosensitive Polymer Films by a Thin Metal Film Placed Above

Azo-modified photosensitive polymers offer the interesting possibility to reshape bulk polymers and thin films by UV-irradiation while being in the solid glassy state. The polymer undergoes considerable mass transport under irradiation with a light interference pattern resulting in the formation of surface relief grating (SRG). The forces inscribing this SRG pattern into a thin film are hard to assess experimentally directly. In the current study, we are proposing a method to probe opto-mechanical stresses within polymer films by characterizing the mechanical response of thin metal films (10 nm) deposited on the photosensitive polymer. During irradiation, the metal film not only deforms along with the SRG formation but ruptures in a regular and complex manner. The morphology of the cracks differs strongly depending on the electrical field distribution in the interference pattern, even when the magnitude and the kinetics of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. In addition, the neutron reflectivity measurements of the metal/polymer interface indicate the penetration of a metal layer within the polymer, resulting in a formation of a bonding layer that confirms the transduction of light-induced stresses in the polymer layer to a metal film

En Route to Practicality of the Polymer Grafting Technology: One-Step Interfacial Modification with Amphiphilic Molecular Brushes

Surface modification with polymer grafting is a versatile tool for tuning the surface properties of a wide variety of materials. From a practical point of view, such a process should be readily scalable and transferable between different substrates and consist of as least number of steps as possible. To this end, a cross-linkable amphiphilic copolymer system that is able to bind covalently to surfaces and form permanently attached networks via a one-step procedure is reported here. This system consists of brushlike copolymers (molecular brushes) made of glycidyl methacrylate, poly­(oligo­(ethylene glycol) methyl ether methacrylate), and lauryl methacrylate, which provide the final product with tunable reactivity and balance between hydrophilicity and hydrophobicity. The detailed study of the copolymer synthesis and properties has been carried out to establish the most efficient pathway to design and tailor this amphiphilic molecular brush system for specific applications. As an example of the applications, we showed the ability to control the deposition of graphene oxide (GO) sheets on both hydrophilic and hydrophobic surfaces using GO modified with the molecular brushes. Also, the capability to tune the osteoblast cell adhesion with the copolymer-based coatings was demonstrated