The objective of this study was to identify chitosan formulations suitable for sustainable functional integration into composite materials. To this end, the influence of solvent type (acetic acid and lactic acid) and chitosan molecular weight on film formation, rheological behavior, thermal response, thermo-optical properties, chemical structure, and piezoelectric performance was systematically investigated. Optimized casting and drying procedures produced transparent, homogeneous, and mechanically stable films suitable for comprehensive characterization. Rheological and thermo-optical analyses demonstrated that solvent selection strongly influenced polymer network formation and molecular mobility. Films prepared using acetic acid exhibited denser and stiffer polymer networks with improved dimensional stability, whereas lactic acid produced more flexible and elastic films. Thermogravimetric analysis revealed only minor differences in the intrinsic thermal stability of the investigated films, while FTIR confirmed that the solvent systems did not alter the chemical structure of chitosan. Electrical measurements carried out whilst the system was subjected to periodic mechanical excitation revealed weak but equally periodic electrical signals, which demonstrate a sensor functionality. These results demonstrate that chitosan films possess tunable structural, thermal, and potential mechanoelectrical sensor properties and highlight their potential as sustainable, functionally integrated components in composite material systems.

Due to their relatively high electrocaloric activity and mechanical flexibility, relaxor ferroelectric terpolymers are being used in the fabrication of electrocaloric cooling and heating devices, in which the heat transfer is done by latent heat when a fluid condenses on (or evaporates from) their surface. This work focuses on improving the surface wettability of flexible polyimide foils, which have been utilized to encapsulate electrocaloric terpolymers for enhancing heat transfer efficiency. The polyimide foils were exposed to a combination of plasma etching and metal oxide thin film deposition using magnetron sputtering technology. With the aim of achieving a complete wetting surface, sputtering parameters such as pulse times, gas concentration and treatment time were varied. The chemical and physical properties of the treated surfaces were analyzed, and their influence on wetting performance was investigated at macro-, micro-, and nanoscale levels. The findings of this study have significant implications for the development of more efficient and reliable electrocaloric heat pumps, contributing to the advancement of environmentally friendly, energy-efficient solid-state cooling and heating technologies.

Electrocaloric materials are currently under investigation because of their potential use in active cooling systems. As electrocaloric transducer materials, electroactive polymers such as PVDF copolymers with trifluoroethylene [P(VDF-TrFE)] and PVDF terpolymers with trifluoroethylene and chlorofluoroethylene play an important role. While the relaxor ferroelectric PVDF terpolymers show significant electrocaloric properties even at room temperature, the ferroelectric PVDF copolymers show high electrocaloric properties mainly at temperatures above the Curie transition, which depend on the copolymer composition and is at least 50 degrees C. Structural modifications are one possibility for converting the ferroelectric PVDF copolymers into a relaxor ferroelectric state and, thus, their possible electrocaloric use at room temperature. Here, we demonstrate the structural changes of P(VDF-TrFE) copolymers (55/45 mol. %) caused by electron irradiation. The use of irradiation doses of around 400 kGy allows a partial conversion from the ferroelectric phase to the relaxor-ferroelectric phase but does not yet lead to a complete degradation or cross-linking process so that a certain polarization can still be used. This is accompanied by the reduction of the Curie temperature and an increase in the permittivity at, e.g., room temperature. Thus, a maximum non-remanent polarization and electrocaloric activity are observed after irradiation of P(VDF-TrFE) copolymers with doses of around 400 kGy. These irradiated copolymers show at room temperature a temperature change of about 1.8 K and a figure of merit of 0.35 at an electric field of 100 V/mu m, in comparison to about 0.7 K and 0.13, respectively, for non-irradiated copolymers. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).

Smart materials can be used as bidirectional transducers responding to various physical fields (e.g. electrical, magnetic, and thermal fields), eanbling a use as sensors, actuators, and generators. One challenge in developing smart material transducers is the access to material data and models. Different working principles, measurement and analysis methods, as well as data storage approaches often lead to heterogeneous and partly inconsistent datasets. However, easy and multiscale access to material data and models enables efficient research and development with regard to the selection of the materials and their optimization towards specific applications. Therefore, we developed a system build on the ontology-based data access (OBDA) approach, a method to access such heterogeneous datasets easily and quickly. This approach is extended in our multidisciplinary work to incorporate a model access, enabling material models to transform material data across multiple scales to compute new responses beyond stored data. The advantages are demonstrated using exemplary use cases for four subclasses of smart material: thermal and magnetic shape memory alloys, piezoelectric ceramics, and dielectric elastomers.

Smart materials react to physical fields (e.g., electric, magnetic, and thermal fields) and can be used as sensors, actuators, and generators due to their bidirectional behavior. Easy and multiscale access to material data and models enables efficient research and development with regard to the selection of appropriate materials and their optimization towards specific applications. However, different working principles, measurement and analysis methods, as well as data storage approaches lead to heterogeneous and partly inconsistent datasets. The ontology‐based data access (OBDA) is a suitable method to access such heterogeneous datasets easily and quickly, while material models can transform material data across certain scales for different applications. In order to connect both capabilities, an extended approach enabling an ontology‐based data and model access (OBDMA) is presented, also supporting findable, accessible, interoperable, and re‐usable (FAIR). The OBDMA system comprises four main levels, the query, the ontology, the mapping, and the database. Storing knowledge at these different levels increases the interchangeability and enables variable datasets, which is essential, especially for dynamic research fields such as smart materials. In this article, the principles and advantages of the OBDMA approach are demonstrated for different subclasses of smart materials, but can be transferred to other materials, too.

Dielectric elastomer transducers exhibit extraordinary actuator properties due to their huge actuation, small construction volume and low energy consumption. Dielectric elastomer actuators (DEA) consist of a thin dielectric elastomer (DE) film covered with stretchable electrodes on both surfaces. If a high voltage is applied, the electrodes attract each other which leads to a reduction of the elastomer film thickness and due to the incompressibility of the elastomer film to an actuator area enlargement. Based on extensive developments, a variety of actuator forms are standard in research and, in some cases, in application. With special designs, such as out-of-plane actuators, dielectric elastomer actuators are able to transmit larger forces with deflections in the range of around one millimeter. Here, we present the fabrication and characterization of DE multilayer actuators as well as their embedding in out-of-plane actuators. In detail, the multilayer actuator consists of eight elastomer layers with thicknesses of 100 mu m each and electrode widths of 30 mm and lengths of 50 mm or 80 mm. The developed multilayer actuators provide in-plane deflections of about 2% and out-of-plane deflections of about 400 mu m and 800 mu m for actuators with lengths of 50 mm and 80 mm, respectively, when operated with an electric field of 50 MV/m. The out-of-plane multilayer actuators exhibiting a blocking force of e.g. 1.8 N at an electric field of 70 MV/m. In order to describe the actuator behavior, an analytical model based on the neo-Hookean hyperelastic material model is developed. The comparison of the calculated and experimental data shows a good agreement for the in-plane investigations of the actuator multilayers and an approximate agreement for the out-of-plane actuators.

Integrated electromechanical actuator modules have been developed which consist of dielectric elastomer actuators (DEA), high voltage electronics to control the actuators and encapsulations to prevent the actuators from contact with surrounding media. As DEA, commercial stack actuators. Different materials have been studied as encapsulations such as silane modified polymers and silicone elastomers. Two different types of integrated actuator modules were developed in order to evaluate different encapsulation concepts. Therefore, the actuator modules are either encapsulated by a polymer film (AMF: Actuator Module encapsulated with Film) or by a polymer hood (AMH: Actuator Module encapsulated with Hood). The polymer films used for encapsulation were processed via doctor blading while the polymer hoods were casted using laser sintered molds. The encapsulations show a suitable dielectric breakdown strength as well as appropriate seal-ing according to gases and water up to pressures of some bar, depending on the kind of material. Force-stroke dependen-cies were investigated in order to evaluate how encapsulation films influence the actuator performance. The developed high voltage electronic unit allows the application of 850 V. It operates at 24 V industrial standard and has a size of approximately 20 mm x 20 mm x 12 mm. Finally, the actuator modules were constructed by integration of the different components such as the stack actuators, the electronics as well as the encapsulations. The integrated actuator modules were characterized regarding their electromechanical properties. Although the encapsulation slightly affects the performance of the actuators, the ability to run the actuator modules in difficult environmental conditions outweighs this disadvantage by far.

In this work, dome structures in PVDF films were prepared as ultrasonic transducer. The domes are realized by a deep drawing process. The dome-forming process leads to a phase transformation from the non-polar a into the polar β phase within dome wall and roof of the PVDF films. A ferroelectric polarization is obtained in these dome areas after suitable electrical poling which yields a piezoelectric activity. Because of the piezoelectric activity within the film plane, a dome-roof up-and-down actuation is observed with resonance frequencies in the range between 65 and 93 kHz.

Dielectric elastomer (DE) transducers consist of a dielectric elastomer layer coated with flexible electrodes on both surfaces. Apart from the dielectric film, the properties of the electrodes affect the electromechanical behavior of the DEtransducers as well. Electrodes must be able to sustain conductivity at large deformations, must exhibit a low stiffness and provide sufficient adhesion to the DE-layer. Different processing technologies exist for application of electrodes suitable for DE-transducer. Among them, the inkjet printing technique gained attention in recent years as a very precise and purely non-contact deposition method to fabricate thin electrode layers. In contrast to other methods, e. g. using a shadow mask in case of spraying, the inkjet technique is very versatile and allows a fast adjustment of the processed electrode geometry. In order to describe the requirements of the inkjet printing process and ink adaptation itself, we present a theoretical description of those processes accompanied with the definition of parameters, which need to be considered during experimental processing. Furthermore, we present first results of our adaptation of an ink formulation and an inkjet printing procedure. For this purpose a commercial electrode paste, Elastosil LR 3162, made of carbon black-silicone composite, was adapted to the inkjet printing process. In first experimental studies, the adapted ink was inkjet printed onto dielectric elastomer layers by varying the inkjet printing parameters. Different measurements were performed in order to characterize separate dots as well as continuous lines and areas of the inkjet printed electrodes. The electrode thicknesses and its shapes were recorded by surface-profile measurements. The electrical properties of the printed electrodes as well as their mechanical influence on the elastic properties of the elastomer layers were measured under continuous and cyclic mechanical stretching.

In high-tech companies operating worldwide innovation is the key driver for long-term market success. Hence, innovative engineering technologies not only provide technological challenges but also investment risks for decision makers who want to tread new paths in product development. As an important example, the typically required high operating voltage and the need for high voltage power supplies constitute physical, economic and psychological restrictions for the application of dielectric elastomer actuators (DEA). Therefore, based on the view of product integration we aimed to limit the applied voltage below 600 V. To achieve this goal, we developed membrane actuators made of dielectric elastomers, which can be driven by lower voltages provided by low-cost power supplies. In detail, a particular device was developed with specially designed compression fittings clamping the DEA-film which enabling a simple electric contact between the actuator and the circuit board. The prefabricated actuator module was integrated in a fast switching, low-cost electronic circuit board. The power supply generates up to 550 V with a slew rate of a few microseconds, whereas the whole circuit has the geometrical dimension of a credit card. A plunger connected to the DEA-film moves out of plane when the actuator is activated. With the use of permanent magnets, interacting with the plunger, the system can be enhanced to meet industrial requirements in force and stroke. The resulting 'embedded' system offers a platform for further applications in different industrial segments and applications for instance in automation with valves, grippers or micro pumps in process automation and life sciences.

Thin-film organic distributed feedback (DFB) lasers processed with elastomeric polymers allow fabrication of flexible and continuously tunable coherent light sources. So far, the realized laser devices fall short on broad continuous tuning range. We demonstrate that the addition of plasticizers to the polymer matrix and the minimization of the thickness of the laser can reduce mechanical impact and, thus, extend the wavelength tuning range to the full gain range of the active medium. A contact-transfer method is used to transfer gently the ultra-thin membrane DFB laser to a silicone support. A continuous tuning of the laser wavelength up to 77 nm in the orange-red spectral range of a single laser dye was achieved by mechanical stretching of the supporting film with a DFB membrane laser on top.

The high coherence of laser light sources is a key to the application of diffractive optics usable in holographic AR/VR displays. This can be combined with switchable diffractive elements, which are advantageous for several optical functions used in immersive holographic displays such as shutters, polarization filters, for rapid beam deflection and selection. We demonstrate a compact, effective and robust diffraction wide-angle switchable beam-deflecting device based on circular polarization gratings possessing Bragg-performances (Bragg-PG) and a polarization switch. Such grating/polarization switch pair may, for instance, be a discrete switchable deflection element or as a switching element for pre-deflection with field lenses for application in holographic AR/VR displays. Micrometer-thick circular polarization gratings characterized by high diffraction efficiency (DE > 95%), large diffraction angles (> 30 degrees) and wide angular and wavelength acceptance were developed. In the presented embodiment, the output signal is controlled between the zero-and first-diffraction orders by the handedness of circular polarization of the incident light. Forming a stack of two such oppositely aligned gratings can double the deflection angle. These gratings are the result of a two-step photochemichal/thermal processing procedure of a photocrosslinkable liquid crystalline polymer (LCP). The holographic patterning provides a high spatial resolution (period < 700 nm) and the arbitrary orientation of the LC director as well as high optical quality and thermal and chemical stability of the final gratings. Highly efficient (diffraction efficiency, DE > 95% in the vis spectral range) and stable symmetric and slanted circular Bragg polarization gratings were fabricated using the developed material and processing technique. The high usable diffraction angles combined with high DE make the Bragg-PG attractive for HMD AR/VR applications because of the system inherent short focus lengths and large numerical apertures needed to meet the low space budget in HMD and other optical systems.

A.R. acknowledges the funding form the Alexander von Humboldt Foundation. The work reported by M.K. was performed within the University of Potsdam’s team of the VIP project EDEL (FKZ 03V0882) funded by the German Federal Ministry for Education and Research (BMBF) via the Projektträger Jülich (PtJ). Support and discussions were provided by the team, in particular by Dipl.-Ing. Hülya Ragusch and cand.phys. Stefan Best.

Transmission and reflection volume gratings were produced in conventional elastic materials by introduction of benzophenone derivatives and following UV-holography exposure.

Ferroelectrets are a recent addition to the family of piezoelectric polymers. Ferroelectrets are space charge electrets with a heterogeneous and usually cellular foam structure. They are flexible, available in large areas and show strong piezoelectric response. Due to their low acoustic impedance they have strong application potential in air-borne ultrasonic transducers. Here, the influence of temperature on the electromechanical and ultrasonic properties of polypropylene (PP) ferroelectrets was addressed. PP ferroelectrets were subjected to repeated temperature variations. The characterization was performed by means of dielectric resonance spectroscopy (DRS) and Laser-Doppler Vibrometry (LDV). Profound variations in the piezoelectric properties during thermal cycling were observed and correlated to the changes in the elastic properties. Exposure to elevated temperatures resulted in a reduction in the piezoelectric response and an increase in the elastic stiffness constant which also shifted the thickness-extension resonance peaks towards higher values. Large differences in piezoelectric properties were discovered between the first and the subsequent cycles. To decrease the influence of temperature cycling on the piezoelectric properties of PP ferroelectrets, annealing was used to advantage. Annealing treatments with different durations and different annealing temperatures were investigated. A particular procedure yielding foam stiffening and a sufficiently high piezoelectric activity was determined and was employed for further investigations. The piezoelectric properties of the annealed ferroelectrets varied much less when compared to non-annealed ferroelectrets. Characterization of thermally cycled annealed and non-annealed films revealed relatively homogeneous phase and amplitude distributions of the surface-vibration below the resonance, which resembles a piston-like response. Piston-like response was not significantly deteriorated by thermal cycling below the resonance frequency. This was corroborated for all samples by measuring the acoustic directivity of them in the farfield, at frequencies below the resonance. At the resonance, much higher distortions of the response were observed as revealed from the phase images. (C) 2016 Elsevier B.V. All rights reserved.

Volume diffraction gratings (VDGs) are inscribed selectively by diffusive introduction of benzophenone and subsequent UV-holographic structuring into an electroactive dielectric elastomer actuator (DEA), to afford a continuous voltage-controlled grating shift of 17%. The internal stress coupling of DEA and optical domain allows for a new generation of true monolithic tunable elastomer optics with voltage controlled properties.

For the processing of dielectric elastomer actuators (DEAs) one promising class of materials are silicones. They are low-cost and easily accessible. At the same time these materials offer unique mechanical, chemical, low temperature, and optical properties. An active field of research is the optimisation of the silicones' properties by modifying their framework on the structural level. The focus of this work is to improve the actuation performance of DEAs made up from polydimethylsiloxane (PDMS) by incorporating organic dipoles directly into the polymer's chains as network points. For this purpose, a diallyl functionalised nitroaniline derivative was utilised as crosslinker for appropriate PDMS starting materials. Silicone films with dipole concentrations varying from 0.5wt% to 1.0wt% were manufactured and the chemical, mechanical, electrical, and electromechanical properties of these novel materials were investigated in dependency of the dipole content.

All‐optical fabrication of elastic volume diffraction gratings in polydimethylsiloxane (PDMS) is presented. Novel material based on the commercially available PDMS with incorporated benzophenone (BPh) photoactive molecules is developed. The gratings are formed by a holographic technique and UV irradiation through an amplitude mask. New material permits to obtain efficient volume gratings with periods ranging from hundreds nanometers to dozens of micrometers in elastic films of different thicknesses. Besides symmetric transmission 1D gratings, slanted and 2D gratings have been fabricated as well. Photoattachment of BPh molecules and their real‐time diffusion within elastic PDMS matrix in accordance with the spatially modulated light is considered as a mechanism of the gratings formation. The refractive index modulation amplitude of about 7.0 × 10−4 is achieved. It is shown that mechanical strain of the elastic volume gratings allows fully reproducible alteration of the gratings parameters. In order to tune the diffracted wavelength over the whole visible spectral range (from 410 up to 700 nm), a strain of about 75% is required. New volume diffraction PDMS gratings represent very successful combination of cheap and widely known materials with one‐step optical fabrication techniques providing high‐performance tunable diffraction elements that can be applied in photonics, sensing, and spectroscopy.

Dielectric elastomer actuators (DEAs) are smart materials that can be optimized by modifying the dielectric or mechanical properties of the electroactive polymer. The incorporation of inorganic particles in silicone elastomers shows a permittivity enhancement and undesired stiffening. We present another concept to obtain comparable properties by dipole grafting. Therefore, the organic dipole N-ally-N-methyl-4-nitroaniline is grafted in competition with the vinyl terminated PDMS to a hydrosilane cross-linker forming the PDMS network. With this procedure PDMS films with up to 25 wt% of the dipole were solvent casted and the chemical, mechanical, electrical, plus electromechanical properties of these novel materials were investigated.