High driving voltages currently limit the commercial potential of dielectric elastomers (DEs). One method used to lower driving voltage is to increase dielectric permittivity of the elastomer. A novel silicone elastomer system with high dielectric permittivity was prepared through the synthesis of siloxane copolymers, thereby allowing for the attachment of high dielectric permittivity molecules through copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC). The synthesized copolymers allow for a high degree of chemical freedom, as several parameters can be varied during the preparation phase. Thus, the space between the functional groups can be varied, by using different dimethylsiloxane spacer units between the dipolar molecules. Furthermore, the degree of functionalization can be varied accurately by changing the feed of dipolar molecules. As a result, a completely tunable elastomer system, with respect to functionalization, is achieved. It is investigated how the different functionalization variables affect essential DE properties, including dielectric permittivity, dielectric loss, elastic modulus and dielectric breakdown strength, and the optimal degree of chemical functionalization, where these important properties are not significantly compromised, is also determined. Thus, the best overall properties were obtained for a silicone elastomer prepared with 5.6 wt% of the dipolar molecule 1-ethynyl-4-nitrobenzene. Here, a high increase in dielectric permittivity (~70%) was obtained without compromising other vital DE properties such as elastic modulus, gel fraction, dielectric and viscous loss and electrical breakdown strength.
Dielectric elastomers (DEs) have many favourable properties. The obstacle of high driving voltages, however, limits the commercial viability of the technology at present. Driving voltage can be lowered by decreasing the Young’s modulus and increasing the dielectric permittivity of silicone elastomers. A decrease in Young’s modulus, however, is often accompanied by the loss of mechanical stability and thereby the lifetime of the DE. New soft elastomer matrices with high dielectric permittivity and low Young’s modulus, with no loss of mechanical stability, were prepared by two different approaches using chloropropyl-functional silicone polymers. The first approach was based on synthesised chloropropyl-functional copolymers that were cross-linkable and thereby formed the basis of new silicone networks with high dielectric permittivity (e.g. a 43% increase). These networks were soft without compromising other important properties of DEs such as viscous and dielectric losses as well as electrical breakdown strength. The second approach was based on the addition of commercially available chloropropyl-functional silicone oil to commercial LSR silicone elastomer. Two-fold increase in permittivity was obtained by this method and the silicone oil decreased the Young’s modulus significantly. The viscous losses, however, also increased with increasing content of silicone oil. Cross-linkable chloropropyl-functional copolymers offer a new silicone elastomer matrix that could form the basis of dielectric elastomers of the future, whereas the chloropropyl silicone oil approach is an easy tool for improvement of the properties of existing commercial silicone elastomers.
The energy density of dielectric elastomers (DEs) is sought increased for better exploitation of the DE technology since an increased energy density means that the driving voltage for a certain strain can be lowered in actuation mode or alternatively that more energy can be harvested in generator mode. One way to increase the energy density is to increase dielectric permittivity of the elastomer. A novel silicone elastomer system with high dielectric permittivity was prepared through the development of interpenetrating networks from ionically assembled silicone polymers and covalently crosslinked silicones. The system has many degrees of freedom since the ionic network is formed from two polymers (amine and carboxylic acid functional, respectively) of which the chain lengths can be varied, as well as the covalent silicone elastomer with many degrees of freedom arising from amongst many the varying content of silica particles. A parameter study is performed to elucidate which compositions are most favorable for the use as dielectric elastomers. The elastomers were furthermore shown to be self-repairing upon electrical breakdown.
The research on soft elastomers with high dielectric permittivity for the use as dielectric electroactive polymers (DEAP)
has grown substantially within the last decade. The approaches to enhance the dielectric permittivity can be categorized
into three main classes: 1) Mixing or blending in high permittivity fillers, 2) Grafting of high permittivity molecules onto
the polymer backbone in the elastomer, and 3) Encapsulation of high permittivity fillers. The approach investigated here
is a new type of encapsulation which does not interfere with the mechanical properties to the same content as for the
traditionally applied thermoplastic encapsulation. The properties of the elastomers are investigated as function of the
filler content and type. The dielectric permittivity, dielectric loss, conductivity, storage modulus as well as viscous loss
are compared to elastomers with the same amounts of high permittivity fillers blended into the elastomer, and it is found
that the encapsulation provides a technique to enhance some of these properties.
A new approach based on silicone interpenetrating networks with orthogonal chemistries has been investigated with
focus on developing soft and flexible elastomers with high energy densities and small viscous losses. The
interpenetrating networks are made as simple two pot mixtures as for the commercial available silylation based
elastomers such as Elastosil RT625. The resulting interpenetrating networks are formulated to be softer than RT625 to
increase the actuation caused when applying a voltage due to their softness combined with the significantly higher
permittivity than the pure silicone elastomers.
Polydimethylsiloxane (PDMS) elastomers are excellent materials for dielectric electroactive polymers (DEAPs) due to
their high efficiency and fast response. PDMS suffers, however, from low dielectric permittivity and high voltages are
therefore required when the material is used for DEAP actuators. In order to improve the dielectric properties of PDMS a
novel system is developed where push-pull dipoles are grafted to a new silicone compatible cross-linker. The grafted
cross-linkers are prepared by reaction of two different push-pull dipole alkynes as well as a fluorescent alkyne with the
new azide-functional cross-linker by click chemistry. The dipole cross-linkers are used to prepare PDMS elastomers of
various chains lengths providing different network densities. The functionalized cross-linkers are incorporated
successfully into the networks and are well distributed as determined by the fluorescent functional cross-linker and
fluorescence microscopy. The thermal, mechanical and electro-mechanical properties of PDMS elastomers of 0 wt% to
3.6 wt% of push-pull dipole cross-linker are investigated. An increase in the dielectric permittivity of 19 % at only
0.46 wt% of pure push-pull dipole is observed. Furthermore, the dielectric losses are found to be very low while the
electrical breakdown strengths are high and adequate for DEAP applications.
Holographic pulsed light induced recording in azobenzene polymers is being extensively studied due to its potential use
in optical storage applications. In this communication we show our studies in the formation of holographic grating
recording in different azobenzene side chain polymethacrylates irradiating with a single 4 ns light pulse at 532 nm.
Holographic gratings have been registered using intensity and polarization patterns. The time response and stability of
this diffraction efficiency have been studied as a function of the recording energy. Stable values of the diffraction
efficiency have been obtained in some of the polymers after one single pulse of several tenths of mJ/cm2. We have also
estimated the relevance of surface and phase contributions at different recording energy regimes. Polarization
holographic gratings with efficiencies of about 0.8% (measured at 632.8 nm) have been registered with no measurable
relief contribution.
We present the improved demonstrator of our rewritable holographic memory card system. High density optical storage is realized in a non-commercial optical set-up. Fourier transformed recording is used in a polarization holographic arrangement realizing reading and writing from the same side of the data carrier which is a modified plastic card. Holograms containing binary information of 300 x 220 bits are as small as 0.0484 square mm. The storage layer is amorphous polyester providing repeated writing and erasure cycles and thousandfold readouts without loss of information. Alternate read only system providing non-volatile storage can be realized using 635 nm laser diode.
Our goal is to develop a re-writable holographic memory card system based on thin film polymer media on credit card size plastic carriers. Data is stored in our system in form of polarization holograms that present high efficiency and excellent suppression of higher orders even for thin material. Data is written on the card in a parallel way using spatial light modulators to encode the object beam that is Fourier transformed by a custom objective lens and interferes with the reference beam (of orthogonal polarization) on the card. We use reflective carrier in order to read out the data from the same side of the card. This allows us to have a compact system and standard ID 1 type carrier card. The optical system and the data organization are optimized to have a data density higher than 1bit/micrometers 2. We expect to pass the limit of 10 bit/micrometers 2 with the introduction of phase coded multiplexing that would provide more than 2Gbyte capacity if using half the card area as active surface.
Optical storage properties of thin azobenzene side-chain polyester films were examined by polarization holographic measurements. The new amorphous polyester film is the candidate material for the purpose of rewritable holographic memory system. Temporal formation of anisotropic and topographic gratings was studied in case of films with and without a hard protective layer. We showed that the dominant contribution to the diffraction efficiency comes from the anisotropy in case of expositions below 1 sec even for high incident intensity. The usage of the same wavelength for writing, reading and erasing was tested. The ability of azobenzene polyester for rewriting was found satisfactory after many writing-erasing cycles.
We present a novel solution for high-density optical storage of data in thin media. The holographic memory card of Optilink provides sixty-fold data density enhancement compared to present commercial LaserCard devices. The 1 - 2 micrometers thin amorphous polyester storage film is capable of rewritable storage using a single laser source for writing and erasing. The polarization holographic principle used in reflection mode requires demanding optical solutions. Successful data evaluations prove applicability of the new system. Density enhancement up to 16 bit/micrometers 2 with the use of 20 - 30 micrometers thick layer is also outlined.
A Two-dimensional holographic memory for archival storage is described. Assuming a coherent transfer function, an A4 page can be stored at high resolution in an area of 1 mm2. Recently developed side-chain liquid crystalline azobenzene polyesters are found to be suitable media for holographic storage. They exhibit high resolution, high diffraction efficiency, have long storage life, are fully erasable and are mechanically stable.
We describe novel organic compounds based on polyester and peptide backbones with azobenzenes in the side chain for erasable holographic storage. These materials exhibit high diffraction efficiency, high resolution and long storage life and can be used for holographic storage in a broad spectra window of 415 - 530 nm. In polyester thin film systems with a chiral azobenzene, diffraction efficiencies of about 50% have been achieved with just 300 ms exposure. Through atomic force and near-field optical microscopic investigations, we have found an aggregation process encompassing both the main and side chains to be responsible for the permanent storage in the case of polyesters. The stored information can be erased globally in this case with heat. On the contrary, holograms written in peptide films are not totally erased even after exposure to 250 degree(s)C for one month. However, the information can be locally erased using circularly polarized light. A strong polarization dependent surface relief is observed both for the polyesters and peptides. Through FTIR and surface profile measurements, we further show that irradiation of the films with p- polarized light results in a large surface roughness. We show that in the case of the polyesters the storage is mostly due to optical anisotropy and in the case of the peptide oligomers, both the anisotropy and surface relief are large.
It has been demonstrated that the photo-induced orientation or reorientation of dye-containing liquid-crystalline side-chain (LCSC) polymers can be used for reversible optical data storage. A method which enables the determination of this orientational behavior in addition to the order parameter is infrared dichroism. The present experimental approach uses Fourier- Transform infrared (FTIR) spectroscopy with polarized radiation to determine the orientation of the main chain and side chains in a LCSC polyester with a dodecamethylene spacing of the ester groups in the main chain and six methylene groups in the spacer, after irradiation with an Argon ion laser beam.
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