For the processing of dielectric elastomer actuators (DEAs) one promising class of materials are silicones. They are lowcost 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.
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.
Dielectric elastomer actuators (DEAs) are smart materials that gained much in interest particularly in recent years. One
active field of research is the improvement of their properties by modification of their structural framework. The object
of this work is to improve the actuation properties of polydimethylsiloxane (PDMS)-based DEAs by covalent
incorporation of mono-vinyl-terminated low-molecular PDMS chains into the PDMS network. These low-molecular
units act as a kind of softener within the PDMS network. The loose chain ends interfere with the network formation and
lower the network’s density. PDMS films with up to 50wt% of low-molecular PDMS additives were manufactured and
the chemical, mechanical, electrical, and electromechanical properties of these novel materials were investigated.
One example of organic electronics is the application of polymer based light emitting devices (PLEDs). PLEDs are very attractive for large area and fine-pixel displays, lighting and signage. The polymers are more amenable to solution processing by printing techniques which are favourable for low cost production in large areas. With phosphorescent emitters like Ir-complexes higher quantum efficiencies were obtained than with fluorescent systems, especially if multilayer stack systems with separated charge transport and emitting layers were applied in the case of small molecules. Polymers exhibit the ability to integrate all the active components like the hole-, electron-transport and phosphorescent molecules in only one layer. Here, the active components of a phosphorescent system – triplet emitter, hole- and electron transport molecules – can be linked as a side group to a polystyrene main chain. By varying the molecular structures of the side groups as well as the composition of the side chains with respect to the triplet emitter, hole- and electron transport structure, and by blending with suitable glass-forming, so-called small molecules, brightness, efficiency and lifetime of the produced OLEDs can be optimized. By choosing the triplet emitter, such as iridium complexes, different emission colors can be specially set. Different substituted triazine molecules were introduced as side chain into a polystyrene backbone and applied as electron transport material in PLED blend systems. The influence of alkyl chain lengths of the performance will be discussed. For an optimized blend system with a green emitting phosphorescent Ir-complex efficiencies of 60 cd/A and an lifetime improvement of 66.000 h @ 1000 cd/m2 were achieved.
Dielectric elastomer actuators (DEAs) can be optimized by modifying the dielectric or mechanical properties of the electroactive polymer. In this work both properties were improved simultaneously by a simple process, the one-step film formation for polyurethane and silicone films. The silicone network contains polydimethylsiloxane (PDMS) chains, as well as cross-linker and grafted molecular dipoles in varying amounts. The process leads to films, which are homogenous down to the molecular level and show higher permittivities as well as reduced stiffnesses. The dipole modification of a new silicone leads to 40 times higher sensitivities, compared to the unmodified films. This new material reaches the sensitivity of the widely used acrylate elatomer VHB4905. A similar silicone modification was obtained by using smart fillers consisting of organic dipoles and additional groups realizing a high compatibility to the silicon network. Polyurethanes are alternative elastomers for DEAs which are compared with the silicones in important properties. Polyurethanes have an intrinsically high dielectric constant (above 7), which is based on the polar nature of the polyurethane fragments. Polyurethanes can be made in roll-to-roll process giving constant mechanical and electrical properties on a high level.
Dielectric elastomer actuators (DEAs) can be optimized by modifying the dielectric or mechanical properties
of the electroactive polymer. In this work both properties were improved simultaneously by a simple process,
the one-step film formation. The silicone elastomer network contains polydimethylsiloxane (PDMS) chains, as
well as crosslinker and grafted molecular dipoles in varying amounts. This leads to films, which are homogenous
down to the molecular level. Films with higher permittivity and reduced stiffness were obtained. As matrix
two PDMS-materials with different molar masses, leading to other network chain lengths, were compared. This
directly influences the network density and thus the mechanical properties. A higher electrical field response for
long chain matrix materials was found. The actuation sensitivities for both materials were enhanced by 6.3 and
4.6 times for the short and long chain matrix material, respectively.
Silicone elastomers are highly suitable for application in the field of dielectric elastomer actuators (DEA) due
to their unique material properties (e.g. low glass temperature, thermal stability, large capability of chemical
tailoring). The elastomer forming Polydimethysiloxane (PDMS) employed for this study consists of chains
with vinyl termination and is cross linked via hydrosilylation to a cross linking molecule in the presence of
platinum catalyst. Here, dipole molecules (N-Allyl-N-methyl-4-nitroaniline) were specifically synthesized such
that they could chemically graft to the silicone network. The most prominent advantage of this approach is the
achievement of a homogeneous distribution of dipoles in the PDMS matrix and a suppression of phase separation
due to the grafting to the junction points of the rubber network. Several films with dipole contents ν ranging
from 0 %wt up to 10.9 %wt were prepared. The films were investigated to determine their mechanical (tensile
testing), dielectric (dielectric relaxation spectroscopy) and electrical (electrical breakdown) properties. This new
approach for composites on the molecular level leads to homogeneous films with enhanced material properties for
DEA applications. An increase in permittivity from 3.3 to 6.0, a decrease in electrical breakdown from 130 V/μm
to 50 V/μm and a lowering of the mechanical stiffness from 1700 kPa to 300 kPa was observed.
The aim of this work is to develop some new polymer materials with typical n-type semiconducting properties and low reduction peak potentials. Therefore new organo-soluble copolyquinoxalines were used in polymer blends with poly-[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenvinylene] or regioregular poly-(3-hexylthiophene). The photovoltaic properties of these polymer blends depend on the blend morphology. So the short circuit current density can be improved by better solvent mixtures and by temper processes. But nevertheless the photovoltaic properties are low and a stable and well ordered phase morphology is difficult to obtain with polymer blend systems. Therefore another approach to receive more effective full polymer photovoltaic cells was done. Block copolymers consisting of n-type and p-type sequences in one polymer chain were synthesized. As n-type material a quinoline monomer and as p-type material 3-hexylthiophene were used. The synthesis of these new materials is described. The spectroscopic and cyclovoltammetric investigations clearly indicate their block copolymer structure. The study of their phase morphology and photovoltaic properties is in progress.
The aim of this work is to develop some new polymer materials with typical n-type semiconducting properties and low reduction peak potentials. Therefore new synthetic routes are presented leading to organo-soluble polyquinolines and polyquinoxalines. The results of the synthesis and characterization of the obtained new organo-soluble polymers are shown. The electrochemical reduction and oxidation behavior of these polymers is studied by cyclovoltammetric measurements. All studied polymers can be reversibly oxidized and reduced. In addition the absorption and luminescence properties are investigated. Polymer/polymer solar cells are prepared from blends of the new polyquinoxalines and poly-[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenvinylen] as active single layer. First results are discussed.
A unusual way is presented to obtain a new class of deep red emitting polymers. Polyurethanes with covalently attached fluorescent dyes were developed. The DCM-dye seems to be a favorable candidate but it has no reactive groups for linking into a polymer structure. DCM can be synthesized by the monofunctional addition of (2,6-dimethyl-4H-pyrane-4-ylidene)-malononitrile with 4-dimethylaminobenzaldehyde. We realized a bifunctional condensation of the pyrane with N-methyl-N-(2-hydroxyethyl)-4-aminobenzaldehyde to enlarge the conjugated system and to shift the emission maximum to more than 650 nm. Simultaneously we introduced two reactive hydroxy terminal groups into the dye molecule. Using this functionality we were able to synthesize several new polyurethanes with covalently attached DCM dye in the main chain. By co-condensation with non-dye molecules like N,N-bis-(2-hydroxyethyl)-aniline or butan-1,4-diole the dye content in the main chain can be varied and the influence of the absorption and emission behavior can be studied. Red emitting device structures were realized and some of the device properties will be given. It will be shown that the stability and the lifetime of the device can be increased by simple structure modification of the polyurethane, e.g. alkylation of the urethane groups or the change of the co-components.
A crosslinkable side chain NLO-polymer of the bis-azobenzene type and an AB-type main chain NLO-polymer of the sulphonyl-tolane type have been synthesized and characterized with respect to their curing and electric poling properties. NLO-susceptibilities d33 of 11 pm/V and 7.5 pm/V, respectively, have been measured after initial relaxation and proved to be highly stable. During poling, transient SH-signal and square of poling current showed similar temporal behavior. Thus transient poling current can be considered to be a useful probe to monitor and to control the poling process. Direct current electrical conductivity was found to be strongly temperature dependent for both materials.