Commercial dielectric elastomers and their modification methods are reviewed. A method is proposed to overcome the complex interdependency of their properties allowing quick comparison and selection of suitable materials for soft actuator applications.
Chemically crosslinked poly (isobornylacrylate-co-isobutylacrylate) was elaborated by radical photo-copolymerization of isobornylacrylate and isobutylacrylate monomers in a 4:1 mass ratio, by adding a crosslinking agent at low concentration. The obtained copolymer was characterized by Fourier transform infrared spectroscopy for structural analysis, by differential scanning calorimetry for the determination of the glass transition temperature, and by thermogravimetric analysis to investigate thermal degradation effects. Storage modulus, dissipation modulus and tan delta were evaluated by dynamic mechanical analysis and modeled using different physical approaches such as the time-temperature superposition principle and the Havriliak-Negami model. The Cole-Cole curve was fitted with the Havriliak-Negami model yielding five parameters which were used to calculate the dynamic mechanical properties of the copolymer over a large frequency range from 1.03x10-4 Hz to 7.58x10 7 Hz. Calculated elastic and dissipative moduli agree well with the experimental data.
A series of linear acrylic copolymers based on Isobornyl acrylate (IBOA) and isobutyl acrylate (IsoBA) were elaborated by radical photopolymerization. In addition, several photochemically crosslinked poly(IBOA‐co‐IsoBA) were prepared by introducing small amounts of 1,6‐hexanedioldiacrylate as crosslinking agent. The evolution of the glass transition temperature was determined experimentally by differential scanning calorimetry as a function of composition for both linear and crosslinked poly(IBOA‐co‐IsoBA), yielding Tg values ranging from (~249) to (~315 K). Theoretical modeling was performed applying Fox, Gordon‐Taylor and Couchman‐Karasz models by simple calculations using experimental data, leading to only fair agreement between theoretical and experimental values, or by applying fitting procedures involving one or two adjustable parameters. Likewise, the Kwei model, known to take into account hydrogen bonding interactions between monomers, could not describe well the evolution of Tg, indicating the existence of other factors influencing Tg. Finally, a thermodynamic approach based on entropy considerations allowed to attribute an explanation of the evolution of Tg.
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