Although possess low dielectric constant, silicones are between the most used polymer in actuation due to their appropriate mechanical properties (low modulus and high elongation). These can be easily tuned by the preparation strategy: proper choice of the molecular mass and microstructure of the polymer matrix; adding or not of more or less active fillers; whether these are incorporated in the polymeric matrix (ex situ) or generated in situ; crosslinking mode (through the side or ending functional groups) or mechanism (condensation, radicalic or by hydrosilylation). A relatively low cost and easy scalable procedure was used in this paper to prepare silicone composites based on high molecular weight polydiorganosiloxane copolymer and hydrophobized silica and titania nanoparticles. The matrix polymer was synthesized by bulk ring opening copolymerization of different substituted cyclosiloxanes and characterized by FTIR, 1 H NMR and GPC. The composites prepared by the mechanical incorporation of the fillers were crosslinked by radicalic mechanism and investigated by dielectrical spectroscopy, mechanical tests, dynamo-mechanical analysis (DMA), dynamic vapors sorption (DVS). The actuation measurements revealed displacement values in the range: 0.04-5.09 nm/V/mm, while energy harvesting measurements revealed impulse electrical voltage in the range 6-20 for a dynamic force of 0.1-1Kgf. The robustness of these composites supported by their thermal, mechanical and surface properties recommends them for use inclusively in harsh environmental conditions, when their behavior is not significantly affected.

Five R-trialkoxysilanes, with R: CH 3 , C 6 H 5 , NH 2 (CH 2 ) 3 , Cl(CH 2 ) 3 , or NC(CH 2 ) 3 are used as crosslinkers for two polydimethylsiloxane-a,v-diols with different molecular masses (35,000 and 125,000 g Á mol À1 ) The crosslinking occurs by condensation at room temperature under the influence of the environmental moisture and in presence of dibutyltindilaurate as a catalyst. After aging, the films are characterized by mechanical testing, dielectric spectroscopy, and thermal analysis. Moisture sorption capacity is evaluated by dynamic vapour sorption analysis, while the morphology of the crosslinked films is observed by scanning electron microscopy in cryo-fracture. The mechanical response to an applied electric field is measured. The results are discussed in correlation with polymeric chain length and the nature of R from crosslinking agent emphasizing in principle an increasing of the dielectric permittivity and actuation with the polarity of the organic group but a worsening of these with increasing length of the polymer chain matrix.

Some films based on electromechanically active polymer composites have been prepared. Polydimethylsiloxane-α,ω-diols (PDMSs) having different molecular masses (Mv=60 700 and Mv=44 200) were used as matrix in which two different active fillers were incorporated: titanium dioxide in situ generated from its titanium isopropoxide precursor and silica particles functionalized with polar aminopropyl groups on surface. A reference sample based on simple crosslinked PDMS was also prepared. The composites processed as films were investigated to evaluate their ability to act as efficient electromechanical actuators for potential biomedical application. Thus, the surface morphology of interest for electrodes compliance was analysed by atomic force microscopy. Mechanical and dielectric characteristics were evaluated by tensile tests and dielectric spectroscopy, respectively. Electromechanical actuation responses were measured by interferometry. The biocompatibility of the obtained materials has been verified through tests in vitro and, for valuable films, in vivo. The experimental, clinical and anatomopathological evaluation of the in vivo tested samples did not reveal significant pathological modifications.

Three different small molecule or polymeric well-determined complex structures containing siloxane moieties and 3d metals were incorporated into a polymeric matrix based on a polydimethylsiloxane of low molecular weight. After the incorporation of the complex, matrix crosslinking was performed with tetraethylorthosilicate, resulting in free-standing films. The films were investigated by scanning and transmission electron microscopy (SEM, TEM), dynamic vapour sorption (DVS) analysis, stress–strain measurements and dielectric spectroscopy. The presence of the siloxane moiety in the ligand (by its surface effect) improves the compatibility between the metal complex and the silicone matrix, which ensures good mechanical properties. Thus, modulus values between 0.10 and 0.50 MPa and elongations of 210–380% were obtained. Depending on the metal type and the complexation pattern, an increasing of the dielectric constant value up to 4.6 as compared with a value of 2.5 for the silicone matrix was obtained. The samples showed good electromechanical actuation behaviour even at small voltages.

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