Well-defined silicone–titania composites with good performances in actuation and energy harvesting

Abstract

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.

Optimization Techniques for Improving the Performance of Silicone‐Based Dielectric Elastomers

“…The traditional choice of fillers for silicones is silica particles, due to their inherent compatibility. These fillers can eithervia the simplest processbe blended directly into one or both of the elastomer premixes [33][34][35][36][37][38][39][40][41][42] or alternativelyvia the more demanding processincorporated through in situ condensation reactions during the crosslinking condensation reaction, [43,44] therebyin both casesyielding a morphology, as illustrated in Figure 2. [32] Silica, however, does not contribute positively to the dielectric permittivity of the resulting elastomer, since the relative permittivities of silica and silicone are similar.…”

Silicone dielectric elastomers based on radical crosslinked high molecular weight polydimethylsiloxane co-filled with silica and barium titanate

“…Harvesting experiments (voltage recording) were performed using a memory oscilloscope, Tektronix DPO 4032 (350 MHz, 2.5 GS s -1 ), as was already described in Refs. [11,23].…”

“…[11], which involved measuring peak-to-peak voltages generated by a mechanical impulse created by falling of a metal ball of 7.1 g from a height of 100 mm on the surface of the elastomeric films placed between two electrodes (Fig. 8).…”

“…Different strategies have been used to improve the dielectric properties [9], but the most promising one is the incorporation of filler particles with high dielectric permittivity, such as ceramic fillers (e.g., barium titanate, titanium dioxide, calcium copper titanium oxide, lead zirconate, etc.) [10][11][12][13][14]. The dielectric relaxation of the crystallites embedded into the polymer matrices was studied [15,16], and the principal role of the interface states on the border polymer-crystallites was established in defining the corresponding dielectric features.…”

“…Continuing our efforts to obtain silicone elastomers with optimized electromechanical properties [11,[25][26][27][28], in this paper, we addressed the working strategy consisting in the original combination of two active fillers with complementary effects: silica, as a reinforcing filler and barium titanate, both from commercial sources, to increase the dielectric permittivity of the composites obtained. In addition, the uniqueness of our approach consists in the use of a matrix of a polydimethylsiloxane of high molecular weight (M w = 642000 g mol -1 ) and its curing by a radical mechanism, which takes place at high temperature and pressure.…”