Abstract
Electroactive polymers with high dielectric constants and low moduli can offer fast responses and large electromechanical strain under a relatively low electric field with regard to theoretical driving forces of electrostriction and electrostatic force. However, the conventional electroactive polymers, including silicone rubbers and acrylic polymers, have shown low dielectric constants (ca. < 4) because of their intrinsic limitation, although they have lower moduli (ca. < 1 MPa) than inorganics. To this end, we proposed the high dielectric PVDF terpolymer blends (PVTC-PTM) including poly(vinylidene fluoride-trifluoroethylene-chlorofluoro-ethylene) (P(VDF-TrFE-CFE), PVTC) as a matrix and micelle structured poly(3-hexylthiophene)-b-poly(methyl methacrylate) (P3HT-b-PMMA, PTM) as a conducting filler. The dielectric constant of PVTC-PTM dramatically increased up to 116.8 at 100 Hz despite adding only 2 wt% of the polymer-type filler (PTM). The compatibility and crystalline properties of the PVTC-PTM blends were examined by microscopic, thermal, and X-ray studies. The PVTC-PTM showed more compatible blends than those of the P3HT homopolymer filler (PT) and led to higher crystallinity and smaller crystal grain size relative to those of neat PVTC and PVTC with the PT filler (PVTC-PT). Those by the PVTC-PTM blends can beneficially affect the high-performance electromechanical properties compared to those by the neat PVTC and the PVTC-PT blend. The electromechanical strain of the PVTC-PTM with 2 wt% PTM (PVTC-PTM2) showed ca. 2-fold enhancement (0.44% transverse strain at 30 Vpp μm−1) relative to that of PVTC. We found that the more significant electromechanical performance of the PVTC-PTM blend than the PVTC was predominantly due to the electrostrictive force rather than electrostatic force. We believe that the acquired PVTC-PTM blends are great candidates to achieve the high-performance electromechanical strain and take all benefits derived from the all-organic system, including high electrical breakdown strength, processibility, dielectrics, and large strain, which are largely different from the organic–inorganic hybrid nanocomposite systems.
Highlights
We suggest that PVTC blends including the poly(3-hexylthiophene)-bpoly (P3HT-b-PMMA) conducting fillers for all organic blend systems yield PVTC-PTM blends with minimal moduli increases and maximized dielectric constant growth
The P(VDF-TrFE-CFE)/ P3HT-b-PMMA (PVTC-PTM) blend films were fabricated by a conventional solution casting method, resulting in about 50 μm in the film thickness (Figure 1a1)
The P3HT-b-PMMA (PTM) block copolymer (Mn : 24,000 g mol−1, Mw /Mn : 1.25, P3HT/PMMA: 25/75 wt%) was synthesized on the basis of our previous reports to use for the conducting fillers [30,31]
Summary
Electroactive polymers (EAPs) have been investigated for potential applications, such as electrical sensors, compact soft actuators, artificial muscles, and micro-robotics [1,2,3,4,5,6,7]. PVDF and P(VDF-TrFE) have been used for the fabrication of electromechanical devices owing to their efficient electrical-to-mechanical energy conversion [12] Those still have limited dielectric constants, large hysteresis because of large permanent polarization domains, and the formation of long-range polar ordering [13]. The ferroelectric relaxor polymers, including poly(vinylidene fluoride-trifluoroethylene-chlorofluoro-ethylene) (P(VDF-TrFE-CFE), PVTC), have been exploited in emerging electrostrictive materials for replacing conventional EAPs. ferroelectric relaxor polymers still have suffered from limitations, including the requirement of relatively strong external electric fields for a high-performance electromechanical property. The electromechanical properties of the PVTC-PTM blends were evaluated by measuring their transverse strain under the electric field They were compared with prepared reference materials, including neat PVTC and PVTC blends with a P3HT homopolymer (PVTC-PT), along with reported electroactive polymers, including silicone rubbers and acrylic polymers. The electromechanical strain mechanisms of the PVTC-PTM were systematically addressed in this study based on the parameter (dielectric constant and modulus) effects and crystalline phase transition behavior
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