Improved energy density and charge-discharge efficiency in solution processed highly defined ferroelectric block copolymer-based dielectric nanocomposites

The development of light and flexible capacitive energy storage devices with high electrical energy densities is of crucial significance to respond to the ever-rising demands in advanced applications and electricity needs. Incorporation of high dielectric constant ceramic fillers inside the ferroelectric polymer matrix offers great potential to improve the energy density of dielectric materials. However, this approach often suffers from highly reduced breakdown strength caused by the large difference of the matrix and filler dielectric constants together with often poor dispersion of the ceramic additives inside the polymer. Here, we demonstrate a simple method for the preparation of improved polymer-based dielectric nanocomposites based on self-assembly of medium dielectric constant hafnium oxide nanorods using ferroelectric block copolymer. The prepared nanocomposites exhibit both improved discharged energy densities and charge-discharge efficiencies, whereas they preserve their function up to comparable electric fields as the pristine block copolymer. The enhancement of the properties is mostly ascribed to the formation of deeper charge traps due to nanorod induced crosslinking inside amorphous domains and the reduction of ferroelectric loss influenced by creation of an additional paraelectric phase in nanocomposites

Physical pinning and chemical crosslinking-induced relaxor ferroelectric behavior in P(VDF-ter-TrFE-ter-VA) terpolymers

Relaxor ferroelectric polymers, having a high energy storage density and efficiency, are rapidly developing for reliable and compact dielectric film capacitors. Until now, they have been based on highly fluorinated monomers lacking functionalities for further modifications, such as good dispersion of nanoparticles or facile crosslinking, to gain enhanced properties. In this work, we study the electroactive properties of a novel class of poly(vinylidene fluoride-ter-trifluoroethylene-tervinyl alcohol) (P(VDF-ter-TrFE-ter-VA)) terpolymers for capacitive energy storage applications. Additionally, we show that the VA units in these terpolymers can be crosslinked using facile urethane chemistry. It is found that introducing VA in the terpolymer backbone leads to cocrystallization with the fluorinated monomeric constituents. The VA defects promote the formation of TTTG monomer sequences favoring relaxor ferroelectric behavior. Consequently, the Curie transition is strongly reduced compared to P(VDF-co-TrFE) analogues. Moreover, chemical crosslinking of P(VDF-terTrFE- ter-VA) terpolymers results in extremely slim hysteresis loops due to the increase in the relative amount of the disordered paraelectric phase and ultrafine crystallites. Therefore, this new class of relaxor ferroelectric polymers, wherein physical pinning and chemical crosslinking are combined, shows great promise for future advanced applications

Chitosan-based microparticles for immobilization of TiO2 nanoparticles and their application for photodegradation of textile dyes

The present paper deals with removal and photocatalytic degradation of the textile dyes by TiO2 nanoparticles immobilized onto chitosan-based microparticles. The microparticles composed of chitosan (Ch) and poly(methacrylic acid) (PMA) were fabricated for the first time by inverse suspension polymerization. They were utilized for colloidal TiO2 nanoparticles immobilization, synthetized by acidic hydrolysis of TiCl4. To evaluate the potential application of Ch/PMA/TiO2 microparticles for treatment of textile wastwaters, their photocatalytic activity was examined by degradation assessment of three different groups of anionic azo dyes in aqueous solutions under solar light simulating source. FTIR analysis revealed that Ch and PMA were incorporated in the polymer network. SEM and optical microscopy confirmed their spherical shape. Under illumination, Ch/PMA/TiO2 microparticles completely removed dyes C.I. Acid Orange 7, C.I. Acid Red 18, C.I. Acid Blue 113, C.I. Reactive Black 5, C.I. Direct Blue 78, while removal degree of C.I. Reactive Yellow 17 was 75%. It was found that pH had significant influence on the photocatalytic activity of Ch/PMA/TiO2 microparticles. Increase of solution pH from acidic to alkaline, lead to decrease in photodegradation rate of C.I. Acid Orange 7 during the first hours of illumination. After three illumination cycles, removal degree of C.I. Acid Orange 7 was maintained at remarkably high level (95% at pH 5.60 and 100% at pH 2.00 and 8.00), indicating that microparticles could be reused without significant loss of photocatalytic efficiency. (C) 2016 Elsevier Ltd. All rights reserved.</p

Electroactive materials with tunable response based on block copolymer self-assembly

Ferroelectric polymers represent one of the key building blocks for the preparation of flexible electronic devices. However, their lack of functionality and ability to simply tune their ferroelectric response significantly diminishes the number of fields in which they can be applied. Here we report an effective way to introduce functionality in the structure of ferroelectric polymers while preserving ferroelectricity and to further tune the ferroelectric response by incorporating functional insulating polymer chains at the chain ends of ferroelectric polymer in the form of block copolymers. The block copolymer self-assembly into lamellar nanodomains allows confined crystallization of the ferroelectric polymer without hindering the crystallinity or chain conformation. The simple adjustment of block polarity leads to a significantly different switching behavior, from ferroelectric to antiferroelectric-like and linear dielectric. Given the simplicity and wide flexibility in designing molecular structure of incorporated blocks, this approach shows the vast potential for application in numerous fields

Can Ferroelectricity Improve Organic Solar Cells?

Blends of semiconducting (SC) and ferroelectric (FE) polymers have been proposed for applications in resistive memories and organic photovoltaics (OPV). For OPV, the rationale is that the local electric field associated with the dipoles in a blend could aid exciton dissociation, thus improving power conversion efficiency. However, FE polymers either require solvents or processing steps that are incompatible with those required for SC polymers. To overcome this limitation, SC (poly(3-hexylthiophene)) and FE (poly(vinylidene fluoride-trifluoroethylene)) components are incorporated into a block copolymer and thus a path to a facile fabrication of smooth thin films from suitably chosen solvents is achieved. In this work, the photophysical properties and device performance of organic solar cells containing the aforementioned block copolymer consisting of poly(vinylidene fluoride-trifluoroethylene): P(VDF-TrFE), poly(3-hexylthiophene): P3HT and the electron acceptor phenyl-C-61-butyric acid methyl ester: [60]PCBM are explored. A decrease in photovoltaic performance is observed in blends of the copolymer with P3HT:[60]PCBM, which is attributed to a less favorable nanomorphology upon addition of the copolymer. The role of lithium fluoride (the cathode modification layer) is also clarified in devices containing the copolymer, and it is demonstrated that ferroelectric compensation prevents the ferroelectricity of the copolymer from improving photovoltaic performance in SC-FE blends