Preparation And Properties Of Self-powered Multicolor Photoluminescent Vinylidene Fluoride Piezoelectric Copolymer/carbon Quantum Dots Composites

Fossil fuel is an important source of energy for social development.However,with the use of fossil fuels,the ecological environment in all regions has been destroyed.Therefore,the use of clean energy instead of fossil fuel has become an urgent problem for the contemporary society.Piezoelectric materials can convert mechanical energy into electrical energy,and have broad research and application prospects in the field of new energy.Vinylidene fluoride copolymer such as P(VDF-TrFE)is a kind of semi-crystalline piezopolymer with a variety of crystalline forms,together with the properties of excellent piezoelectricity,flexibility,chemical corrosion resistance and easy processing.The piezoelectric properties of vinylidene fluoride polymers are mainly attributed to their internal polar crystals.The formation of polar crystals can be obtained by electrostatic field polarization,induction of nanoparticles,and high-pressure melting crystallization.Carbon quantum dots(CQDs)are the newcomers in the family of carbon nanomaterials.With a size of 5-10 nm,they have the characteristics of high fluorescence intensity and strong fluorescence stability.In particular,compared with CdSe or CdTe quantum dots,carbon QDs have the advantages of low toxicity,environmental friendliness and good biocompatibility.In this paper,by means of the combination of high-pressure crystallization and nanoparticle induction approaches,the in situ formation and evolution of the polar crystalline structures in a P(VDF-TrFE)/CQDs composite were investigated at high pressure,and novel piezoelectric hybrids,with high-efficiency electromechanical conversion and multicolor fluorescence effect,were successfully prepared via the sequential self-organizational and-assembly processes.The main conclusions are as follows:(1)Study on the high pressure crystallization behaviors of P(VDF-TrFE)/CQDs compositesThe nanoscale uniform dispersion of CQDs was achieved in the polymer matrix of P(VDF-TrFE)/CQDs,fabricated through the solution mixing method.With the increase of crystallization temperatures,the crystallinity of the pressure crystallized P(VDF-TrFE)/CQDs increased gradually,and there was a competetion in the growth of?and?form crystals.When the crystallization temperature reached 240~oC,the ratio of?to?in the composite system attained the maximum value.Likewise,an appropriate increase in the crystallization pressure contributed to the improvement of the crystallinity of the composite system.The prolongation of crystallization time had little effect on the melting point of the composite system,but the crystallinity of the sample increased with the increase of crystallization time as well.The crystallinity of the P(VDF-TrFE)/CQDs reached 21.97%when the crystallization time was increased to 60 min.(2)Study on the piezoelectric and fluorescent properties of P(VDF-TrFE)/CQDs hybridsWhen the content of CQDs varied between 1%and 3%,the homogeneous dispersion of CQDs in P(VDF-TrFE)matrix could be achieved by the solution mixing approach.However,the fluorescent CQDs at high pressure managed to assemble together in P(VDF-TrFE),forming unique self-organized micro/nanoscale architectures.With the increase of CQDs content,the polar crystalline structures in the high-pressure crystallized P(VDF-TrFE)/CQDs were obviously different,changing from disorderly petal-like nanosheets to orderly nanosheets and 3D micro-/nanorod assemblies to high melting point polygonal crystals assembled by nanowire arrays.The piezoelectric properties of P(VDF-TrFE)/CQDs hybrids were related to the external forces,and the higher the frequency of the applied forces,the better the energy harvesting performance of the hybrid materials.Also,the piezoelectric outputs of P(VDF-TrFE)/CQDs hybrids increased with the increase of CQDs content.For the P(VDF-TrFE)/CQDs(97/3,wt/wt)hybrid,the open-circuit voltage and short-circuit current outputs,under the conditions of mechanical force of20 N and impact frequency of 3 Hz,reached up to 21.3 V/cm~2 and 550 nA/cm~2,respectively.The P(VDF-TrFE)/CQDs based hybrid nanogenerator showed excellent durable and reliable features during the real time demonstration of the powering of commercial LEDs,and no attenuation of the electrical signals was observed for?10000 continuous working cycles.Moreover,the P(VDF-TrFE)/CQDs hybrids demonstrated stable photoluminescence properties.They displayed excellent multi-color fluorescence emission effect,whether in solution,thin film or high-pressure crystallization state.