Controlling The Interfacial Architecture Of PVDF-based Nanocomposite Fibers Towards Improving Piezoelectric Properties

Polyvinylidene fluoride(PVDF)based nanocomposites have great potential for wide range of applications,such as flexible electronic devices,due to their outstangding piezoelectric properties.However,the weak interfacial interaction between the fillers and matrix always limits the improvement of piezoelectric properties.The key to preparing PVDF-based piezoelectric composite devices is how to regulate the interface interaction in order to synergistically enhance their piezoelectric properties.In view of this,based on polyvinylidene fluoride nanocomposite fibers,we explore some new interface design and regulation strategies between polyvinylidene fluoride and nanofillers(i.e.,piezoelectric or non-piezoelectric nanoparticles).Mechanisms responsible for interface interactions between nanofillers and molecular chains are clarified.The evolutions in the surface microstructure and macromolecular condensed structure of nanocomposite fibers are revealed,as well we their relationship between the piezoelectric output performances.This thesis clearly shows the microscopic mechanism for the interfacial control in PVDF-based nanocomposite fibers towards tailoring the resulting piezoelectric properties control This study will help expand their applications in flexible self-powered equipments,energy acquisition and conversion andsensors,etc.The main contents are as follows:(1)Firstly,using electrospun polyvinylidene fluoride/carbon nanotubes(PVDF/CNTs)composite nanofibers as the model system,the effect of maleic anhydride grafted polyvinylidene fluoride(PVDF-g-MA)on interfacial interactions in such filled nanocomposites is demonstrated.we have clarified the influencial mechanisms governing the evolutions in surface microstructure and macromolecular condensed structure of nanocomposite fibers during electrospinning,as well their influence on the resultant piezoelectric properties of composite nanofibers.It is found that a very small amount of PVDF-g-MA could act as a macromolecular compatilizer,thereby significantly enhancing the interfacial compatibility between PVDF-g-MA and CNTs through the interaction between the maleic anhydride groups and the hydroxyl groups of CNTs and the physical enttanglements between PVDF-g-MA and PVDF chains.Such strong interfacial interactions between PVDF and CNTs drive the transformation of the molecular chain into an all-trans conformation by coupling the in-situ high speed stretching and polarization of the PVDF molecular chain under the electrospinning field.This significantly promotes the formation of piezoelectric?-phase crystals.Interestingly,when a very small amount of PVDF-g-MA(1 wt%)is added,the relative content of?-phase in PVDF/CNTs nanofibers reaches 71.65%.The resulting output voltage and current can reach 10.6 V and 0.94?A,respectively,and the output power can reach up to 3.15?W/cm².The piezoelectric device based on PVDF/CNTs composite nanofibers can not only charge to low-power consumption electronics,but also act as sensors to detect physiological signals.(2)Secondly,Ba Ti O₃@PVDF hybrid nanocomposite fibers were prepared by loading piezoelectric nano-barium titanate(Ba Ti O₃)particles are onto the surface of polyvinylidene fluoride(PVDF-g-MA)nanofibers through a facile but efficient interfacial chemical control strategy.The effect of interface control via an interface chemical modification on the nanoparticle-loaded composite fibers was studied.The influencial mechanism responsible for the microstructure evolution and piezoelectric output performance of the nanofibers is clarified.It was demonstrated that the dopamine-coated Ba Ti O₃(Pdop-BT)nanoparticles could be well-loaded onto the surface of PVDF-g-MA nanofibers.Specifically,Ba Ti O₃ particles are anchored firmly on the surface of nanofibers by the colvant bonding between the amino groups on the surface of Pdop-BT and the anhydride groups of PVDF-g-MA chains.Under the action of external force,piezoelectric particles on the surface of nanocomposite fibers can effectively promote the deformation and polarization processes of PVDF dipoles.This characteristic could be coupled with these polarizations from the electroactive?-phase crystals inside the fiber,thus synergically improving the piezoelectricity.The piezoelectric output performances are enhanced with the increase in the loadings of Ba Ti O₃.Particularly,at a Ba Ti O₃ loading of 21.39%,the open-circuit voltage and short-circuit current of the hybrid nanofibers reach 11.8 V and 1?A,respectively,thus achieving an output power of 0.71?W/cm².More importantly,compared with the filled composite fibers,nanoparticle-loaded composite fibers with interfaces tailored by interfacial chemistry show the excellent piezoelectric output performances and energy harvesting capability.