Piezoelectric Nanofiber Mats With Enhanced Elastic Recovery for Smart Fabrics

A novel additive manufacturing route using a tailored resin containing Poly(vinylidene fluoride) Trifluoroethylene (PVDF‐TrFE) to 3D print piezoelectric films is demonstrated. Piezoelectric films are printed within 2 seconds in a single step by simultaneously focusing initiating and inhibiting excitations within the liquid resin to locally confine the photochemical reaction. The printed films are patterned with an array of holes with a diameter of 30 µm and a pitch of 55 µm. The piezoelectric response is homogeneous across the film, indicating that the print pattern does not impact the PVDF‐TrFE microstructure. Although the printed films contain only a small volume fraction of PVDF‐TrFE (3 wt.%), their piezoelectric response (d33 = 20.3 pC/N) is comparable to the highest literature values reported for PVDF‐TrFE films. The printed PVDF‐TrFE films are predominantly β‐phase, and no electrical poling, post‐processing, piezoelectric or inorganic additives are used in the fabrication. Analysis using piezoresponse force microscopy (PFM) and scanning electron microscopy (SEM) reveals that the enhanced piezoelectric response is due to the preferential formation of oriented PVDF‐TrFE phases during printing. These results demonstrate how the dedicated design of photoactive resins in combination with volumetric additive manufacturing can be applied to rapidly fabricate functional 3D structures.

In an effort to fabricate a wearable piezoelectric energy harvester based on core-shell piezoelectric yarns with external electrodes, flexible piezoelectric nanofibers of BNT-ST (0.78Bi0.5Na0.5TiO3-0.22SrTiO3) and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) were initially electrospun. Subsequently, core-shell piezoelectric nanofiber yarns were prepared by twining the yarns around a conductive thread. To create the outer electrode layers, the core-shell piezoelectric nanofiber yarns were braided with conductive thread. Core-shell piezoelectric nanofiber yarns with external electrodes were then directly stitched onto the fabric. In bending tests, the output voltages were investigated according to the total length, effective area, and stitching interval of the piezoelectric yarns. Stitching patterns of the piezoelectric yarns on the fabric were optimized based on these results. The output voltages of the stitched piezoelectric yarns on the fabric were improved with an increase in the pressure, and the output voltage characteristics were investigated according to various body movements of bending and pressing conditions.

A study was conducted to ascertain the effect of variation in spin speed and baking temperature on $$\upbeta $$ -phase content in the spin-coated poly(vinylidene fluoride) (PVDF) thick films ( $${\sim }4{-}25\,\upmu \hbox {m}$$ ). Development of $$\upbeta $$ -phase is dependent on film stretching and crystallization temperature. Therefore, to study the development of $$\upbeta $$ -phase in films, stretching is achieved by spinning and crystallization temperature is adjusted by means of baking. PVDF films are characterized using Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy. It is observed that crystallization temperature lower than $$60^{\circ }\hbox {C}$$ and increase in spin speed increases the $$\upbeta $$ -phase content in PVDF films. Crystallization temperature above $$60^{\circ }\hbox {C}$$ reduces $$\upbeta $$ -phase content and increases $$\upalpha $$ -phase content. It was also observed that viscosity of the PVDF solution affects the $$\upbeta $$ -phase development in films at a particular spin speed.

Flexible, electrospun boron nitride nanosheets (BNNS)/hydroxyapatite –PVDF nanofibers with superior piezoelectric/ferroelectric, biocompatible features for effective bone tissue regeneration

In this study, piezoelectric composite nanofiber films were fabricated by introducing nitrogen-doped-reduced-graphene-oxide as a conductive material to a P(VDF-TrFE) polymer and a BiScO3–PbTiO3 ceramic composite employing an electrospinning process. Nitrogen was doped/substituted into rGO to remove or compensate defects formed during the reduction process. Electro-spinning process was employed to extract piezoelectric composite nanofiber films under self-poling condition. Interdigital electrodes was employed to make planner type energy harvesters to collect electro-mechanical energy applied to the flexible energy harvester. From the piezoelectric composite with interdigital electrode, the effective dielectric permittivity extracted from the conformal mapping method. By introducing BS–PT ceramics and N-rGO conductors to the P(VDF-TrFE) piezoelectric composite nanofiber films, the effective dielectric permittivity was improved from 8.2 to 15.5. This improved effective dielectric constant probably come from the increased electric flux density due to the increased conductivity. Fabricated interdigital electrode using this thin composite nanofiber film was designed and tested for wearable device applications. An external mechanical force of 350 N was applied to the composite nanofiber-based energy harvester with interdigital electrodes at a rate of 0.6 Hz, the peak voltage and current were 13 V and 1.25 μA, respectively. By optimizing the device fabrication, the open-circuit voltage, stored voltage, and generated output power obtained were 12.4 V, 3.78 V, and 6.3 μW, respectively.

Self-powered cardiac pacemaker by piezoelectric polymer nanogenerator implant

Flexible ferroelectrics being exploited as energy harvesting and conversion materials are highly desirable for wearable and skin-mountable electronic devices. As one of the most typical ferroelectric polymers, poly(vinylidene fluoride) (PVDF) has been widely used in modern electronic systems and devices, whose ferroelectric performance relies heavily on its β phase content. In this work, to achieve high-β-phase-content PVDF, we first introduced CoFe2O4 nanoparticles into PVDF. With the incorporation of CoFe2O4 nanoparticles used as an effective polymer nucleation agent, the percentage of the β phase in the PVDF has been significantly enhanced, e.g., 84% in the nanocomposite with 5 wt. % CoFe2O4 versus only 73% in the pure PVDF. In order to further increase the β phase content in PVDF, we subsequently proposed an easily realized strategy. By applying DC magnetic fields during the solution-casting process of the PVDF/CoFe2O4 nanocomposites, a further improved β phase content as high as 95% can be achieved. The further improvement of the β phase content is attributable to the tensile stress at the CoFe2O4/PVDF interfaces created by the coupling of magnetic field and CoFe2O4 by means of the magnetostriction effect. The high β-phase content makes the PVDF/CoFe2O4 nanocomposites a promising candidate for flexible and wearable electronic device applications.

In this paper, sub-20 nm ferroelectric PVDF–TrFE copolymer nanograss structures with aspect ratios up to 8.9 were developed. This study demonstrated sub-20 nm PVDF–TrFE nanograss structures that are nanoimprinted using a silicon nanograss mold in a single step. Vertically oriented PVDF–TrFE nanopillars were poled using the developed flip-stacking poling method. According to the PFM measurements, the piezoelectricity of flat thin films fabricated in this work reaches 14.0 pm/V. The maximum output voltage of the single PVDF–TrFE nanopillar was 526 mV, and the maximum piezoelectricity of the single PVDF–TrFE nanopillar was 210.4 pm/V. The piezoelectricity of the developed PVDF–TrFE nanograss structures was 5.19 times larger than that of the PVDF–TrFE flat thin films. The developed technique is simple, economical, and easy to fabricate. The developed ferroelectric PVDF–TrFE copolymer nanograss structures, which showed enhanced piezoelectricity compared to the PVDF–TrFE flat thin films, have potential applications in nanotip-based protein biosensors, nanotip-based tactile sensors, and power nanogenerators.

The paper presents in vitro contractile myocardial cell pattern on piezoelectric nanofiber mats with applications in energy harvesting. The cell-based energy harvester consists of myocardial cell sheet and a PDMS substrate with a PVDF nanofiber mat on. Experimentally, cultured on specifically distributed nanofiber mats, neonatal rat ventricular cardiomyocytes are characterized with the related morphology and contraction. Previously, we have come up with the concept of energy harvesting from heart beating using piezoelectric material. A bio-hybrid energy harvester combined living cardiomyocytes, PDMS polymer substrate and piezoelectric PVDF film with the electrical output of peak current 87.5nA and peak voltage 92.3mV. However, the thickness of the cardiomyocyte cultured on a two-dimensional substrate is much less than that of the piezoelectric film. The Micro Contact Printing (μCP) method used in cell pattern on the PDMS thin film has tough requirement for the film surface. As such, in this paper we fabricated nanofiber-constructed PDMS thin film to realize cell pattern due to PVDF nanofibers with better piezoelectricity and microstructures of nanofiber mats guiding cell distribution. Living cardiomyocytes patterned on those distributed piezoelectric nanofibers with the result of the same distribution as the nanofiber pattern.

PET/PTT bicomponent filaments yarn is produced by two polymers: the polyethylene terephthalate (PET) and the polytrimethylene terephtalate (PTT) extruded side by side. This yarn is known for its high mechanical properties in particular elasticity and elastic recovery. However, differences between physical and chemical properties of the two components make the dyeing step of this yarn complicated. The aim of this work is the development of a dyeing process for bicomponent filaments without altering their physical and chemical properties. Different techniques such as SEM, FTIR, and differential scanning calorimetry (DSC) were used to characterize the studied yarn. For dyeing, three different disperse dyes CI Disperse Red 167.1, CI Disperse Yellow 211, and CI Disperse Red 60 with different energy classes were studied. The influence of dyeing conditions in particular dyeing temperature, pH of dye bath, dyeing time, and carrier concentration in the dye bath was evaluated. Responses analyzed are color strength (K/S), colorimetric coordinates and color fastness of samples dyed with studied dyes. In addition, the stability of elasticity and elastic recovery of bicomponent filament fabrics after the dyeing process has been also verified and proved.

The electroactive β-phase is the most desirable due to its highest piezo-, pyro-, and ferroelectric properties in Poly (vinylidene fluoride) (PVDF). The β- phase can be nucleated by incorporation of nanoparticles into PVDF. The objective of this study is the preparation and characterization of the pristine PVDF film, and intensified dosages of the ZrO2 modified composite PVDF films, further piezoelectric properties of nanocomposites films are evaluated. The nanocomposite films have been prepared by solution casting method with different loadings of ZrO2. The prepared films are characterized by Scanning electron microscope (SEM), x-ray diffraction (X-RD) analysis, Fourier transform infrared spectra (FTIR), and Differential scanning calorimetry (DSC), to study surface morphology, β- phase content, crystallinity, and melting temperature. The experimental analysis shows that the β- phase percentage and melting temperature of the films increases with ZrO2 loading, but the percentage of crystallinity decreases. Nanogenerators are fabricated by using the films, and piezoelectric performances of the nanogenerators are evaluated under various external stresses. The maximum voltage generated in the case of 5 wt% loading of ZrO2 is 1560 mV for 100 g of load, which is approximately eight times higher than the voltage generated in the pristine- PVDF and 2.2 V is generated while tapping by hand.

We developed a flexible two-ply piezoelectric yarn-type generator using an electrospun polyvinylidenefluorideco- trifluoroethylene (PVDF–TrFE) mat and a commercially available silver-coated nylon fiber. By rolling the silvercoated nylon fiber into the electrospun PVDF–TrFE mat as the inner electrode, the two-dimensional piezoelectric PVDF– TrFE mat was easily transformed into a one-dimensional fiber. Then silver-coated nylon fiber rolled in PVDF–TrFE was plied with another similar fiber to make a flexible two-ply piezoelectric yarn. The overall fabrication processes of the flexible two-ply piezoelectric yarn are simple and have a high application potential. The flexible two-ply piezoelectric yarn can generate up to 0.7 V in compression and 0.55 V in tension. The yarn retained the piezoelectric performance in various shapes, such as a sewn structure. In addition, the piezoelectric performance was sensitive to velocity and pressure. The flexible two-ply piezoelectric yarn has potential applications as a human motion sensor, as a building block of energy- harvesting textiles, and in self-powered biomedical applications. Keywords: Energy harvester, Flexible, Piezoelectric, Two-ply, Wearable, Yarn.

To improve the structure and hard elasticity of poly(vinylidene fluoride) (PVDF) fibers, a small amount of the plasticizer dibutyl phthalate (DBP) was added to PVDF. The PVDF/DBP blend fibers were prepared by melt spinning and subsequent annealing. The crystalline structure and thermal properties of the blend fibers were analyzed in terms of the long‐period lamellar spacing, crystal structure, and degree of crystallinity with X‐ray diffraction, differential scanning calorimetry, and small‐angle X‐ray scattering. The results indicated that stacked crystalline lamellae, which were aligned normal to the fiber axis, existed in the blend fibers, and they were in the form of an α‐crystal phase. The total crystallinity of the blend fibers was higher than that of the pure PVDF fibers, and it reached its highest value when the DBP concentration was 2 wt %; then, it decreased with an increase in the DBP content. The morphology and mechanical properties of the fibers were also investigated with scanning electron microscopy and electronic tensile experimentation. The results of scanning electron microscopy apparently exhibited a small porous structure on the surface of the blend fibers, and the more DBP there was in the PVDF fibers, the more porous structure was obtained. Mechanical experiments indicated that the fibers with a 5 wt % concentration of DBP had better elastic recovery and breaking strain than the pure PVDF fibers. These results all indicated that DBP‐modified PVDF fibers have potential applications in preparing microporous membranes by a melt spinning and stretching process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The ferroelectric nature of polymer ferroelectrics such as poly(vinylidene fluoride) (PVDF) has been known for over 45 years. However, its role in interfacial transport in organic/polymeric field-effect transistors (FETs) is not that well understood. Dielectrics based on PVDF and its copolymers are a perfect test-bed for conducting transport studies where a systematic tuning of the dielectric constant with temperature may be achieved. The charge transport mechanism in an organic semiconductor often occurs at the intersection of band-like coherent motion and incoherent hopping through localized states. By choosing two small molecule organic semiconductors - pentacene and 6,13 bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) – along with a copolymer of PVDF (PVDF-TrFe) as the dielectric layer, the transistor characteristics are monitored as a function of temperature. A negative coefficient of carrier mobility is observed in TIPS-pentacene upwards of 200 K with the ferroelectric dielectric. In contrast, TIPS-pentacene FETs show an activated transport with non-ferroelectric dielectrics. Pentacene FETs, on the other hand, show a weak temperature dependence of the charge carrier mobility in the ferroelectric phase of PVDF-TrFE, which is attributed to polarization fluctuation driven transport resulting from a coupling of the charge carriers to the surface phonons of the dielectric layer. Further, we show that there is a strong correlation between the nature of traps in the organic semiconductor and interfacial transport in organic FETs, especially in the presence of a ferroelectric dielectric.

Fabrication and modeling of β-phase PVDF-TrFE based flexible piezoelectric energy harvester