Β-phase Of Poly Research Articles

Controlled formation of the β-phase in poly(9,9-dioctylfluorene) by blending with low-molecular-weight polystyrene

The poly(9,9-dioctylfluorene) (PFO) solid film exhibits various phases including disordered α-phase and well-ordered β-phase. Especially, the formation of the β-phase in PFO is crucial for enhancing its carrier transport properties. Recently, the β-phase conformation of the PFO chains was reported to be formed by blending PFO with polystyrene (PS). Here, the weight-average molecular weight (Mw) of PS was investigated to clarify the formation mechanism of the β-phase conformation in a PFO:PS blend film. The β-phase conformation was formed only when PFO was blended with low-Mw PS. The temperature for the formation of the β-phase in the PFO:PS blend film was likely to be reduced to near room temperature owing to the thermal properties of low-Mw PS. Furthermore, we demonstrated that the amount of conformational change and the content of β-phase of the PFO chains in the PFO:PS blend film can be controlled by adjusting the blending ratio of low-Mw PS.

Investigation of the enhancement in the β-phase of PVDF as a function of MoSe2 concentration and its effect on the piezoelectric performance of the nanogenerator

Self-powered devices, which can harvest energy from various ambient mechanical sources, are being explored and have immense potential. In this regard, piezoelectric nanogenerators have attracted considerable attention for their ability to harvest energy from the kinetic movements of the body. In this paper, we have investigated the enhancement in the β-phase of Poly(vinylidene fluoride) (PVDF), which contributes to its piezoelectric property, as a function of MoSe2 weight percentages (0%, 3%, 7%, 10%) and studied its effect on the piezoelectric performance of the nanogenerator. PVDF is a biocompatible and flexible material that has delivered promising results for use in wearable technology. However, it has a low piezoelectric coefficient, and can be improved by the addition of a filler material. We have demonstrated that the addition of MoSe2 resulted in the enhancement of the β-phase content in PVDF, from 66.59% to 84.48%. This is supported by the X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) of the thin films. The piezoelectric performance of the films was evaluated by measuring the open-circuit voltage (VOC) generated when periodically hit by tapping them with a finger at regular intervals. A maximum peak-to-peak VOC of 18.8 V was obtained from the 10 wt% MoSe2-PVDF film without any load resistance. This work showcases the immense potential of flexible nanogenerators in wearable technology.

Three-Dimensional MOF-Assisted Self-Polarized Ferroelectret: An Effective Autopowered Remote Healthcare Monitoring Approach.

In recent years, flexible and sensitive pressure sensors are of extensive interest in healthcare monitoring, artificial intelligence, and national security. In this context, we report the synthetic procedure of a three-dimensional (3D) metal-organic framework (MOF) comprising cadmium (Cd) metals as nodes and isoniazid (INH) moieties as organic linkers (CdI2-INH═CMe2) for designing self-polarized ferroelectret-based highly mechano-sensitive skin sensors. The as-synthesized MOF preferentially nucleates the stable piezoelectric β-phase in poly(vinylidene fluoride) (PVDF) and also gives rise to a porous ferroelectret composite film. Benefiting from the porous structure of 3D MOFs, composite ferroelectret film-based ultrasensitive pressure sensor (mechano-sensitivity of 8.52 V/kPa within 1 kPa pressure range) as well as high-throughput ( power density of 32 μW/cm2) mechanical energy harvester (MEH) has been designed. Simulation-based finite element method (FEM) analysis indicates that the geometrical stress confinement effect within the interpore region of the ferroelectret structure synergistically influences the mechano-electrical property of the MEH. In addition, 143 pC/N (∼4.5 times higher than commercial piezoelectric PVDF films) piezoelectric charge coefficient (d33) magnitude and superior response time (tr ∼ 8 ms) of this composite ferroelectret film enable the detection of different physiological signals such as coughing, pronunciation, and gulping behavior, making it a promising candidate for early intervention of healthcare, which may play a significant role in accurate alert of influenza and chronic obstructive pulmonary disease (COPD)-related symptoms. In addition, MEH enables the tracking of the subtle pressure change in the wrist pulse, indicating its usefulness in effective mechano-sensitivity. Since the cardiovascular signal is one of the vital parameters that can determine the on-going physiological conditions, the wireless transmission of the detected wrist pulse signal has been demonstrated. All of these features coupled with wireless data transmission indicate the promising application of MOF-assisted composite ferroelectret films in noninvasive real-time remote healthcare monitoring.

Immobilized ionic liquid induced electroactive β-phase in poly(vinylidene fluoride) thin films

Ferroelectric poly(vinylidene fluoride) (PVDF) has been proposed in the past decades as an electroactive material for various applications in microelectronic devices due to its ferro/piezo/pyroelectric properties. However, fabrication of smooth PVDF thin films with a high content of β-phase and controlled chain orientation is a long-standing problem. Here we report on the control over polymorphs of PVDF thin films by exploring the interfacial ion-dipolar interactions. The ion-dipolar interactions are provided by CF2 bonds of PVDF and imidazolium type ionic liquid immobilized onto substrates via biomimetic catecholic attachment chemistry. By simply melt crystallization of spin-coated PVDF thin films at elevated temperatures, the ferroelectric polar β-phase with a lying-down chain orientation is formed. The thin films exhibit excellent ferro/piezoelectric properties when applying electric field due to the immobilization of ionic liquids. The results may boost the applications of PVDF in microelectronic devices.

Influence of Ni-Zn-Cu-ferrite on electroactive β-phase in poly(vinylidene fluoride)-Ni-Zn-Cu-ferrite nanocomposite film: Unique metamaterial for enhanced microwave absorption

In search of a new radar absorbing material for microwave applications, the nanoparticles of Ni0.40Zn0.40Cu0.20Fe2O4 (NZCF) are successfully incorporated in the matrix of poly(vinylidene fluoride) (PVDF), and this NZCF-PVDF nanocomposite system has evolved as the potential one for absorbing radiations in the microwave/GHz frequency range. The enhancement of electroactive β-phase of PVDF has been observed in the NZCF-PVDF nanocomposite system due to the formation of NZCF-PVDF interfaces. Also, the magnetic dipoles of ferrite nanoparticles are present in the same resultant nanocomposite system. Both these factors play a significant role in the interaction of microwave radiation with the medium of the nanocomposite system. The optimization of wave matter interaction leads to the superior reflection loss property of the NZCF-PVDF nanocomposite system. The mutual contributions of both magnetic nano-fillers and electroactive PVDF polymers make this NZCF-PVDF nanocomposite system a unique metamaterial for enhanced microwave absorption. Many articles have been published on polymer-ferrite systems but in true sense the involvement of NZCF-PVDF interfaces as active centres during wave matter interactions has not been considered by anyone else. Reflection loss property of all the NZCF-PVDF nanocomposite films has been observed, and a maximum of −49.7 dB at 13.2 GHz is obtained for 10 wt. % of NZCF loaded PVDF nanocomposite films. This is the highest reflection loss ever found in these types of polymer based metamaterials. Also, the high reflection loss in NZCF-PVDF nanocomposite films (X and Ku bands) makes it the most suitable one for the applications in the area of microwave devices.

From Starting Formation to the Saturation Content of the β-Phase in Poly(9,9-dioctylfluorene) Toluene Solutions

In this research, the relationship between chain aggregation and poly(9,9-dioctylfluorene) (PFO) β-phase content with a change of the PFO solution concentration is investigated. Photoluminescence and UV–vis absorption spectra are used to explore the PFO β-phase and its content. Chain aggregation is explored by dynamic light scattering (DLS). It is found that the chain aggregation size of the starting to form PFO β-phase is approximately 100 nm. The β-phase content increases with the chain aggregation degree. When the β-phase content is in the range of 44% ± 2%, the maximum value of the content (saturation content) of the β-phase is reached and cannot be changed by any external field that could induce β-phase formation. Therefore, the concept of the saturation content of the PFO β-phase is first proposed. The mechanism from PFO β-phase formation to saturation content is explored by DLS and atomic force microscopy. This research is significant to understand and control the molecular chain condensed-state process as well as phase transition from solution to film to achieve a photoelectric device with high charge carrier mobility, stability, and efficiency.

Improving efficiency and color purity of poly(9,9-dioctylfluorene) through addition of a high boiling-point solvent of 1-chloronaphthalene

In this work, the β-phase of poly(9,9-dioctylfluorene) (PFO) was used as a probe to study the effects of the addition of a high boiling-point solvent of 1-chloronaphthalene on the nanostructures and electroluminescence of PFO films. Both absorption and photoluminescence spectra showed that the content of the β-phase in PFO film was obviously enhanced as a result of the addition of a small amount of 1-chloronaphthalene into the processing solvent of p-xylenes. Apparently rougher morphology associated with the effectively enhanced ordering of polymer chains across the entire film was observed for films processed from p-xylene solutions consisting of a certain amount of 1-chloronaphthalene, as revealed by atomic force microscopy and grazing incidence x-ray diffraction measurements. In addition to the effects on the nanostructures of films, of particular interest is that the performance and color purity of polymer light-emitting devices can be noticeably enhanced upon the addition of 1-chloronaphthalene. These observations highlight the importance of controlling the nanostructures of the emissive layer, and demonstrate that the addition of a low volume ratio of high boiling-point additive can be a promising strategy to attain high-performance polymer light-emitting diodes.

Probing the synergism of halloysite nanotubes and electrospinning on crystallinity, polymorphism and piezoelectric performance of poly(vinylidene fluoride)

Halloysite nanotubes (HNT) and electrospinning synergistically promoted the formation of β-phase in poly(vinylidene fluoride) (PVDF) from which a maximum piezoelectric response of 955 mV was obtained under a load of 100 g.

Piezoelectric formation mechanisms and phase transformation of poly(vinylidene fluoride)/graphite nanosheets nanocomposites

The β-phase of poly(vinylidene fluoride) (PVDF) is of great technical importance because of its high dielectric constant and piezoelectric effect. In this work, we exfoliated and dispersed natural graphite to prepare 2D-graphite nanosheets (GNS) and prepared PVDF/GNS nanocomposites with different GNS volumes from 1 to 7 ml as film via solution casting method. The concentration of the supernatant was about 0.3 mg/mL. The effect of GNS on the β-phase formation and mechanisms of piezoelectric formation in the PVDF/GNS nanocomposites were investigated. The results showed that with the varying amounts of GNS, the crystalline structure, the morphology, and the dielectric and piezoelectric properties of PVDF/GNS nanocomposites changed. GNS acts as an effective nucleation agent with the orientation almost parallel to the surface of the film meanwhile increasing the amount of beta phase in the PVDF matrix with increasing amount of GNS, also the relative dielectric constant and dielectric loss of the nanocomposites increased with increasing amount of GNS. The value d33 also increased with increasing amount of GNS, and reached a maximum (6.7 pC/N) with 6 ml GNS. The mechanism of piezoelectric formation was proposed based on experiment results of PVDF/GNS nanocomposites.

Silicon carbide-induced piezoelectric β-phase in poly(vinylidene fluoride) and its properties

Abstract

Swift Heavy Ion Induced Ordering and Piezoelectric β-phase in Poly(vinylidene fluoride)

Ion flux dependent swift heavy ions (SHI) induced structural changes have been reported for pristine poly(vinylidene fluoride) (PVDF). Ordering phenomena has been observed first followed by its transformation from α to β-form (polar metastable piezoelectric phase). The ordering of (020) plane become prominent at higher ion flux SHI irradiation and its further increase induces structural change from α to β phase as revealed by XRD and FTIR analyses. Structural changes are also supported by morphological evidence and thermal studies before and after SHI irradiation.

Degradation studies of transparent conductive electrodes on electroactive poly(vinylidene fluoride) for uric acid measurements

Biochemical analysis of physiological fluids using, for example, lab-on-a-chip devices requires accurate mixing of two or more fluids. This mixing can be assisted by acoustic microagitation using a piezoelectric material, such as the β-phase of poly(vinylidene fluoride) (β-PVDF). If the analysis is performed using optical absorption spectroscopy and β-PVDF is located in the optical path, the material and its conductive electrodes must be transparent. Moreover, if, to improve the transmission of the ultrasonic waves to the fluids, the piezoelectric transducer is placed inside the fluidic structures, its degradation must be assessed. In this paper, we report on the degradation properties of transparent conductive oxides, namely, indium tin oxide (ITO) and aluminum-doped zinc oxide, when they are used as electrodes for providing acoustic microagitation. The latter promotes mixing of chemicals involved in the measurement of uric acid concentration in physiological fluids. The results are compared with those for aluminum electrodes. We find that β-PVDF samples with ITO electrodes do not degrade either with or without acoustic microagitation.

β-Phase of poly(vinylidene fluoride) formation in poly(vinylidene fluoride)/poly(methyl methacrylate) blend from solutions

The effect of single and mixed solvent on the crystallization behavior of the PVDF/PMMA blend from solutions was investigated. The films cast from the good solvent N, N-dimethylformamide (DMF) dominantly yielded the β-phase crystal with the highest crystallinity of PVDF. Those deposited from the methyl ethyl ketone (MEK) and tetrahydrofuran (THF) exhibited a mixture of α- and some extra β-phase crystals and presented the low crystallinity of PVDF. The crystallization behavior and morphology of the films cast from the mixed solvent (THF/DMF) revealed an enormous dependence on the DMF content. The increased DMF content in the mixed solvent enhanced the interactions between polymers and solvents, and favored the β-crystal of PVDF formation but hindered the α-phase of PVDF formation. Thus, the total crystallinity of PVDF in the blend film was decreased with the DMF content increasing, because of the decreased α-phase of PVDF. In addition, the morphological feature revealed that the voids between the PVDF spherulites were eliminated remarkably by blending with PMMA. The average size of the connected spherulite on top surface of the film can grow into larger as DMF content increased.

The β‐Phase of Poly(9,9‐dioctylfluorene) as a Potential System for Electrically Pumped Organic Lasing

The β-phase of poly(9,9-dioctylfluorene) (PFO) shows a very low amplified spontaneous emission threshold because of its well-resolved emission spectrum. Within the amorphous PFO, the β-phase sites act similar to a dopant as they trap excitons and charges. The figure shows the blue-light-emitting β-phase in a PFO solution.

Triplet exciton state and related phenomena in the β-phase of poly(9,9-dioctyl)fluorene

Using both time-resolved emission and cw photoinduced absorption spectroscopy as a function of temperature, the aggregation phenomena ($\ensuremath{\beta}$-phase formation) observed in poly(9,9-dioctyl)fluorene is studied. All spectra of the $\ensuremath{\beta}$ phase, including absorption, prompt and delayed fluorescence, phosphorescence, and photoinduced triplet absorption feature very narrow linewidths, which are unique within the class of conjugated polymers. From the comparison of the latter data with amorphous polyfluorene, poly(9,9-diethylhexyl)fluorene, as well as with the fully planar ladder-type poly(paraphenylene), we conclude that the origin of the $\ensuremath{\beta}$ phase cannot simply be an extended intrachain conjugation, but interchain interactions are involved. Furthermore, the $\ensuremath{\beta}$ phase acts as an energetic trap for both singlet and triplet excitons initially created on amorphous chain segments. The delayed fluorescence kinetics of the $\ensuremath{\beta}$ phase were measured at different temperatures. From the analysis of these decays within the framework of dispersive triplet migration in a Gaussian density of states distribution, further evidence is provided that the delayed fluorescence originates from triplet-triplet annihilation. At room temperature, it is clear that triplet excitons migrate over large distances, exceeding that of singlet excitons. Also, the segregation time between dispersive triplet migration and classical thermally activated hopping, is in the case of $\ensuremath{\beta}$-phase containing samples, dependent on the separation of the $\ensuremath{\beta}$-phase domains.