Fluoride Oligomer Research Articles

Deeper Spectroscopic Characterizations of Vinylidene Fluoride (VDF) Oligomers Prepared via Iodine Transfer Polymerization (ITP)

Deeper Spectroscopic Characterizations of Vinylidene Fluoride (VDF) Oligomers Prepared via Iodine Transfer Polymerization (ITP)

Improvement of thermal stability of an organic pyroelectric infrared sensor with Parylene C coating

We fabricated a protective Parylene C layer coated with vinylidene fluoride (VDF) oligomer thin films to improve their thermal stability and investigated the temperature dependence of their pyroelectric properties. Following the heat resistance test (at 398 K for 500 h in the presence of air at atmospheric pressure), the deterioration of voltage sensitivity of the Parylene C coated sensor was approximately 20% (553 → 430 V W−1) and approximately 100% in the case of the sensor without Parylene C (551 → 0.86 V W−1). Parylene C coating prevented structural disturbances of VDF oligomer thin films and electrode cracking. Comparison of the VDF oligomer, Parylene-C-coated VDF oligomer, and Parylene-C-coated P(VDF-TrFE), demonstrated the superior thermal stability of the Parylene-C-coated VDF oligomeric pyroelectric sensor.

Engineering Solid Electrolyte Interphase Composition by Assessing Decomposition Pathways of Fluorinated Organic Solvents in Lithium Metal Batteries

Studies have shown fluorinated electrolyte solvents can form desirable solid electrolyte interphase (SEI) in lithium metal batteries. In this study, we develop a detailed mechanistic understanding of two high performing electrolytes, Fluoroethylene Carbonate (FEC) and Difluoroethylene Carbonate (DFEC) to demonstrate minimal structural variations can lead to different decomposition products, and thereby the nature of the SEI. Using density functional theory (DFT) calculations, we find different initial bond-breaking mechanisms between FEC and DFEC. We develop free energy diagrams for the decomposition pathways including both electrochemical and chemical steps. Using the computational Li electrode, we identify the largest limiting potential of 1.77 V for FEC decomposition, associated with the formation of lithium fluoride, lithium oxide and FEC oligomers, and 1.53 V for DFEC, which correspond to the formation of polymerized vinylene carbonate and lithium fluoride. We suggest the formation of oligomers in the case of FEC instead of long polymers may lead to better SEI compactness. We also demonstrate the SEI components of FEC and DFEC are not stable on typical cathode voltage (3.87 V). This study presents a unified electrocatalytic perspective on SEI formation and decomposition.

Characteristics of an infrared sensor formed with a few molecular layers of vinylidene fluoride oligomers with in situ poling during vacuum evaporation

Perpendicularly oriented vinylidene fluoride oligomer thin films with six molecular layers were poled during vacuum evaporation (in situ poling) using a micro-gapped comb-like electrode, and their pyroelectric characteristics were investigated. The extent of polarization achieved with in situ poling performed by applying a low electric field (7.7 MV m−1) is the same as that achieved by conventional post-poling with the application of a high electric field (>100 MV m−1). Despite using a film with a few molecular layers, the in situ poled sensor showed pyroelectric response without the use of an infrared ray absorption layer; voltage sensitivity of 198 V W−1 was obtained, which is much higher than that of the post-poled sensor (∼16 V W−1). The improvement in sensitivity is attributed to the amount of charge injected during the poling treatment.

Ferroelectricity and the phase transition in large area evaporated vinylidene fluoride oligomer thin films

Organic ferroelectric materials, including the well-known poly(vinylidene fluoride) and its copolymers, have been extensively studied and used for a variety of applications. In contrast, the VDF oligomer has not been thoroughly investigated and is not widely used, if used at all. One key advantage the oligomer has over the polymer is that it can be thermally evaporated in vacuum, allowing for the growth of complex heterostructures while maintaining interfacial cleanliness. Here, we report on the ferroelectric properties of high-quality VDF oligomer thin films over relatively large areas on the order of mm2. The operating temperature is identified via differential scanning calorimetry and pyroelectric measurements. Pyroelectric measurements also reveal a stable remanent polarization for these films which persists over very long time scales, an important result for non-volatile data storage. Temperature dependent pyroelectric and capacitance measurements provide compelling evidence for the phase transition in these films. Capacitance-voltage and current-voltage measurements are used to confirm ferroelectricity, quantify the dielectric loss, and calculate the spontaneous polarization. Finally, piezoresponse force microscopy is used to demonstrate large area, low-voltage ferroelectric domain reading/writing in VDF oligomer thin films. This work enables new channels for VDF oligomer applications and research.

The metal/organic interface in cobalt/vinylidene fluoride heterostructures

Organic-based electronic devices are rapidly increasing in popularity, making it essential to understand and characterize the interface between organic materials and metallic electrodes. This work reports on the characterization of the interface between thin films of an emerging organic ferroelectric, vinylidene fluoride (VDF) oligomer, and Co, an important high Curie temperature ferromagnet. Using a wide battery of experimental techniques, it is shown that VDF oligomer thin films as thin as 15 nm can halt, or prevent, Co oxidization in atmospheric conditions, a necessary condition for device applications. Selectivity of magnetic properties, such as remanent magnetization, is enabled by the clarification of the time scale of Co oxidation, a topic on which there are many conflicting reports. Furthermore, this work shows evidence of chemical bonding at the interface between VDF oligomer and Co, a result with important implications for organic spintronic devices. These results establish the suitability of VDF oligomer for organic-based electronic devices.

A Versatile Method for the Preparation of Ferroelectric Supramolecular Materials via Radical End-Functionalization of Vinylidene Fluoride Oligomers.

A synthetic method for the end-functionalization of vinylidene fluoride oligomers (OVDF) via a radical reaction between terminal olefins and I-OVDF is described. The method shows a wide substrate scope and excellent conversions, and permits the preparation of different disc-shaped cores such as benzene-1,3,5-tricarboxamides (BTAs), perylenes bisimide (PBI), and phthalocyanines (Pc) bearing three to eight ferroelectric oligomers at their periphery. The formation, purity, OVDF conformation, and morphology of the final adducts has been assessed by a combination of techniques, such as NMR, size exclusion chromatography, differential scanning calorimetry, polarized optical microscopy, and atomic force microscopy. Finally, PBI-OVDF and Pc-OVDF materials show ferroelectric hysteresis behavior together with high remnant polarizations, with values as high as Pr ≈ 37 mC/m(2) for Pc-OVDF. This work demonstrates the potential of preparing a new set of ferroelectric materials simply by attaching OVDF oligomers to different small molecules. The use of carefully chosen small molecules paves the way to new functional materials in which ferroelectricity and electrical conductivity or light-harvesting properties coexist in a single compound.

In-plane polarization switching of highly crystalline vinylidene fluoride oligomer thin films

The ferroelectric properties of perpendicularly oriented, highly crystalline vinylidene fluoride (VDF) oligomer thin films were investigated by using a planar device configuration consisting of comblike Cr–Au electrodes with a 1 µm gap. In-plane polarization switching was induced by the rotation of the VDF oligomer. As the measurement temperature was increased from 295 to 380 K, the coercive field (Ec) decreased drastically from 124 to 7.7 MV/m. Furthermore, the thermal stability of our device significantly improved compared with that of conventional sandwiched devices utilizing VDF oligomer films with a parallel orientation.

Coplanar switching of polarization in thin films of vinylidene fluoride oligomers

Switching of vinylidene fluoride oligomer thin with molecular chains aligned normal to the substrate and exhibiting a preferential in-plane have been investigated using coplanar geometry of inter-digital via high-resolution It has been shown that in-plane switching proceeds via non-180° rotation of dipoles mediated by non-stochastic expansion, and coalescence of domains. As-grown multidomain configuration is found to be strongly pinned aided by charged and the electrically induced (in-plane) mono-domain states relax to the as-grown state. The observed (approximately 0.6 MV/m) is two to three orders of magnitude smaller than that for the oligomer with out-of-plane It is suggested that the low steric hindrance to the rotation of molecular dipoles gives rise to the observed low

Investigation of ferroelectric domains in thin films of vinylidene fluoride oligomers

High-resolution vector piezoresponse force microscopy (PFM) has been used to investigate ferroelectric domains in thin vinylidene fluoride oligomer films fabricated by the Langmuir-Blodgett deposition technique. Molecular chains are found to be preferentially oriented normal to the substrate, and PFM imaging shows that the films are in ferroelectric β-phase with a predominantly in-plane polarization, in agreement with infrared spectroscopic ellipsometry and X-ray diffraction measurements. The fractal analysis of domain structure has yielded the Hausdorff dimension (D) in the range of ∼1.3–1.5 indicating a random-bond nature of the disorder potential, with domain size exhibiting Landau-Lifshitz-Kittel scaling.

Uniaxially aligned nucleation of vinylidene fluoride oligomer single-crystals on highly ordered ultrathin films of poly(vinylidene fluoride-trifluoroethylene) copolymer

Uniaxially aligned single-crystals of ferroelectric vinylidene fluoride (VDF) oligomer were obtained on a highly-oriented ultra-thin film of vinylidene fluoride–trifluoroethylene copolymer P(VDF/TrFE). Trapezoidal shaped plate-like VDF oligomer crystals with 20nm thickness were selectively grown perpendicularly on P(VDF/TrFE) lamella crystals as a structural template. Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS) and synchrotron two-dimensional grazing incidence X-ray diffraction (2D-GIXD) revealed that the molecular chain axis (c-axis) of P(VDF/TrFE) oriented to the friction transfer direction with the a-axis perpendicular to the film surface, and the friction-transferred P(VDF/TrFE) film induced the uniaxially aligned nucleation of the VDF oligomer with an epitaxial relationship (010)[001]VDF-oligomer//(100)[001]P(VDF/TrFE) in initial crystal growth of VDF oligomer.

Ferroelectric Tunnel Junction Memory Devices made from Monolayers of Vinylidene Fluoride Oligomers

Conductance bistability in Pt/Si–vinylidene fluoride (VDF) oligomer–Au ferroelectric tunnel junction devices is demonstrated. I–V and C–V measurements reveal bistable conductance switching within biasing voltage of ±0.5V with stable memory retention up to 1 × 104 cycles. The memory element exhibits a low switching voltage of ±1.0 V, coincides with the coercive field of the ferroelectric VDF oligomer monolayer films in use.

Structural and Ferroelectric Characterization of Uniaxially Oriented Vinylidene Fluoride Oligomer Thin Films

A uniaxially oriented film of ferroelectric vinylidene fluoride (VDF) oligomer was fabricated by vacuum deposition on a friction-transferred vinylidene fluoride–trifluoroethylene copolymer; i.e., P(VDF/TrFE), film as a structural template. Fourier transform infrared spectroscopy and scanning electron microscopy measurements revealed that the ultra thin P(VDF/TrFE) film induced the formation of the ferroelectric form I crystal phase and the uniaxial orientation of what to the VDF oligomer by epitaxial growth. The VDF oligomer/P(VDF/TrFE) films exhibit ferroelectric hysteresis loops with a coercive field and a remanent polarization of 150 MV/m and 77 mC/m2, respectively; however, VDF oligomer films without a structural template showed no ferroelectric properties.

Structural and Ferroelectric Characterization of Uniaxially Oriented Vinylidene Fluoride Oligomer Thin Films

Structural and Ferroelectric Characterization of Uniaxially Oriented Vinylidene Fluoride Oligomer Thin Films

Numerical Analysis of Palpation in vivo Using Tactile Sensor Composed of Organic Ferroelectrics

Tactile sensors using organic ferroelectrics are promising from the viewpoint of palpation because poly(vinylidene fluoride) [PVDF] tactile sensors have already been developed to evaluate living tissue. Moreover, vinylidene fluoride (VDF) oligomer is a new substance with a smaller number of VDF units than PVDF. As the piezoelectric coefficient of VDF oligomer is great and its film is thin and uniform, it is suitable for preparation of thinner film tactile sensor. On the other hand, in our previous study, we also developed a computer-based surgical simulator to simulate a catheter and guidewire in blood vessels of the brain. In this study, we investigated the palpation in vivo by the tactile sensor composed of organic ferroelectrics using our catheter/guidewire simulator. Using this simulator, the output of the sensor attached on the guidewire tip was calculated when the proximal part of the guidewire model was pushed and pulled. We used the blood vessel model where the friction coefficient or the stiffness was changed partially assuming that these changes occur by a disease. When the friction coefficient between the guidewire and the vessel was large, the sensor outputs became large. When the stiffness of the vessel was small, the sensor outputs became small.

Inclusion and dielectric properties of a vinylidene fluoride oligomer in coordination nanochannels

The dynamics of oligo(vinylidene fluoride) (OVDF) confined in regular nanochannels of a porous coordination polymer (PCP) was studied by means of dielectric spectroscopy. The OVDF chains in the PCP nanopores showed two Arrhenius-type relaxation processes at lower temperatures than the relaxation temperature observed for the neat OVDF, showing the enhanced mobility of the confined OVDF.

Structural and ferroelectric behaviours in blends of vinylidene fluoride oligomer and poly(vinylidene fluoride-trifluoroethylene) copolymer thin film

The structure and ferroelectric properties of ultrathin blend films fabricated by the spin-coating process at room temperature from the mixed solution of vinylidene fluoride oligomers (OVDF) (n = 18) and poly(vinylidene fluoride-trifluoroethylene) copolymers (PVDF-TrFE) are investigated in detail. When OVDF content in mixture is between 40% and 60%, the remanent polarization and fatigue behaviour of the P(VDF-TrFE)/OVDF blend films are all improved. The ferroelectric thin film capacitor with poly(styrenesulfonate) (PSSH) interlayer exhibits a prominent performance with a remanent polarization of 120 mC m−2 even as the thickness of the blend film is 80 nm. Meanwhile, we demonstrate that the increase in the OVDF content from 0% to 100% cannot affect the molecular chain orientation of the P(VDF-TrFE)/OVDF blend films and the molecular chains are in parallel with the substrate.

High electric breakdown strength and energy density in vinylidene fluoride oligomer/poly(vinylidene fluoride) blend thin films

Dense α-phase blend films of vinylidene fluoride (VDF) oligomer and poly(vinylidene fluoride) (PVDF) of various compositions were prepared from chemical solution deposition. The dielectric constant of the films was unexpectedly lower, and the mechanical strength was higher than either of the two components, leading to high electromechanical dielectric breakdown strength (>850 MV/m vs. 300∼500 MV/m for typical PVDF-based films). The properties were attributed to the unique blend structure with high crystallinity and densely packed rigid amorphous phase incorporating long and short chains. A maximum polarization of 162 mC/m2 and a large electric energy density up to 27.3 J/cm3 were obtained.

Solution‐derived ferroelectric vinylidene fluoride oligomer thin films with large polarization

AbstractDense and uniform vinylidene fluoride (VDF) oligomer thin films with a highly polar β phase were prepared for the first time by a low‐cost and scalable solution casting approach, after treatments of substrate surface functionalization and hot‐pressing. Introducing hydrated salt in the precursor solution effectively promoted the ferroelectric β phase. The VDF oligomer thin films obtained with short molecular chains exhibited high crystallinity and high remnant polarization (91 mC m−2), which is larger than both the polymer and copolymer counterpart films. The reasons for the observed low dielectric constant at low electric field, despite its larger polarization at high field, and the relatively high coercive field are discussed on the basis of the distinct structural characteristics of VDF oligomers. The low polar bulky end‐groups and difficulties in kink formation and propagation may result in the observed low dielectric constant at low electric field and the high coercive field. Copyright © 2011 Society of Chemical Industry

Cluster synthesis of monodisperse rutile-TiO2 nanoparticlesand dielectric TiO2–vinylidene fluoride oligomer nanocomposites

The embedding of oxide nanoparticles in polymer matrices produces a greatly enhanceddielectric response by combining the high dielectric strength and low loss of suitable hostpolymers with the high electric polarizability of nanoparticles. The fabrication ofoxide–polymer nanocomposites with well-controlled distributions of nanoparticles is,however, challenging due to the thermodynamic and kinetic barriers betweenthe polymer matrix and nanoparticle fillers. In the present study, monodisperseTiO2 nanoparticles having an average particle size of 14.4 nm and predominant rutile phase wereproduced using a cluster-deposition technique without high-temperature thermalannealing and subsequently coated with uniform vinylidene fluoride oligomer(VDFO) molecules using a thermal evaporation source, prior to deposition asTiO2–VDFO nanocomposite films on suitable substrates. The molecular coatings onTiO2 nanoparticles serve two purposes, namely to prevent theTiO2 nanoparticles from contacting each other and to couple the nanoparticlepolarization to the matrix. Parallel-plate capacitors made ofTiO2–VDFO nanocomposite film as the dielectric exhibit minimum dielectric dispersion and lowdielectric loss. Dielectric measurements also show an enhanced effective dielectric constant inTiO2–VDFO nanocomposites as compared to that of pure VDFO. This study demonstrates forthe first time a unique electroactive particle coating in the form of a ferroelectric VDFOthat has high-temperature stability as compared to conventionally used polymers forfabricating dielectric oxide–polymer nanocomposites.