Dipolar Polymers Research Articles

Polyvinylidene fluoride (PVDF) direct printing for sensors and actuators

This paper represents a polymeric piezoelectric manufacturing process for sensing and actuation applications. The electric poling-assisted additive manufacturing (EPAM) process combining additive manufacturing (AM) with polymeric poling process has been recently introduced. This process keeps piezoelectric polymer dipoles well-aligned and uniform over a large area in a single-step direct printing process. Here, the EPAM process was employed to directly print polyvinylidene fluoride (PVDF) polymer; sensing and actuation performance was tested with dynamometer, a baseline comparison measuring instrument. Also, the plasma-assisted poling process that potentially increases piezoelectricity was briefly introduced and discussed with a preliminary result. As a result, this study promises new multi-functional materials, novel designs, and approaches in a single AM and fabrication step by combining AM with piezoelectric polymer poling methods in convenient, fast, and precise manner.

High dielectric constant dipolar glass polymer based on sulfonylated poly(ether ether ketone)

In this work, a new kind of dipolar glass polymer, containing strongly polar sulfonyl groups, was synthesized by post functionalization of the corresponding poly(ether ether ketone) containing carboxyl groups (PEEK-COOH). The sulfonylated PEEK (PEEK-SO2) exhibited strong β transition at −100 °C and 1 Hz due to the large dipole moment (4.25 D) of the side-chain sulfonyl groups, which were attached to the backbone via flexible ester bonds. Because of this strong β dipole relaxation, the glassy PEEK-SO2 exhibited a high dielectric constant of 5.0 at 25 °C and 1 Hz, nearly 32% higher than that of PEEK-COOH. From an electric displacement-electric field loop study, PEEK-SO2 exhibited a relative high discharge energy density of 2.35 J/cm3 at 300 MV/m and room temperature, which was 1.4 times that of PEEK-COOH. However, the hysteresis loss was only 0.008 at 100 Hz and 25 °C. This work further reveals that dipolar glass polymers with high mobile dipolar side groups are suitable for high energy density and low loss dielectric applications.

Giant permittivity materials with low dielectric loss over a broad temperature range enabled by weakening intermolecular hydrogen bonds

High-temperature polymer dielectrics are of great interest for next generation capacitors demanded in harsh-environment electronics and electrical-power applications. Although some high-Tg engineering polymers have been considered as possible high-temperature dielectric materials, the low permittivity has significantly limited their development. Hence it is still a great challenge in dielectric polymers to achieve a high permittivity while maintain low dielectric loss over a broad temperature range. Here we report a highly scalable and low cost strategy to develop such high-performance polymer dielectrics. Two high-Tg glassy state dipolar polymers, i.e., poly(ether imide) and poly(ether-methyl-ether-urea) are blended by properly engineered to increase dipole mobility in polymer chains caused by combined effects of disruption of hydrogen bonds and improved free volume for dipoles in the glassy state blend. Consequently, such polymer blend displays thermally stable dielectric properties with an intrinsic giant permittivity of 5.8 and low dielectric loss (<1%) over a broad temperature.

New poly(itaconate)s with bulky pendant groups as candidates for “all-polymer” dielectrics

This work presents the synthesis and characterizaiton of three new poly(itaconate)s containing nitriles functional groups as high dipole moment entities and three different cycloalkyl pendant groups, in order to increase the rigidity of the system and therefore, their dipolar glass polymer temperature interval. The structural, thermal and dielectric characterization has been carried out in terms of Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), respectively. All polymers showed good thermal properties with degradation temperatures above 250 °C, presenting higher glass transition temperatures than those of recently reported poly(itaconate)s. Regarding dielectric properties, dielectric constant values between 4.0 and 4.3 (at 25 °C and 1 kHz) and relative low loss tangent values (below 0.01) were obtained. BDS measurements showed in all cases, notorious sub-glass transitions even at temperatures below −100 °C, resulting in a broad temperature interval in which these polymers could work without high dielectric losses. Therefore, these materials seem to be good candidates for dielectric applications such as energy storage, among others.

Dipolar Glass Polymers Containing Polarizable Groups as Dielectric Materials for Energy Storage Applications. A Minireview.

Materials that have high dielectric constants, high energy densities and minimum dielectric losses are highly desirable for use in capacitor devices. In this sense, polymers and polymer blends have several advantages over inorganic and composite materials, such as their flexibilities, high breakdown strengths, and low dielectric losses. Moreover, the dielectric performance of a polymer depends strongly on its electronic, atomic, dipolar, ionic, and interfacial polarizations. For these reasons, chemical modification and the introduction of specific functional groups (e.g., F, CN and R−S(=O)2−R´) would improve the dielectric properties, e.g., by varying the dipolar polarization. These functional groups have been demonstrated to have large dipole moments. In this way, a high orientational polarization in the polymer can be achieved. However, the decrease in the polarization due to dielectric dissipation and the frequency dependency of the polarization are challenging tasks to date. Polymers with high glass transition temperatures (Tg) that contain permanent dipoles can help to reduce dielectric losses due to conduction phenomena related to ionic mechanisms. Additionally, sub-Tg transitions (e.g., γ and β relaxations) attributed to the free rotational motions of the dipolar entities would increase the polarization of the material, resulting in polymers with high dielectric constants and, hopefully, dielectric losses that are as low as possible. Thus, polymer materials with high glass transition temperatures and considerable contributions from the dipolar polarization mechanisms of sub-Tg transitions are known as “dipolar glass polymers”. Considering this, the main aspects of this combined strategy and the future prospects of these types of material were discussed.

Synthesis of new poly(itaconate)s containing nitrile groups as high dipolar moment entities for the development of dipolar glass polymers with increased dielectric constant. Thermal and dielectric characterization

This work presents the synthesis of new poly(itaconate)s containing one or two nitrile pendant groups through conventional radical polymerization. To the best of our knowledge, this is the first time in which the synthesis of poly(itaconate)s containing nitrile groups is reported in the literature. The effect of nitrile groups on the main properties is analyzed. Polymer structures were confirmed by Fourier transform infrared spectroscopy (FTIR), 1H and 13C NMR. Molecular weights were measured by size exclusion chromatography (SEC), while thermal characterization was achieved by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Dielectric properties were measured using broadband dielectric spectroscopy at different temperatures. Polymers with one or two nitrile groups presented dielectric constant values (at 25 °C and 1 kHz) of around 7 and 12.5, respectively, with relatively low dielectric losses with values below 0.02. BDS measurements showed notorious sub-glass transitions attributed to the movement of the dipolar groups under the electric field, even below −100 °C, allowing to achieve dielectric constant values above the average for polymers even at extremely low temperatures. Therefore, these materials could be considered as good candidates for energy storage applications.

Manipulating H-bonds in glassy dipolar polymers as a new strategy for high energy storage capacitors with high pulse discharge efficiency

The formation of H-bonds results in improved dielectric strength of glassy polystyrene-based polymers.

Enhanced scattering induced by electrostatic correlations in concentrated solutions of salt-free dipolar and ionic polymers.

We present a generalized theory for studying the static monomer density-density correlation function (structure factor) in concentrated solutions and melts of dipolar as well as ionic polymers. The theory captures effects of electrostatic fluctuations on the structure factor and provides insights into the origin of experimentally observed enhanced scattering at ultralow wavevectors in salt-free ionic polymers. It is shown that the enhanced scattering can originate from a coupling between the fluctuations of electric polarization and monomer density. Local and non-local effects of the polarization resulting from finite sized permanent dipoles and ion-pairs in dipolar and charge regulating ionic polymers, respectively, are considered. Theoretical calculations reveal that, similar to the salt-free ionic polymers, the structure factor for dipolar polymers can also exhibit a peak at a finite wavevector and enhanced scattering at ultralow wavevectors. Although consideration of dipolar interactions leads to attractive interactions between monomers, the enhanced scattering at ultralow wavevectors is predicted solely on the basis of the electrostatics of weakly inhomogeneous dipolar and ionic polymers without considering the effects of any aggregates or phase separation. Thus, we conclude that neither aggregation nor phase separation is necessary for observing the enhanced scattering at ultralow wavevectors in salt-free dipolar and ionic polymers. For charge regulating ionic polymers, it is shown that electrostatic interactions between charged monomers get screened with a screening length, which depends not only on the concentration of "free" counterions and coions, but also on the concentration of "adsorbed" ions on the polymer chains. Qualitative comparisons with the experimental scattering curves for ionic and dipolar polymer melts are presented using the theory developed in this work.

Facile synthesis of fluorinated poly(arylene ether nitrile) and its dielectric properties

ABSTRACTA new class of specialty polymer, fluorinated poly(arylene ether nitrile) (PAEN‐F), was synthesized via the aromatic nucleophilic substitution reaction. Due to its rigid structure, PAEN‐F exhibited enhanced heat resistance and thermal stability. Consequently, the glass‐transition temperature and initial degradation temperature of PAEN‐F reached as high as 179°C and 554°C, respectively. PAEN‐F also showed excellent solubility in low‐boiling solvents owing to fluorine groups and the nonplanar structure in the repeat unit. Due to its strong 6F dipoles, PAEN‐F exhibited a high dielectric constant (ɛr) of 3.6, a high electrical breakdown strength of 346 MV/m, and a reasonably low dissipation factor (tan δ) of 0.014 at 25°C and 100 Hz. Therefore, this dipolar glass polymer is promising for high‐temperature and low‐loss electric energy storage applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46837.

Understanding the effects of symmetric salt on the structure of a planar dipolar polymer brush.

The effects of added salt on a planar dipolar polymer brush immersed in a polar solvent are studied using a field theoretic approach. The field theory developed in this work provides a unified framework for capturing effects of the inhomogeneous dielectric function, translational entropy of ions, crowding due to finite sized ions, ionic size asymmetry, and ion solvation. In this paper, we use the theory to study the effects of ion sizes, their concentration, and ion-solvation on the polymer segment density profiles of a dipolar brush immersed in a solution containing symmetric salt ions. The interplay of crowding effects, translational entropy, and ion solvation is shown to exhibit either an increase or decrease in the brush height. Translational entropy and crowding effects due to finite sizes of the ions tend to cause expansion of the brush as well as uniform distribution of the ions. By contrast, ion-solvation effects, which tend to be stronger for smaller ions, are shown to cause shrinkage of the brush and inhomogeneous distribution of the ions.

High Dielectric Constant Sulfonyl-Containing Dipolar Glass Polymers with Enhanced Orientational Polarization

Dipolar glass (DG) polymers, which utilize sub-Tg orientational polarization (Tg is the glass transition temperature) to enhance dielectric constants, are promising candidates for use in advanced e...

Linear Viscoelasticity and Cation Conduction in Polyurethane Sulfonate Ionomers with Ions in the Soft Segment–Single Phase Systems

PEO-based polyurethane sulfonate ionomers with various PEO chain lengths and sodium counterions were synthesized and characterized by both linear viscoelasticity (LVE) and dielectric relaxation spectroscopy (DRS). Since p-phenylene diisocyanate is a small hard segment, the ionomers were found to be single phase with only one DSC Tg which increases with both ion content and hard segment content. An electrode polarization model was used to simultaneously determine the temperature dependence of conducting ion concentration and their mobility, which show Arrhenius and Vogel–Fulcher–Tammann (VFT) temperature dependences, respectively. The polymer dipole relaxation probed by DRS was found to be between 103 and 106 times faster than the mechanical segmental relaxation observed in LVE data near Tg, suggesting that most polymer modes need to wait for the ions to rearrange. The dielectric relaxation, mechanical relaxation, and ionic conductivity all show good correlation with DSC Tg and are related to ion rearrange...

Nature of Ferroelectric Behavior in Main-Chain Dipolar Glass Nylons: Cooperative Segmental Motion Induced by High Poling Electric Field

Main-chain dipolar glass polymers such as aromatic nylons are promising for high energy density and low loss dielectric applications because of the limited, noncooperative oscillation of highly dipolar amide groups. However, quenched aromatic nylons have been reported to exhibit significant ferroelectric switching upon high field poling. It is desirable to suppress ferroelectric switching for electric energy storage application, and this requires a fundamental understanding of the nature of ferroelectric behavior in dipolar glass nylons. In this work, a nearly 100% amorphous aromatic nylon, Selar, was used to investigate the origin of ferroelectricity in glassy nylons. Using Fourier transform infrared spectroscopy, it was found that hydrogen-bonding strength played an important role in the ferroelectric switching of amide dipoles in the loosely packed glassy matrix. When hydrogen bonding was weak such as in the quenched film, significant ferroelectric switching took place. In contrast, quenched and anneal...

High‐Temperature and High‐Energy‐Density Dipolar Glass Polymers Based on Sulfonylated Poly(2,6‐dimethyl‐1,4‐phenylene oxide)

AbstractA new class of high‐temperature dipolar polymers based on sulfonylated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SO2‐PPO) was synthesized by post‐polymer functionalization. Owing to the efficient rotation of highly polar methylsulfonyl side groups below the glass transition temperature (Tg≈220 °C), the dipolar polarization of these SO2‐PPOs was enhanced, and thus the dielectric constant was high. Consequently, the discharge energy density reached up to 22 J cm−3. Owing to its high Tg , the SO2‐PPO25 sample also exhibited a low dielectric loss. For example, the dissipation factor (tan δ) was 0.003, and the discharge efficiency at 800 MV m−1 was 92 %. Therefore, these dipolar glass polymers are promising for high‐temperature, high‐energy‐density, and low‐loss electrical energy storage applications.

High-Temperature and High-Energy-Density Dipolar Glass Polymers Based on Sulfonylated Poly(2,6-dimethyl-1,4-phenylene oxide).

A new class of high-temperature dipolar polymers based on sulfonylated poly(2,6-dimethyl-1,4-phenylene oxide) (SO2 -PPO) was synthesized by post-polymer functionalization. Owing to the efficient rotation of highly polar methylsulfonyl side groups below the glass transition temperature (Tg ≈220 °C), the dipolar polarization of these SO2 -PPOs was enhanced, and thus the dielectric constant was high. Consequently, the discharge energy density reached up to 22 J cm-3 . Owing to its high Tg , the SO2 -PPO25 sample also exhibited a low dielectric loss. For example, the dissipation factor (tan δ) was 0.003, and the discharge efficiency at 800 MV m-1 was 92 %. Therefore, these dipolar glass polymers are promising for high-temperature, high-energy-density, and low-loss electrical energy storage applications.

Attraction between Opposing Planar Dipolar Polymer Brushes.

We use a field theory approach to study the effects of permanent dipoles on interpenetration and free energy changes as a function of distance between two identical planar polymer brushes. Melts (i.e., solvent-free) and solvated brushes made up of polymers grafted on nonadsorbing substrates are studied. In particular, the weak coupling limit of the dipolar interactions is considered, which leads to concentration-dependent pairwise interactions, and the effects of orientational order are neglected. It is predicted that a gradual increase in the dipole moment of the polymer segments can lead to attractive interactions between the brushes at intermediate separation distances. Because classical theory of polymer brushes based on the strong stretching limit (SSL) and the standard self-consistent field theory (SCFT) simulations using the Flory's χ parameter always predicts repulsive interactions at all separations, our work highlights the importance of dipolar interactions in tailoring and accurately predicting forces between polar polymeric interfaces in contact with each other.

Generating high dielectric constant blends from lower dielectric constant dipolar polymers using nanostructure engineering

It is a great challenge in dielectric polymers to achieve a high dielectric constant while maintaining low dielectric loss and high operating temperatures. Here we report that by blending two glassy state dipolar polymers i.e., poly(arylene ether urea) (PEEU, K=4.7) and an aromatic polythiourea (ArPTU, K=4.4) to form a nanomixture, the resulting blend exhibits a very high dielectric constant, K=7.5, while maintaining low dielectric loss (<1%). The experimental and computer simulation results demonstrate that blending these dissimilar dipolar polymers causes a slight increase in the interchain spacing of the blend in its glassy state, thus reducing the barriers for reorientation of dipoles in the polymer chains along the applied electric field and generating a much higher dielectric response than the neat polymers.

Vertical Phase Segregation Induced by Dipolar Interactions in Planar Polymer Brushes

We present a generalized theory for studying structural properties of a planar dipolar polymer brush immersed in a polar solvent. We show that an explicit treatment of the dipolar interactions yields a macroscopic concentration dependent effective “chi” (the Flory–Huggins-like interaction) parameter. Furthermore, it is shown that the concentration dependent chi parameter promotes phase segregation in polymer solutions and brushes so that the polymer-poor phase consists of a finite/nonzero polymer concentration. Such a destabilization of the homogeneous phase by the dipolar interactions appears as vertical phase segregation in a planar polymer brush. In a vertically phase segregated polymer brush, the polymer-rich phase near the grafting surface coexists with the polymer-poor phase at the other end. Predictions of the theory are directly compared with prior reported experimental results for dipolar polymers in polar solvents. Excellent agreements with the experimental results are found, hinting that the di...

Increased Exciton Dipole Moment Translates into Charge-Transfer Excitons in Thiophene-Fluorinated Low-Bandgap Polymers for Organic Photovoltaic Applications

In this study, we investigate the role of thiophene fluorination in a low-bandgap polymer for organic photovoltaic applications. We use a combined theoretical and experimental approach to investigate charge generation and recombination dynamics, and their correlation with blend microstructure and polymer dipole moment. We find that fluorination results in an increased change in the dipole moment upon exciton formation, which is correlated with the appearance of charge-transfer excitons, as evidenced from ultrafast transient absorption studies. Fluorination also results in smaller yet purer domains, evidenced by atomic force microscopy and resonant soft X-ray scattering, and in agreement with photoluminescence quenching measurements. This change in film morphology is correlated with a modest retardation of nongeminate recombination losses. The efficient charge generation and slower recombination are likely to be partly responsible for the enhanced device efficiency in the fluorinated polymer/fullerene devices.

Physical force-sensitive touch responses in liquid crystal-gated-organic field-effect transistors with polymer dipole control layers

We report the sensing performances of liquid crystal-gated-organic field-effect transistors with a polymer dipole layer (DCL-LC-g-OFETs) upon physical touches. The DCL-LC-g-OFET devices, which were fabricated by employing 4-cyano-4’-pentylbiphenyl (5CB) as a sensing gate insulating layer, poly(methyl methacrylate) (PMMA) DCL, and 50 nm-thick poly(3-hexylthiophene) (P3HT) channel layer, which were optically semi-transparent and exhibited p-type transistor behavior. A pencil-like load (0.6 g–4.8 g) was introduced as a means for physical touch, while a human finger was used to examine the practical sensing capability of devices. Results showed that the drain current responded quickly upon physical touch and increased linearly with the strength of physical touch. The response time upon physical touch was slightly affected by the touch strength but was as fast as less than 1 s, while the drain current signals were quite reproducible and stable even after repeated physical touches. The present DCL-LC-g-OFET devices exhibited excellent sensing performances and reproducibility upon the human finger touch.