Cyanoethyl Pullulan Research Articles

Ultra‐High Energy Density in Cyanoethyl Biomass Polymers

AbstractDielectric polymers are essential to capacitive capacitors widely used in modern electronic and electrical systems. Most useful dielectric polymers are derived from petroleum while environmentally sustainable dielectric biomass remains mostly unexplored although they are abundant, renewable, and cost‐effective. Here an ultrahigh energy density in cyanoethyl cellulose (CEC) and cyanoethyl pullulan (CEP) obtained by replacing the hydroxyl groups of cellulose and pullulan with cyanoethyl is reported. Large dielectric constants of 16.7 and 20.0 in CEC and CEP due to the strong polarity of cyanoethyl which are comparable to high‐dielectric ferroelectric polymers are shown. CEC and CEP show nearly no degradation of the dielectric constant with increasing electric fields, inhabiting the early polarization saturation and thus leading to improved energy density, which is different from relaxor ferroelectric polymers. Consequently, solution‐processable CEP films exhibit an ultrahigh discharged energy density of 28.2 J cm−3 with an efficiency of 72% at 600 MV m−1, outperforming other all‐organic dielectric biomass materials. The work paves the way for the development of high‐performance dielectric biomass for energy storage applications.

Innovative all-organic dielectric composite for dielectric capacitor with great energy storage performance based on thermodynamic compatibility.

In modern electronics and power systems, good-performance dielectric capacitors have an essential function. Polymer-based dielectrics are widely used in the field of dielectric capacitors because of their large dielectric constant, flexibility, low density, and ease of processing. At present, ferroelectric polymers suffer from low breakdown field strength and high dielectric losses. How to improve the performance of dielectric materials in capacitors is still a promising research. This paper chooses the ferroelectric polymer poly(vinylidene fluoride) (PVDF) that worked as the matrix, and the linear polymers polyimide, cyanoethyl pullulan (CR-S), polyethersulfone, and cyanoethylated cellulose served as fillers. This all-organic dielectric composite produced as films working in electrostatic energy storage devices is prepared by using a casting method. Analyzing the test results, the composite film exhibited excellent electrical properties when the CR-S doping content was 5 wt. %. The organic composite dielectric based on CR-S/PVDF has a breakdown field strength of 450 MV/m, a discharge energy storage density (Ue) of 10.3 J/cm3, a high dielectric constant of 10.9, and a low dielectric loss of 0.004 at 1kHz, which is a significant improvement compared with other dielectric composites. This all-organic dielectric composite strategy offers a new approach to achieve better-performance dielectric energy storage materials.

Graphene quantum dots as shallow traps in a high-k polymer matrix for bipolar resistive switching

Graphene quantum dots (GQDs) have broad applications in electronic and photonic devices. As a typical zero-dimensional material, a GQD has a stronger quantum confinement effect than do two-dimensional graphene or one-dimensional graphene nanoribbons, and provide efficient charge trapping sites, which are useful in nonvolatile memory devices. Here, we report the fabrication of 30-nm-thick GQD-blended high-k polymer cyanoethylated pullulan (CEP) thin films sandwiched between an Al top electrode and an indium tin oxide (ITO) bottom electrode. Bipolar resistive switching behavior was observed with a low onset (−1.7 V) and offset (1.3 V) voltages. The resistive switching behavior originates from shallow traps that induce space-charge-limited current conduction. The morphology, crystallinity and photoluminescence of the GQDs were also studied by atomic force microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The CEP/GQD blended films may have applications in nonvolatile resistive memory devices.

Miscibility, microstructure, and dielectric properties of the polymer blends of cyanoethyl pullulan and fluoroterpolymer

The blending of two polymers is often used as a strategy to improve the dielectric properties of polymers. In this work, the blends of cyanoethyl pullulan (CEP) and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)], both of which have high dielectric properties, are systematically studied. We show that although there exists a certain level of interaction between the two polymers, the blends are not completely miscible. The CEP-rich phase forms a particulate phase in the terpolymer matrix. Evidence indicates that the addition of CEP impedes the inclusion of bulky CTFE monomer units into the crystalline phase of the terpolymer, leading to a more polar crystalline structure of the terpolymer. Furthermore, a high-temperature thermal treatment (HTT) was conducted on the blended films to study the relationship between microstructure and dielectric properties. Experimental results suggest that the HTT process favors the incorporation of CTFE units into the crystalline phase and induces a less polar crystal structure of the terpolymer, resulting in a more relaxor ferroelectric–dielectric behavior, a higher dielectric constant, and a lower dielectric loss. By optimizing the composition of the blends and heat treatment, the dielectric energy storage performance of the blends can be improved in comparison with that of the terpolymer.

Bipolymer-Cross-Linked Binder to Improve the Reversibility and Kinetics of Sodiation and Desodiation of Antimony for Sodium-Ion Batteries.

Although the volume of antimony tremendously expands during the alloying reaction with sodium, it is considered a promising anode material for sodium-ion batteries (SIBs). Repeated volume changes along the sodiation/desodiation cycles encourage capacity fading by triggering pulverization accompanying electrolyte decomposition. Additionally, the low cation transference number of sodium ions is another hindrance for application in SIBs. In this work, a binder was designed for the antimony in SIB cells to ensure bifunctionality and improve (1) the mechanical toughness to suppress the serious volume change and (2) the transference number of sodium ions. A cross-linked composite of poly(acrylic acid) and cyanoethyl pullulan (pullulan-CN) was presented as the binder. The polysaccharide backbone of pullulan-CN was responsible for the mechanical toughness, while the cyanoethyl groups of pullulan-CN improved the lithium-cation transfer. The antimony-based SIB cells using the composite binder showed improved cycle life with enhanced kinetics. The capacity was maintained at 76% of the initial value at the 200th cycle of 1C discharge following 1C charge, while the capacity at 20C was 61% of the capacity at 0.2C, implying that the composite binder significantly improved the sodiation/desodiation reversibility of antimony.

Solution-processed polymer-sorted semiconducting carbon nanotube network transistors with low-k /high-k bilayer polymer dielectrics

Solution-processed semiconducting carbon nanotube transistors with a high mobility and an ON/OFF ratio are the most promising for use in flexible electronics. In this paper, we report low-k/high-k bilayer polymer dielectrics for solution-processed semiconducting single-walled carbon nanotube (s-SWNT) field-effect transistors (s-SWNT-FETs) with efficient charge transport and operation at low voltage. Thin low-k polystyrene (10 nm) is used for the first contact insulator with a channel in order to passivate the dipolar disorder induced by high-k insulators. The second gate insulator for low voltage operation is cyanoethyl pullulan (CEP), which is an environmentally friendly high-k insulator based on cellulose. Moreover, poly[(vinylidenefluoride-co-trifluoroethylene) is chosen as a single layer dielectric for comparison. A reasonably low operational voltage (<10 V) and high operational stability are achieved by the s-SWNT-FETs with polystyrene/CEP bilayer gate dielectrics. In addition, this indicates that the interface between the s-SWNTs and the low-k insulator is of critical importance for efficient charge transport.

Cyanoethylated pullulan as a high-k solution processable polymer gate dielectric for SWCNT TFTs

Cyanoethylated pullulan (CEP), a high-k solution processable polymer gate dielectric, is used to fabricate bottom gated single wall carbon nanotube (SWCNT) network thin film transistors (TFTs). Both aqueous and organic dispersions of highly semiconducting enriched SWCNTs are used as the channel material. Use of CEP as the dielectric enables fabrication of devices operating at low voltage (<3 V) with high on-state currents, good on/off ratios (∼105), low subthreshold swings (∼200 mV/decade) and minimal hysteresis (<1 V). However, despite high apparent mobilities extracted from gate voltage sweeps, driving these devices at even modest frequencies (>1 Hz) is found to significantly decrease the transconductance. This is shown to be related to a significant frequency dependence of the capacitance associated with a slow polarization response of the dielectric. Despite this limitation, CEP could be a useful dielectric in SWCNT TFTs for applications such as sensors and low frequency amplifiers.

High Electroluminescence of ZnS:Cu Phosphor with a CNT-Incorporated Dielectric Layer

High brightness was obtained for alternating current-driven inorganic ZnS:Cu powder electroluminescence (EL) devices by incorporating carbon nanotubes in a barium titanate (BaTiO3) based dielectric layer. The inorganic EL devices were consisted of four layers: a top electrode, a dielectric layer, an emitting layer, and an ITO layer which was pre-coated on the glass substrate. As an emitting material, ZnS:Cu power of particle size 9 µm (green emission) was mixed with the cyanoethyl pullulan polymer (CEP), as an organic binder, and the dimethyl formamide (DMF) organic solvent. The emitting solution was spin-coated on the ITO glass at the fixed speed of 1200 rpm. The BaTiO3 power were mixed with a CNT-CEP binder, which was also spin-coated on the emitting layer. In order to optimize the EL performance, the concentration of CNTs were varied by controlling the mixing ratio of CNTs—0, 0.0018, 0.0039, 0.0071, 0.011 and 0.014 wt%. Finally, a 500-nm-thick aluminum top electrode was thermally evaporated onto the dielectric layer. Up to 50% higher brightness was obtained for the CNT concentration of 0.011 wt%. The high brightness might be caused by the high dielectric constant of the CNT-incorporated BaTiO3 dielectric layer, thanks to the micro-capacitor effect. [Z. M. Dang et al., Small 12, 1688 (2016).] Roughly speaking, the higher concentration of the CNT yielded to the higher brightness, until a certain concentration, here, between 0.011 and 0.014 wt%. It implies that too high concentration of CNTs might lead to the formation of the unwanted percolation network of a leakage current within the dielectric layer. Finally, the role of the chlorine was investigated by inclusion of chlorobenzene into the CNT-containing dielectric layer. [J.-Y. Kim et al., Adv. Mater. 25, 2308 (2013).] Based on the above results, incorporation of CNTs within the dielectric layer enhanced the brightness (and the efficiency, possibly) of the ZnS:Cu-based EL device, which would help to extend the potential applications of EL devices.

Synthesis of BaTiO3/polymer composite ink to improve the dielectric properties of thin films

To investigate the material design of inks for high performance dielectric thin films constructed using BaTiO3 nanoparticles and polymer resin, the BaTiO3 mono-dispersed sol and the polymer solution were simply mixed and stirred to obtain the composite ink. The polymers chosen were cyanoethyl pullulan (CEP) and an epoxy. The dielectric constant of the BaTiO3/CEP composite thin film was higher than that of the BaTiO3 thin film and the BaTiO3/epoxy composite thin film because the dielectric constant of CEP is higher. Conversely, the resistance of the BaTiO3/epoxy composite thin films to frequency change was clearly greater than that of the BaTiO3/CEP composite thin films. Thus, the polymer component strongly affected the performance of dielectric constant. These results offer an important method for designing the dielectric composite ink for the development of thin film capacitors.

Reducing electrowetting-on-dielectric actuation voltage using a novel electrode shape and a multi-layer dielectric coating

This paper presents design and fabrication of an electrowetting-on-dielectric (EWOD) device using a novel electrode shape and a multi-layer dielectric coating that reduce the actuation voltage of the device to less than 12.6 V. The fabrication of the EWOD electrodes is carried out in several steps including laser exposure, wet developing, etching, and stripping. A high-dielectric-constant multi-layer dielectric coating containing a 770 nm thick Polyvinylidene difluoride (PVDF) layer and a 1 µm thick Cyanoethyl pullulan (CEP) layer, is deposited on the EWOD electrodes for insulation. This multi-layer dielectric structure exhibits a high capacitance per unit area, and the novel electrode shape changes the actuation force at the droplet contact line reducing the voltage required to operate the device. In addition, an overlaying Teflon layer of 50 nm is placed on top of the dielectric structure to provide a hydrophobic surface for droplet manipulation. It is observed from the experiments that the electrode shape and the dielectric structure have contributed to the reduction of the actuation voltage of the EWOD device.

Crosslinked polymer-mixture gate insulator for high-performance organic thin-film transistors

In this paper, we report on the fabrication of a crosslinked polymer-mixture gate insulator for high-performance organic thin-film transistors (TFTs). We used cyanoethylated pullulan (CEP) as a crosslinkable high-k polymer matrix and poly(ethylene-alt-maleic anhydride) (PEMA) as a polymeric crosslinking agent. Because PEMA has a high number of functional groups reactive to the hydroxyl groups of CEP, the use of PEMA is effective for minimizing the amount of remaining hydroxyl groups strongly related to the large current hysteresis and high off current of the organic TFTs. To investigate the potential of the CEP-PEMA mixture as a gate insulator, we fabricated 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) TFTs. The C8-BTBT TFT with the 60 nm-thick CEP-PEMA gate insulator showed excellent TFT performance with a field-effect mobility of 1.4 cm2/V s and an on/off ratio of 2.4 × 106.

High-performance dielectric thin film nanocomposites of barium titanate and cyanoethyl pullulan: controlling the barium titanate nanoparticle size using a sol–gel method

Nanocomposite thin film with high dielectric performance composed of size-controlled BaTiO3 nanoparticles and cyanoethyl pullulan.

Fabrication and Electrical Characteristics of P(VDF-TrFE) Films on Si(100) Substrates Using Cyanoethyl Pullulan Buffer Layers

We fabricated a metal-ferroelectric-insulator-semiconductor structure using a poly(vinylidene fluoride trifluorethylene) as a ferroelectric layer and a cyanoethyl pullulan as an insulating buffer layer for the first time. The CEP thin films were deposited on Si substrate by using a sol-gel method. The coated P(VDF-TrFE) films on CEP/Si structure were crystallized. For the Au/P(VDF-TrFE)/CEP/Si structure, the capacitance-voltage characteristics showed hysteresis loops, the memory window width was about 4.6V at a bias sweep range of ±5V. The leakage current density was about 5.5 × 10−7 A/cm2 at 5V for the thick film from the 5 wt% solution.

Effect of halohydrocarbon solvents on the dielectric performance of a polymer film and its application to inorganic electroluminescent devices

Polymer films with halohydrocarbon solvents as additive solvents were fabricated to investigate the solvent effect on dielectric performance. Bromobenzene, chlorobenzene (CB), chloroform, and fluorobenzene (FB) were used as halohydrocarbon solvents. The cyanoethyl pullulan (CRS) polymer film with CB had a dielectric constant of 21.5 with a dielectric loss of 0.017 at 100 Hz, which exhibited a 37% increase in dielectric constant compared to the neat CRS polymer film. Increment of the dielectric constant is attributed to the high polarizability of carbon–chlorine bonds originated from CB absorbed in CRS. For the case of the CRS polymer film with FB, the dielectric constant did not increase due to the low polarizability of carbon–fluorine bonds. In order to verify the dielectric performance of the CRS polymer film with CB (CRS/CB), AC-driven inorganic powder electroluminescent (EL) device was fabricated using the green emission ZnS:Cu,Cl phosphor particles. An EL device with CRS/CB polymer film as a dielectric layer exhibited a 37% and 55% increase in luminance and efficiency, respectively compared to that with neat CRS polymer. This increase in EL performance was attributed to the increase of charge carrier density at the interface between the emitting and dielectric layers, resulting in the increased possibility of the charge carrier tunneling into phosphor particles.

Design and analysis of a low actuation voltage electrowetting-on-dielectric microvalve for drug delivery applications.

This paper presents a low actuation voltage microvalve with optimized insulating layers that manipulates a conducting ferro-fluid droplet by the principle of electrowetting-on-dielectric (EWOD). The proposed EWOD microvalve contains an array of chromium (Cr) electrodes on the soda-lime glass substrate, covered by both dielectric and hydrophobic layers. Various dielectric layers including Su-8 2002, Polyvinylidenefluoride (PVDF) and Cyanoethyl pullulan (CEP), and thin (50 nm) hydrophobic Teflon and Cytonix are used to analyze the EWOD microvalves at different voltages. The Finite Element Method (FEM) based software, Coventorware is used to carry out the simulation analysis. It is observed that the EWOD microvalve having a CEP dielectric layer with dielectric constant of about 20 and thickness of 1 μm, and a Cytonix hydrophobic layer with thickness of 50 nm operated the conducting ferro-fluid droplet at the actuation voltage as low as 7.8 V.

Study of cyanoethyl pullulan as insulator for electrowetting

In this paper, the dielectric and electrowetting properties of cyanoethyl pullulan (CEP) are studied as the insulator in electrowetting on dielectric (EWOD) device. The CEP film is formed by spin-coating and low-temperature annealing in atmosphere. The characterization results show that CEP can serve as the dielectric of EWOD with a high dielectric constant of 18 and a great electrowetting performance when annealed at 100°C in atmosphere. The reversibility, stability, polarity-dependence, and frequency-dependence of electrowetting on CEP are fully investigated. The spin-coated CEP exhibits little polarity-related electrowetting while having better driving performance under negative-potential. Frequency-related electrowetting is more sensitive at low-frequency alternating current (AC) potentials than at high-frequency ones. It also shows reversible and stable electrowetting with a small irreversibility of 2° after a 700-cycle test. Based on the above results, an EWOD device with 1μm thick CEP dielectric layer is fabricated. The EWOD device successfully manipulates water droplet at a low driving voltage of 20V and a large velocity under low voltage of DC or AC signals with different frequencies. The easy fabrication and excellent performance of CEP qualifies it as a superior dielectric material in the future EWOD devices and lab-on-a-chip system.

Solution Processable High Dielectric Constant Nanocomposites Based on ZrO2 Nanoparticles for Flexible Organic Transistors

A solution-based strategy for fabrication of high dielectric constant (κ) nanocomposites for flexible organic field effect transistors (OFETs) has been developed. The nanocomposite was composed of a high-κ polymer, cyanoethyl pullulan (CYELP), and a high-κ nanoparticle, zirconium dioxide (ZrO2). Organic field effect transistors (OFETs) based on neat CYELP exhibited anomalous behavior during device operation, such as large hysteresis and variable threshold voltages, which yielded inconsistent devices and poor electrical characteristics. To improve the stability of the OFET, we introduced ZrO2 nanoparticles that bind with residual functional groups on the high-κ polymer, which reduces the number of charge trapping sites. The nanoparticles, which serve as physical cross-links, reduce the hysteresis without decreasing the dielectric constant. The dielectric constant of the nanocomposites was tuned over the range of 15.6-21 by varying the ratio of the two components in the composite dielectrics, resulting in a high areal capacitance between 51 and 74 nF cm(-2) at 100 kHz and good insulating properties of a low leakage current of 1.8 × 10(-6) A cm(-2) at an applied voltage of -3.5 V (0.25 MV cm(-1)). Bottom-gate, top-contact (BGTC) low operating voltage p-channel OFETs using these solution processable high-κ nanocomposites were fabricated by a contact film transfer (CFT) technique with poly(3-hexylthiophene) (P3HT) as the charge transport layer. Field effect mobilities as high as 0.08 cm(2) V(-1) s(-1) and on/off current ratio of 1.2 × 10(3) for P3HT were measured for devices using the high-κ dielectric ZrO2 nanocomposite. These materials are promising for generating solution coatable dielectrics for low cost, large area, low operating voltage flexible transistors.

High performance organic field-effect transistors using cyanoethyl pullulan (CEP) high-k polymer cross-linked with trimethylolpropane triglycidyl ether (TTE) at low temperatures

Low-voltage operable organic field-effect transistors (OFETs) were fabricated using a low-temperature curable high-k polymer cyanoethyl pullulan (CEP) as a gate insulator with trimethylolpropane triglycidyl ether (TTE) as a crosslinking agent. With this crosslinking agent, the gate insulators showed low leakage current and a high dielectric constant of 14.8–16, and most importantly, could be cured at low temperatures around 100 °C, which is compatible with most plastic substrates for future plastic electronics. The favorable semiconductor–dielectric interface was obtained due to the surface alignment of well-packed pentacene domains, which enabled excellent transistor performance, with one of the highest mobilities around 6 cm2 V−1 s−1, an on/off current ratio (Ion/Ioff) ∼105, and a steep subthreshold (SS) ∼0.095 V dec−1. The high mobility was found to be closely correlated with the surface CN dipole density rather than other possibilities, such as dielectric roughness and surface energy. The initial growth of the semiconductors was also studied and correlated with the affecting variables.

Quasi-ordering in spontaneously associated surface dipoles: an intrinsic interfacial factor for high-kpolymer insulated organic field-effect transistors

In this study, we report the observation of quasi-ordering in spontaneously associated highly polar surface functional groups (CN) in the high-kpolymer dielectric, cyanoethyl pullulan, and its impact on the organic field-effect transistor (OFET) characteristics. We find that the association originates from CN⋯H–C–CN hydrogen bonding as confirmed by XPS, NEXAFS experiments and molecular simulations. The quasi-ordered surface dipoles preferentially induce vertically well-stacked local semiconductor molecular clusters during the initial deposition process, which then promote large-area layer-by-layer growth. By maintaining sufficient quasi-ordering, high transistor performance (μ ≈ 6.5 cm2 V−1 s−1, SS ≈ 0.062 V dec−1) is obtained under low driving voltages (−3 to −5 V), while breakup of the association at higher baking temperatures leads to a dramatic drop in μ by a factor of ∼10. Our results demonstrate that local quasi-ordering of polymeric surface dipoles, which has a significant effect on the initial semiconductor molecular growth, represents a novel and sensitive factor affecting OFET characteristics.

“Knitting up” the inter-dipole gaps in dielectric surfaces: an efficient route for high performance organic field-effect transistors

Suberoyl chloride (SCL) or ethylenediaminetetraacetic dianhydride (EDT) was added as crosslinking agents into the high-k cyanoethyl pullulan (CEP) polymer and the mixture was cured at temperatures of 90–120 °C. In the crosslinking reaction of the CEP polymer chain with SCL, ester groups were produced to knit up the gaps between the self-associated dipole clusters. Well-stacked pentacene molecular clusters were formed on the dipole clusters and 2-dimensional (2D) layer-by layer growth of the pentacene layer was observed. On the other hand, the dangling carboxylic acid (COOH) group in EDT-cured dielectrics disrupted the quasi-order by shielding the dipoles. This caused discontinuous 3D pentacene grains, which degraded the pentacene organic field effect transistor performance. A high field-effect mobility of ∼8.62 cm2 V−1 s−1, an on/off current ratio (Ion/Ioff) of ∼105 and a steep subthreshold slope (SS) of 0.099 V dec−1 were obtained using SCL as a cross-linking agent.