Compositional Gradient Films Research Articles

Significantly enhanced high-temperature energy storage performance for polymer composite films with gradient distribution of organic fillers

Film capacitors as one of the most important electronic devices are heading in large capacity, heightened integration and excellent extreme-condition tolerance, which faces the challenges in maintaining outstanding performance under harsh conditions of high temperature and large electric field. Nonetheless, polymer capacitive films, which are renowned for their exceptional thermal stability, experience an escalation in conduction losses at elevated temperatures, resulting in degradation of energy storage performance. This study presents the gradient distribution of organic fillers content in all-organic polymer capacitive films utilizing electrospinning technique, the significantly improved high-temperature energy storage performance has been achieved. Glucose (GLC), a weak polar molecule rich in hydroxyl groups, is blended with the most promising polyetherimide (PEI). Experimental and theoretical calculations confirm that the formed hydrogen bond between GLC and PEI acts as a trapping site for capturing carriers and suppressing conduction losses. Furthermore, the spatial distribution of organic fillers was designed on the basis of direct mixing. The results demonstrate that the gradient composite film introduces interlayer interfacial polarization, while the dielectric mismatch between adjacent layers increases the height of potential barriers for the charge carriers across the interfaces, thereby achieving a synergistic enhancement of dielectric response and insulation strength. The maximum discharge energy density of 6.52 J/cm3 with an efficiency of 85.6 % has been achieved at 150℃ for the modified capacitive films. This work establishes a decoupling relationship between permittivity and electric breakdown strength, offering insights for the advancement of polymer films with outstanding energy storage capabilities in extreme environments.

Rational design of continuous gradient composite films for high-performance zinc-ion batteries

• Continuous gradient composite films was firstly fabricated by one-step electrospinning strategy. • The gradient compositional distributions can be accurately controlled. • The strategy is universal and can be feasible for a variety of functional materials. • Many different components can be simultaneously introduced into one gradient film with independently adjustable gradient distribution and orientation. • The VO-based gradient composite films displayed ultrahigh capacity and superior rate capability as cathodes of aqueous ZIBs. Gradient materials are attracting extensive attention since the gradient compositional distributions endow them with excellent environmental adaptability in specific working conditions. However, the universal and accurately controllable synthesis of continuous gradient materials remains a challenge. Here, a universal strategy is developed to fabricate continuous gradient composite films (GCFs) with different components and gradient distributions by combining the dynamic concentration-regulation method and electrospinning technique. The gradient compositional distributions can be accurately regulated in such GCFs. Furthermore, a variety of functional materials can be also introduced into the continuous gradient composite films, respectively or simultaneously with controllable gradient orientation. As a proof of concept, the GCFs with VO nanoparticles were fabricated and used as the cathodes of aqueous zinc ion batteries. The matching of gradient compositional distribution and electron/ion transport within the electrodes would contribute to the ultrahigh capacity as well as superior rate capability. The universality and ease of this strategy would make it a promising route to design continuous GCFs with desired components and gradient distributions for various potential applications in many fields.

Construction of gradient conductivity cellulose nanofiber/MXene composites with efficient electromagnetic interference shielding and excellent mechanical properties

The development of electronic communication technology leads to a complex electromagnetic (EM) environment, which is urgent for the design of high-performance EM interference (EMI) shielding materials. In this work, cellulose nanofiber (CNF) and MXene were used to construct ordered multi-layer composite films with a controllable conductive gradient by layer-by-layer vacuum filtration method. Especially, the films were composed of four transition layers (with low MXene content) and one reflection layer (with high MXene content), which not only effectively reduced the reflection of EM waves on the surface of materials but also greatly increased the multiple internal reflections of reflected EM waves. Besides, the dielectric loss provided by MXene, and the coordination of polarization with loss at the interfaces contribute to the outstanding EMI shielding effectiveness (EMI SE) (39 dB) and absorption effectiveness (28 dB) of the films. And practical application simulation proves that the composite membrane can limit the mobile phone communication signal. Moreover, the nacre-like structure was constructed by 1D CNF and 2D MXene, resulting in high tensile strength of 90.5 ± 6.7 MPa and elongation at a break of 8.0 ± 1.0%. Therefore, this work provided a feasible approach for preparing gradient composite films with high EMI shielding and mechanical properties, which is highly promising to be a competitive candidate for the application in the new-generation of intelligent electronic devices.

A universal spray printing strategy to prepare gradient hybrid architectures

AbstractFunctionally gradient materials (FGMs) have attracted tremendous attention due to their unique properties and structures. However, it is still a great challenge to prepare scalable FGMs by a universal, cost‐effective, and highly efficient method. Here, a strategy of combining in situ concentration regulation and spraying is developed to fabricate continuously gradient composite films (GCFs), where the component gradient variation can be well controlled. This strategy is universal and versatile, which is beneficial to inducing different components into GCFs with gradient distributions and further constructing them with diverse configurations on various substrates. The gradient design endows the composite films with excellent mechanical strength and gradient electron transport pathways, which ensures that GCFs directly serve as the electrodes in electrochemical devices. As a proof of concept, free‐standing GCFs based on V2O5 nanomaterials are used as cathodes of aqueous zinc‐ion batteries. The resultant devices deliver superior electrochemical performances in comparison with the counterparts of homogeneous case. Therefore, this universal strategy provides a promising route in the scalable production of FGMs and further extends their applications in various fields.

Phase thermal stability and mechanical properties analyses of (Cr,Fe,V)-(Ta,W) multiple-based elemental system using a compositional gradient film

High-entropy alloys (HEAs) generally possess complex component combinations and abnormal properties. The traditional methods of investigating these alloys are becoming increasingly inefficient because of the unpredictable phase transformation and the combination of many constituents. The development of compositionally complex materials such as HEAs requires high-throughput experimental methods, which involves preparing many samples in a short time. Here we apply the high-throughput method to investigate the phase evolution and mechanical properties of novel HEA film with the compositional gradient of (Cr,Fe,V)-(Ta,W). First, we deposited the compositional gradient film by co-sputtering. Second, the mechanical properties and thermal stability of the (Cr0.33Fe0.33V0.33)x(Ta0.5W0.5)100−x (x = 13–82) multiple-based-elemental (MBE) alloys were investigated. After the deposited wafer was annealed at 600°C for 0.5 h, the initial amorphous phase was transformed into a body-centered cubic (bcc) structure phase when x = 33. Oxides were observed on the film surface when x was 72 and 82. Finally, the highest hardness of as-deposited films was found when x = 18, and the maximum hardness of annealed films was found when x = 33.

Gradient composite film with calcium phosphate silicate for improved tendon -to-Bone intergration

The tendon enthesis is a very complex tissue interface that connects a flexible tissue (tendon) to a stiff tissue (bone). Few available forms of gradient scaffolds with multiple components have been fabricated for applications in vivo because of the complexities of enthesis. In the present work, gradient-poly(ε-caprolactone)/calcium phosphate silicate (G-P/C) composite films were fabricated with tape casting technique. Films with different P/C ratio were used to evaluate the material’s properties and effects of composition on cellular behaviors. The results showed that the G-P/C composite film offered a gradually changing composition transition. The higher levels of calcium phosphate silicate of each film stimulated stronger osteogenic differentiation and mineralized matrix deposition. When the films were interposed between the supraspinatus tendon and humerus bone, the G-P/C composite film group exhibited more tissue cellularity, better collagen alignment, better gradient mineralized cartilage formation and gradient Ca distribution than other groups. All these histological improvements were well consistent with the biomechanical results of the G-P/C composite film group. Thus, the G-P/C composite film may be a promising scaffold for tendon-to-bone interface engineering.

Rolling contact fatigue behavior of TiN based coatings deposited on ADI by cathodic arc deposition and plasma based ion implantation and deposition

This work studies the surface characteristics and, particularly, the rolling contact fatigue (RCF) behavior of austempered ductile iron (ADI) samples coated with TiN based coatings of about 1 μm in thickness. Films synthesized by cathodic arc deposition (CAD) at a fixed nitrogen flow, compositional gradient films synthesized by CAD at a variable nitrogen flow and plasma based ion implanted and deposited (PBIID) films were comparatively analyzed.The results indicated that CAD films showed a strong TiN (111) preferred orientation while PBIID films a more randomly orientation. The crystallite size of CAD films was more than the double of PBIID films. Residual stresses of the PBIID films were lower than those of CAD films, the lowest hardness and elastic modulus were obtained for CAD films grown at variable nitrogen flow, while no significant differences in roughness, H/E ratio and adhesion were observed among the different films. Regarding RCF tests, failures in samples coated with TiN at constant flow were characterized by a progressive coating delamination followed by the formation of fatigue spalls inside the delaminated areas. Failures in samples coated with PBIID and gradient TiN were characterized by the formation of fatigue spalls with slight coating delamination. There were no significant differences between the RCF resistance of uncoated ADI and the samples with CAD films while the samples with PBIID films had a noticeably higher resistance. The better performance could be associated with the low compressive residual stresses and the fine grained microstructure induced by the PBIID process.

Composition Gradient, Structure, and Mechanical Properties of Mono Epoxy Terminated Polydimethylsiloxanes Grafted Gelatin Films

In present study, α-[3-(2,3-epoxy propoxy) propyl]-ω-butyl-polydimethylsiloxanes grafted gelatin (PGG) compositional gradient film was successfully fabricated by combining a solvent induced self-assembly procedure and the interaction between polymer and air/substrate induced migration. The variation of gelatin superstructures and the transformation of PGG aggregate structure with tuning volume ratio of water/ethanol studied by Atomic force microscopy (AFM), Fourier-transform infrared (FTIR) and High-resolution transmission electron microscopy (HR–TEM). At 1 : 3 vol/vol, gelatin chains self-assembled to cyclic aggregates that tended to deposit on the gelatin substrate, while PGG formed core–shell structure which should migrate to air-liquid interface driven by low free energy of PDMS chain during drying. X-ray photoelectron spectroscopy (XPS) showed that the surface of gradient film was covered with PDMS component and strong intermolecular interactions existed in between polymer and solvent molecules at 1 : 3 vol/vol. The gradients of PDMS composition along longitudinal orient in film were further confirmed by scanning electron microscopy-energy dispersive spectroscopy (SEM−EDS) with line scan. Contact angle results exhibited a successive decrease of hydrophobicity along longitudinal orient in gradient film. Dynamic mechanical analysis (DMA) results showed two tan δ and lower storage modulus in gradient than that of blank gelatin film, which led to good flexibility of gradient film.

Compositional gradient films constructed by sputtering in a multicomponent Ti–Al–(Cr, Fe, Ni) system

Abstract

Deposition of Diamond/β-SiC Composite Interlayers for Improved Machining Performance of Diamond Coated Cemented Carbide Cutting Tools

Diamond/β-SiC composite films and diamond film with composite interlayers were synthesized on cemented carbide substrates and hard metal cutting tools. Diamond top layers and the interlayers were deposited in one single process by hot filament chemical vapor deposition (HFCVD) technique using a gas mixture of hydrogen, methane and tetramethylsilane (TMS). Two different kinds of interlayers have been employed, namely, gradient interlayer and interlayer with constant composition. The gradient composite film, featuring a cross-sectional gradient with increasing diamond/β-SiC content from film-substrate interface to the top of the film, showed the best film adhesion. Turning test was carried out using diamond coated and uncoated cutting tools to machine aluminum alloy. It was confirmed that the diamond films with gradient interlayer showed best adhesion to the hard metal cutting tools. Diamond coated cutting tool with gradient composite interlayer showed also higher wear resistance than uncoated cutting tool. The tool lifetime of such diamond coated cutting tool was 10 times higher than that of uncoated cutting tool. Moreover, diamond coated cutting tools performed non-sticking machining, which leaded to much higher surface quality of machined surface than uncoated insert.

Bias-graded deposition and tribological properties of Ti-contained a-C gradient composite film on Ti6Al4V alloy

Ti-contained a-C gradient composite film with a thickness 1.5μm was deposited on medical Ti6Al4V alloy substrate using a closed field unbalanced magnetron sputtering with bias-graded voltage through −20V to −150V. The mechanical and tribological properties were evaluated from nanoindentation, scratch test and ball-on-disk tribometer. Compared with the constant-bias film deposited at −150V, the bias-graded film has the approximate hardness (19GPa) but high toughness and adhesion strength. At a normal load of 10N, the bias-graded composite film shows a low friction coefficient of 0.08 and wear rate of 2.89×10−16m3N−1m−1 in ambient air. While in Hanks’ solution, the film has the same low friction coefficient but low wear rate of 4.63×10−17m3N−1m−1. Excellent wear resistance in Hanks’ solution may bring about a biological application for the Ti-contained a-C gradient composite film.

Microporous network-assisted formation of copper-in-polymer gradient composite film

In this article, a copper-in-polymer-gradient composite film (CPGCF) was synthesized by electrochemical strategy via reducing a solvent-swollen cathode film (SCF). The latex nanoparticles of a ternary copolymer including styrene, butyl acrylate, and acrylic acid structural units play the key role to form well-graded copper distribution in this ternary copolymer matrix through the porous morphological structure developed by latex nanoparticle semimelt joining. The morphological structure along cross-section of CPGCF includes three layers: (1) a dense copper layer in ternary copolymer matrix whose most outside was originally attached to cathode in electrochemical reactor, (2) a shrublike layer that grew from dense copper layer, and (3) a clear layer in which there is no obvious reduced copper phase whose most outside was originally contacted with liquid electrolyte medium in electrochemical reactor. As experimental aspects, the influences of emulsion polymerization conditions of ternary copolymer, predrying time and temperature of SCF, dc voltage in electrochemical reduction on CPGCF structure were investigated. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Microstructure, mechanical and tribological properties of Ti(C, N)/a-C gradient composite films

Ti(C, N)/a-C composite films with compositional gradient from Ti–TiN–Ti(C, N) to Ti-containing a-C layers have been prepared by closed-field unbalanced magnetron sputtering. Within the composite films, the carbon contents gradually increase and achieve maximum in the a-C layer by increasing the power applied to the graphite targets, the nitrogen contents gradually decrease to zero from Ti(C, N) layer of the interface to a-C layer of the films. In order to achieve a good combination of the mechanical and tribological properties in the composite films, a designed experimental parameter basing on various substrate rotation speeds is also selected. Results show that the compositional gradient result in the microstructure change of composite films where the Ti(C, N) layers consist of fine nanocolumnar Ti(C, N) grains and the a-C layers consist of 2–7 nm TiC nanocrystallites embedded in an amorphous C matrix. The Ti(C, N) layers also exhibit clear multilayer structure where the period thickness gradually decreases as substrate rotation speed increases. Under higher rotation speed, disappearance of the multilayer structure is accompanied with simultaneous increase in the crystallinity of Ti(C, N) layer and also the Ti(C, N) grain size. In the a-C layer, the TiC nanocrystallites embedded in the a-C matrix is produced by the high rotation speeds. The Ti(C, N)/a-C gradient composite films exhibit high microhardness values (~5000 H V) and low friction coefficient (~ 0.15), which is related to the hard Ti(C, N) layer and self-lubricate a-C layer, respectively. The combination of the Ti(C, N) layer with a-C layer increases the load and the wear resistance capacity of the composite films, which gives satisfactory friction performance in the pin-on-disk tests with a wear rate of 3.7 × 10 − 17 m 3/mN.

Preparation and characterization of gradient distribution of silicon in emulsion blend films

In this work, a functional gradient polymeric material derived from silicon-containing acrylate blend emulsion film is prepared in two steps. Firstly, 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate (TRIS)-modified acrylate latex is prepared using multiple emulsifiers by the two-stage semicontinuous emulsion copolymerization method. Next, blend latexes composed of TRIS-containing and TRIS-free acrylate latexes are obtained. Detailed studies on the effects of the film-formation temperature and the glass transition temperature (Tg) differences on the compositional gradient film are conducted. Surface energy analysis shows that silicon elements enriched at the film-air (F-A) interface and Tg differences facilitate the fabrication of silicon gradient in emulsion blend films. Scanning electron microscopy-energy dispersive X-ray further reveals that the concentration of silicon components varies in a gradient-like manner along the overall transaction of the film when the film-formation temperature is 55 °C. However, excessive temperature creates the formation of a segmental gradient distribution of silicon in the emulsion blend films.

Preparation and structure of fluorinated/non-fluorinated polyacrylate gradient emulsion blend film

The emulsion blend method, which is environmentally friendly and energy saving, was used to prepare a compositional gradient film of fluorinated/non-fluorinated polyacrylate in this paper. The size and glass-transition temperature ( T g) of the emulsion particles were designed to enhance the driving force of their selective congregation and promote the formation of gradient structure. The structures and surface properties of the obtained films were characterized. The results showed that when the fluorinated components have much smaller particle size and higher T g than those of fluorine-free polyacrylate components, the gradient structures formed in the direction across the film thickness of the films. The concentration of the fluorinated component increased gradually from film–glass interface to film–air interface in the blend film, making the surface free energies of the two sides of the gradient film distinctively different.

EFFECT OF C2H2 FLOW RATE ON THE DEPOSITION OF TI-TIC-TIC/DLC GRADIENT NANO-COMPOSITE FILM ON NITI ALLOY

Ti - TiC - TiC / DLC gradient nano-composite films have been prepared on the NiTi substrates by the technique of plasma immersion ion implantation and deposition (PIIID) combining with plasma-enhanced chemical vapor deposition (PECVD). The influence of C 2 H 2 flow rate ranging from 30sccm to 50sccm on the chemical structure, microstructure, mechanical properties and corrosion resistance of resulting thin films are investigated by XPS, XRD, friction coefficient test, nano-indentation, electrochemical corrosion test and atomic absorption spectrometry. XPS and XRD results indicate that on the outmost layer, the Ti ions are mixed with the DLC film and form TiC phase, the binding energy of C 1s and the composition concentration of TiC depend heavily on the C 2 H 2 flow rate. With the increase of C 2 H 2 flow rate, the content of TiC and the ratio of carbon sp 3/ sp 2 decreases. The nano-indentation and friction experiments indicate that the gradient composite film at 30 sccm has a higher hardness and lower friction coefficient compared with that of the bare TiNi alloy. The microscratch curve tests indicate that Ti - TiC - TiC / DLC gradient composite films have an excellent bonding property with the substrate. Based on the electrochemical measurement and ion releasing tests, we have found that the Ti - TiC - TiC / DLC gradient composite films exhibit better corrosion resistance property and higher depression ability for the Ni ion releasing from the NiTi substrate in the Hank's solution at 37°C.

Enhanced dielectric property from highly (100)-oriented barium zirconate titanate compositional gradient films

Via the sol–gel process, compositionally graded and homogeneous BaZr x Ti 1 − x O 3 (BZT) thin films were grown on (100)-oriented LaNiO 3 (LNO)/Si substrates, respectively. The compositionally graded BZT thin film consisted of BaZr 0.05Ti 0.95O 3 (BZT5), BaZr 0.10Ti 0.90O 3 (BZT10) and BaZr 0.15Ti 0.85O 3 (BZT15). Homogeneous thin films of above three compositions were fabricated for comparison. X-ray diffraction measurements show all the BZT thin films exhibit a single perovskite phase with highly (100)-preferred orientation. The temperature-dependent dielectric properties of these films show typical diffuse phase transition, and the phase transition temperature are all lower than −35 °C. A prominent increase of the dielectric constant and a more aligned surface morphology is observed in the compositionally graded thin film compared to the homogeneous samples.

Gelatin/Poly(ethylene oxide) Blend Films with Compositional Gradient: Fabrication and Characterization

AbstractIn this study, novel protein/biodegradable polymer blend biomaterials‐gelatin/poly(ethylene oxide) blend films with compositional gradients were successfully fabricated by a dissolution/diffusion method. Two kinds of compositional gradient films, which were different in gradient structure, were prepared. The compositional gradient structure in the films was characterized by polarized optic microscopy, ATR‐FTIR, and trans‐FT‐IR mapping measurement. In addition, the mechanical properties of the gradient films were characterized with reference to their gradient structure. It is found that the compositional gradient films have better mechanical properties than the pure gelatin film. These protein/biodegradable polymer compositional gradient films have a potential for many biomedical applications.magnified image

Deposition of stress-free diamond films on Si by diamond/β-SiC nanocomposite intermediate layers

Stress-free diamond films have been synthesized by using microwave plasma enhanced chemical vapour deposition (MWCVD) technique. Nanocrystalline diamond/β-SiC gradient composite film system was used as an interlayer for the diamond top layers. As a result, Raman phonon line shifts (obtained from diamond top layers) corresponding to diamond are recorded very close to the stress-free value of 1332 cm − 1 . This implies an extraordinarily low biaxial compressive stress state in the diamond films. The interlayer accommodates to a considerable extent, the stress that occurs due to the difference in the thermal expansion coefficient of the diamond film and the underlying substrate.

Effect of C<sub>2</sub>H<sub>2</sub> Flow Rate on the Deposition of Zr-ZrC-ZrC/DLC Gradient Nano-Composite Film on Biomedical NiTi Alloy

Zr-ZrC-ZrC/DLC gradient nano-composite films have been prepared on the NiTi substrates by the technique of plasma immersion ion implantation and deposition (PIIID) combining with plasma-enhanced chemical vapor deposition (PECVD). The influence of C2H2 flow rate ranging from 30 sccm to 50 sccm on the chemical structure, microstructure, mechanical properties and corrosion resistance of resulting thin films are investigated by Raman spectrum, XPS, XRD, friction coefficient test, nano-indentation, electrochemical corrosion test and atomic absorption spectrometry. XPS and XRD results indicate that on the outmost layer, the Zr ions are mixed with the DLC film and form ZrC phase, the binding energy of C 1s and the composition concentration of ZrC depend heavily on the C2H2 flow rate. With the increase of C2H2 flow rate, the content of ZrC and the ratio of carbon sp3/sp2 decreases. The nano-indentation and friction experiments indicate that the gradient composite film at 30 sccm has a higher hardness and lower friction coefficient compared with that of the bare TiNi alloy. The microscratch curve tests indicate that Zr-ZrC-ZrC/DLC gradient composite films have an excellent bonding property with the substrate. Based on the electrochemical measurement and ion releasing tests, we have found that the Zr-ZrC-ZrC/DLC gradient composite films exhibit better corrosion resistance property and higher depression ability for the Ni ion releasing from the NiTi substrate in the Hank’s solution at 37°C.