Free-standing Composite Films Research Articles

Fabrication of PVDF-transition metal dichalcogenides based flexible piezoelectric Nanogenerator for energy harvesting applications

In the present work, we have studied the enhancement of polar crystalline β‐phase of PVDF, which is responsible for its piezoelectric property, after the addition of transition metal dichaclcogenides (TMDs). MoS2 and MoSe2, which belong to the library of TMDs were synthesized by hydrothermal method and then we have synthesized the freestanding flexible composite thin films of Polyvinylidene fluoride (PVDF), and TMDs. A systematic investigation of PVDF‐TMDs nanocomposite films by using X‐ray diffractometer, Fourier transform infrared spectroscopy, and polarization‐ electric field loop measurements supports the enhancement of β‐phase in the flexible nanocomposite polymer thin films. It has been observed that content of β‐phase was enhanced form 54% to ∼80% by adding TMDs into the PVDF. The resulting remnant polarization of the PVDF‐TMD composite films were found to be enhanced as compared to bare PVDF film.

Facile Preparation of Lightweight and Flexible PVA/PEDOT:PSS/MWCNT Ternary Composite for High-Performance EMI Shielding in the X-Band Through Absorption Mechanism

Electromagnetic safeguards are key factors for electronic devices. Lightweight and highly flexible polymer composite films with high electrical conductivity are considered to be efficient electromagnetic interference (EMI) shielding materials. Polymer composites offer alternative to metal-based composites which have poor flexibility, corrodibility, and are difficult to process. Here, highly flexible polyvinyl alcohol/poly (3, 4-ethylenedioxythiophene):polystyrene sulfonate/multiwalled carbon nanotube (PVA/PEDOT:PSS/MWCNT) free-standing composite films were fabricated by a solution mixing process followed by a simple solvent casting technique. PVA/PEDOT:PSS/MWCNT composite films of thickness around 20 microns showed high EMI shielding effectiveness (SE) in the X-band over the frequency range of 8–12 GHz. Incorporation of MWCNT into the polymer matrix considerably increased the mechanical strength of the PVA/PEDOT:PSS/MWCNT composite free-standing film. This investigation revealed that PVA/PEDOT:PSS/MWCNT composite film with 0.5 wt.% of MWCNT showed excellent absorption-dominated EMI SE of 60 dB over the frequency range of 8–12 GHz with extensive tensile strength. Our study opens a facile way to design flexible, lightweight and free-standing films as EMI shielding for next-generation flexible electronic devices.

BODIPY-based organic color conversion layers for WLEDs

The usage of organic dyes in phosphor conversion layer of WLED is an attractive approach since they have high molar extinction coefficient and photostability. Various types of organic pigments have been employed for this purpose such as BODIPY, perylene diimide, Rhodamine B, pyrene, Nile red, etc. Among those, BODIPY-based organic dyes appear to be promising candidate for white light generation. In this work, for the first time, red and green emitting BODIPY-based organic molecules have been used as colour conversion layer. These molecules were associated with PMMA in DMF solution and the resulting solution was subjected to electrospinning. Colorful electrospun mats were embedded into PDMS matrix and their free-standing PDMS composite films were used as color conversion layers over blue LED to produce white light such that CRI of 95 and CCT of 4200 K was achieved. These values show that BODIPY-based organic molecules containing fiber composites are promising candidates to be used as color conversion layers for white light applications.

Ferromagnetic properties in CuO-nanocrystals embedded in PVDF matrix

CuO in nanocrystalline form (nano-CuO) was obtained by chemical route. These nano-CuO crystallites were incorporated in polyvinylidene fluoride (PVDF) to form nano-CuO/PVDF free-standing composite films containing varying amounts of nano-CuO by using sol-gel method. These films indicated ferromagnetism at room temperature. All the films were appropriately characterized. Magnetization was found to decrease with increase in temperature. The observed ferromagnetism in nano-CuO/PVDF samples could be due to possible interaction between magnon scatterings arising from the Cu2+ ions of nano-CuO particles when embedded in PVDF matrix which in turn would alter the electronic configuration of Cu ions for inducing ferromagnetic property in these films under study.

Effects of nanoparticles size and interactions on dielectric properties of polymer matrix flexible dielectric nanocomposites

Effects of particle size on the dielectric properties of polymer matrix flexible nanocomposites were studied. Synthesized barium titanate (BaTiO3; BT) nanoparticles (NPs) with different sizes were effectively dispersed in the matrix polymer using a simple phase separation method. The dielectric responses of free-standing thin composite films were studied by impedance spectroscopy. The interactions between nanoparticles were also studied by finite element analysis and compared with experimental data using a time harmonic-electric current solver in the AC/DC module of COMSOL Multiphysics® 5.2. The dielectric permittivity of polymer matrix nanocomposites was remarkably affected by the BT particle size, while the dielectric loss did not show any noticeable changes. The real permittivity exhibited the highest value when the BT particle size was near 100 nm. The calculated energy density based on measured real permittivity and breakdown strength was as high as 17.24 J/cm3. The dielectric properties of polymer matrix nanocomposites can be improved by controlling the particle size of nanofillers in conjunction with surface treatment of fillers.

Effect of Cellulose Nanofibrils and TEMPO-mediated Oxidized Cellulose Nanofibrils on the Physical and Mechanical Properties of Poly(vinylidene fluoride)/Cellulose Nanofibril Composites.

Cellulose nanofibrils (CNFs) are high aspect ratio, natural nanomaterials with high mechanical strength-to-weight ratio and promising reinforcing dopants in polymer nanocomposites. In this study, we used CNFs and oxidized CNFs (TOCNFs), prepared by a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation process, as reinforcing agents in poly(vinylidene fluoride) (PVDF). Using high-shear mixing and doctor blade casting, we prepared free-standing composite films loaded with up to 5 wt % cellulose nanofibrils. For our processing conditions, all CNF/PVDF and TOCNF/PVDF films remain in the same crystalline phase as neat PVDF. In the as-prepared composites, the addition of CNFs on average increases crystallinity, whereas TOCNFs reduces it. Further, addition of CNFs and TOCNFs influences properties such as surface wettability, as well as thermal and mechanical behaviors of the composites. When compared to neat PVDF, the thermal stability of the composites is reduced. With regards to bulk mechanical properties, addition of CNFs or TOCNFs, generally reduces the tensile properties of the composites. However, a small increase (~18%) in the tensile modulus was observed for the 1 wt % TOCNF/PVDF composite. Surface mechanical properties, obtained from nanoindentation, show that the composites have enhanced performance. For the 5 wt % CNF/PVDF composite, the reduced modulus and hardness increased by ~52% and ~22%, whereas for the 3 wt % TOCNF/PVDF sample, the increase was ~23% and ~25% respectively.

Antibacterial free-standing polysaccharide composite films inspired by the sea

The adhesive capabilities of marine mussel proteins are well-known, exhibiting the ability to stick to different underwater substrates, either inorganic or organic. These unique adhesive properties are due to the high levels of amino acid, 3,4-dihydroxyphenyl-l-alanine (DOPA), which presents the reactive catechol group. Herein, novel antibacterial free-standing (FS) films were developed with natural polymers, namely chitosan (CHT) and hyaluronic acid (HA), being the catechol-functionalized hyaluronic acid (HA-DN) also included to provide wet adhesive properties. In order to obtain composite films, silver doped bioglass nanoparticles (Ag-BGs) were incorporated to promote bactericidal and bioactive properties, being tested four distinct formulations of FS films. Their surface morphology and topography, wettability, weight loss, swelling, mechanical, adhesion and bioactivity was analyzed. In particular, bioactivity tests revealed that upon immersion in simulated body fluid, there was the formation of a bone-like apatite layer. Moreover, upon 16 h in direct contact with Staphylococcus aureus and Escherichia coli cultures, these FS films exhibited a clear antibacterial effect. Therefore, such bioactive, antibacterial and adhesive free-standing films could potentially be used as temporary guided bone regeneration films, in particular to regenerate small bone defects and also periodontal tissues.

Agar-based antioxidant composite films incorporated with melanin nanoparticles

Melanin nanoparticles (MNP) were isolated from the sepia ink using a centrifugation method and used as a functional filler for the preparation of agar-based functional films. The MNP were spherical with an average diameter of 95.6 ± 21.2 nm. Field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FTIR) test results indicated that the MNP were well dispersed in agar polymer to form free-standing composite films. The addition of MNP enhanced the UV-blocking, hydrophobicity, mechanical, and water vapor barrier properties of the agar film. Also, the agar/MNP composite films showed a high antioxidant activity comparable to ascorbic acid. The MNP separated from sepia ink can be used as a functional filler to develop antioxidant biopolymer films for food packaging and biomedical applications.

Dielectric property and ac conductivity of P(VDF-CTFE)-PLZST polymer-ceramic composite films

Free-standing and flexible polymer-ceramic composite films were fabricated using P(VDF-CTFE) 91/09 mol.% (VC91) as polymer matrix and (Pb0.94La0.04)[(Zr0.56Sn0.44)0.84Ti0.16]O3 (PLZST) nanoparticles as ceramic filler. All the VC91-PLZST composite films are dense and homogeneous in microstructure, and are flexible with a uniform thickness of about 5 μm. It is experimentally found that as the PLZST content increases, the dielectric constant of the composite films increases, while the dielectric loss decreases. Besides the glass-transition process, there is another relaxation process related to the motion of entire polymer chains of VC91. These two relaxation processes determine the frequency dependences and temperature dependences of the dielectric properties observed in the composite films. The ac conductivity of the VC91-PLZST composite films was investigated at different temperatures and the results indicate that the conductive mechanisms are related to the relaxation processes of the VC91 matrix at different temperatures and all the VC91-PLZST composite films are good insulators.

Free-Standing Molybdenum Disulfide Composite Film Electrode for High Performance and Waterproof Flexible Supercapacitor

Molybdenum disulfide (MoS2) has been studied extensively for energy storage because of its excellent electrical properties and unique structure. In this work, the freestanding flexible composite films were prepared by reduced graphene oxide (RGO), polyaniline (PANI), and MoS2 via a facile method. The all-solid-state flexible supercapacitor based on the ternary composite film shows good electrochemical properties. The special capacitance of supercapacitor is 643.3 mF/cm2 (∼2144.3 F/cm3). And the all-solid-state flexible supercapacitor presents no particularly obvious fading after bending 200 times. Furthermore, the ternary composite film electrode has certain waterproof effect due to the high content of MoS2. The ternary composite film remained high capacitance (614.9 mF/cm2) after soaking in water for 8 h. This work not only develops a facile approach to prepare MoS2 composite film with flexibility, but also provides a guideline for preparing functional supercapacitor by utilizing properties of MoS2 such as photoelectric conversion, catalytic function and so on.

Magnetic and dispersible FeCoNi-graphene film produced without heat treatment for electromagnetic wave absorption

Magnetic metal and graphene hybrids possess the high dielectric properties of graphene and the high magnetic properties of the metal, which render them suitable as electromagnetic (EM) wave-absorbing materials. In this research, we fabricated an EM wave-absorbing film with excellent performance (reflection loss of −68 dB) based on a FeCoNi@graphene hybrid. We developed a new electroless plating method for fabricating magnetic metal@graphene hybrids without any heat treatment, and the new hybrid material showed a higher saturation magnetization (120.4 emu/g) than that of a hybrid material prepared by conventional electroless plating (56.8 emu/g). The sizes, structures, and oxidation ratios of the FeCoNi nanoparticles on graphene were different depending on the synthesis method, and Ni played an important role in the growth of the FeCoNi nanoparticles. The FeCoNi@graphene hybrid was well dispersed in tetrahydrofuran, and thus, could be fabricated into free-standing and flexible composite films by mixing with thermoplastic polyurethane. The high permeability of the FeCoNi@graphene film resulted in a high EM wave-absorbing performance due to impedance matching. These results provide an important advancement toward not only the commercialization of EM wave-absorbing films for healthcare, electronic reliability, and tactical security applications but also the development of magnetic metal and graphene hybrid materials using a scalable process.

Efficient and angle-stable white top-emitting organic light emitting devices with patterned quantum dots down-conversion films

Abstract Efficient white top-emitting organic light-emitting devices (TEOLEDs) are fabricated by combining blue TEOLEDs with down-conversion films. Quantum dots (QDs) are integrated with polymethyl methacrylate (PMMA) to obtain freestanding composite films, and the films are used as down-conversion films to produce red emission by converting blue emission from blue TEOLEDs. The blue and white TEOLEDs exhibit the maximum current efficiency of 37.4 and 22.2 cd/A, respectively. Through integrating a microstructure QDs down-conversion film by transfer printing on blue TEOLED, the light extraction performance of white TEOLEDs is improved and the angular distribution of the white emission is almost Lambertian. The CIE color coordinates of white TEOLEDs with patterned QDs down-conversion films shift only (0.025, 0.005) from 0° to 60°.

Towards high-powered remote WLED based on flexible white-luminescent polymer composite films containing S, N co-doped graphene quantum dots

In this article, a new application of using S, N co-doped graphene quantum dots (S, N-GQDs) as ideal color converters in solid-state white light-emitting diode (WLED) is reported. To this end, the S, N-GQDs with an average diameter of ∼4.46 nm are obtained by a hydrothermal approach using citric acid and thiourea as source materials. The PL spectra of S, N-GQDs show an excitation-independent behavior in the range of 300–380 nm. Under UV illumination, the S, N-GQDs display intense blue-light with the quantum yield of 51.2%. The PL mechanism is also investigated. Then, we fabricate freestanding luminescent composite films in a solution casting method by combining S, N-GQDs with YAG:Ce3+ phosphors based on a polyvinyl alcohol (PVA) matrix. The luminescent films have superior foldability and photostability and excellent heat resistance, and retain their optical performances in the solid-state. To realize their potential, a high-powered remote WLED has been demonstrated. The results indicate that S, N-GQDs and YAG:Ce3+ can be homogeneously dispersed in the PVA without aggregation so that uniform white-light emission can be obtained. These composite films containing S, N-GQDs are promising to be used in state-of-the-art UV-pumped remote WLED according to their wide wavelength emission and collapsible illumination device.

Effect of microstructure on the dielectric properties of poly(vinyl alcohol)–poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonate) composite films

ABSTRACTPoly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT–PSS) was blended with poly(vinyl alcohol) (PVA) to form 0, 10, 20, 30, 40, and 50 vol % PEDOT–PSS/PVA solutions, and their freestanding films were prepared with a simple and cost‐effective solution casting technique at 27 °C in the absence of additives. Field emission scanning electron microscopy images revealed changes in the cocontinuous network to a rodlike morphology in the composite films from 10 to 50 vol % PEDOT–PSS/PVA. The alternating‐current conductivity was found to obey Jonscher's power law. The obtained values of the dielectric constant at 27 °C were relatively high, and a maximum value of 6.7 × 104 at 100 Hz for 40 vol % PEDOT–PSS'/PVA was observed. The dielectric loss attained a maximum value of about 106 at 100 Hz for 40 vol % PEDOT–PSS/PVA. However, a decrease in the dielectric parameters was observed at 50 vol % PEDOT–PSS/PVA because of locally induced strain in the microstructure. The variations in polarization with respect to the applied electric field (P–E) were determined for 50, 100, and 500 Hz at 500 V for the freestanding composite films of lower concentrations up to 20 vol % PEDOT–PSS/PVA. In summary, the dielectric and P–E measurements confirmed that the electrical characteristics changed in accordance to the contribution from both resistive and capacitive sites in the PEDOT–PSS/PVA composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45079.

Air/Water Interfacial Formation of “Clean” Tiny AuNPs Anchored Densely on CNT Film for Electrocatalytic Alcohol Oxidation

Tiny gold nanoparticles without any surfactant are synthesized via air/water interfacial reaction to be anchored in suit on the surfaces of supported carbon nanotubes in high density. The resultant 2D Janus freestanding composite films exhibit efficient electrocatalytic ability for alcohol oxidation, mainly due to abundant active sites and facile electron transfer. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Flexible Electrode Design: Fabrication of Freestanding Polyaniline-Based Composite Films for High-Performance Supercapacitors.

Polyaniline (PANI) is a promising pseudocapacitance electrode material. However, its structural instability leads to low cyclic stability and limited rate capability which hinders its practical applications. In view of the limitations, flexible PANI-based composite films are developed to improve the electrochemical performance of electrode materials. We report in the research a facile and cost-effective approach for fabrication of a high-performance supercapacitor (SC) with excellent cyclic stability and tunable energy and power densities. SC electrode containing a very high mass loading of active materials is a flexible film of PANI, tissue wiper-based cellulose, graphite-based exfoliated graphite (ExG), and silver nanoparticles with potential applications in wearable electronics. The optimum preparation weight ratios of silver nitrate/aniline and ExG/aniline used in the research are estimated to be 0.18 and 0.65 (or higher), respectively. Our results show that an ultrahigh capacitance of 3.84 F/cm(2) (240.10 F/g) at a discharge rate of 5 mA can be achieved. In addition, our study shows that the power density can be increased from 1531.3 to 3000 W/kg by selecting the weight ratio of ExG/aniline to be more than 0.65, with a sacrifice in the energy density. The obtained promising electrochemical properties are found to be mainly attributed to an effective combination of PANI, ExG, cushiony cellulose scaffold, and silver as well as the porosity of the composite.

Drug loading and release behaviors of freestanding polysaccharide composite films

We developed freestanding, water-insoluble thin films made of polyion complexes (PICs) that consist of glycosaminoglycans such as chondroitin sulfate C (CS) and chitosan (CHI) by utilizing hot press techniques. In this study, material loading and release abilities of CS/CHI composite films were spectroscopically examined using small dye molecules; cationic methylene blue (MB) and anionic carboxyfluorescein (CF) were used as model drugs. The dye-loading films were prepared using pre- and post-loading methods. Microscopic film morphologies were not affected by the dye loadings. The mechanical strengths of the dye-loaded CS/CHI films were almost identical to those of the unloaded films. The dye release behaviors of the films in various aqueous solutions were examined, and the results demonstrated that the CS/CHI films exhibited media-responsive dye release abilities. The experimental results obtained under different conditions were compared and discussed based on the chemical structures of the polysaccharides used to generate the film components and the dye molecules. The present results demonstrate that these polysaccharide composite films are promising materials for use in applications that require sustained drug release under physiological conditions. Drug loading and release abilities of freestanding films made of polyion complexes of chondroitin sulfate C and chitosan were examined using dye molecules such as methylene blue and carboxyfluorescein. The dye-loading films were prepared using pre- and post-loading methods. Microscopic film morphologies were not affected by the dye loadings. The mechanical strengths of the dye-loaded films were almost identical to those of the unloaded films. The dye release behaviors of the films in various aqueous solutions were examined, and the results demonstrated that the films exhibited media-responsive dye release abilities.

Fabrication of freestanding silk fibroin films containing Ag nanowires/NaYF4:Yb,Er nanocomposites with metal-enhanced fluorescence behavior.

Solar cells containing upconversion nanoparticles (UCNPs) used as a power source in biomedical nanosystems have attracted great interest. However, such solar cells further need to be developed because their substrate materials should be biocompatible, flexible and highly luminescent. Here, we report that freestanding silk fibroin (SF) films containing a mesh of silver nanowires (AgNWs) and β-NaYF4:Yb,Er nanocrystals with metal-enhanced fluorescence behavior can be fabricated. The freestanding composite films exhibit properties such as good optical transparency, conductivity and flexibility. Furthermore, they show significantly enhanced upconversion fluorescence due to surface plasmon polaritons (SPPs) of AgNWs compared to the SF-UCNP films without AgNWs. The freestanding composite films with metal-enhanced fluorescence behavior show great promise for future applications in self-powered nanodevices such as cardiac pacemakers, biosensors and nanorobots.

Null Extinction of Ceria@silica Hybrid Particles: Transparent Polystyrene Composites.

Scattering of light in optical materials, particularly in composites based on transparent polymer and inorganic pigment nanoparticles, is a chronic problem. It might originate mainly from light scattering because of a refractive index mismatch between the particles and transparent polymer matrix. Thus, the intensity of light is rapidly diminished and optical transparency is reduced. Refractive index matching between the pigment core and the surrounding transparent matrix using a secondary component at the interface (shell) has recently appeared as a promising approach to alter light scattering. Here, CeO2 (ceria) nanoparticles with a diameter of 25 nm are coated with a SiO2 (silica) shell with various thicknesses in a range of 6.5-67.5 nm using the Stöber method. When the hybrid core-shell particles are dispersed into transparent polystyrene (PS), the transmission of the freestanding PS composite films increases over both the ultraviolet (UV) and visible region as the shell thickness increases particularly at 37.5 nm. The increase of transmission can be attributed to the reduction in the scattering coefficient of the hybrid particles. On the other hand, the particles in tetrahydrofuran (THF) absorb over UV and the intensity of absorption shows a systematic decrease as the shell thickness increases. Thus, the silica shell suppresses not only the scattering coefficient but also the molar absorptivity of the core ceria particles. The experimental results regarding the target shell thickness to develop low extinction (scattering + absorption) composites show a qualitative agreement with the predictions of Effective Medium Theory.

Fabrication of hybrid nanocomposite scaffolds by incorporating ligand-free hydroxyapatite nanoparticles into biodegradable polymer scaffolds and release studies.

We report on the optical fabrication approach of preparing free-standing composite thin films of hydroxyapatite (HA) and biodegradable polymers by combining pulsed laser ablation in liquid and mask-projection excimer laser stereolithography (MPExSL). Ligand-free HA nanoparticles were prepared by ultrafast laser ablation of a HA target in a solvent, and then the nanoparticles were dispersed into the liquid polymer resin prior to the photocuring process using MPExSL. The resin is poly(propylene fumarate) (PPF), a photo-polymerizable, biodegradable material. The polymer is blended with diethyl fumarate in 7:3 w/w to adjust the resin viscosity. The evaluation of the structural and mechanical properties of the fabricated hybrid thin film was performed by means of SEM and nanoindentation, respectively, while the chemical and degradation studies were conducted through thermogravimetric analysis, and FTIR. The photocuring efficiency was found to be dependent on the nanoparticle concentration. The MPExSL process yielded PPF thin films with a stable and homogenous dispersion of the embedded HA nanoparticles. Here, it was not possible to tune the stiffness and hardness of the scaffolds by varying the laser parameters, although this was observed for regular PPF scaffolds. Finally, the gradual release of the hydroxyapatite nanoparticles over thin film biodegradation is reported.