Free-standing Hybrid Films Research Articles

Free-Standing and Self-Crosslinkable Hybrid Films by Core-Shell Particle Design and Processing.

The utilization and preparation of functional hybrid films for optical sensing applications and membranes is of utmost importance. In this work, we report the convenient and scalable preparation of self-crosslinking particle-based films derived by directed self-assembly of alkoxysilane-based cross-linkers as part of a core-shell particle architecture. The synthesis of well-designed monodisperse core-shell particles by emulsion polymerization is the basic prerequisite for subsequent particle processing via the melt-shear organization technique. In more detail, the core particles consist of polystyrene (PS) or poly(methyl methacrylate) (PMMA), while the comparably soft particle shell consists of poly(ethyl acrylate) (PEA) and different alkoxysilane-based poly(methacrylate)s. For hybrid film formation and convenient self-cross-linking, different alkyl groups at the siloxane moieties were investigated in detail by solid-state Magic-Angle Spinning Nuclear Magnetic Resonance (MAS, NMR) spectroscopy revealing different crosslinking capabilities, which strongly influence the properties of the core or shell particle films with respect to transparency and iridescent reflection colors. Furthermore, solid-state NMR spectroscopy and investigation of the thermal properties by differential scanning calorimetry (DSC) measurements allow for insights into the cross-linking capabilities prior to and after synthesis, as well as after the thermally and pressure-induced processing steps. Subsequently, free-standing and self-crosslinked particle-based films featuring excellent particle order are obtained by application of the melt-shear organization technique, as shown by microscopy (TEM, SEM).

Fabrication of Biocompatible, Functional, and Transparent Hybrid Films Based on Silk Fibroin and Epoxy Silane for Biophotonics.

In this work we explored the fabrication of flexible and transparent hybrids of silk fibroin (SF) and epoxy-modified siloxane for photonic applications. It is well-known that regenerated SF solutions can form free-standing films with high transparency. Although SF has a restricted number of chemically reactive side groups, the main issues of as-cast pristine SF films regard the high solubility into aqueous media, brittleness, and low thermal stability. The design of SF films with enhanced functionality but high transparency triggers new opportunities on a broader range of applications in biophotonics. Here we present a simple, functional, yet remarkably versatile hybrid material derived from silica sol-gel process based on SF protein and (3-glycidyloxypropyl)trimethoxysilane (GPTMS), an organically modified silicon-alkoxide owning a reactive terminal epoxy group. Specifically, we investigated the effect of the addition of GPTMS into SF solutions on the processability, morphology, crystallinity, and mechanical and optical properties of the resulting hybrid films. Highly transparent (ca. 90%) and flexible free-standing hybrid films were achieved. Cell viability assays revealed that the hybrid films are noncytotoxic to rat osteoblast cells even at high GPTMS content (up to 70 wt %). The hybrid films showed enhanced thermal stability and were rich in organic (epoxy) and inorganic (silanol) functional groups according to the content of GPTMS. We also evaluated the successful preparation of high-quality optical red emissive SF hybrid films by loading YVO4:Eu3+ nanoparticles at low concentration (<5 wt %). A meaningful description of the hybrid film structure is reported from the combination of scanning electron and atomic force microscopies, vibrational spectroscopy, solid-state NMR, and X-ray diffraction analyses.

Preparation and properties of organic–inorganic hybrid materials using titanium phosphonate cluster

Organic–inorganic hybrids containing [Ti4(μ3-O)(OiPr)5(μ-OiPr)3(O3PPh)3]·thf as element-blocks were prepared by hybridization with poly(dimethylsiloxane), poly(methylsilsesquioxane), poly(ethoxysilsesquioxane), poly(methyl methacrylate), poly(vinyl alcohol), poly(4-vinylphenol), poly(styrene-co-allyl alcohol) or poly(bisphenol A-co-epichlorohydrin). The concentration of the titanium cluster was increased to 40 wt% to form crack-free films with high transparency. The temperature at which 10 wt% weight loss occurred increased with the concentration of the titanium cluster because an alcohol exchange reaction was expected between the titanium cluster and polymers. The mechanical strengths and strains of poly(dimethylsiloxane) hybrids were very low. The tensile strengths and elongations of poly(methyl methacrylate) hybrids increased with the increase in the titanium cluster concentration. The tensile strengths and elongations of poly(vinyl alcohol) hybrids were highest when the titanium cluster concentration was 10 wt%. Organic–inorganic hybrids containing [Ti4(μ3-O)(OiPr)5(μ-OiPr)3(O3PPh)3]·thf (TiOPPh) as element-blocks were prepared by hybridization with silicone polymers (poly(dimethylsiloxane) (PDMS), poly(methylsilsesquioxane) (PMS) or poly(ethoxysilsesquioxane) (PEOS)), the hydroxyl groups substituted organic polymers (poly(vinyl alcohol) (PVA), poly(4-vinylphenol), poly(styrene-co-allyl alcohol) or poly(bisphenol A-co-epichlorohydrin) (PBE)) or poly(methyl methacrylate) (PMMA). The concentration of TiOPPh was increased to 40 wt% to form free-standing hybrid films with PDMS, PMS, PVA and PBE polymers. The tensile strengths and elongations of PMMA and PVA films were higher improved than only polymers because TiOPPh acted good crosslinkers.

Flexible and Free-Standing Organic/Carbon Nanotubes Hybrid Films as Cathode for Rechargeable Lithium-Ion Batteries

Organic carbonyl compounds are promising electrode materials for high-performance lithium-ion batteries (LIBs), but generally suffer from poor cycling stability, low utilization, inferior rate performance, and relatively low reduction potential. In order to solve these problems, we report a dissolution-recrystallization method to prepare flexible, binder-free, and free-standing hybrid films of sodium 1,4-dioxonaphthalene-2-sulfonate and multiwalled carbon nanotubes (NQS/MWNTs) as high-performance cathode for rechargeable LIBs. The hybrid films demonstrate high utilization of NQS, stable cycling, and high-rate capability. The superior electrochemical performance is attributed to decreased size and high polarity of NQS, three-dimensional intertwined conductive network formed by MWNTs. Moreover, NQS/MWNTs show high initial reduction potential at 2.97 V, which is well explained via density functional theory (DFT) calculations. Meanwhile, the reversible redox mechanism of NQS/MWNTs during discharge/charge proc...

Free-standing hybrid films based on graphene and porous carbon particles for flexible supercapacitors

A novel route towards high-performance, free-standing and flexible hybrid papers made up of porous carbon particles combined with graphene sheets.

Successful entrapment of carbon dots within flexible free-standing transparent mesoporous organic-inorganic silica hybrid films for photonic applications

The effective entrapment of Carbon dots (CDs) into a polymer-silica hybrid matrix, formed as free standing transparent flexible films, is presented. The composite's synthesis, characterization, device application and properties -mechanical, thermal and optical- are being provided and discussed. CDs of 3nm mean size with strong photoluminescence are embedded into a silica matrix during the sol-gel procedure, using tetraethyl orthosilicate as the precursor and F127 triblock copolymer as the structure directing agent under acidic conditions. The final hybrid nanostructure forms free standing transparent films that show high flexibility and long term stable CDs luminescence indicating the protective character of the hybrid matrix. It is crucial that the photoluminescence of the hybrid's CDs is not seriously affected after thermal treatment at 550°C for 30min. Moreover, the herein reported hybrid is demonstrated to be suitable for the fabrication of advanced photonic structures using soft lithography processes due to its low shrinkage and distortion upon drying, both attributable to its porosity. Finally, it is reported that addition of F127 ethanolic solution in aqueous solution of CDs induces a blue-shift of their photoluminescence.

Free-standing hybrid film of less defective graphene coated with mesoporous TiO2 for flexible lithium ion batteries with fast charging/discharging capabilities

Benefiting from extremely high conductivity, graphene sheets (GS) with very low defect density are preferable to reduced graphene oxide sheets for constructing the free-standing hybrid electrodes of flexible electrochemical energy storage devices. However, due to the hydrophobic nature and deficiency of nucleation sites, how to uniformly and intimately anchor electrochemically active materials onto less defective GS is a challenge. Herein, a free-standing and mechanically flexible hybrid film with two-layer structure, mesoporous TiO2 anchored less defective GS hybrid (mTiO2-GS) upper-layer and graphene under-layer, denoted as mTiO2-GS/G, is fabricated. The hydrolysis of a Ti glycolate aqueous sol solution were applied to form mTiO2. The decoration of less defective GS with sodium lignosulfonate (SLS) surfactant is crucial for anchoring TiO2 nanoparticles (NPs). The aromatic rings of SLS favor a non-destructive functionalization of GS through the π-π stacking interaction. The sulfonic acid groups and hydroxyl groups of SLS, respectively, greatly improve the dispersity of GS in water and trigger the nucleation of TiO2 through the oxolation in the hydrolysis of Ti glycolate sol solution. The following characteristics of free-standing mTiO2-GS/G electrode benefit the fast charging/discharging capabilities: highly conductive graphene framework, ultra-small NPs (∼5.0 nm) in mTiO2 anchored, high specific surface area (202.5 m2 g−1), abundant mesopores (0.32 cm3 g−1), intimate interfacial interaction between mTiO2 and GS, robust contact between the mTiO2-GS upper-layer and an under-layer of bare graphene as the current collector. In coin half-cells, the mTiO2-GS/G electrode delivers a capacity of 130 mA h g−1 at 50 C, and 71 mA h g−1 at 100 C, and it also exhibits excellent cycle stability up to 10 000 cycles under 10 C, with a degradation rate of 0.0033% per cycle. When packed in flexible cells, the mTiO2-GS/G electrode maintains fast charging/discharging capabilities regardless of being flat or bent. Furthermore, because of the high durability of mTiO2-GS/G electrode, repeated deformations do not cause extra capacity degradation.

2D titanium carbide and transition metal oxides hybrid electrodes for Li-ion storage

Abstract The combination of nanomaterials with complementary properties in a well-designed architecture is an attractive strategy to develop multi-functional, high-performance materials for applications in energy conversion and storage, catalysis, electronic devices, and more. Herein, we propose three different methods: alternating filtration, spray coating, and in-situ wet chemistry synthesis, to achieve the hybridization of two-dimensional (2D) Ti 3 C 2 T x MXene and transition metal oxides (TMOs), such as Co 3 O 4 and NiCo 2 O 4 . The resulting flexible free-standing hybrid films were free of binders, conductive additives, or current collectors. When used directly as anodes for Li-ion batteries, these hybrid films successfully combined the metallic conductivity of Ti 3 C 2 T x and high capacity of TMOs, showing excellent electrochemical performance for Li-ion storage. High reversible capacities over 1200 mA h g −1 were achieved by the MXene/TMO hybrid film electrodes fabricated by all three methods. All films also exhibited impressive long cycling stabilities and excellent rate performances. In particular, the spray-coated Ti 3 C 2 T x /NiCo 2 O 4 hybrid film electrode achieved high reversible capacities of 1330, and 650 and 350 mA h g −1 at 0.1, 5 and 10 C, respectively, along with no capacity decay over hundreds of cycles. This work demonstrates that the hybridization of MXenes, a large family of 2D transition metal carbides/nitrides, and TMOs has a significant potential for energy storage, and is promising for expansion into other applications.

Highly Flexible, Freestanding Supercapacitor Electrode with Enhanced Performance Obtained by Hybridizing Polypyrrole Chains with MXene

Though polypyrrole (PPy) is widely used in flexible supercapacitors owing to its high electrochemical activity and intrinsic flexibility, limited capacitance and cycling stability of freestanding PPy films greatly reduce their practicality in real‐world applications. Herein, we report a new approach to enhance PPy's capacitance and cycling stability by forming a freestanding and conductive hybrid film through intercalating PPy into layered Ti3C2 (l‐Ti3C2, a MXene material). The capacitance increases from 150 (300) to 203 mF cm−2 (406 F cm−3). Moreover, almost 100% capacitance retention is achieved, even after 20 000 charging/discharging cycles. The analyses reveal that l‐Ti3C2 effectively prevents dense PPy stacking, benefiting the electrolyte infiltration. Furthermore, strong bonds, formed between the PPy backbones and surfaces of l‐Ti3C2, not only ensure good conductivity and provide precise pathways for charge‐carrier transport but also improve the structural stability of PPy backbones. The freestanding PPy/l‐Ti3C2 film is further used to fabricate an ultra‐thin all‐solid‐state supercapacitor, which shows an excellent capacitance (35 mF cm−2), stable performance at any bending state and during 10 000 charging/discharging cycles. This novel strategy provides a new way to design conductive polymer‐based freestanding flexible electrodes with greatly improved electrochemical performances.

Binder-free flexible LiMn2O4/carbon nanotube network as high power cathode for rechargeable hybrid aqueous battery

Highly flexible LiMn2O4/carbon nanotube (CNT) electrodes are developed and used as a high power cathode for the Rechargeable Hybrid Aqueous Battery (ReHAB). LiMn2O4 particles are entangled into CNT networks, forming a self-supported free-standing hybrid films. Such hybrid films can be used as electrodes of ARLB without using any additional binders. The binder-free LiMn2O4/CNT electrode exhibits good mechanical properties, high conductivity, and effective charge transport. High-rate capability and high cycling stability are obtained. Typically, the LiMn2O4/CNT electrode achieves a discharge capacity of 72 mAh g−1 at the large-current of 20 C (1 C = 120 mAh g−1), and exhibits good cycling performance and high reversibility: Coulombic efficiency of almost 100% over 300 charge-discharge cycles at 4 C. By reducing the weight, and improving the large-current rate capability simultaneously, the LiMn2O4/CNT electrode can highly enhance the energy/power density of ARLB and hold potential to be used in ultrathin, lightweight electronic devices.

Fabrication of free-standing bio-template mesoporous hybrid film for high and selective phosphate removal

An efficient and selective free-standing mesoporous hybrid film adsorbent is templated with nanocrystalline cellulose for the first time. The film material exhibited highly ordered chiral nematic structures and superior adsorption for phosphate. In the batch adsorption tests, the sorbent material was able to selectively adsorb phosphate due to lanthanum loading (from 4.21wt% to 18.41wt%). For adsorption kinetics studies, the adsorption followed a pseudo-second order model well, with particularly rapid adsorption observed in the case of phosphate. And the resulting adsorption isotherms of the sorbent was better represented by the Langmuir model than the Freundlich model. Moreover, the sorbent achieved high adsorption capacity within pH between 3.0 and 7.0. Also a high selectivity of phosphate was observed in coexisting anions system. The proposed film sorbent demonstrated a higher degree of reusability in cycle test and easy separation from the solution. In addition, the hybrid film revealed a fast phosphate adsorption in actual environmental sample at low phosphorus concentration.

General Strategy for Fabricating Sandwich-like Graphene-Based Hybrid Films for Highly Reversible Lithium Storage.

We report a general strategy for the fabrication of freestanding sandwich-like graphene-based hybrid films by electrostatic adsorption and following reduction reaction. We demonstrate that by rational control of pH value in precursors, graphene oxide (GO) sheets can form three-dimensional (3D) sandwich frameworks with nanoparticles decorated between the layers of graphene. In our proof-of-concept study, we prepared the graphene/Si/graphene (G@Si@G) sandwich-like films. When used as negative electrode materials for lithium-ion batteries, it exhibits superior lithium-ion storage performance (∼1800 mA h g(-1) after 40 cycles at 100 mA g(-1)). Importantly, with this simple and general method, we also successfully synthesized graphene/Fe2O3/graphene and graphene/TiO2/graphene hybrid films, showing improved electrochemical performance. The good electrochemical property results from the enhanced electron transport rate, and the 3D flexible matrix to buffer volume changes during cycling. In addition, the porous sandwich structure consisting of plate-like graphene with high surface area provides effective electrolyte infiltration and promotes diffusion rate of Li(+), leading to an improved rate capability.

2D Janus Hybrid Materials of Polymer‐Grafted Carbon Nanotube/Graphene Oxide Thin Film as Flexible, Miniature Electric Carpet

Ultrathin, freestanding polymer hybrid film with macroscopic sizes and molecular thicknesses have received significant interest due to their applications as functional devices, microsensors or nanoactuators. Herein, a 2D Janus hybrid of polymer‐grafted carbon nanotubes/graphene oxide (CNTs/GO) thin film is fabricated using microcontact printed CNTs/GO as photo active surface to grow polymer brushes by self‐initiated photografting and photopolymerization selectively from one side of CNTs/GO film. This achieved 2D Janus hybrid materials with grafted polymer layer as insulative carpet and supported CNTs/GO thin film as conductive element have the potential application as flexible and miniature electric carpet for heating micro‐/nano devices locally.

Hybrid Materials: Strongly-Coupled Freestanding Hybrid Films of Graphene and Layered Titanate Nanosheets: An Effective Way to Tailor the Physicochemical and Antibacterial Properties of Graphene Film (Adv. Funct. Mater. 16/2014)

S. Park, S.-J. Hwang, and co-workers report the fabrication of strongly coupled hybrid films of reduced graphene oxide-layered titanate with an unexpected high sterilization efficiency for Escherichia coli. On page 2288, E. coli cells exposed to the hybrid film are irreversibly destroyed by the edges of the nanosheets. The enhanced adhesion of bacteria on the rough surface of the hybrid films additionally contributes to their excellent antibacterial activity.

Biocompatible and flexible graphene oxide/upconversion nanoparticle hybrid film for optical pH sensing

Free-standing optical hybrid film which is composed of positively-charged polyethylenimine-coated NaYF4:Yb,Er nanoparticles and negatively-charged graphene oxide (GO) has been developed to measure pH based on the pH-dependent luminescence quenching effect caused by GO. The isothermal titration calorimetry analyses indicate that the interaction between GO and NaYF4:Yb,Er nanoparticles becomes stronger with increasing pH, leading to a more significant fluorescence quenching of NaYF4:Yb,Er nanoparticles at high pH values. The excellent mechanical properties of the hybrid film endow the thin-film pH sensor with better repeatability and higher stability during the measurements. Quantitatively, the upconversion luminescence intensity of the hybrid film exhibits a linear trend over the pH range of 5.00-8.00. Because of excitation with a 980 nm laser, as expected, the hybrid film sensor is also sensitive to the urine measurements with reduced background absorption. In addition to its good biocompatibility, our free-standing hybrid film sensor would be a promising candidate for biological, medical, and pharmaceutical applications.

Strongly‐Coupled Freestanding Hybrid Films of Graphene and Layered Titanate Nanosheets: An Effective Way to Tailor the Physicochemical and Antibacterial Properties of Graphene Film

An effective way to tailor the physicochemical properties of graphene film is developed by combining colloidal suspensions of reduced graphene oxide (rG‐O) nanosheets and exfoliated layered titanate nanosheets for the fabrication of freestanding hybrid films comprised of stacked and overlapped nanosheets. A flow‐directed filtration of such mixed colloidal suspensions yields freestanding hybrid films comprised of strongly‐coupled rG‐O and titanate nanosheets with tunable chemical composition. This is the first example of highly flexible hybrid films composed of graphene and metal oxide nanosheets. The intimate incorporation of layered titanate nanosheets into the graphene film gives rise not only to an increase of mechanical strength but also to increased surface roughness, chemical stability, and hydrophilicity; thus, the physicochemical properties of the graphene film can be tuned by hybridization with inorganic nanosheets. These freestanding hybrid films of rG‐O‐layered titanate show unprecedentedly high antibacterial property, resulting in the complete sterilization of Escherichia coli O157:H7 (≈100%) in the very short time of 15 min. The antibacterial activity of the hybrid film is far superior to that of the pure graphene film, underscoring the beneficial effect of the layered metal oxide nanosheets in improving the functionality of the graphene film.

Thermally stable and highly conductive free-standing hybrid films based on reduced graphene oxide

Thermally stable and highly conductive films have been prepared based on thermally reduced graphene oxide and exfoliated α-zirconium phosphate nanoplatelet (ZrP) hybrids. Exfoliated ZrP and graphene oxide (GO) were first mixed in aqueous solution to form a stable dispersion and then cast into free-standing films through flow-directed assembly. Upon annealing at 750 °C in Argon atmosphere, significant amounts of oxidized species were removed from the GO and a noticeable recovery of sp2 structure of the reduced GO sheets was observed. With the incorporation of the inorganic nanoplatelets, the thermal stability and structural integrity of the hybrid films were greatly improved, while the good electrical conductivity of the reduced GO was maintained. Potential applications for graphene-based hybrid films based on the current approach are discussed.

Hybrid films of reduced graphene oxide with noble metal nanoparticles generated at a liquid/liquid interface for applications in catalysis

Free-standing ultra-thin hybrid films of reduced graphene oxide (rGO) with Au, Ag and Pd nanoparticles are generated at an aqueous/organic interface by in situ chemical reduction and spontaneous assembly. The reduction is initiated at a ‘bare’ interface or a ‘modified’ interface in a single step or two-step synthetic strategy. The hybrid materials are characterized by UV-visible, infra-red and Raman spectroscopies, X-ray diffraction, scanning electron (SEM), transmission electron (TEM) and atomic force microscopies (AFM). UV-visible spectra confirm the presence of isolated metal nanoparticles grafted on to rGO layers and Raman spectra signal a charge transfer across the constituent metal nanoparticles and rGO in the hybrid material. SEM and AFM studies show that the morphology of the hybrid films constitutes a homogeneous dispersion of metal nanoparticles and rGO for reduction at the ‘bare’ interface, and a random grafting of metal nanoparticles on rGO for reduction at the ‘modified’ interface. A mechanism for the formation of the films is proposed that involves a simultaneous transport and reduction of GO sheets and metal precursor at the interface or a directed reduction of metal precursor on rGO surface, facilitated by external aids. The utility of these hybrid films as catalysts is exemplified in p-nitrophenol reduction. Our method provides a fast, simple and inexpensive route to obtain free-standing hybrid films of rGO with metal nanoparticles for various applications.

Preparation and characterization of novel polyimide‐silica hybrids

Polyimide‐silica (PI‐SiO2) hybrids were prepared from a novel polyimide (PI), derived from pyromellitic dianhydride (PMDA), 1,6‐bis(4‐aminophenoxy)hexane (synthesized) and 4,4′‐oxydianiline. SiO2 networks (5–30 wt%) were generated through sol–gel process using either tetraethylorthosilicate (TEOS) or a mixture of 3‐aminopropyltriethoxysilane‐PMDA‐based coupling oligomers (APA) and TEOS. Thin, free standing hybrid films were obtained from the respective mixtures by casting and curing processes. The hybrid films were characterized using Fourier transform infrared, 29Si nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray spectrometry and atomic force microscopy (AFM) techniques. 29Si NMR results provide information about formation of organically modified silicate structures that were further substantiated by FE‐SEM and AFM micrographs. Contact angle measurements and thermogravimetric thermograms reveal that the addition of APA profoundly influences surface energy, interfacial tension, thermal stability and the residual char yield of modified hybrids in comparison to those obtained by mixing only TEOS. It was found that reduced particle size, efficient dispersion and improved interphase interactions were responsible for the eventual property enhancement. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Flexible free-standing TiO2/graphene/PVdF films as anode materials for lithium-ion batteries

Graphene composites were prepared by hydrothermal method using titanium dioxide (TiO2) adsorbed graphene oxide (GO) sheets as precursors. Free-standing hybrid films for lithium-ion batteries were prepared by adding TiO2/graphene composites to the polyvinylidene fluoride (PVdF)/N-methyl-2-pyrrolidone (NMP) solution, followed by a solvent evaporation technique. These films were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and various electrochemical techniques. Flexible films show an excellent cycling performance, which was attributed to the interconnected graphene conducting network, which depressed the increasing of electric resistance during the cycling.