Free-standing Composite Films Research Articles

Burst plasma preparation of metallic nanoparticles on carbon fabrics for antibacterial and electrocatalytic applications

Metal nanoparticles have extraordinary properties, but their integration into mesostructures has been challenging. Producing uniformly dispersed nanoparticles attached to substrates in industrial quantities is difficult. Herein, a “plasmashock” method was developed to synthesize metal nanoparticles anchored on different types of carbonaceous substrates using liquid salt solution precursors. These self-supporting, nanoparticle-loaded carbon fabrics are mechanically robust and have been tested as antibacterial substrates and electrocatalysts for reducing carbon dioxide and nitrite. A piece of silver–carbon nanotube paper with a silver loading of ~0.13 mg cm−2 treated after a few-second plasmashock presents good antibacterial and electrocatalytic properties in wastewater, even after 20 bactericidal immersion cycles, due to the strong bonding of the nanoparticles to the substrate. The results prove the effectiveness of this plasmashock method in creating free-standing functional composite films or membranes.

Ionic Liquid Crystal-Polymer Composite Electromechanical Actuators: Design of Two-Dimensional Molecular Assemblies for Efficient Ion Transport and Effect of Electrodes on Actuator Performance.

We present the development of free-standing ionic liquid crystal-polymer composite electrolyte films aimed at achieving high-frequency response electromechanical actuators. Our approach entails designing novel layered ionic liquid-crystalline (LC) assemblies by complexing a mesomorphic dimethylphosphate with either a lithium salt or a room-temperature ionic liquid through the formation of ion-dipole interactions or hydrogen bonds. These electrolytes, exhibiting room-temperature ionic conductivities on the order of 10-4 S cm-1 and wide LC temperature ranges up to 77 °C, were successfully integrated into porous polymer networks. We systematically investigated the impact of ions and electrodes on the performance of ionic electroactive actuators. Specifically, the Li+-based liquid crystal-polymer composite actuator with PEDOT:PSS electrodes demonstrated the highest bending deformation, achieving a strain of 0.68% and exhibiting a broad frequency response up to 110 Hz, with a peak-to-peak displacement of 3 μm. In contrast, the ionic-liquid-based liquid crystal-polymer composite actuator with active carbon electrodes showcased a bending response at a maximum frequency of 50 Hz and a force generation of 0.48 mN, without exhibiting the back relaxation phenomenon. These findings offer valuable insights for advancing high-performance electromechanical systems with applications ranging from soft robotics to haptic interfaces.

Superhydrophobic, flexible and high thermal stable ANFs/CNTs film for controllable light driven actuators

Superhydrophobic and light-responsive actuators (SLRAs) can be driven to move on water surface remotely and in a non-contact manner, and have shown promising applications in soft robotics, environmental protection, etc. It remains a big challenge to develop high performance SLRAs with excellent thermal stability, fast light responsivity and controllable motion. Here, we propose a layer-by-layer vacuum filtration method to prepare flexible, freestanding and superhydrophobic composite films composed of alternately deposited oleylamine modified acid carbon nanotubes (O-ACNTs) and aramid nanofibers (ANFs). The composite film has excellent thermal stability with the maximum weight loss rate temperature as high as 520 ℃. The closely packed structure and strong interlayer interaction ensure the surface stability and durability of the composite film. The composite film possesses excellent photothermal conversion performance, and can maintain the structure integrity without deformation when its surface temperature reaches 208 °C. When used as a self-propelled actuator, the SLRA film can response to the light quickly and move on the water surface, and the motion speed and direction can be controlled by adjusting the irradiation intensity and position. The outstanding thermal stability guarantees the stability and reliability of the self-propelled motions. The present study opens a new avenue to design high performance SLRAs.

Utilization of Physical Anisotropy in Metal-Organic Frameworks via Post-Synthetic Alignment Control with Liquid Crystal.

Metal-organic frameworks (MOFs) represent crystalline materials constructed from combinations of metal and organic units to often yield anisotropic porous structures and physical properties. Postsynthetic methods to align the MOF crystals in bulk remain scarce yet tremendously important to fully utilize their structure-driven intrinsic properties. Herein, we present an unprecedented composite of liquid crystals (LCs) and MOFs and demonstrate the use of nematic LCs to dynamically control the orientation of MOF crystals with exceptional order parameters (as high as 0.965). Unique patterns formed through a facile multidirectional alignment of MOF crystals exhibit polarized fluorescence with the fluorescence intensity of a pattern dependent on the angle of a polarizer, offering potential use in various optical applications such as an optical security label. Further, the alignment mechanism indicates that the method is applicable to numerous combinations of MOFs and LCs, which include UV polymerizable LC monomers used to fabricate free-standing composite films.

Dual-emitting cellulose nanocrystal hybrid materials with circularly polarized luminescence for anti-counterfeiting labels

Cellulose nanocrystal (CNC) hybrid materials with numerous optical states have great potential as anti-counterfeiting labels and information encryption materials. However, it is challenging to construct multicolor emitting materials with tunable behaviors, which can dramatically enhance anti-counterfeiting abilities. Here, free-standing composite films with vivid multi-structural colors and dual-emitting fluorescence are successfully fabricated through a host-guest coassembly strategy. The lanthanide complex and an aggregation-induced emission molecule (tetraphenylethylene derivative, TPEC) are selected as luminescent guests, which are integrated into the chiral nematic structure of CNCs. The obtained photonic films display broadband reflection across the visible spectrum, which may be attributed to the chiral nematic domains with variations in the helical pitches and helical axis orientations. Under 254 nm excitation, the film exhibits bright red emission, while blue–green emission switching occurs under 365 nm excitation. The broad reflection band of the film covers both the green and red fluorescent emission centers, and right circularly polarized luminescence emission with different dissymmetry factors is produced due to the selective reflection of the left chiral nematic structure. A large glum value up to −0.21 at 600 nm was realized. Additionally, CNC-based materials with tailored shapes are further used in anti-counterfeit tags and decorative applications.

Free-Standing Li4Ti5O12/Carbon Nanotube Electrodes for Flexible Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been used in many fields, such as consumer electronics and automotive and grid storage, and its applications continue to expand. Several studies have attempted to improve the performance of LIBs. In particular, the use of high-capacity silicon and tin as anodes has been widely studied. Although anodes composed of silicone and tin have high theoretical capacities, poor electrical conductivity and considerable volume expansion of such anodes deteriorate the LIB performance. Thus, Li4Ti5O12 (LTO), a zero-strain material, has attracted much attention with high cycle stability and rate capability through improved electrical conductivity. However, LTO has the disadvantages of a low electrical conductivity (10−8 to 10−13 S cm−1) and moderate Li+ ion diffusion coefficient (10−9 to 10−16 cm2 s−1). In this study, the flexible and free-standing composite films were fabricated using only LTO and multi-walled carbon nanotube(CNT) with high electrical conductivity and ion diffusivity. The prepared LTO/CNT films showed a higher charge/discharge capacity than the theoretical capacity of the LTO electrode.

Sequential electrodeposition fabrication of graphene/polyaniline/MnO2 ternary supercapacitor electrodes with high rate capability and cyclic stability

The incorporation of various capacitive materials to fabricate multi-component electrodes has emerged as a feasible methodology toward high-performance supercapacitors. In this paper, a facile two-step electrodeposition method is proposed to construct polyaniline (PANI)/MnO2 hybrid nanostructure on reduced graphene oxide (RGO) matrix for the ternary supercapacitor electrodes. By the sequential potentiostatic methods, PANI is first electropolymerized on RGO hydrogel films before MnO2 granules are electrodeposited on the RGO/PANI conductive substrates to obtain the free-standing composite films. The resulting RGO/PANI/MnO2 ternary composite electrodes present significantly promoted capacitive properties compared with the binary RGO/PANI electrodes. Particularly, the optimized electrode and corresponding all-solid-state device could achieve the high specific capacitances of 942.6 and 205.0 F g–1 at 1 A g–1 with superb capacitance retention of 86.4% and 80.3% at 30 A g–1, respectively. The device delivers a maximum energy density of 41.0 Wh kg–1 and demonstrates outstanding capacitance holdings of 96.1% after 10,000 cycles at 30 A g−1, 87.8% after 5000 cycles at 10 A g−1, and 82.5% after 3000 cycles at 5 A g−1, respectively. The prominent electrochemical performances of the ternary composite can be ascribed to the fact that graphene supplies the conductive matrix to immobilize the active pseudocapacitive constituents, while PANI and MnO2 can compensate each other to surmount the disadvantages of inferior conductivity or stability.

Interlayer and intralayer co-modified flexible V2CTX MXene@SWCNT films for high-power Li-ion capacitors

As an emerging member of the two-dimensional (2D) material family, V2CTX MXene shows great potential in the application of lithium-ion capacitors (LICs) due to its unique structure and excellent electrical conductivity. However, severe nanosheets stacking and intra-layer transport barriers have limited the further development of V2CTX MXene-based materials. Herein, we prepared K+ ions and –O functional group co-modified V2CTX MXene (VCT-K) and further incorporated it with single-walled carbon nanotube (SWCNT), obtaining freestanding V2CTX composite films (VCT-K@C) with the 3D conductive network. Significantly, K+ ions were introduced into V2CTX MXene to stabilize the interlayer structure and prevent the aggregation of nanosheets, the terminal group of –O was controllably modified on the surface of MXene to improve the Li+ ions storage reversible capacities and the SWCNT acted as the bridge between MXene nanosheets to opens up the channels for ion/electron transportation in the longitudinal direction. Benefited from the synergistic effect of VCT-K and SWCNT, the VCT-K@C exhibits superior reversible specific capacities of 671.8 mA h g−1 at 0.1 A g−1 and 318 mA h g−1 at 1.0 A g−1. Furthermore, the assembled LICs with VCT-K@C anode coupling activated carbon (AC) cathode deliver an outstanding power density of 19.0 kW kg−1 at 67.4 Wh kg−1, a high energy density of 140.5 Wh kg−1 at 94.8 W kg−1 and a stable capacitance retention of 86% after 6000 cycles at 10 A g−1. Such unique structures and excellent electrochemical properties are expected to pave the way for the large-scale application in LICs of MXene-based materials.

High Energy Storage Density in Nanocomposites of P(VDF-TrFE-CFE) Terpolymer and BaZr0.2Ti0.8O3 Nanoparticles.

Polymer materials are actively used in dielectric capacitors, in particular for energy storage applications. An enhancement of the stored energy density can be achieved in composites of electroactive polymers and dielectric inorganic fillers with a high dielectric permittivity. In this article, we report on the energy storage characteristics of composites of relaxor terpolymer P(VDF-TrFE-CFE) and BaZr0.2Ti0.8O3 (BZT) nanoparticles. The choice of materials was dictated by their large dielectric permittivity in the vicinity of room temperature. Free-standing composite films, with BZT contents up to 5 vol.%, were prepared by solution casting. The dielectric properties of the composites were investigated over a wide range of frequencies and temperatures. It was shown that the addition of the BZT nanoparticles does not affect the relaxor behavior of the polymer matrix, but significantly increases the dielectric permittivity. The energy storage parameters were estimated from the analysis of the unipolar polarization hysteresis loops. The addition of the BZT filler resulted in the increasing discharge energy density. The best results were achieved for composites with 1.25–2.5 vol.% of BZT. In the range of electric fields to 150 MV/m, the obtained materials demonstrate a superior energy storage density compared to other P(VDF-TFE-CFE) based composites reported in the literature.

Electrospun Ti3C2T x MXene and silicon embedded in carbon nanofibers for lithium-ion batteries

In spite of outstanding theoretical specific capacity (∼3590 mAh g−1), huge volume change during lithiation/delithiation and poor conductivity hinder the practical applications of pure Si anodes for lithium ion batteries (LIBs), requiring conductive additives and porous architectures. In this work, flexible and freestanding composite films made of two-dimensional Ti3C2T x MXene nanosheets and silicon particles embedded in carbon nanofiber (denoted as Ti3C2T x -Si@CNF) were prepared via electrospinning and used as LIB anodes. This new electrode design provides a 3D network architecture and high conductivity favorable for good electrochemical performance and long cycle life. Ti3C2T x -Si@CNF electrodes, containing 28% silicon retained high specific capacity of ∼1580 mAh g−1 after 100 cycles at 0.1 A g−1 and 720 mAh g−1 after 1000 cycles at 1 A g−1, and delivered a great rate performance with 289 mAh g−1 at a current density of 5 A g−1. This is a significantly enhanced performance compared with Si particles embedded in CNF without Ti3C2T x (denoted Si@CNF). This work proposes a scalable manufacturing strategy for developing high-performance silicon-based anodes, overcoming the low conductivity and volume expansion issues.

Durable Biopolymer Films From Lignin-Carbohydrate Complex Derived From a Pulp Mill Side Stream

Valorization of side streams offers novel types of raw materials to complement or replace synthetic and food-based alternatives in materials science, increasing profitability and decreasing the environmental impacts of biorefineries. Lignocellulose biomass contains lignin and carbohydrates that are covalently linked into lignin-carbohydrate complexes (LCCs). In biomass fractionation processes, these complexes are conventionally considered as waste, which hinders the biomass fractionation process, and they may solubilize into aqueous effluents. This study presents how LCCs, derived from pulp mill effluent, can be turned into valuable biopolymers for industrial polymer film applications. Free-standing composite films containing hydroxyethyl cellulose (HEC) and LCCs with varying molar mass, charge density and lignin/hemicellulose ratio were prepared to study the effect of LCC amount on mechanical properties and oxygen permeability. Increasing the LCC content increased the yield point and Young’s modulus of the films. Breaking strain measurements revealed a non-linear correlation with the LCC concentration for the samples with higher lignin than hemicellulose content. The addition of LCC enhanced oxygen barrier properties of HEC films significantly even at high relative humidity. The present research demonstrates how a currently underutilized fraction of the biorefinery side stream has the potential to be valorized as a biopolymer in industrial applications, for example as a barrier film for paper and board packaging.

Free-Standing Composite Films Based on Thiol-Ene and PEDOT: PSS Layers for Optoelectronic Applications.

Free-standing composite films were fabricated by combining the plane parallel layers of thiol-ene based on pentaerythritol tetrakis(3-mercaptopropionate)-1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (PETMP-TTT) UV curable polymer and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) conductive polymer. A systematic analysis was performed with the focus on mechanical performance of the free-standing composite films. The PEDOT:PSS/PETMP-TTT composite exhibited higher values of adhesion force compared to the free-standing PETMP-TTT film due to hydrophilic nature of the PEDOT:PSS layer. The composite was found to be highly transparent in the range of 380–800 nm. The Young’s modulus and tensile strength of PETMP-TTT were found to be 3.6 ± 0.4 GPa and 19 ± 3 MPa, while for PEDOT:PSS/PETMP-TTT to be 3.5 ± 0.3 GPa and 20 ± 3 MPa, respectively. The sheet resistance values of the PEDOT:PSS layer in the composite film were found to be highly stable after a number of bending iterations with slight increase in sheet resistance from 108 to 118 ± 2 Ω/□. The resultant PEDOT:PSS/PETMP-TTT composite can be further used in optoelectronic applications.

Cellulose Based Photonic Materials Displaying Direction Modulated Photoluminescence.

Photonic materials featuring simultaneous iridescence and light emission are an attractive alternative for designing novel optical devices. The luminescence study of a new optical material that integrates light emission and iridescence through liquid crystal self-assembly of cellulose nanocrystal-template silica approach is herein presented. These materials containing Rhodamine 6G were obtained as freestanding composite films with a chiral nematic organization. The scanning electron microscopy confirms that the cellulose nanocrystal film structure comprises multi-domain Bragg reflectors and the optical properties of these films can be tuned through changes in the relative content of silica/cellulose nanocrystals. Moreover, the incorporation of the light-emitting compound allows a complementary control of the optical properties. Overall, such findings demonstrated that the photonic structure plays the role of direction-dependent inner-filter, causing selective suppression of the light emitted with angle-dependent detection.

Biomimetic Approach to Facilitate the High Filler Content in Free-Standing and Flexible Thermoelectric Polymer Composite Films Based on PVDF and Ag2Se Nanowires

A high filler content is often needed in polymer composite-based thermoelectric (TE) films to improve their performance. Nevertheless, this often leads to poor processability and poor mechanical performance. Herein, a biomimetic approach is adopted to facilitate the filler content up to 90.5 wt % in free-standing and flexible n-type PVDF/Ag2Se TE films, where PVDF dendricolloids are a solution mixed with Ag2Se nanowires (NWs), followed by filtration. These soft dendric nanoparticles within PVDF dendricolloids have high adhesivity and strong network-building ability, which allows the formation of "grapevine-grape"-like networks with soft dendritic particles and inorganic TE fillers as "grapevine" and "manicure finger grapes", respectively. The maximum power factor of 189.02 μW m-1 K-2 is achieved for a PVDF/Ag2Se mass ratio of 1:9.5 at 300 K. Meanwhile, excellent flexibility with only 15.8% decrease in electrical conductivity after 1000 bending cycles was observed. These properties at such a high filler content are attributed to the long-range grapevine-like network of soft PVDF dendritic particles and entanglement between numerous Ag2Se NWs. This work carves a path to fabricate high-performance free-standing flexible n-type TE composite films as well as other functional polymer composites requiring high inorganic filler loading.

Modulating transparency and colour of cellulose nanocrystal composite films by varying polymer molecular weight

HypothesisCellulose nanocrystals (CNC) can produce photonic composite films that selectively reflect light based on their periodic cholesteric structure. The hypothesis of this research is that by incorporating water-soluble polymer, photonic properties of CNC composite film can be designed by manipulating the polymer molecular weight. ExperimentalFlexible free-standing composite films of five different poly (ethylene glycol) (PEG) molecular weights were prepared via air drying under a controlled environment, and characterised by reflectance UV–vis spectrometer, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Films with each molecular weight were investigated over a concentration range. FindingsThe colour and transmission haze of the composite films was modified by varying both the PEG molecular weight and concentration. Depending on the molecular weight, the films were able to reflect light from the UV region (242 nm) across the visible spectrum to the near-infrared region (832 nm). Different trends in variation of the reflected light based on the molecular weight was found with increasing PEG concentration and was explained by weak depletion interactions occurring between CNC and PEG, which was reduced with increasing PEG molecular weight.

Free-standing three-dimensional carbon nanotubes/amorphous MnO2 cathodes for aqueous zinc-ion batteries with superior rate performance

Rechargeable aqueous zinc-ion batteries (ZIBs) have gained particular attention in recent years because of their low cost and high safety. However, most of their performances are limited by unsatisfied architecture of cathodes. In addition, the degree of crystallinity of active materials also plays an important role in their electrochemical performance. Herein, we fabricated free-standing composite films with amorphous MnO2 (a-MnO2) and carbon nanotubes (CNTs) by an in situ deposition method. The free-standing a-MnO2@CNTs composite films can directly serve as the cathodes of ZIBs without binder and current collector. The resultant cathode exhibits highly electrical conductivity and fast ion-diffusion because of the corporation of interconnected three-dimensional CNTs architectures and ultra-thin a-MnO2 nanosheets. As a result, the resultant ZIB displays high energy and power density, as well as stable cycling performance. Moreover, based on composite films, flexible ZIBs were constructed, and they could remain stable electrochemical performance under different bending states, which have great potential for the application in flexible and wearable electronics.

Freestanding α-zirconium phosphate based nacre-like composite films cast from water

Freestanding nacre-like composite films based on alpha-Zirconium phosphate (α-ZrP) and poly(etheramine) were prepared by casting from water. The α-ZrP nanoplatelets self-assemble and organise to produce a unidirectional nanoplatelet layered structure with the poly(etheramine) acting as both an exfoliating agent and binder for neighbouring nanoplatelets. The terminal amine binds to the α-ZrP through a cationic exchange reaction and once ionically bound, the hydrophobic polyether chain repels the adjacent α-ZrP sheet aiding effective exfoliation. Consequently, the spacing between nanoplatelets increases with increasing poly(etheramine) content. The resultant nacre-like structures can dissipate energy via different mechanisms such that when under tensile or compressive loading significant increases in mechanical properties are possible. Several mechanical property improvements (with respect to the 95:5 composition) were achieved, including a 44- and 200-fold increase in reduced Young’s modulus (Er) and Hardness (H) (from nanoindentation measurements) and, 341% in tensile modulus E, (83:17), 572% in tensile strength σ, (77:23), 707% in maximum strain ε (71:29) and 3981% in tensile toughness UT, (71:29) (from tensile testing). The barrier performance, to water vapour, of these freestanding nacre-like films per unit thickness was comparable to several polymers, such as EVOH, Nylon 6,6 and poly(lactic acid)(PLA).

Freestanding Photoresist Film: A Versatile Template for Three‐Dimensional Micro‐ and Nanofabrication

AbstractUltrathin freestanding films with well‐defined micro/nanostructures and robust mechanical properties are applied in many engineering applications including microelectronics, optics, filtration and separation, biomedical engineering, and nanotechnology. Although considerable efforts have been made toward the fabrication of freestanding thin films, it is still a significant challenge to develop a simple and reliable process for producing freestanding films with ultrathin thickness, well‐regulated micro/nanopatterns, robust mechanical properties, macroscopic coverage area, and multi‐layered composite structures. Here, a significant advancement is reported in this regard. This study shows a new sacrificial‐layer‐free (SLF) lifting‐off process, integrated with conventional micro‐ and nanolithography, enabling the release of micro‐ and nanopatterned photoresist (PR) films from the supporting substrate with unprecedented pattern coverage and structure characteristics. The freestanding PR film is resilient, can withstand significant bending and deformation, and is sufficiently flexible to be transferred onto substrates with 3D topography as a conformal soft stencil for further technological processing and applications. Moreover, the SLF lifting‐off process provides a simple approach to prepare single‐layered and multi‐layered freestanding composite films. The results suggest that the novel SLF lifting‐off process can significantly extend the capability of 3D micro‐/nanofabrication.

Cellulose Nanocrystal and Water-Soluble Cellulose Derivative Based Electromechanical Bending Actuators.

This study reports a versatile method for the development of cellulose nanocrystals (CNCs) and water-soluble cellulose derivatives (methyl cellulose (MC), hydroxypropyl cellulose (HPC), and sodium carboxymethyl cellulose (NaCMC)) films comprising the ionic liquid (IL) 2-hydroxy-ethyl-trimethylammonium dihydrogen phosphate ([Ch][DHP]) for actuator fabrication. The influence of the IL content on the morphology and physico–chemical properties of free-standing composite films was evaluated. Independently of the cellulose derivative, the ductility of the films increases upon [Ch][DHP] incorporation to yield elongation at break values of nearly 15%. An increase on the electrical conductivity as a result of the IL incorporation into cellulosic matrices is found. The actuator performance of composites was evaluated, NaCMC/[Ch][DHP] showing the maximum displacement along the x-axis of 9 mm at 8 Vpp. Based on the obtained high electromechanical actuation performance, together with their simple processability and renewable nature, the materials fabricated here represent a step forward in the development of sustainable soft actuators of high practical relevance.

Free-standing composite films of multiple 2D nanosheets: Synergetic photothermocatalysis/photocatalysis for efficient removal of formaldehyde under ambient condition

Thermocatalysis and photocatalysis have been widely investigated to removal of volatile organic compounds (VOCs). However, thermocatalysis needs high-temperature to activate oxygen species, therefore resulting in additional energy consumption. Meanwhile, photocatalysis suffers the rapid charge recombination and the slow surface process. Herein, we combined thermocatalysis and photocatalysis into a free-standing composite film catalyst that was prepared through a facile filtration method using two-dimensional graphene oxide (GO), manganese oxide (MnOx) and polymeric carbon nitride (CN) nanosheets as building blocks. The superior photothermal effect of GO rapidly enhanced the film temperature to ~85 °C, and then initiated the MnOx thermocatalysis. Furthermore, the increased temperature also promoted the charge diffusion and the surface reaction process of CN photocatalyst. Impressively, with the synergetic photothermocatalysis and photocatalysis, this composite film catalyst presented improved performance for catalytic oxidation of gaseous formaldehyde at ambient condition under xenon light irradiation, compared with the individual thermocatalyst and photocatalyst, as well as the photothermocatalyst. In addition, cycling experiments demonstrated the film catalyst possessed good durability. This investigation associates photothermocatalysis with photocatalysis for improving formaldehyde catalytic degradation, hopefully providing a new and efficient strategy not only for VOCs removal, but also for other catalytic applications.