Developing a Novel Terahertz Fabry-Perot Microcavity Biosensor by Incorporating Porous Film for Yeast Sensing.

We present a novel terahertz (THz) Fabry-Perot (FP) microcavity biosensor that uses a porous polytetrafluoroethylene (PTFE) supporting film to improve microorganism detection. The THz FP microcavity confines and enhances fields in the middle of the cavity, where the target microbial film is placed with the aid of a PTFE film having a dielectric constant close to unity in the THz range. The resonant frequency shift increased linearly with increasing amount of yeasts, without showing saturation behavior under our experimental conditions. These results agree well with finite-difference time-domain (FDTD) simulations. The sensor's sensitivity was 11.7 GHz/µm, close to the optimal condition of 12.5 GHz/µm, when yeast was placed at the cavity's center, but no frequency shift was observed when the yeast was coated on the mirror side. We derived an explicit relation for the frequency shift as a function of the index, amount, and location of the substances that is consistent with the electric field distribution across the cavity. We also produced THz transmission images of yeast-coated PTFE, mapping the frequency shift of the FP resonance and revealing the spatial distribution of yeast.

Reliability Characteristics of Metal-Insulator-Semiconductor Capacitors with Low-Dielectric-Constant Materials.

In this study, the reliability characteristics of metal-insulator-semiconductor (MIS) capacitor structures with low-dielectric-constant (low-k) materials have been investigated in terms of metal gate area and geometry and thickness of dielectric film effects. Two low-k materials, dense and porous low-k films, were used. Experimental results indicated that the porous low-k films had shorter breakdown times, lower Weibull slope parameters and electric field acceleration factors, and weaker thickness-dependence breakdowns compared to the dense low-k films. Additionally, a larger derivation in dielectric breakdown projection model and a single Weilbull plot of the breakdown time distributions from various areas merging was observed. This study also pointed out that the porous low-k film in the irregular-shaped metal gate MIS capacitor had a larger dielectric breakdown time than that in the square- and circle-shaped samples, which violates the trend of the sustained electric field. As a result, another breakdown mechanism exists in the irregular-shaped sample, which is required to explore in the future work.

Site-Selective Synthesis and Concurrent Immobilization of Imine-Based Covalent Organic Frameworks on Electrodes Using an Electrogenerated Acid.

Imine-based covalent organic frameworks (COFs) are crystalline porous materials with prospective uses in various devices. However, general bulk synthetic methods usually produce COFs as powders that are insoluble in most of the common organic solvents, arising challenges for the subsequent molding and fixing of these materials on substrates. Here, we report a novel synthetic methodology that utilizes an electrogenerated acid (EGA), which is produced at an electrode surface by electrochemical oxidation of a suitable precursor, acting as an effective Brønsted acid catalyst for imine bond formation from the corresponding amine and aldehyde monomers. Simultaneously, it provides the corresponding COF film deposited on the electrode surface. The COF structures obtained with this method exhibited high crystallinities and porosities, and the film thickness could be controlled. Furthermore, such process was applied for the synthesis of various imine-based COFs, including a three-dimensional (3D) COF structure.

Flexible core/shelled PPy@PANI nanotube porous films for hybrid supercapacitors.

Flexibility of the films and the limited ion transport in the vertical direction of film highly restrict the development of flexible supercapacitors. Herein, we have developed hybrid porous films consisting of N-doped holey graphene nanosheets (NHGR) with abundant in-plane nanopores and the vertically aligned polyaniline nanowires arrays on polypyrrole nanotubes (PPy@PANI) via a two-step oxidative polymerization strategy and vacuum filtration. The rational design can efficiently shorten the diffusion path of electrons/ions, alleviate volume variation of electrodes during cycling, enhance electric conductivity of the hybrids, and while offer abundant active interfacial sites for electrochemical reaction. Benefiting from the distinctive structural and compositional merits, the obtained PPy@PANI/NHGR film electrode manifests an excellent electrochemical properties in terms of specific capacity (1348 mF cm-2at a current density of 1 mA cm-2), rate capability (81.2% capacitance retention from 1 to 30 mA cm-2), and cycling stability (capacitance retention of 73.7% at 20 mA cm-2after 7000 cycles). Matched with NHGR negative electrode, the assembled flexible all-solid-state asymmetric supercapacitor displays a remarkable areal capacitance of 359 mF cm-2at 5 mA cm-2, maximum areal energy density of 112.2µWh cm-2at 3.747 mW cm-2, and good flexibility at various bending angles while preserving stable cycling performance. The result shows the PPy@PANI/NHGR film with high flexibility and 3D ions transport channels is highly attractive for flexible energy storage devices.

Thermally Reduced Graphene/MXene Film for Enhanced Li-ion Storage.

Two-dimensional transition-metal carbides called MXenes are emerging electrode materials for energy storage due to their metallic electrical conductivity and low ion diffusion barrier. In this work, we combined Ti2 CTx MXene with graphene oxide (GO) followed by a thermal treatment to fabricate flexible rGO/Ti2 CTr film, in which electrochemically active rGO and Ti2 CTr nanosheets impede the stacking of layers and synergistically interact producing ionically and electronically conducting electrodes. The effect of the thermal treatment on the electrochemical performance of Ti2 CTx is evaluated. As anode for Li-ion storage, the thermally treated Ti2 CTr possesses a higher capacity in comparison to as-prepared Ti2 CTx . The freestanding hybrid rGO/Ti2 CTr films exhibit excellent reversible capacity (700 mAh g-1 at 0.1 Ag-1 ), cycling stability and rate performance. Additionally, flexible rGO/Ti3 C2 Tr films are made using the same method and also present improved capacity. Therefore, this study provides a simple, yet effective, approach to combine rGO with different MXenes, which can enhance their electrochemical properties for Li-ion batteries.

Sodium alginate/ager colourimetric film on porous substrate layer: Potential in intelligent food packaging.

Colourimetric indicators have potential applications in monitoring food freshness and offer a simple, rapid, effective, and economical approach. Blending sodium alginate (SA) with agar (AG), an ideal choice for solid substrates in colourimetric indicators, can modify mechanical compliance and optical properties. However, the limitations in the water-sustaining capacity and dye migration of hydrogel substrates significantly impede the scalability and commercial application of these indicators. In this study, we designed and prepared a bilayer-structured indicator featuring an SA/AG colourimetric film on a porous Polypropylene fluoride (PVDF)/SiO2 encapsulation film. This design aims to enhance the water-sustaining capacity and reduce dye migration from the SA/AG colourimetric film. The PVDF/SiO2 composite film was prepared using a peeling-assisted phase-conversion process, which enabled the indicator to selectively allow gas, but not water, to pass through its porous substrate. Furthermore, we tested the layered indicator film by monitoring changes in shrimp freshness. The results revealed significant and distinguishable colour changes in the indicators corresponding to the freshness and spoilage of the shrimp.

Thermal-Rectified Gradient Porous Polymeric Film for Solar-Thermal Regulatory Cooling.

Solar-thermal regulation concerning thermal insulation and solar modulation is pivotal for cooling textiles and smart buildings. Nevertheless, a contradiction arises in balancing the demand to prevent external heat infiltration with the efficient dissipation of excess heat from enclosed spaces. Here, a concentration-gradient polymerization strategy is presented for fabricating a gradient porous polymeric film comprising interconnected polymeric microspheres. This method involves establishing an electric field-driven gradient distribution of charged crosslinkers in the precursor solution, followed by subsequent polymerization and freeze-drying processes. The resulting porous film exhibits a significant porosity gradient along its thickness, leading to exceptional unidirectional thermal insulation capabilities with a thermal rectification factor of 21%. The gradient porous film, with its thermal rectification properties, effectively reconciles the conflicting demands of diverse thermal conductivity for cooling unheated and spontaneously heated enclosed spaces. Consequently, the gradient porous film demonstrates remarkable enhancements in solar-thermal management, achieving temperature reductions of 3.0 and 4.1 °C for unheated and spontaneously heated enclosed spaces, respectively, compared to uniform porous films. The developed gradient-structured porous film thus holds promise for the development of thermal-rectified materials tailored to regulate solar-thermal conditions within enclosed environments.

Preparation of ZnO Nanosheet Array and Research on ZnO/PANI/ZnO Ultraviolet Photodetector.

High-performance ultraviolet photodetectors have important scientific research significance and practical application value, which has been the focus of researchers. In this work, we have constructed a highly photosensitive UV photodetector with a unique "sandwich" structure, which was mainly composed of two layers of ZnO nanosheet arrays and one layer of polyaniline (PANI). The results showed that the UV current of ZnO/PANI devices was 100 times higher than that of pure ZnO devices under the same UV irradiation time. At a 365 nm wavelength, the device had excellent photocurrent responsiveness and photoconductivity. This high performance was attributed to the large specific surface area of ZnO nanosheets and the p-n junction formed between P-type PANI nano-porous film and N-type ZnO nanosheets. This provides a solid theoretical basis for the application of ZnO nanosheets in ultraviolet detection, and possesses significance for the development of ultraviolet photodetectors.

A Comparison between Porous to Fully Dense Electrodeposited CuNi Films: Insights on Electrochemical Performance.

Nanostructuring of metals is nowadays considered as a promising strategy towards the development of materials with enhanced electrochemical performance. Porous and fully dense CuNi films were electrodeposited on a Cu plate by electrodeposition in view of their application as electrocatalytic materials for the hydrogen evolution reaction (HER). Porous CuNi film were synthesized using the hydrogen bubble template electrodeposition method in an acidic electrolyte, while fully dense CuNi were electrodeposited from a citrate-sulphate bath with the addition of saccharine as a grain refiner. The prepared films were characterized chemically and morphologically by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The Rietveld analysis of the XRD data illustrates that both CuNi films have a nanosized crystallite size. Contact angle measurements reveal that the porous CuNi film exhibits remarkable superhydrophobic behavior, and fully dense CuNi film shows hydrophilicity. This is predominately ascribed to the surface roughness of the two films. The HER activity of the two prepared CuNi films were investigated in 1 M KOH solution at room temperature by polarization measurements and electrochemical impedance spectroscopy (EIS) technique. Porous CuNi exhibits an enhanced catalysis for HER with respect to fully dense CuNi. The HER kinetics for porous film is processed by the Volmer-Heyrovsky reaction, whereas the fully dense counterpart is Volmer-limited. This study presents a clear comparison of HER behavior between porous and fully dense CuNi films.

Controlling the structure of spin-coated multilayer ethylcellulose/hydroxypropylcellulose films for drug release.

Porous phase-separated ethylcellulose/hydroxypropylcellulose (EC/HPC) films are used to control drug transport out of pharmaceutical pellets. Water-soluble HPC leaches out and forms a porous structure that controls the drug transport. Industrially, the pellets are coated using a fluidized bed spraying device, and a layered film exhibiting varying porosity and structure after leaching is obtained. A detailed understanding of the formation of the multilayered, phase-separated structure during production is lacking. Here, we have investigated multilayered EC/HPC films produced by sequential spin-coating, which was used to mimic the industrial process. The effects of EC/HPC ratio and spin speed on the multilayer film formation and structure were investigated using advanced microscopy techniques and image analysis. Cahn-Hilliard simulations were performed to analyze the mixing behavior. A gradient with larger structures close to the substrate surface and smaller structures close to the air surface was formed due to coarsening of the layers already coated during successive deposition cycles. The porosity of the multilayer film was found to vary with both EC/HPC ratio and spin speed. Simulation of the mixing behavior and in situ characterization of the structure evolution showed that the origin of the discontinuities and multilayer structure can be explained by the non-mixing of the layers.

Biodegradable Mulching Films Based on Polycaprolactone and Its Porous Structure Construction.

Polycaprolactone (PCL) is one of the promising linear aliphatic polyesters which can be used as mulching film. Although it has suitable glass transition temperature and good biodegradability, further practical applications are restricted by the limited temperature-increasing and moisturizing properties. The rational design of the PCL structure is a good strategy to enhance the related properties. In this study, thermally-induced phase separation (TIPS) was introduced to fabricate a PCL nanoporous thin film. The introduction of a nanoporous structure on the PCL surface (np-PCL) exhibited enhanced temperature-increasing and moisturizing properties when used as mulch film. In detail, the average soil temperature of np-PCL was increased to 17.81 °C, when compared with common PCL of 17.42 °C and PBAT of 17.50 °C, and approaches to PE of 18.02 °C. In terms of water vapor transmission rate, the value for np-PCL is 637 gm-2day-1, which was much less than the common PCL of 786 and PBAT of 890 gm-2day-1. As a result, the weed biomass under the np-PCL was suppressed to be 0.35 kg m-2, almost half of the common PCL and PBAT. In addition, the np-PCL shows good thermal stability with an onset decomposition temperature of 295 °C. The degradation mechanism and rate of the np-PCL in different pH environments were also studied to explore the influence of nanoporous structure. This work highlights the importance of the nanoporous structure in PCL to enhance the temperature-increasing and moisturizing properties of PCL-based biodegradable mulching film.

Characterization and application of porous polylactic acid films prepared by nonsolvent-induced phase separation method.

Nonsolvent-induced phase separation (NIPS) method was employed to prepare polylactic acid (PLA) films using N-methyl-2-pyrrolidone (NMP) as a nonsolvent. The morphology and structure of PLA films were characterized, and the application of the films in pork preservation was investigated. When 10 wt% NMP was added, film with uniform porous structures was obtained. The crystalline and Fourier-transform infrared spectra analyses indicated that the addition of NMP during the preparation of PLA films caused their crystalline properties to change, but had no effect on their composition. However, the 10 wt% NMP/PLA film had improved thermal stability, water vapor transmission and oxygen permeability. The results on the changes in pH, total volatile basic nitrogen content and total viable counts of pork during refrigerated storage indicated that the 10 wt% NMP/PLA film could more effectively extend the shelf life of pork than polyethylene film. This work demonstrates the potential of the porous PLA film in pork packaging.

Ultrapermeable and Wet-Adhesive Monolayer Porous Film for Stretchable Epidermal Electrode.

Noninvasive electrophysiological signal monitoring is significant for health care and scientific research. The simultaneous achievement of wet adhesion, stretchability, breathability, and low contact impedance is highly recommended in the epidermal electrode but still challenging. In this work, a monolayer porous film electrode with a pore size and wall thickness of less than ∼10 µm is fabricated via the breath figure method (BFM) and metal sputtering, and it was subsequently applied using epidermal electrophysiological monitoring. The ultrahigh permeability is comparable to the naked skin because the through holes of the monolayer porous film match well with the pores on human skin. The stretchability of 50% is realized with the combination of Au microcrack and the monolayer porous structure. The wet adhesion of 0.17 N/cm is established on the chemical bonding between the electrode and the epidermis. The contact impedance is comparable with the gold standard Ag/AgCl gel electrode, especially after sweating. Stable and precise electrophysiological signals are measured. Especially, the perspiration resistance of the monolayer porous film outperforms that of the gel electrode. The monolayer porous structure provides a new avenue to improve the breathability of the epidermal electronics.

Mesoporous WS2/MoO3 Hybrids for High-Performance Trace Ammonia Detection.

Mesoporous WS2/MoO3 hybrids were synthesized by a facile two-step and additive-free hydrothermal approach and employed for high-performance trace ammonia gas (NH3) detection. Compared with single WS2 and MoO3 counterparts, WS2/MoO3 sensors exhibited an improvement in NH3-sensing performance at room temperature (22 ± 3 °C). Typically, the optimal WS2/MoO3 sensor showed a higher and quicker response of 31.58% within 57 s toward 3 ppm of NH3, which was 17.7- and 57.4-fold larger than that of pure MoO3 (1.78% within 251 s) and WS2 (0.55% within 153 s) ones. Meanwhile, good reversibility, sensitivity, and selectivity, reliable long-term stability, and the lowest detection limit of 9.0 ppb were achieved. These superior properties were probably ascribed to numerous heterojunctions favorable for additional carrier-concentration modulation via the synergetic effect between WS2 and MoO3 components and the large specific surface area beneficial for richer sorption sites and faster molecular transfer at room temperature. Such achievements also imply that the designed WS2/MoO3 heterostructure nanomaterials have the potential in achieving trace NH3 recognition catering for the requirements of high sensitivity and low power consumption in future gas sensors.

Modified Breath Figure Methods for the Pore-Selective Functionalization of Honeycomb-Patterned Porous Polymer Films.

Recent developments in the field of the breath figure (BF) method have led to renewed interest from researchers in the pore-selective functionalization of honeycomb-patterned (HCP) films. The pore-selective functionalization of the HCP film gives unique properties to the film which can be used for specific applications such as protein recognition, catalysis, selective cell culturing, and drug delivery. There are several comprehensive reviews available for the pore-selective functionalization by the self-assembly process. However, considerable progress in preparation technologies and incorporation of new materials inside the pore surface for exact applications have emerged, thus warranting a review. In this review, we have focused on the pore-selective functionalization of the HCP films by the modified BF method, in which the self-assembly process is accompanied by an interfacial reaction. We review the importance of pore-selective functionalization, its applications, present limitations, and future perspectives.

Hierarchically Porous Films Architectured by Self-Assembly of Prolamins at the Air-Liquid Interface.

Artificial recapitulation of hierarchically porous films gained great interest due to their versatile functionalities and applications. However, the development of novel eco-friendly and nontoxic biopolymer-based porous films is still limited by the time-consuming fabrication processes and toxic organic reagents involved. Here, we reported a novel approach to rapidly (within 5 s) fabricate biopolymer-based hierarchically porous films via inducing the laterally occurring interfacial self-assembly of prolamins at the air-liquid interface during an antisolvent dripping procedure. The as-prepared films exhibited a hierarchically porous microstructure (with sizes of about 500 nm to 5 µm) with location-graded and Janus features. The formation mechanism involved the solvent gradient controlled self-assembly of prolamin into an anisotropic defect structure in longitudinal and lateral directions. Accordingly, the macroscopic morphologies together with the porosity and pore size could be precisely tuned by solvents and operating parameters in a convenient way. Furthermore, alcohol-soluble but water-insoluble bioactive compounds could be incorporated simultaneously via a one-step loading procedure, which endowed films with large loading efficiency and sustained release features suitable for controlled release applications. The effect of the curcumin-loaded porous film on skin wound healing, as one of the potential applications of this novel material, was then investigated in vivo in a full-thickness wound model, wherein satisfying wound healing effects were achieved through multitarget and multipathway mechanisms. This pioneering work offers a novel strategy for the rapid architecture of biopolymer-based hierarchically porous film with versatile application potentials.

Liquid-Infused Porous Film Self-Assembly for Superior Light-Transmitting and Anti-Adhesion.

Liquid-Infused Surfaces (LISs), particularly known for their liquid-repelling feature, have demonstrated plenty of applications in the medical, marine, and energy fields. To improve the durability and transparency highly demanded on glass-based vision devices such as an endoscope, this study proposed a novel self-assembly method to fabricate well-ordered porous Poly-Styrene (PS)/Styrene-Butadiene-Styrene (SBS) films by simply dripping the PS/SBS dichloromethane solutions onto the glass before spinning. The effects of the solutions' concentrations and spin speeds on the porous structure were experimentally investigated. The results showed that a certain mass ratio of PS/SBS can make the structure of the ordered porous film more regular and denser under the optimal solution concentration and spin-coating speed. Superior transparency and durability were also realized by dripping silicone oil on the porous film to build a liquid-infused surface. Applications of the as-prepared surface on devices like endoscopes, viewfinders, and goggles have been explored respectively.

Fabrication of Highly Porous and Pure Zinc Oxide Films Using Modified DC Magnetron Sputtering and Post-Oxidation.

Porous films of metals and metal oxides exhibit larger surface areas and higher reactivities than those of dense films. Therefore, they have gained growing attention as potential materials for use in various applications. This study reports the use of a modified direct current magnetron sputtering method to form porous Zn-ZnO composite films, wherein a subsequent wet post-oxidation process is employed to fabricate pure porous ZnO films. The porous Zn-ZnO composite films were initially formed in clusters, and evaluation of their resulting properties allowed the optimal conditions to be determined. An oxygen ratio of 0.3% in the argon gas flow resulted in the best porosity, while a process pressure of 14 mTorr was optimal. Following deposition, porous ZnO films were obtained through rapid thermal annealing in the presence of water vapor, and the properties and porosities of the obtained films were analyzed. An oxidation temperature of 500 °C was optimal, with an oxidation time of 5 min giving a pure ZnO film with 26% porosity. Due to the fact that the films produced using this method are highly reliable, they could be employed in applications that require large specific surface areas, such as sensors, supercapacitors, and batteries.

Observable removal of pharmaceutical residues by highly porous photoactive cellulose acetate@MIL-MOF film.

Pharmaceutical products are used tremendously worldwide and subsequently released into wastewater even at very low concentration caused serious environmental problem due to their high activity. Therefore, the present work focuses on remarkable removal of paracetamol as one from the most used pharmaceutical intermediates, by using porous film based on cellulose acetate@metal organic framework (CA@Ti-MIL-NH2). The film was designed to achieve extreme removal of paracetamol by action of both of adsorption and degradation. Metal organic frame work was directly synthesized and inserted within the pre-prepared porous CA film to obtain porous CA@Ti-MIL-NH2 film. The synthesized films were applied in adsorption and photo-degradation of paracetamol separately and together. Due to the photocatalytic activity of Ti-MIL-NH2, the photo-degradation of paracetamol in visible-light was much effective and considerably high degradation of paracetamol was observed (k1 = 760.0 m-1) comparing to the adsorption (k1 = 160.0 m-1). The overall removal of paracetamol was significantly enlarged from 82.7 mg/g for CA film to 519.1 mg/g for porous CA@Ti-MIL-NH2 film. The used film exhibited quite good reusability and the removal of paracetamol was lowered from 96% to 85% after 5 regeneration cycles. Results of total organic carbon confirmed that paracetamol was fully degraded to CO2 and water.

Porous Film Coating Enabled by Polyvinyl Pyrrolidone (PVP) for Enhanced Air Permeability of Fabrics: The Effect of PVP Molecule Weight and Dosage.

This study developed a versatile and facile method for creating pores and tuning the porous structure in the polymer latex films by selectively etching the added functional polyvinyl pyrrolidone (PVP) molecules. The pore formed in the latex films had a similar morphology to that of PVP aggregation before etching. This observation promotes us to regulate the pore morphology that determines the film's property, such as air permeability through varying the PVP molecule weight and dosage. To this end, the effects of PVP molecule weight and dosage on the pore formation were systematically studied. The results showed that the average pore size of porous film decreased from >10 µm to sub-micron (about 0.4 µm) as the molecular weight or the dosage of PVP increased. This was ascribed to the strong adsorption affinity of PVP molecule onto the latex particle surface, which further hindered the diffusion and self-assembly of PVP molecule. In addition, this interaction became much stronger when the higher molecule weight of PVP or the higher dosage of PVP was employed, leading to the decreased size of PVP aggregation, as well as the formed pores in the latex films. Furthermore, the addition of PVP had little effect on the color of coated fabric based on the results of CIE L*a*b* measurement. The proposed facile method can be used to improve the air permeability of coated fabrics.