Microporous Films Research Articles

Sustainable Solution for Plastic Pollution: Upcycling Waste Polypropylene Masks for Effective Oil-Spill Management.

The use of Polypropylene PP in disposable items such as face masks, gloves, and personal protective equipment has increased exponentially during and after the COVID-19 pandemic, contributing significantly to microplastics and nanoplastics in the environment. Upcycling of waste PP provides a useful alternative to traditional thermal and mechanical recycling techniques. It transforms waste PP into useful products, minimizing its impact on the environment. Herein, we synthesized an oil-sorbent pouch using waste PP, which comprises superposed microporous and fibrous thin films of PP using spin coating. The pouch exhibited super-fast uptake kinetics and reached its saturation in fewer than five minutes with a high oil uptake value of 85 g/g. Moreover, it displayed high reusability and was found to be effective in absorbing oil up to seven times when mechanically squeezed between each cycle, demonstrating robust oil-sorption capabilities. This approach offers a potential solution for managing plastic waste while promoting a circular economy.

A novel high efficiency Reactive Ion Figuring technique based on artificial microporous mask

Reactive Ion Figuring (RIF) is a promising technical solution for fabrication of meter-scale aperture optical substrates due to its high efficiency parallel processing and low surface damage feature. However, the existing RIF technique needs multiple cycles of photolithography and etching process which is time-consuming and expensive. An artificial microporous film was designed and fabricated as a mask to perform high efficient RIF process. The location of the artificial microporous is distributed gradually from high-density to the low-density state along the radius according to the law of power aberration, and then fluid simulation was carried out. A designed power aberration was superimposed on a 100 mm aperture quartz substrate in a single cycle of RIF process, proving that the artificial microporous mask is capable of tailoring etching rate distribution. The result shows that the power aberration difference between the designed figure and real fabricating one is around 6 nm, and the reasons behind this were analyzed and discussed. This work demonstrates feasibility of high efficiency RIF based on artificial microporous mask and laid the foundation for future arbitrary surface figuring processes.

Light Weight, Flexible and Ultrathin PTFE@Ag and Ni@PVDF Composite Film for High-Efficient Electromagnetic Interference Shielding.

Dopamine was used to modify polytetrafluoroethylene (PTFE) in order to obtain functional polydopamine (PDA) surface-modified PTFE microporous film (PTFE@PDA). Ag was deposited on the surface of PTFE@PDA using electroless plating in order to obtain Ag-wrapped PTFE@PDA film (PTFE@Ag). A liquid-phase chemical reduction method was employed to prepare nickel nanochains. A Ni@PVDF cast film was obtained by mechanically blended nickel nanochains and polyimide (PVDF). The above two films were hot pressed to give a flexible, ultra-thin, and highly effective electromagnetic shielding composite film with a "3+2" layered structure. IR, XRD, and TEM results showed the PTFE@PDA film surface was coated by a tight plating layer of Ag particles with a particle size of 100~200 nm. PTFE@Ag+Ni@PVDF composite film exhibited excellent electromagnetic shielding effectiveness, with the conductivity of 7507.5 S/cm and the shielding effectiveness of 69.03 dB in the X-band range. After a 2000-cycle bending, this value still remained at 51.90 dB. Furthermore, the composite film presented excellent tensile strength of 62.1 MPa. It has great potential for applications in flexible and wearable intelligent devices.

Multifunctional composite membranes for interfacial solar steam and electricity generation

Emerging water purification technology, known as interfacial solar steam generation (ISSG), has been rapidly developing in recent years. ISSG offers a promising solution to address both freshwater shortage and energy demand by simultaneously producing freshwater and electricity. This is achieved through the combination of microporous films and highly efficient photothermal materials. In this study, we have developed a composite film using a 2D material, reduced graphene oxide (rGO), and a combination of 1D materials, chitin fiber@multi-walled carbon nanotube (Chiber@CNT). Through a hybrid dimensional design, these materials’ advantages are integrated, resulting in a composite film with a distinct laminar porous structure and excellent broadband absorption. Notably, under 1 kW·m−2 sunlight irradiation, the composite film achieves a water evaporation flux of 2.10 kg·m−2·h−1 with a photothermal conversion efficiency of 75.79%. In addition, by utilizing an energy-harvesting strategy based on natural water evaporation in porous nanomaterials for power generation, the composite film successfully enables the simultaneous production of freshwater and electricity. Its output voltage reaches 0.39 V in a 3.5 wt% NaCl solution. Furthermore, the film’s output voltage varies with the concentration of NaCl, increasing from 0.26 V (in deionized water) to 0.45 V (in the saturated NaCl solution). Molecular dynamic simulation results indicate that the enhanced power generation can be attributed to the difference in interatomic interaction strength between ions and hydrophilic functional groups in chitin fiber (Chiber). This finding provides a deep physical mechanism and opens up possibilities for the film’s application in highly concentrated salt solutions.

CO2 Escaping In Situ Endowed the Antimicrobial Nanocellulose Packaging Film with a Microporous Structure

The atmosphere and the mold under high humidity severely determine the shelf-life of fruits and vegetables. The microporous structure is helpful to regulate the atmosphere in the package. In this study, we designed a nanocellulose film with a microporous structure by CO2 escaping in situ. The microporous structure provided a pathway that enhanced the gas transmission rate, with the porosity of the film reaching 79.60% and O2 and CO2 transmission reaching 115.57 ± 1.81 cm3/m2 day bar and 145.91 ± 11.71 cm3/m2 day bar, respectively. Polyethyleneimine was exposed around the micropores accompanied by CO2 escaping in situ, which endowed the film with excellent antimicrobial property. The film could regulate the atmosphere and inhibit the microbial growth to maintain the color and taste of green plums and loquats for a long time. CO2 escaping in situ provides a green and sustainable strategy for the development of packaging materials of the microporous structured nanocellulose films with antimicrobial property.

Development of breathable and liquid/wet bacterial penetration barrier composite laminated fabrics for surgical gown applications

Disposable surgical gowns are used to protect health care workers from microorganisms and body fluids to meet the needs of surgical applications. In addition to protection, it has a significant impact on the surgical team members’ comfort and thus, the success of the operations. In this study, a dual layer surgical gown-an outer layer of film and an inner layer of nonwoven fabric-was developed. Produced composite laminated fabrics are SMS (spunbond/meltblown/spunbond) nonwoven fabric laminated microporous polyethylene film and SMS (spunbond/meltblown/spunbond) nonwoven fabric laminated thermoplastic polyurethane films. These fabrics were compared with nonporous polyethylene film-coated SS (spunbond/spunbond) nonwoven fabric available in the local market. The study aims to investigate the effect of some structural factors of composite nonwoven laminated fabrics, including lamination process, manufacturing process, and film type; microporous or monolithic, nonwoven fabric manufacturing process, and helium atmospheric-pressure glow discharge plasma treatment, on their functional performance properties, including air permeability, water vapour permeability, hydrostatic pressure resistance, and wet bacterial penetration resistance. The results showed that the produced composite fabrics offer outstanding breathability and, thus, the surgical team members' comfort. Produced composite fabrics had no wet bacterial penetration of Staphylococcus aureus and thus contributed to the prevention of the transfer of bacterial pathogens to prevent surgical site infection or post-operative infection. Produced composite fabrics offer superior liquid barriers according to the barrier protection classification of the Association for the Advancement of Medical Instrumentation (ANSI/AAMI PB 70:12) and thus contribute to the prevention of the transfer of body fluids during surgical operations.

RESISTANCE OF ADDITIONAL ROOFING UNDERLAYS OF PITCHED ROOFS AGAINST ARTIFICIAL AND NATURAL AGEING

In this paper, the author deals with the resistance of light polymer foils based on microporous functional film, used as additional waterproofing layers of pitched roofs. He exposes these foils to the effects of natural ageing and the effects of artificial ageing according to the methodology of the European test standard. Subsequently, it verifies the tensile properties of the exposed foils and compares the effects of natural and artificial ageing in order to determine the possible cause of premature degradation of these materials, which often occurs in practice. He concludes that the cause of this degradation is not excessive leniency of testing standards, but the insufficient quality of materials supplied to the European market.

Porous polymer film formation by water droplet templating using polystyrene.

Studies show that the formation of breath figures over polystyrene is not clearly understood-sometimes the patterns are regular and sometimes they are barely formed. In an attempt to understand this process a little more, breath figures over polystyrene of three molecular weights and on the smooth and grooved DVD surfaces are prepared and studied. The microporous films are prepared by the evaporation of the chloroform solution of the polymers in a humid environment. The thus formed breath figure patterns are studied under a confocal laser scanning microscope and the images are analyzed. Breath figures were formed for (a) three molecular weights of the polymer (b) two casting techniques, and (c) on smooth and grooved surfaces (of a commercial DVD). The wetting of the breath figures formed by water is also reported here. The pore diameters were found to increase with increase in molecular weight and also with concentration of the polymer used. Only drop-casting method yield breath figures. Voronoi entropy, calculated from the images, indicates ordered pores on the grooved surface compared to smooth surfaces. Contact angle studies indicate a hydrophobic nature of the polymer, with the hydrophobicity increasing by the patterning.

Manipulative pore-formation of polyimide film for tuning the dielectric property via breath figure method

Polyimide (PI) films have been extensively used in the field of microelectronic as insulating materials. With the rapid development of microelectronic devices towards miniaturization and large power, the development of low dielectric properties of PI materials has attracted more and more attention. In this study, the breath figure (BF) process was used to prepare single-layered and multi-layered microporous PI films, for obtaining the low dielectric properties. The BF porous structure of PI film was successfully constructed by two implementing strategies, i.e., solution casting for direct preparation of PI film and solvent treatment upon pre-shaped PI film for in-situ pore-formation. By changing solution concentration, environmental humidity and temperature, efficient manipulation of the pore morphology of the film both on the surface and in the bulk layer was achieved. Such multi-layered porous BF structure has been proved to significantly lower the dielectric constant of PI film, from 3.7 of non-porous film to 1.7 of porous film. In order to further expand the application range of BF microporous PI film, both ways of alkali treatment and thermal oxidation were taken for the cross-linking of the porous PI films, greatly improving the solvent resistance of the film. The original porous morphology was completely retained, ensuring that the low dielectric properties were not affected. This is the first report on the preparation of multi-layered microporous low dielectric PI films by BF process.

Non-Solvent- and Temperature-Induced Phase Separations of Polylaurolactam Solutions in Benzyl Alcohol as Methods for Producing Microfiltration Membranes

The possibility of obtaining porous films through solutions of polylaurolactam (PA12) in benzyl alcohol (BA) was considered. The theoretical calculation of the phase diagram showed the presence of the upper critical solution temperature (UCST) for the PA12/BA system at 157 °C. The PA12 completely dissolved in BA at higher temperatures, but the resulting solutions underwent phase separation upon cooling down to 120–140 °C because of the PA12’s crystallization. The viscosity of the 10–40% PA12 solutions increased according to a power law but remained low and did not exceed 5 Pa·s at 160 °C. Regardless of the concentration, PA12 formed a dispersed phase when its solutions were cooled, which did not allow for the obtention of strong films. On the contrary, the phase separation of the 20–30% PA12 solutions under the action of a non-solvent (isopropanol) leads to the formation of flexible microporous films. The measurement of the porosity, wettability, strength, permeability, and rejection of submicron particles showed the best results for a porous film produced from a 30% solution by non-solvent-induced phase separation. This process makes it possible to obtain a membrane material with a 240 nm particle rejection of 99.6% and a permeate flow of 1.5 kg/m2hbar for contaminated water and 69.9 kg/m2hbar for pure water.

Modeling the anisotropic behavior of highly orthotropic lithium-ion batteries polymer separators

Separators in commercial lithium-ion batteries are microporous polymeric films characterized by highly anisotropic mechanical behavior. An accurate characterization of their mechanical and fracture behavior is essential for optimal design, performance, and safety of lithium-ion batteries. In this work, the mechanical and fracture behavior of battery separators subjected to uniaxial tension and punch tests are characterized and discussed. An anisotropic continuum damage coupled elastic-hyperelastic-viscoplastic model is developed in the framework of the large deformation theory to capture the mechanical and fracture behavior of battery separators. A robust implicit integration scheme is developed then the model is implemented as a user-defined material subroutine (UMAT) in commercial finite-element software in order to solve boundary-value problems. The capability of the proposed model to predict the anisotropic mechanical behavior up to fracture for two different types of battery separators highlights the versatility of the proposed modeling approach. The model results showed a good agreement with the experimental data. Moreover, the model was able to predict the failure of the separators under different loading conditions.

Catalyst-free synthesis of diverse fluorescent polyoxadiazoles for the facile formation and morphology visualization of microporous films and cell imaging.

The development of facile polymerizations toward functional heterocyclic polymers is of great significance for chemistry and materials science. As an important class of heterocyclic polymers, polyoxadiazoles (PODs) have found applications in various fields. However, the synthetic difficulties of PODs greatly restrict their structural diversity and property investigation. Herein, we report a series of catalyst-free multicomponent polymerizations (MCPs) that can facilely synthesize functional PODs with well-defined and diversified topological structures from commercially available or readily accessible aldehydes, carboxylic acids, secondary amines, and (N-isocyanimino)triphenylphosphorane at room temperature. Unlike conventional Ugi polycondensations, the present Ugi-type MCPs can in situ generate oxadiazole moieties in polymer backbones. The obtained PODs possess good solubility, high thermal and morphological stability, and excellent film-forming ability. The introduction of aggregation-induced emission (AIE) moieties together with the inherent structural features of PODs endow these polymers with multiple functionalities. The AIE-active linear PODs can form fluorescent microporous films with stable and ordered structures based on the simple breath figure patterning method, and the self-assembly morphologies can be directly visualized by fluorescence microscopy in a high-contrast and sensitive manner. Moreover, both the linear and hyperbranched AIE-active PODs possess excellent biocompatibility, good lysosome specificity, and excellent photobleaching resistance, which enable them to serve as promising lysosome-specific fluorescent probes in biological imaging.

Sensing interface based on electrodeposited Cu-BTC microporous film for electrochemical detection of the painkiller paracetamol.

The use of metal-organic framework materials in electrochemical sensors has been gaining more attention in the last few years due to their highly porous structure and electrocatalytic activity. In this work, a novel paracetamol electrochemical sensor based on a Cu-BTC microporous film electrochemically grown onto glassy carbon electrode was introduced. The Cu-BTC film was deposited directly onto the electrode surface via an electrochemical approach using a Et3N probase to accelerate the growth of Cu-BTC. The fast growth enables the formation of a microporous structure with better adsorption of targeted molecules. The two-dimensional arrangement of units made of dimeric copper cations coordinated to carboxylate anions helped to improve the electrochemical conductivity and electron transfer rate at the electrode surface (charge transfer resistance was dramatically decreased from 2173 Ω to 86 Ω). The electrocatalytic activity of copper ion centers in Cu-BTC was studied with peak separation between oxidation and reduction peaks of pseudo-redox paracetamol molecules much shortened (from 629 mV to 87 mV). Consequently, the sensing parameters (sensitivity and detection limit) of the as-prepared paracetamol sensor were considerably improved. Further works need to be conducted on tailoring ligand structure in order to much improve the electrical conductivity of metal-organic frameworks for sensing purposes.

Self-assembling nanofibrous bacteriophage microgels as sprayable antimicrobials targeting multidrug-resistant bacteria

Nanofilamentous bacteriophages (bacterial viruses) are biofunctional, self-propagating, and monodisperse natural building blocks for virus-built materials. Minifying phage-built materials to microscale offers the promise of expanding the range function for these biomaterials to sprays and colloidal bioassays/biosensors. Here, we crosslink half a million self-organized phages as the sole structural component to construct each soft microgel. Through an in-house developed, biologics-friendly, high-throughput template method, over 35,000 phage-built microgels are produced from every square centimetre of a peelable microporous film template, constituting a 13-billion phage community. The phage-exclusive microgels exhibit a self-organized, highly-aligned nanofibrous texture and tunable auto-fluorescence. Further preservation of antimicrobial activity was achieved by making hybrid protein-phage microgels. When loaded with potent virulent phages, these microgels effectively reduce heavy loads of multidrug-resistant Escherichia coli O157:H7 on food products, leading to up to 6 logs reduction in 9 hours and rendering food contaminant free.

High-performance dual-sensitive flexible sensors based on conductive alginate sponge electrode/polyvinylidene fluoride microporous composite film

This work reported a novel dual-sensitive flexible sandwich sensor based on conductive natural biopolymers sponge electrode and polyvinylidene fluoride (PVDF) film with superiorities of high sensitivity, long lifespan and low density. The unique natural biopolymers sponge electrode, consisting of bidisperse magnetic particles and sodium alginate/chitosan (SA/CHI) with physically-crosslinked double-network structure, showed a high response capability to external magnetic fields. Besides, by combining the advantages of SA/CHI sponge electrode (high elasticity and flexibility) and PVDF film (exceptional stiffness and piezoelectricity), the SA/CHI/PVDF composite film also exhibited preferable mechanical strength and strain-dependent electrical property, which can simultaneously satisfy the requirements of high sensitivity detection to external magnetic fields and strains. Specifically, the relative resistance variation of SA/CHI/PVDF-1.00 sensor reached as high as 60.4% under a cycling loading of 240 mT magnetic field. Meanwhile, their electrical responses could also display a significant variation and relatively stable recoverability under periodic stretching, bending or compressing excitations. Afterwards, a potential working mechanism and equivalent circuit model were provided to study the magnetic/mechanic sensitivity of SA/CHI/PVDF sensors. Furthermore, a 4 × 4 SA/CHI/PVDF sensor array was developed to perceive and distinguish both magnetic field and compressive force, which indicated its favorable potential in wearable electronics and soft robotics.

Tissue paper-liked conjugated microporous polymers film for bacteria inhibition

Conjugated microporous polymers (CMPs) film featuring with unique two-dimensional structure and well-developed microporosity inheriting from CMPs shows outstanding function for separation and water purification. However, it is still a great challenge to synthesize truly self-standing CMPs films or membranes with large areas and processible intensity. In this work, inspired by surface-assisted polymerization, taking 1,4-diethynylbenzene and 1,3,5-triethynylbenzene as monomer models, we fabricated three soft tissue paper-liked CMPs films with highly mechanical robustness and flexibility through Pd/Cu-catalyzed homocoupling polymerization combined with a facile template method. All the resulting CMPs films consisted of hollow nanotubes whose physical strength and continuity could be tuned by alkynyl monomers. ACMP1 derived from 1,4-diethynylbenzene showed the maximum elongation and tensile strength with a large area of ∼46 cm2. Moreover, ACMP1 was served as an efficient supporter to prepare ACMP1/silver nanoparticles composite by one-step reduction reaction. The silver nanoparticles were uniformly coated the outer surface of nanotubes and retained the original microporosity of ACMP1, endowing the composite good antibacterial activity against E. coli in water. Our work is expected to provide a platform to develop macroscale CMPs-based film with antibacterial function for water purification and environment remediation.

Design, electrosynthesis and electrochromic properties of conjugated microporous polymer films based on butterfly-shaped diphenylamine-thiophene derivatives

Conjugated microporous polymers (CMPs) have attracted much attention owing to the existence of extended π-conjugated skeleton, which possess 3D cross-linked framework that benefits for charge transporting in the polymer film due to the non-planar structure for active groups of the monomers. In this manuscript, two novel CMP films based on butterfly-shaped diphenylamine-thiophene derivatives were synthesized via electropolymerization. Both the polymer film showed good electrochemical properties. The microstructure and thickness of polymer films were characterized by SEM, TEM and AFM, and the results indicated uneven surface of the polymer films were observed, which consisted of many particles and aggregations. The change of bridge group has little effect on the showing color feature, both the films displayed reversible color change from green to blue upon the different applied potentials. Comparing with the linear intermediate polymer films, both the CMP films held faster switching time (about 1 s). Moreover, the polymers possessed good coloration efficiency and stability, which promised them potential application for electrochromic device.

Hydrogen‐bonded polymer multilayer coatings via dynamic layer‐by‐layer assembly

AbstractWe developed the dynamic assembly of the hydrogen‐bonded multilayers of (poly(N‐vinylpyrrolidone/poly(methacrylic acid)) (PVPON/PMAA)) and compared their properties to the static multilayers. We found that dynamic multilayers, wherein a planar substrate is shaken during polymer adsorption, leads to a 15‐time faster deposition of the planar coatings. The thicknesses and roughness of the dynamic coatings were found to be ⁓30% larger than those of static (no shaking) multilayer films as measured by spectroscopic ellipsometry and atomic force microscopy. We examined the film growth, mechanical properties, wettability, hydration, and pH stability of the planar static and dynamic multilayers and demonstrated that these properties were insignificantly affected by the assembly mode. Both static and dynamic coatings produced microporous films when exposed to pH = 5.9, close to the film critical dissolution pH = 6. We discovered that during the release of the multilayer films into a solution to produce free‐standing films either as planar membranes or multilayer capsule shells, the molecular chain rearrangements result in the decreased roughness for both static and dynamic multilayers and lead to a decreased thickness of the dynamic multilayers. Our findings can help develop a rapid synthesis of thicker nanostructured polymer coatings for sensing and controlled delivery applications.

Switching ionic diode states with proton binding into intrinsically microporous polyamine films (PIM-EA-TB) immersed in ethanol

Intrinsically microporous polyamines (PIM-EA-TB) provide tertiary amine binding sites for protons and in this way allow switching/gating from a low ionic conductivity state to semipermeable anion conductivity through micropores. In ethanolic NaClO4 media ionic conductivity in PIM-EA-TB films (approx. 10 μm thick; deposited asymmetrically onto a 10 μm diameter microhole in 5 μm thick Teflon) is lowered by ion exclusion compared to conductivity observed in aqueous environments. However, in the presence of protons in ethanol PIM-EA-TB films are shown to switch from essentially insulating to anionic diode behaviour. Similar observations are reported for Cu2+ but not for other types of cations such as Na+, K+, Mg2+ (all as perchlorate salts). Binding constants are evaluated, and protonation is identified to cause gating for both H+ and Cu2+. Both chemical and electrochemical gating/switching is demonstrated by placing a platinum electrode close to the PIM-EA-TB film and applying positive or negative bias to locally generate acid/base.

Equilibrium modified atmosphere packaging on postharvest quality and antioxidant activity of strawberry

SummaryMicroporous film and MAP were evaluated to find the optimal method for extending the postharvest storage of strawberry. To determine the most suitable MAP system for strawberry, fruits were stored in controlled atmospheres (O2/CO2 partial pressures in kPa: 5/10; 10/10; 5/15), and in a separate experiment, strawberries were sealed in the container with different microporous PET/PE films. Results showed that the optimum atmosphere of strawberries was 10 kPa O2 + 10 kPa CO2 which could be achieved and maintained by using the microporous film with four perforations of 100 μm. By maintaining the optimal atmosphere, active EMAP could increase polyphenol compounds accumulation, with total phenolic content increased by 25% and the content of anthocyanin and total flavonoid was 13% and 29% higher than control at the end of storage. Meanwhile, active EMAP significantly increased CAT PAL and APX activities and the shelf‐life was prolonged for 6 and 3 days, respectively, compared with strawberries packed in control and passive EMAP.