Porous Polymer Films Research Articles

Self-assembled porous polymer films for improved oxygen sensing

Absolute oxygen sensors based on quenching of phosphorescence have been the subject of numerous studies for the monitoring of biological environments. Here, we used simple fabrication techniques with readily available polymers to obtain high performance phosphorescent films. Specifically, evaporation-based phase separation and the breath figure technique were used to induce porosity. The pore sizes ranged from ∼37 nm to ∼141 μm while the maximum average porosity achieved was ∼74%. The oxygen sensing properties were evaluated via a standarised calibration procedure with an optoelectronic setup in both transmission and reflection based configurations. When comparing non-porous and porous films, the highest improvements achieved were a factor of ∼7.9 in dynamic range and ∼7.3 in maximum sensitivity, followed by an improved linearity with a half-sensitivity point at 43% O2 V/V. Also, the recovery time was reduced by an order of magnitude in the high porosity film and all samples prepared were not affected by variations in the humidity of the surrounding environment. Despite the use of common polymers, the fabrication techniques employed led to the significant enhancement of oxygen sensing properties and elucidated the relation between porous film morphologies and sensing performance.

Unexploited Design and Application of Dynamic Covalent Networks: Phenol-yne Click Reaction and Porous Film Generation

Dynamic covalent networks (DCNs) have attracted great attention because of their capacity for reprocessing and remolding, based on macromolecular architecture transformations or rearrangements through dynamic exchange reactions. Here, a new dynamic exchange reaction between a phenol and an enol-one motif yielded from the phenol-yne click reaction is introduced, and the phenol-yne click reaction is facilely integrated into the fabrication of a novel DCN. To expand the scope of material recycling, another degradable DCN prepared using the same click reaction but with a degradable diacetal motif is introduced. After thermal fusion of these two DCNs and subsequent acidic hydrolysis, a porous polymer film with a porosity of 46% is afforded, which is verified to possess excellent oil absorption capacity and recyclability. The strategic design and fabrication of porous polymer films provide an entirely new pathway for the application of DCNs.

Porous Polymer Films with Tunable Pore Size and Morphology by Vapor Deposition.

The fabrication of porous polymer thin films with precise thickness and morphological control through conventional solvent-based techniques is challenging. Herein, we present a fabrication method for porous polymer thin films based on chemical vapor deposition that provides control over pore size, pore morphology, and film thickness. The porous films are prepared by co-depositing crystallizable porogen molecules with cross-linked poly(glycidyl methacrylate) (pGMA) thin films, which are synthesized by initiated chemical vapor deposition (iCVD). As the porogen is deposited, it crystallizes and phase-separates from the polymer film; simultaneous polymerization of pGMA limits crystal growth, controlling the size of crystals. Using naphthalene as porogen resulted in thin films with pore sizes from 5.9 to 24.2 μm and porosities ranging from 59.4 to 78.4%. Using octamethylcyclotetrasiloxane as porogen, which is miscible with the GMA monomer, drastically reduced the pore dimensions, ranging from 14.4 to 65.3 nm with porosities from 8.0 to 33.2%. The film morphology was highly dependent on the relative kinetics of porogen crystallization, phase separation, and heterogeneous polymerization. The kinetics of these competing processes are discussed qualitatively based on nucleation theory and Cahn–Hilliard theory. Fourier-transform infrared spectroscopy confirmed the retention of the reactive epoxide functionality of glycidyl methacrylate, which can enable further chemical derivatization as required for application in optoelectronics, sensing, separations, and biomedical devices.

The use of brown coal in Ukraine to obtain water-soluble sorbents

Purpose. To develop a method of using salts of humic acids obtained from brown coal of Ukraine for sorption of heavy metal ions and their extraction using ultrafiltration membranes. Methodology. Unique laboratory equipment has been developed to determine the sorption capacity of humic substances with a concentration of 0 to 20 mg/l in relation to heavy metal ions (Cu2+, Pb2+, Cd2+, Hg2+, Zn2+, Co2+) with a concentration of 5 mg/l. The results of proximate and ultimate analyzes, as well as infrared and optical emission spectroscopy were used to assess the quality of brown coal, humic substances and the solution of humic substances with heavy metal ions. Findings. Ukrainian brown coal of Oleksandriia geological-industrial district contains a large amount (about 80%) of humic acid, which is the basis for obtaining effective water-soluble sorbents. It is proved that humic substances obtained from brown coal of Ukraine allow binding up to 99% of heavy metal ions in complexes. The most optimal concentration of humic substances in terms of their concentration and selectivity of heavy metal ions extraction is 5 mg/l. Originality. The possibility of practical using of humic substances obtained from brown coal of Ukraine for sorption of heavy metal ions has been proved. As ultrafiltration membranes, UF-20-PAN membranes are used, which are porous polymer films based on polyacrylonitrile with a pore size of 20 m, the working surface area of the membrane is 28.26 10-4 m2. Practical value. The introduction of the developed technology will allow, firstly, restoring the practical use of large deposits of brown coal in Ukraine, and secondly, introducing deep treatment of industrial and wastewater.

Polyhedral Oligomeric Silsesquioxane as a Polarity Mediator and Reinforced Nanofiller for Fabricating Robust and Hierarchical Porous Film for Cell Bioengineering

A hierarchical porous polymer film that can provide a balance of mechanical properties and specific surface areas and sustain cell functions has become a major target for material scientists and bioengineers in the past decade. However, the limited availability of materials that exhibit high mechanical performance and easily form hierarchical porous structures hinder the progress in practical application. Here, we show the design of a polyhedral oligomeric silsesquioxane (POSS) hybrid polymer by incorporating a bi-functional glycidyl-propyl POSS (G-POSS) into the epoxy polymer backbone, in which POSS functions as both a nanofiller to reinforce the mechanical performance and as the polarity mediator to induce self-assembly of the polymer chains into a three-dimensional (3D) connected porous structure. Nanoindentation shows that the incorporation of POSS leads to a 25 and 36% increase in modulus and hardness, respectively. Scanning electron microscopy results show that POSS helps tune the hydrophobicity of the polymer and assists in the interface assembly, allowing easy formation of a densely packed two-dimensional or 3D hierarchical porous structure. Culture of mouse embryonic fibroblast cells demonstrates that the hybrid polymer scaffold provides prominent advantages ranging from enhanced cell adhesion to proliferation. Particularly, the 3D hierarchical porous film allows good nutrient supply and cell communication, which better mimics the in vivo microenvironment with less cell morphology change during cell proliferation. Hence, the successful integration of high material strength and easy formation of an interconnected porous structure shows that POSS hybrid polymers have strong potential for applications in the fabrication of cell culture platforms and future translation in tissue repair and regeneration.

Flexible random laser from a porous polymer film

Flexible random lasers have attracted a great deal of interest due to their potential in light-weight, flexible optical sensors and devices. Among many alternatives, flexible thin film random lasers are very interesting because they can be easily fabricated via a simple solution-based process. Herein, we demonstrate a dye-doped porous polyvinyl alcohol film that can work as a flexible random laser source under optical pumping. The film is fabricated by a drop cast technique and has a nearly circular shape with a diameter of ∼5 mm. Owing to the inverted photonic glass structure that is air voids in the polymer matrix, light emission from dye molecules is multiple scattering and lasing emission is achieved. In the central area, the film laser works reliably with the lasing threshold of ∼166μJ/mm2 and lasing wavelength of around 595 nm. In the edge area, the lasing properties are more fluctuated indicating that the structure may not be uniform. It is found that the lasing wavelength in the edge area is 4.5 nm red-shifted compared to that in the central area of the film. Interestingly, the thin film laser can operate well under bending conditions with a minor change in the lasing wavelength.

Back Cover: Electrochemical Preparation of Porous Organic Polymer Films for High‐Performance Memristors (Angew. Chem. Int. Ed. 38/2022)

Electrochemical polymerizations can be used to obtain porous organic polymer films for advanced electronic devices. In their Research Article (e202205796), Bao-Hang Han and co-workers report the preparation of carbazole-based porous organic polymer films with electron transfer properties by a simple and efficient electrochemical polymerization method and their application in high-performance memristors.

Rücktitelbild: Electrochemical Preparation of Porous Organic Polymer Films for High‐Performance Memristors (Angew. Chem. 38/2022)

Elektrochemische Polymerisationen ermöglichen die Synthese von porösen organischen Polymerfilmen für moderne elektronische Funktionseinheiten. In ihrem Forschungsartikel (e202205796) berichten Bao-Hang Han et al. über die Herstellung poröser organischer Polymerfilme auf Carbazolbasis mit Elektronentransfereigenschaften durch eine einfache und effiziente elektrochemische Polymerisationsmethode und deren Anwendung in Hochleistungs-Memristoren.

Electrochemical Preparation of Porous Organic Polymer Films for High-Performance Memristors.

Porous organic polymer films (PFs) with intrinsical porosity and tuneable pore environment are ideally suited for application in electronic devices. However, the huge challenges still exist for construction of electronic devices based on PFs owing to lack of robustness, processability, and controllable preparation. Herein, we report the electrochemical preparation of carbazole-based porous organic polymer films (eCPFs) as switchable materials for the memristors. These eCPFs possess the characteristics of controllable thickness/size, high stability, and excellent porosity. Carbazole and cyano groups are introduced into the eCPFs to constructing electron transfer systems. Thus, the memristors constructed based on these eCPFs exhibit excellent switching performance, reliability, and reproducibility. The electrochemically controllable preparation method of porous organic polymer membranes proposed in this paper provides a feasible idea for the developments of electronic devices.

Electrochemical Preparation of Porous Organic Polymer Films for High‐Performance Memristors

AbstractPorous organic polymer films (PFs) with intrinsical porosity and tuneable pore environment are ideally suited for application in electronic devices. However, the huge challenges still exist for construction of electronic devices based on PFs owing to lack of robustness, processability, and controllable preparation. Herein, we report the electrochemical preparation of carbazole‐based porous organic polymer films (eCPFs) as switchable materials for the memristors. These eCPFs possess the characteristics of controllable thickness/size, high stability, and excellent porosity. Carbazole and cyano groups are introduced into the eCPFs to constructing electron transfer systems. Thus, the memristors constructed based on these eCPFs exhibit excellent switching performance, reliability, and reproducibility. The electrochemically controllable preparation method of porous organic polymer membranes proposed in this paper provides a feasible idea for the developments of electronic devices.

P‐86: Ink‐Jet Printed Stable Full‐Color Perovskite and Quantum Rod Color Filter

Photoluminescence color filter (PLCF) array using quantum color converters is recently a strong candidate to replace traditional absorptive CF in various display applications. PLCF displays are expected to have higher efficiency and wider color gamut. Ink‐jet printing is a versatile and low‐cost method to pattern color converting films, but uniformity problem is to be concerned. To utilize perovskite nanoparticles (PNP) and low dimension semiconductor material, maintaining good photoluminescence (PL) properties in the processing and long‐term stability is challenging. In our work, we use a porous polymer film (PF) as the ink jet printing template. Capillary effect of the sub‐micron pores in the PF promotes uniform coffee‐ring free printing with reduced size (<50 μm). Without using any mask or bank structures, green PNP and red Quantum Rod (QR) arrays can be printed with high quality. The PF CF is endowed with good PL stability for more than 80 days. In terms of device application, ambient contrast ratio become problematic considering the ambient light excitation of color converters. We adapted bottom CF structure for LCD to solve this problem. A LCD equipped with a printed full‐color PNP‐QR PF CF was demonstrated. The color gamut of the design can reach 96.9% BT.2020.

Nanoporous SiOx plasma polymer films as carrier for liquid‐infused surfaces

AbstractLiquid‐infused surfaces are based upon the infusion of a liquid phase into a porous solid material to induce slippery and repellent character. In this context, porous SiOx plasma polymer films represent a relevant candidate for a robust nanoporous carrier layer. Intermittent low‐pressure plasma etching of O2/hexamethyldisiloxane‐derived coatings is investigated to enhance the intrinsic porosity inherent to residual hydrocarbons in the silica matrix. Simulations of the resulting Si–O ring network structure using reactive molecular dynamics indicate formation of interconnected voids with Si–OH functionalized pore walls allowing water penetration with almost Fickian diffusive behavior. The corresponding porosity of up to 18%, well agreeing with simulations, Fourier‐transform infrared spectroscopy, and ellipsometry measurements, was found to be suitable for the liquid infusion of polyethylene glycol molecules into about 80 nm thick SiOx films providing ongoing lubricating properties, thus revealing their suitability as liquid‐infused surfaces.

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.

Single-use porous polymer thin-film device: A reliable sampler for analysis of drugs in small volumes of biofluids

The response to the demand for biomedical testing on small volumes of biofluids has led to a range of new microsampling devices and related techniques. Simple cost-effective sampling devices are available, but most do not incorporate sample clean-up and necessitate extensive sample processing by the analyst. To address both cleanup and analyte stability, a porous polymeric thin film made of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) coated (5 × 18 mm2) on a stainless steel substrate was used for the extraction of seven tricyclic antidepressants (TCAs) from plasma spots, with analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Essential factors such as sample volume, extraction time, matrix effects, and the desorption process were investigated. The optimized method is comprised of a quick 3-min extraction from 10 μL of plasma, a wash (10 s in 1 mL of 1% aqueous triethylamine (TEA) to remove plasma matrix interferences, and 2-min desorption (200 μL of ACN with 0.1% formic acid (FA)). For the purpose of sample archiving, thin film devices containing extracted TCAs were stored for 30 days at room temperature and showed a consistent analyte recovery. Inter-device reproducibility was evaluated without internal standard (%RSD 8.2–19.3%), and using two methods of introducing a single deuterated internal standard (imipramine-D3) either prior to (%RSDs 5.6–13.9%) or after (%RSDs 4.9–10.2%) sample loading to the device. Although the intention of this study was to introduce a single use device for rapid and easy analysis, reusability showed the feasibility of 15 consecutive extractions using same device without any performance loss. The optimized method revealed excellent linearity (R2 > 0.99) in the range of 1–1000 ng mL−1, with good intra- and inter-day accuracy (81.4–118%) and precision (≤12%) in human plasma.

Inkjet‐Printed, Flexible Full‐Color Photoluminescence‐Type Color Filters for Displays

Photoluminescence‐type color filters (PLCFs) are supposed to offer vivid colors and higher power efficiency for modern displays by removing absorption losses of the conventional color filters (CFs). Inkjet printing (IJP) is a versatile and low‐cost method to pattern color converters. But uniformity of the patterns is a big concern. Poor photoluminescence stability is also problematic, especially for the perovskite nanoparticles (PNPs) and quantum color converters. Herein, a porous polymer film (PF) is deployed as a template for IJP. The capillary effect of sub‐micron pores in the PF modifies the rheological process of ink spreading that eliminates the coffee‐ring effect and simultaneously provides photoluminescence (PL) stability. A high‐quality green PNP, and red quantum rod (QR) based CF array onto the PF is successfully printed. A liquid crystal display (LCD) deploying this full‐color PF CFs is demonstrated. Color gamut of the device could reach 96.9% of BT2020. The PF CFs show good PL stability for more than 218 days. Furthermore, the fabricated PF CFs possess great flexibility, and any chromaticity and brightness change after 10 000 times of folding were not observed. Thus, the proposed CF using the PF is highly suitable for flexible display and photonics components.

Analytical solutions for nonionic and ionic diffusio-osmotic transport at soft and porous interfaces

In this paper, we develop one of the first models for closed-form fully analytical solutions for describing the nonionic and ionic diffusio-osmotic (DOS) transport at interfaces grafted with a soft and porous polymeric film in the presence of a neutral solute concentration gradient (for nonionic diffusio-osmosis) and a salt concentration gradient (for ionic diffusio-osmosis). The nonionic DOS velocity depends on this solute concentration gradient and the drag force from the polymeric film. The ionic DOS transport is characterized by the diffusio-osmotically induced electric field and the diffusio-osmotically induced velocity field. This induced electric field is primarily dictated by the conduction of the mobile ion imbalance present within the electric double layer, induced at the charged solid, in the presence of the applied salt concentration gradient. The DOS velocity, on the other hand, is driven by a combination of the induced pressure gradient and an induced electro-osmotic body force (triggered by this induced electric field) and is opposed by the drag from the polymer layer. The result is a velocity field whose magnitude increases rapidly at near wall locations, decreases away from the wall, and depending on the salt concentration, may or may not increase outside the polymeric layer. This unique velocity profile ensures the presence of significant hydrodynamic shear stress across a wide zone extending from the wall in a non-confined fluidic system: This will ensure that finite-sized species (e.g., biological cells) can be conveniently made to access locations of large hydrodynamic stresses for a myriad of engineering and biological applications.

Flexible Random Laser from a Porous Polymer Film

Flexible Random Laser from a Porous Polymer Film

Self-Assembled Porous Polymer Films for Improved Oxygen Sensing

Self-Assembled Porous Polymer Films for Improved Oxygen Sensing

Hydrogel Ionotronics with Ultra‐Low Impedance and High Signal Fidelity across Broad Frequency and Temperature Ranges

AbstractIonotronics, emerging devices that couple gel ionic conductors and electronic circuits, have shown great promise as stretchable alternatives with multi‐functionalities to conventional rigid devices, ranging from energy harvesting to sensing, displaying, and actuation. However, current hydrogel ionotronics’ performances are still unsatisfactory: i) upon high alternating current frequency (> 1000 Hz), the ionic conductivity dominates but is rather low and drops further drastically as temperature decreases; ii) upon low frequency (< 1000 Hz), the unstable and high impedance at the electrode/hydrogel interface dominates unfavorably but has been overlooked previously. To remedy these issues, herein, a systematic strategy is proposed by employing a highly ionically‐conductive anti‐freezing hydrogel and electronically‐conductive porous polymer films with high electrical‐double‐layer capacitance as electrodes to connect the hydrogel and metal leads. The hydrogel has an ultra‐high conductivity, while being transparent, stretchable, and easily prepared by one‐step photo‐gelation. Meanwhile, the conducting polymer electrodes realize a stable and low interfacial impedance and improved voltage tolerance, enabling much higher fidelity of ion‐electron signal transduction than using gold electrodes. This strategy can be applied to construct various ionotronics for broad applications, including triboelectric nanogenerators, touch panels, displays, soft robotics, and multifunctional electronics with broad operational frequency and temperature ranges.

Biomimetic Porous Fluoropolymer Films with Brilliant Whiteness by Using Polymerization‐Induced Phase Separation

AbstractInspired by the Cyphochilus scale with extreme whiteness, fluoropolymer is used as the matrix to prepare highly scattering porous polymer films through polymerization‐induced phase separation (PIPS) method. The mixture used for the PIPS technique contains a fluoride monomer, a UV photoinitiator, and porogens (cyclohexanol and perfluorooctanol). By carefully tuning the mixture parameters (cyclohexanol–perfluorooctanol and monomer–porogen weight ratios), the porous morphology can be well tailored, which induces different scattering performances. With an optimized formulation (50 wt% monomer, 25 wt% cyclohexanol, and 25 wt% perfluorooctanol), the porous film with a thickness of 55 µm can achieve an average total reflectance of ≈90%, featuring a measured transport mean free path of 1.3–1.7 µm (comparable to the 1.5 µm of the benchmark Cyphochilus scale). Further, the porous films are applied to the light‐emitting diode (LED) device and it is demonstrated that they can effectively improve the light extraction efficiency of the LED and thus enhance the luminous performance. Due to the simplicity, cost‐effectiveness, and scalability of the PIPS method, the as‐developed porous fluoropolymer films with such excellent scattering ability can find many potential applications not only in the field of optoelectronics, but also in various complex scenarios, such as daytime passive radiative cooling.