Breath Figure Research Articles

Overall Improvement in Dielectric, Water Resistance and Mechanical Properties of Polyimide Film via Synergy between GO and Sandwich-type Porous Structure.

Simultaneous improvement in dielectric, water resistance and mechanical properties of polyimide (PI) films is critical for their practical use, but difficult to achieve. Herein, a sandwich-type porous GO/PI film with excellent comprehensive properties was obtained through integrating a GO-containing complex, fluorine-containing porous structure and sandwich-type distribution of porous structure by a simple, low-cost and green breath figure method. With the addition of only a small amount of GO-containing complex, a low dielectric constant of 2.21, water absorption of 0.51%, increment in dielectric constant after moisture treatment of 1.60% and high tensile strength of 113.1 MPa, tensile modulus of 1.70 GPa, with 35.39%, 79.42%, 81.81% of reduction and 17.22%, 21.43% of increase compared to PI film were shown, respectively. Moreover, these properties could be adjusted through regulating the component and porous structure by changing the parameters of breath figure method. These outstanding properties make the film a promising candidate for high-performance low-dielectric materials.

Polystyrenes with both hydrophilic and hydrophobic moieties: synthesis and self-assembly behaviors.

Fluorinated polymers are emerging as important alternatives for isoporous film fabrication by the breath figure technique, originating from the special characteristics endowed by fluorine elements such as low surface energy and good chemical stability. In this work, we design and synthesize polystyrenes (∼3600 Da) with perfluoroalkyl groups (-C3F7 or -C7F15) at both chain ends and hydrophilic oligo(ethylene glycol) units ((C2H4O)n, n = 1/2/3) in the chain middle by taking advantage of the bifunctional atom transfer radical polymerization (ATRP) initiators and post-substitution of the terminal bromine. We investigate the influence of the two disparate groups on the physical characteristics of the polymers and self-assembly behaviors during the dynamic breath figure process. It shows that the elongation of hydrophilic segments can greatly decrease the interfacial tension between the polymer solution and water (from 41.8 to 37.4 mN m-1), and the functionalization with perfluoroalkyl end groups diminishes the ability of the polymers to precipitate at the interface, as demonstrated by the cloud point results. Studies of the morphology of the porous films suggest that both low interfacial tension and strong capability of interfacial precipitation are beneficial to droplet stabilization and honeycomb pattern formation at low solution concentrations.

Exploiting breath figure reversibility for in situ pattern modulation and hierarchical design.

The breath figure (BF) method employs condensation droplets as dynamic templates for patterning polymer films. In the classical approach, dropwise condensation and film solidification are simultaneously induced through solvent evaporation, leading to empirically derived patterns with limited predictability of the final design. Here we use the temporally arrested BF methodology, controlling condensation and polymerisation independently to create diverse BF patterns with varied pore size, arrangement and distribution. External temperature control enables us to further investigate and exploit the inherent reversibility of the phase change process that governs the pattern formation. We modulate the level of subcooling and superheating to achieve subsequent regimes of condensation and evaporation, permitting in situ regulation of the droplet growth and shrinkage kinetics. The full reversibility of the phase change processes joined with active photopolymerisation in the current approach thus allows arresting of predictable BF kinetics at intermediate stages, thereby accessing patterns with varied pore size and spacing for unchanged material properties and environmental conditions. This simultaneous active control over both the kinetics of phase change and polymer solidification offers affordable routes for the fabrication of diverse predictable porous surfaces; manufacture of monolithic hierarchical BF patterns are ultimately facilitated through the advanced control of the BF assembly using the method presented here.

Selenium-decorated biocompatible honeycomb films with redox-switchable surface for controlling cell adhesion/detachment

Hypothesis.Selenium (Se)-containing compound is sensitive to redox stimulation, showing hydrophobic-hydrophilic reversible transition. Introduction of such compound into honeycomb film could confer on it redox-switchable surface wettability, which is expected to control cell adhesion/detachment behavior.Experiments.Didodecyl selenide was designed and mixed with polystyrene to prepare honeycomb films using “breath figure” method. The film microstructures were characterized by scanning electron microscope and atomic force microscopy, and the arrangement of Se atoms in honeycomb film was determined by X-ray photoelectron spectroscopy and energy dispersive spectrometry. The variation of film wettability upon the alternating stimulation of H2O2 and Vc was examined. Then the cell adhesion, proliferation, and controlled detachment on honeycomb films were conducted.Findings.The introduction of didodecyl selenide helps to form ordered honeycomb film, and Se atoms were found to located on the bottom, pore walls, and top surface of the film. The presence of didodecyl selenide not only greatly improves film biocompatibility by enhancing cell thioredoxin reductase activity, but also imparts the film with H2O2–/vitamin C-regulated tunable wettability that controls cell adhesion and detachment. H2O2 treatment produces a hydrophilic surface for cell adhesion and proliferation, whereas the addition of vitamin C generates hydrophobic surfaces and allows cells to detach while remaining alive with high activity.

Iron oxide nanoparticles embedded in porous films for tannic acid detection

A novel method was developed for the detection of tannic acid (TA) by iron oxide (Fe2O3) nanoparticles (NPs) immobilized on the porous films prepared by the modified breath figure (mBF) method. For the mBF method, ferric chloride (FeCl3) was included in the polystyrene polymer solution and sodium borohydride (NaBH4) was added in the humidity to induce an interfacial reaction between the two materials during the BF process. FeCl3 present in the polymer solution is driven towards the water droplets containing NaBH4 due to the coffee stain effect. This phenomenon induces the formation of Fe2O3 NPs at the pore surface as FeCl3 reacts with NaBH4 at the air/polymer solution interface. The morphology of the hybrid films was evaluated by scanning electron microscopy (SEM). The doped Fe2O3 NP on the porous film was analyzed by energy dispersive X-ray (EDS), Fourier transform infrared spectroscopy (FT-IR), UV–vis spectrophotometer, thermogravimetric analyses (TGA), and X-ray diffraction (XRD). The wettability and conductivity of the films were also measured to further support the incorporation of Fe2O3 NP into the porous film. Detection of TA by Fe2O3 NPs is due to the binding of Fe(III) with galloyl groups of TA forming a coordination compound (Fe2O3-TA complex) which induces the color change of the TA solution from yellow to bluish-black for quick and easy naked-eye detection. The developed sensor system yields a limit of detection (LOD) and limit of quantitation (LOQ) of 370 nM and 1230 nM, respectively. The films exhibited excellent stability and selectivity towards TA and showed no sensitivity towards other compounds possessing a similar structure such as gallic acid, phenol, and glucose.

Fabrication of wrinkle-patterned polydimethylsiloxane films as light out-coupling structure for white OLEDs

Light out-coupling is an important strategy for the performance enhancement of white organic light-emitting diodes (OLEDs). Polydimethylsiloxane (PDMS), as a famous transparent elastomer, has the potential of using as a light extraction structure for OLED devices. Here, wrinkle-patterned PDMS films were in-situ fabricated via breath figure method together with spin coating process in a highly humid environment onto the glass side of the ITO substrate. The effect of solvent additive on the wrinkle morphology were investigated. The PDMS films were introduced into two different white OLED devices to extract the light of the substrate mode at the substrate-air interface. The maximum luminance improves 30.7% and 50.4%, respectively. While OLEDs also show appreciable enhancement with 31% and 11% in external quantum efficiencies due to luminance increase. Additionally, finite-difference time-domain (FDTD) simulations were performed to get insight into the mechanism of the light extraction enhancement due to the PDMS wrinkle structure. The reduced total internal reflections at the substrate-glass interface seems to increase the light out-coupling. We infer from these results that wrinkle-patterned PDMS films help to extract more light confined to the interior of white OLEDs, thereby improving the device performance. This work provides a relatively simple method to efficiently extract light from white OLEDs.

Electrosprayed hierarchically porous microparticles with tunable morphology for selective dye adsorption

Hierarchically porous structures play crucial roles on the biological and artificial materials, hence, the development of readily method to prepare microparticles with hierarchical pores and tunable morphologies is of great significance. Here, a facile electrospray technique combining breath figure (BF) or nonsolvent induced phase separation (NIPS) was developed to prepare hierarchically porous microparticles with various morphologies based on polymers of intrinsic microporosity (PIM-1). The relationship between the ternary system composition of the electrospraying (PIM-1 and cosolvent) and the microparticle architectures (morphology and pore structure) was carefully investigated. The as-prepared PIM-1 microparticles possess predominant micropores and abundant macropores with high surface areas in range from 548 m2 g−1 to 747 m2 g−1. Their adsorption capacities for CO2 and organic dye were facilitated by the generation of macropores, owing to the increased accessibility of isolated micro-mesopores. More importantly, they perform enhanced selective adsorption abilities towards malachite green (MG) for the methyl orange/MG mixture pairs.

Polymethyl Methacrylate/Polypyrrole Porous Membranes Prepared by Breath Figure Method with Superior Salt Resistance for High‐Efficiency Interfacial Solar Evaporation

A simple method for the fabrication of the double‐layer and salt‐resistant evaporator consists of a porous structure polymethyl methacrylate/polypyrrole (PMMA/PPy) photothermal membrane as the top layer and plant fiber‐wrapped expanded polyethylene (EPE) foam as the insulating bottom layer is demonstrated for the first time for efficient solar‐driven interfacial evaporation. For the fabrication of the porous PMMA/PPy membranes, a straightforward and affordable breath figure approach is used. Owing to its porous structure with low tortuosity and large pore size, excellent insulation of the EPE sponge, and the strong light absorption of PPy coating, the as‐prepared PMMA/PPy evaporator exhibits a stable photothermal conversion efficiency of 95.3%, corresponding to a high evaporation rate of 1.65 kg m−2 h−1, and outstanding salt resistance performance in 15%wt NaCl solution (evaporation rate of 1.54 kg m−2 h−1), under 1 sun irradiation, thus showing great potential for practical desalination application by combination with its simple, cost‐efficient, and easily scale‐up fabrication process. More importantly, the findings herein may also provide a versatile method for the design of novel photothermal materials with large pores using various polymers as substrates without limitation by shape or size only via a simple and “green” breath figure approach.

Wetting and Adhesion of a Polymer Melt on Porous Self‐Assembled Polymer Substrates by Breath Figure Templating

AbstractThis study addresses the wetting and adhesion of a low molecular mass poly(n‐butyl acrylate) homopolymer melt, used as a weak acrylic adhesive, on two types of textured polymer films prepared by the breath figure templating method. The first film is a polystyrene homopolymer honeycomb‐like structure with well‐defined porous structure and long‐range ordering. The second is a disordered poly(n‐butyl acrylate)‐block‐polystyrene diblock copolymer film featuring a broad distribution of pore diameters. Static contact angle measurements show that porous films repel better the polymer melt than the corresponding nontextured films. Contact angles and spreading of polymer melt droplets on these textured surfaces reveals a Cassie‐Baxter state on the ordered porous film and a partial Wenzel state on the disordered porous films. In addition, probe tack results show that the textured surfaces tend to induce cavitation. The correlation between the wetting and adhesion highlights the major role of melt insertion into the pores, which is primarily controlled by the pores’ dimensions.

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.

Breath-Figures to Design Novel Functional Materials with Regular Features at Nanoscale

This article gives a brief account of how Breath-Figures (BF) are used as a dynamic templating method to prepare periodic nanostructures in sizes ranging from nanometers to micrometers. Although a defined, exact mechanism for BF formation is not yet known, literature surveys do conclude some important overviews. The formation of honeycomb structures, quasi-crystalline arrays, hexagonal arrays and highly ordered BFs of different shapes and pore sizes are summarized.

Dual-Color Emission from Spatially Distributed Quantum Dots in Poly(l-lactide) Films with Diverse Morphologies.

Polymer-based multicolor emissive materials have growing demand due to their potential applications in various fields such as full-color displays, bioimaging, and light sources because of their processability and high stability. Herein, we report dual-color emissive hybrid materials based on biocompatible poly(l-lactide) and polyethylene glycol-modified two-dimensional layered double hydroxide quantum dots (PEG-LDHQDs). The morphology of polymer films tunes the spatial distribution of QDs within the polymer matrix, modulating the energy transfer between the QDs and affording the dual emission behavior in the aggregated states. The amorphous hybrid films show single emission (blue) from the finely dispersed QDs (mostly isolated) within the polymer matrix. In contrast, dual emission (blue and red) was observed when the polymer was crystallized due to the possible accumulation of QDs at the interface of crystalline and amorphous phases in the lamellar structure. Furthermore, the dual emission could be enhanced by the aggregation of QDs on the pores of the breath figure pattern constructed on the surface of the hybrid film.

Highly stretchable, durable, and superfine fiber-shaped strain sensor with a porous core-sheath microstructure

A stretchable fiber-shaped strain sensor benefits from its high aspect ratio and can be easily integrated into textiles, which has attracted extensive attention. Introducing microstructures such as porous or buckling microstructures into elastic fibers are often used to obtain high-performance strain-sensing fibers. However, the fabrication of high-performance superfine fiber-shaped strain sensor still faces the difficulty of preparing controllable microstructures on the surface of the fiber. In this work, we propose a breath figure method to fabricate CNTs/SEBS film with porous microstructure on the polyurethane fiber (PU fiber). By adjusting the process parameters, the morphology of the porous microstructure can be controlled conveniently. The optimized fiber-shaped strain sensor has a superfine diameter (58 μm), large detection range (240%), low strain detection limit (0.025%), high sensitivity (GF of 1439.83 at 230 %–250%), fast response time (≈62.7 ms), and excellent stability with 100,000 cycles at a large deformation of 100%. Finally, the fiber-shape strain sensor was sewn into the textile to verify its application in gesture recognition, breath sensing and limbs activity monitoring. This work proposes a simple and efficient strategy to realize the superfine fiber-shaped strain sensor with controlled porous microstructure, which has great potential in the field of wearable electronic devices.

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.

3D porous structure assembled from MXene via breath figure method for electrochemical detection of dopamine

Restacking or aggregation inhibition of MXene nanosheets is crucial to the maintenance of their excellent electrochemical performance during use. In this study, a positively charged surfactant is inserted into the MXene nanolayers through a simple self-assembly process based on electrostatic interaction, producing a MXene/surfactant complex with enlarged interlayer spacing. Then 3D MXene-based porous structure could be prepared by the facile and low-cost breath figure method, in which MXene/surfactant complex is used as a casting material, therefore the inhibition of restacking or aggregation and increase of surface area at multiscale are realized in one system at the same time. Benefiting from the high conductivity of MXene and increased surface area of 3D porous structure that can provide massive active sites and facilitate the electrolyte infiltration and ion or electron access, enhanced electrochemical performance, for instance, electrochemical sensing of dopamine (DA) is shown. A low detection limit of 36.8 nM with excellent anti-interference, reproducibility, repeatability and long-term stability is realized. Good accuracy for DA detection in real biological samples is also confirmed by determining DA concentration in complex human urine samples. More importantly, porous structure such as pore size, uniformity, order and porosity can be adjusted through tuning the fabrication conditions, thereby regulating its electrochemical properties. This work not only provides a high-performance electrode for electrochemical sensing, but also offers a simple and practical strategy for the construction of 3D porous MXene film that holds great potential in electromagnetic interference shielding, supercapacitors and batteries.

Electrospun Porous Nanofibers: Pore-Forming Mechanisms and Applications for Photocatalytic Degradation of Organic Pollutants in Wastewater.

Electrospun porous nanofibers have large specific surface areas and abundant active centers, which can effectively improve the properties of nanofibers. In the field of photocatalysis, electrospun porous nanofibers can increase the contact area of loaded photocatalytic particles with light, shorten the electron transfer path, and improve photocatalytic activity. In this paper, the main pore−forming mechanisms of electrospun porous nanofiber are summarized as breath figures, phase separation (vapor−induced phase separation, non−solvent−induced phase separation, and thermally induced phase separation) and post−processing (selective removal). Then, the application of electrospun porous nanofiber loading photocatalytic particles in the degradation of pollutants (such as organic, inorganic, and bacteria) in water is introduced, and its future development prospected. Although porous structures are beneficial in improving the photocatalytic performance of nanofibers, they reduce their mechanical properties. Therefore, strategies for improving the mechanical properties of electrospun porous nanofibers are also briefly discussed.

Honeycomb-patterned porous graphene film for electrochemical detection of dopamine

Development of simple, low-cost and facile electrochemical sensor for DA detection is of great significance for the study and treatment of several neurological and psychiatric disorders. Herein, an innovative integration of honeycomb-patterned ordered porous structure with conductive reduced graphene oxide (rGO) was realized through the convenient breath figure method, in which the self-assembly of nontoxic and inexpensive water droplets were involved. Graphene oxide (GO) can be transferred to organic phase by surfactant via a simple self-assembly process to acquire the GO/surfactant complex, which was used as the casting solution in the breath figure method, and thus the skeleton of the porous structure. After electrochemical reduction, honeycomb-patterned porous rGO film was obtained. The prepared rGO-based porous structure modified electrode exhibited a high sensitivity of 1.18 μA/μM and low detection limit of 0.12 μM to DA detection, which are 2.5 and 0.07 folds to corresponding flat films, and are also comparable or even exceeding several functionalized graphene, GO or rGO composites sensor. In addition, excellent anti-interference, reproducibility, repeatability, long-term stability and good accuracy for DA detection in real samples were shown. Importantly, the porous structure can be easily adjusted by changing the preparation conditions, thereby regulating or optimizing the electrochemical sensing performance.

Nanoporous polymer films based on breath figure method for stretchable chemiresistive NO2 gas sensors

Wearable electronics targeting toxic gas analytes have raised tremendous concerns for human-centric intelligent healthcare electronics and systems. A remaining challenge is to combine excellent sensing performance with good mechanical robustness, which has limited the practical applications. Here, we report stretchable, hypersensitive chemiresistive gas sensors based on the breath figure strategy and the transfer printing technique. In a demonstration of the Poly(3-hexylthiophene-2,5-diyl) (P3HT) @ polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) composite film/serpentine Au electrode, sensitivity up to 467 ppm−1, the ultralow limit of detection of 2.45 ppb, and a gas detection stability at 40 % tensional strain were achieved due to the more active sites and stress dispersion provided by the porous structure of the P3HT@SEBS composite film. To demonstrate the universality of this breath figure strategy, porous polymer diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT) was utilized to build stretchable NO2 sensors. This work reveals that the porous structure could enhance considerable sensing and stretchable properties of gas sensors, and provide a general solution for more stretchable wearable electronics.

Fabrication of Adsorption-Type Hierarchical Functional Films by Using a Facile Swollen Based Breath Figure Method.

The morphology transition from primary to hierarchical adsorption-type microporous domains of amphiphilic block copolymer (BCP) honeycomb-structured films is demonstrated by a facile swollen based breath figure (BF) method. The characteristic parameters of poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS) hierarchical micro- and submicroporous films can be controlled by changing the length of segments or subsequent swelling conditions. A plausible mechanism is demonstrated in this research. A typical amphiphilic BCP with very low volume content of hydrophilic blocks (fP4VP ≤ 0.050) can efficiently stabilize water droplets and inherently assist in the formation of morphology transition. This BCP film can be used for Cr(VI) removal from wastewater, which additionally has enormous potential application in the field of novel optical devices, soft lithography, size-selective separation, etc.

Selective assembly of microbe on patterned porous interfaces as potential membrane reactors for enhanced biodegradation of phenol

The carriers of membrane reactors faced challenges of high cost, and decrease of adsorption and efficiency on the long-term use for wastewater treatment. A facile method to prepare a novel membrane reactor by assembly of microbe on porous interfaces via breath figure for efficient biodegradation of phenol was developed. After the preparation and localized modification of porous interfaces, microbe was selectively incorporated into the patterned cavities, with an extremely high loading amount of 1.56 × 108 /cm2. A much better degradation rate (23.08 mg·L−1·h−1) was achieved in the membrane reactor than free cells (15.7 mg·L−1·h−1), which was improved nearly 50%. The high activity of phenol hydroxylase and catechol 1,2-dioxygenase, and low level of SOD, CAT and POD gave rise to the efficient phenol degradation rate in membrane reactor. Moreover, a good stability under a wider pH (3−8) of membrane reactor presented the degradation efficiency 5–8 times higher than free microbe. Further, at the stress of heavy metal ions, an excellent treatment of phenol was still existed, enhancing the degradation efficiency 3–6 times than free microbe. This strategy provides a new route on the preparation of a cheap, highly efficient and stable membrane reactor, demonstrating its potential on environment and biomedicine.