Breath Figure Research Articles

Construction of 3D Ordered Honeycomb Films with Controllable Pores as Efficient Catalytic Supports

AbstractThe facile construction of 3D porous film using the breath figure technique is critically important in diverse practical applications. However, the discovery of easy synthetic methods and preparation of stimuli‐responsive 3D ordered nano‐/micro‐architectures remain challenging. Herein, the promotive breath figure technique is presented to construct 3D honeycomb porous films on curved substrates using an azobenzene‐containing copolymer. The nanopore size of honeycomb structure decreases gradually with the increase of surface curvature, due to the different solvent drying speeds. Upon irradiation with directional linear polarization light, the round‐shaped nanopores are converted into rectangular‐ and rhombic‐shaped nanopores under different polarization directions. Moreover, these porous films are employed as substrates to load various metal nanoparticles, successfully preparing the nanocomposites. The catalytic capacity of both control and these nanocomposites are evaluated using the NaBH4‐mediated reduction reaction from 4‐nitrophenol to 4‐aminophenol. Compared to the control and nonporous films, the porous films with smaller nanopores exhibit larger catalytic activity. Additionally, UV irradiation upon the nanocomposites promotes the catalytic action, due to the change in surface hydrophilicity caused by the photoisomerization of azobenzene. Recyclable use of nanocomposites demonstrates the high stability. This research provides an innovative strategy to prepare 3D curved porous films for potential on catalysis.

ISO2‐PU Honeycomb Porous Films with a Peculiar Crystalline Structure by the Breath Figure Method Promote Osteogenic Differentiation of Stem Cells

AbstractThe breath figure (BF) method is a handy strategy to prepare porous films. Linear shape memory polyurethanes (SMPUs) are among the most promising polymers for bone repair or regeneration. However, little attention has been paid to the fabrication of SMPU films by using the BF method. In this work, an amorphous SMPU containing isosorbide (ISO) in the long‐chain hard segments (ISO2‐PU) is fabricated into honeycomb porous films. Strikingly, a peculiar crystalline structure with a “Z” configuration and highly regional orientation is formed on the hexagonal holes of the porous films, which results in significantly enhanced mechanical properties. Moreover, the ISO2‐PU honeycomb porous films can markedly accelerate the osteogenic differentiation of rat mesenchymal stem cells, indicating that the porous films have great potentials as bone repair materials. It is further speculated that the Marangoni effect in the condensed water droplets and the molecular assembly of ISO2‐PU due to the strong hydrogen bonds and the chiral center effect of ISO are key contributors. This work, to the best of authors’ knowledge, is the first time that this special crystalline structure on BF‐based porous films is observed and also the first speculation that combines Marangoni effect with the microstructure of BF‐based porous films.

Two Innovative Fumaric Acid Bridging Lanthanide-Encapsulated Hexameric Selenotungstates Containing Mixed Building Units and Electrochemical Performance for Detecting Mycotoxin.

Two particular fumaric acid bridging lanthanide-encapsulated selenotungstates [H2N(CH3)2]16Na8[Ln3(H2O)7]2 [W4O8(C4H2O4) (C4H3O4)]2[SeW6O25]2[B-α-SeW9O33]4·46H2O [Ln = Ce3+ (1), La3+ (2)] were acquired by the deliberately designed step-by-step synthetic strategy, which are composed of four trilacunary Keggin [B-α-SeW9O33]8- and two original [SeW6O25]10- building units together with one fumaric acid bridging heterometallic [Ln3(H2O)7]2[W4O8(C4H2O4) (C4H3O4)]228+ entity. Particularly, this heterometallic cluster contains four fumaric acid ligands, which play two different roles: one works as the pendant decorating the cluster and the other acts as the linker connecting the whole structure. In addition, the 1@DDA hybrid material was produced through the cation exchange of 1 and dimethyl distearylammonium chloride (DDA·Cl) and its beehive-shaped film of 1@DDA was prepared by the breath figure method, which can be further used to establish an electrochemical biosensor for detecting a kind of mycotoxin-ochratoxin A (OX-A). The 1@DDA beehive-shaped film-based electrochemical biosensor exhibits good reproducibility and specific sensing toward OX-A with a low detection limit of 29.26 pM. These results highlight the huge feasibility of long-chain flexible ligands in building lanthanide-encapsulated selenotungstates with structural complexity and further demonstrate great electrochemical application potentiality of polyoxometalate-involved materials in bioanalysis, tumor diagnosis, and iatrology.

Highly ordered asymmetric cellulose-based honeycomb membrane for moisture-electricity generation and humidity sensing

Moisture-trigged electricity generator (MEG) that can convert ubiquitous moisture into electricity are highly desirable for developing renewable energy supply and ameliorating the crisis in energy. Constructing an asymmetric ordered, namely gradient ordered porous membrane has great potential in MEG. Herein, a series of cellulose acetate (CA)-based membranes with ordered asymmetric honeycomb membranes were fabricated by Breath Figure method, along with silver nanowires (AgNWs) coating. The asymmetric gradient honeycomb pores were achieved by graft modification of lauroyl chloride and adjustment of relative humidity, which not only endowed the MEG with sensitive sensing signals transport under tension and humidity fluctuations but also enhanced voltages generation speed under flowing moisture. The current study provides a facile and scalable strategy for constructing asymmetric gradient ordered porous materials and creates more possibilities for MEG self-powered flexible wearable electronic devices.

Transparent and fluorescent breath figure arrays prepared from end-functionalized copolymers

Fluorescent and transparent polymer films with exquisite micro-structures are ideal candidates for anti-counterfeiting tags. However, it is still a great challenge to embed such properties in one breath figure array due to the restriction of the film-forming ability of polymers. In this work, we designed and synthesized fluorescent copolymers from styrene and 1-pyrenylmethyl methacrylate (PYMMA) and studied their self-assembly behaviors via the breath figure method. The significance of end groups and topologies have been investigated in detail. Novel hexagonal breath figure arrays with high transparency are formed at extremely low concentration (down to 0.06 mg/mL). The breath figure arrays display blue honeycomb pattern when irradiated by ultraviolet light. Breath figure arrays with such special optical properties demonstrated an ideal solution for anti-counterfeiting tags. Besides, this work demonstrates the significance of polymer architecture on the morphology of breath figure arrays and may enlighten the polymer design for a broad range of applications. • Fluorescent copolymers were designed and synthesized for self-assembly by the breath figure method. • A highly regular breath figure array can be formed at polymer concentration of as low as 0.06 mg/mL. • Transparent and fluorescent breath figure arrays are potential for anti-counterfeiting. • Effects of end groups and topologies of polymers on the morphology of breath figure arrays were studied.

Honeycomb-Structured Porous Films from Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Physicochemical Characterization and Mesenchymal Stem Cells Behavior.

Surface morphology affects cell attachment and proliferation. In this research, different films made of biodegradable polymers, poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-HV), containing different molecular weights, with microstructured surfaces were investigated. Two methods were used to obtain patterned films—water-assisted self-assembly (“breath figure”) and spin-coating techniques. The water-assisted technique made it possible to obtain porous films with a self-assembled pore structure, which is dependent on the monomer composition of a polymer along with its molecular weight and the technique parameters (distance from the nozzle, volume, and polymer concentration in working solution). Their pore morphologies were evaluated and their hydrophobicity was examined. Mesenchymal stem cells (MSCs) isolated from bone marrow were cultivated on a porous film surface. MSCs’ attachment differed markedly depending on surface morphology. On strip-formed stamp films, MSCs elongated along the structure, however, they interacted with a larger area of film surface. The honeycomb films and column type films did not set the direction of extrusion, but cell flattening depended on structure topography. Thus, stem cells can “feel” the various surface morphologies of self-assembled honeycomb films and change their behavior depending on it.

Ordered porous films of biomass-based polymers by breath figure: a review

Ordered porous films of biomass-based polymers by breath figure: a review

Micro-Sphere PDMS for Enhancing Light Extraction in Organic Light-Emitting Devices.

We present a micro-sphere PDMS film to improve the external quantum efficiency (EQE) in OLEDs. The micro-sphere PDMS film was fabricated with the breath figure (BF) and replica molding process. The polymer template was prepared through stabilization of the water droplets at the polymer/water interface. The micro-sphere PDMS film was fabricated by pouring PDMS on the polymer template. At a 45 mg/mL concentration, the size of the spheres was approximately 12.3 µm and they had the most circular shape, so this condition yielded the best performance, with an improvement of 33% in the EQE and the widest viewing angle ranging from 0° to 50°. As a result, the sphere film’s size and distribution seem to play important roles in enhancing the EQE in OLEDs. Furthermore, the flexible sphere film based on polymeric materials could offer an effective, large-scale, mass-produced product and a simple process and approach to achieve high efficiency in flexible OLEDs.

Breath‐Figure Self‐Assembled Low‐Cost Janus Fabrics for Highly Efficient and Stable Solar Desalination

AbstractSolar‐driven interfacial evaporation materials for seawater desalination and wastewater treatment have attracted extensive research interest in recent years. Nevertheless, salt accumulation, costly materials, and complex preparation processes greatly hinder the practical application of solar steam generation. Herein, with low‐cost materials such as carbon black (CB), polystyrene‐b‐polybutadiene‐b‐polystyrene (SBS), and commercial cotton fabric, the CB@SBS/cotton fabric Janus evaporator is fabricated via a breath figure template (BFT) method for scalable, long‐term, and stable solar‐driven interfacial desalination. The BFT is a simple yet efficient self‐assembly method that endows the hydrophobic surface of CB@SBS/cotton fabric with a porous structure for high light absorption (≈95.5%) and steam escape. As a result, the CB@SBS/cotton fabric Janus evaporator can achieve a water evaporation rate of 1.37 kg m–2 h–1 and conversion efficiency of 91.3% even in a 3.5 wt% NaCl solution, as well as stably cycling over 15 times without salt accumulation (each cycle: 8 h for illumination and 16 h for rest). The work demonstrates an effective strategy for achieving high‐performance solar steam generation and superior salt rejection capability, which can be potentially utilized in seawater desalination, sterilization, and disinfection.

Temporally Arrested Breath Figure.

Since its original conception as a tool for manufacturing porous materials, the breath figure method (BF) and its variations have been frequently used for the fabrication of numerous micro- and nanopatterned functional surfaces. In classical BF, reliable design of the final pattern has been hindered by the dual role of solvent evaporation to initiate/control the dropwise condensation and induce polymerization, alongside the complex effects of local humidity and temperature influence. Herein, we provide a deterministic method for reliable control of BF pore diameters over a wide range of length scales and environmental conditions. To this end, we employ an adapted methodology that decouples cooling from polymerization by using a combination of initiative cooling and quasi-instantaneous UV curing to deliberately arrest the desired BF patterns in time. Through in situ real-time optical microscopy analysis of the condensation kinetics, we demonstrate that an analytically predictable self-similar regime is the predominant arrangement from early to late times O(10–100 s), when high-density condensation nucleation is initially achieved on the polymer films. In this regime, the temporal growth of condensation droplets follows a unified power law of D ∝ t. Identification and quantitative characterization of the scale-invariant self-similar BF regime allow fabrication of programmed pore size, ranging from hundreds of nanometers to tens of micrometers, at high surface coverage of around 40%. Finally, we show that temporal arresting of BF patterns can be further extended for selective surface patterning and/or pore size modulation by spatially masking the UV curing illumination source. Our findings bridge the gap between fundamental knowledge of dropwise condensation and applied breath figure patterning techniques, thus enabling mechanistic design and fabrication of porous materials and interfaces.

Facile fabrication and SERS performance of polymer/Ag core-shell microspheres via the reverse breath figure accompanied by in situ reduction

A new facile fabrication process of the polymer/Ag core-shell microspheres is demonstrated via the reverse breath figure method accompanied by in situ reduction. In contrast to traditional approaches, which require the prior preparation of polymer microspheres, the star-shaped polyhedral oligomeric silsesquioxane (POSS) amphiphilic block copolymers solution containing AgNO3 is cast under ethanol vapor for the formation of polymer/AgNO3 core-shell microspheres in one step. The influence of polymer molecular structures, solvent, non-solvent and metal salt on the morphology of polymer microspheres was analyzed. Then the AgNO3 can be reduced in situ to form Ag nanoparticles on the surface of polymer microspheres, which resulted in the formation of polymer/Ag core-shell microspheres. The reduced Ag nanoparticles were homogeneously deposited on the surfaces of polymer microspheres, which can exhibit good performance in the surface-enhanced Raman scattering (SERS). The polymer/Ag core-shell microspheres substrate showed a high detection sensitivity (enhancement factor 2.49 × 106) with excellent uniformity and reproducibility for Rhodamine 6G (R6G) (relative standard deviation of the intensity at 612 cm−1 was 6.19%＜20%). The proposed strategy is facile to implement and thus a promising new method for the preparation of polymer/metal core-shell microspheres.

Ultrasensitive flexible NO2 gas sensors via multilayer porous polymer film

Micro-nano structure engineering of active materials in sensors have attracted broad attention for hazardous component detection, which enables creating electronic noses that could detect gas analytes efficiently without introducing abundant functional groups and defects. However, challenges still remain on realizing flexible gas sensors with both decent sensing performance and good mechanical robustness, which are extremely important for wearable electronics. Here we present a scalable and facile manufacturing method to construct the three-dimensional (3D) multilayer porous organic semiconductors (OSCs) structure for transistor based gas sensor, showing largely enhanced gas sensing properties as well as bendability down to 1 mm radius with stable operation. The multilayer porous film of OSCs is assembled via breath figure method, followed by layer-by-layer transferring process. The formed 3D porous structure provides efficient hazardous gas diffusion pathways, abundant gas molecules adsorption active sites and immunity towards mechanical deformation simultaneously. Consequently, an obvious increase of responsivity (from 122% to 1053% at 30 ppm) was achieved for NO2 detection, along with an ultralow limit of detection (∼2.3 ppb), and good gas selectivity. This work demonstrates a scalable and low-cost fabrication strategy for high-performance flexible sensors, which delivers an alternative way for next-generation wearable electronics.

Development of poly(vinylidene fluoride) graft random copolymer membrane for antifouling and antimicrobial applications

Biocidal and anti-fouling properties in the same polymeric membranes are important in biomedical field for their capability to protect serious infection and filtration of biological molecules. For this purpose we report random graft copolymer of poly(vinylidene fluoride) (PVDF-graft-poly(tBAEMA-ran-OEGMA, PVBO) membranes showing both antifouling and antibacterial activity. The PVBO copolymer is synthesised using ATRP technique and the polymer membranes are produced by breath figure (PVBO-1) and phase inversion (PVBO-2) techniques. The former shows well-developed hexagonal pores (diameter 15 ± 3.5 nm), and good hydrophilicity (contact angle 41.3°). PVBO-1 membrane exhibits good antifouling property for both lysozyme and BSA solutions. Antimicrobial activity measured from agar diffusion method indicates that PVBO-1 shows a large zone of inhibition in case of gram-negative E coli and gram-positive S. aureus bacteria, whereas PVBO-2 and its HCl treated state (PVBO-3) membranes exhibit only a moderate zone of inhibition. The MBC and MIC values indicate that the synthesized membranes are bactericidal in nature and not bacteriostatic. Live and dead cell assay indicates that PVBO-1 can significantly inhibit growth of bacteria even at high bacteria concentration confirming high antimicrobial activity. MTT assay suggests PVBO-1 is non-cytotoxic to mammalian cells and co-culturing activity result suggests high cellular selectivity of PVBO-1.

Effect of Polymer Concentrations on Pores Mechanism in Electrospun Fibre

Advanced material science has resulted in materials with atomic-scale dimensions whose tremendous application includes filtration, drug delivery, membrane, sensor, and encapsulation. Nanoporous fibre has been formed using temperature-induced phase separation (TIPS) and vapour-induced phase separation (VIPS) mechanism, but polymer concentration has been underestimated in the electrospinning parameter. This work aims at showcasing the effect of electrospinning parameters including polymer concentration and resultant phases on pore formation on fibre. Pore formation in electrospun fibre was carried out by electrospinning expanded polystyrene (EPS). The surface morphology of the resulting nanoporous fibre was characterized with Scanning Electron Microscope (SEM) while the pore distribution was analyzed with a BET (Brunauer, Emmet, Teller) micromeritics analyzer. From the result, an increased concentration of polymer from 10 % decreased bead population to zero, meanwhile, bombardment with high electrostatic power resulted in beaded fibres at 10% and 15% w/v. Further increase in EPS concentration resulted in beadless fibres and electrospun 20% EPS fibre at 8.5 kV resulted in porous fibre with meso, micro and macropores. At 11.5 kV, pore dimension in fibre reduced with predominant pore width less than 100 nm. An increased voltage to 13.5 kV resulted in morphologies showing brittled fibre probably due to excess pores formed. Conclusively, polymer concentration moderates variables interaction that resulted in phase separation which controls fibre orientation. Therefore, pore formation does not solely depend on TIPS, VIPS, and breath figures but also polymer concentration.

The microstructure and surface characteristics of fluorine‐based copolymer coatings deposited by the static breath method

We constructed a coating with controllable microstructure on the substrate by static breath figure (BF) method. In the atmosphere of water, when the fluorine‐containing 1H,1H,2H,2H‐perfluorooctyl polyacrylate‐block‐polystyrene copolymer (PTFOA‐b‐PS (4 h)) synthesized via atom transfer radical polymerization for 4 h was dissolved in carbon disulfide (CS2) and then coated on the silicon wafer, the concentrated pore size and uniform micro‐pore structure was successfully constructed on the surface. However, the hydrophobicity of the resulting microporous coating was not so good. An interesting result is that when the copolymer solution of PTFOA‐b‐PS (2 h) in tetrahydrofuran (THF) was used under the MeOH/H2O atmosphere (the methanol content was 60% or 80%), the microsphere coating can be produced on the substrate surface to obtain the excellent hydrophobicity. The water contact angles (WCAs) were 148.8 ± 1.8° and 150.3 ± 1.8°, respectively. Energy dispersive X‐ray spectrometer (EDS) results showed that the fluorine element was enriched in the outerfield of the microsphere coating. The low surface energy of fluorine combined with the rough and complex structure of the microspheres can effectively improve the hydrophobicity of the coating.

Honeycomb films of polyoxomolybdate-surfactant hybrids and electrochemical detection of hydroquinone

Giant polyoxomolybdate Na48[H496Mo368O1464S48]·ca.1000 H2O (Mo368) is a strong candidate in materials due to its electrical properties. However, the drawbacks as instability in water and agglomeration in solid are detrimental to their readily integration into functional devices. Surface modification of Mo368 by surfactant can protect Mo368 in chloroform, and disperse Mo368 clusters avoiding to direct contact with each other, further promote the self-assembly of surfactant-encapsulated Mo368 hybrids into ordered porous honeycomb films. A water breath figure acts as good template for the self-assembly into porous honeycomb film at air/water interface. Varying the length of surfactant carbon chains, surfactant concentration, and supporting solution can influence the film morphology. Attributing to the embedded functional inorganic Mo368 clusters and the pore adsorption, as-prepared porous honeycomb film is active to detect hydroquinone with the detection limit of 3.53 µM by an amperometric response method.

Self-Assembly of CsPbBr3 Perovskites in Micropatterned Polymeric Surfaces: Toward Luminescent Materials with Self-Cleaning Properties.

In this work, we present a series of porous, honeycomb-patterned polymer films containing CsPbBr3 perovskite nanocrystals as light emitters prepared by the breath figure approach. Microscopy analysis of the topography and composition of the material evidence that the CsPbBr3 nanocrystals are homogeneously distributed within the polymer matrix but preferably confined inside the pores due to the fabrication process. The optical properties of the CsPbBr3 nanocrystals remain unaltered after the film formation, proving that they are stable inside the polystyrene matrix, which protects them from degradation by environmental factors. Moreover, these surfaces present highly hydrophobic behavior due to their high porosity and defined micropatterning, which is in agreement with the Cassie–Baxter model. This is evidenced by performing a proof-of-concept coating on top of 3D-printed LED lenses, conferring the material with self-cleaning properties, while the CsPbBr3 nanocrystals embedded inside the polymeric matrix maintain their luminescent behavior.

Enzyme-responsive food packaging system based on pectin-coated poly (lactic acid) nanofiber films for controlled release of thymol

Foodborne diseases caused by foodborne pathogens lead to serious harm to food safety and human health. This work fabricated an enzyme-responsive packaging film based on porous poly (lactic acid) (PLA) nanofibers modified by positively charged polyethyleneimine (PEI) and further to adsorb negatively charged pectin coating, which loaded with thymol (THY) for protecting fruits from microbial infection. The porous PLA nanofibers were fabricated by combining “Breath Figure” principle and electrospinning technique. The XPS and FTIR characterizations showed that PLA nanofiber membrane was successfully modified by PEI. The prepared nanofiber membrane significantly inhibited the growth of E. coli, S. aureus and Bacillus subtilis (＞95%), especially showed excellent antifungal activity against Aspergillus niger. The release of THY from pectin-coated porous nanofiber membrane (THY@PLA-PEI-Pectin) was triggered by pectinase, which was secreted by microorganisms from food contamination. Besides, the biocompatible THY@PLA-PEI-Pectin nanofiber membrane prolonged the shelf life of citrus. Therefore, this pectinase-responsive nanofiber membrane has desirable application prospects in the development of active or smart packaging systems.

Self‐Assembly of Adjustable Micropatterned Graphene Oxide and Reduced Graphene Oxide on Porous Polymeric Surfaces

AbstractThe breath figure (BF) method is a simple technique for fabricating micropatterned surfaces but has been rarely studied using graphene oxide (GO) or reduced GO (rGO). Additionally, fabrication of GO or rGO micropatterned (MPGO or MPrGO) by the BF method focuses on smooth and dense inorganic substrates, and the investigation of adjusting the MPGO morphology has been limited. This research systematically studies self‐assembly of MPGO and MPrGO on the surface of two model porous polymers by the BF method and explores its potential applications for surface modification. It is found that the size range of the MPGO is 1–50 µm and that the structures can be adjusted by changing the process parameters. Specifically, under specific conditions, a uniform honeycomb MPGO is obtained. Surface characteristics demonstrate that the unique MPGO morphology alters the surface water contact‐angle from ≈65° to ≈100° and that MPrGO decreases the surface resistivity to 1–5 kΩ cm−2. Additionally, MPGO coating on a microfiltration membrane gives it a much greater permeability than GO coating without micropatterned morphology and antibiofilm properties. Overall, this study shows that MPGO and MPrGO with adjustable morphologies are easily obtained on polymeric surfaces, thus altering the surface properties and giving the polymers various potential applications.

Antibacterial Activity of Polyaniline Coated in the Patterned Film Depending on the Surface Morphology and Acidic Dopant.

We have fabricated poly(ε-caprolactone) (PCL) films with flat and honeycomb-patterned (HCP) structures to coat polyaniline (PANI) on the film surface. In addition, the effect of chemical modification of PANI by sulfuric acid (H2SO4) was also studied for antibacterial activity. The flat and HCP PCL films were obtained by simple evaporation of the solvent and via the breath figure (BF) method, respectively. The morphology and chemical composition of PANI coated on the film surface were evaluated by scanning electron microscopy (SEM) and X-ray spectroscopy (EDX). Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analyses (TGA) were obtained to identify the PANI coating. The wettability and conductivity of the films were also measured. Applicational aspects were evaluated by assessing antibacterial and antibiofilm activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The EDX, TGA, and FT-IR findings indicated chemical modification of PCL film by PANI and H2SO4. The conductivity of the films was increased by the coating of PANI to the patterned surface and additionally increased by the chemically modified PANI. The antibacterial activity was 69.79%, 78.27%, and 88% against E. coli, and 32.73%, 62.65%, and 87.97% against S. aureus, for flat PANI, HCP PANI, and H2SO4-treated HCP films, respectively. Likewise, the PANI coated flat, HCP, and H2SO4-treated HCP films inhibited E. coli biofilm formation by around 41.62%, 63%, and 83.88% and S. aureus biofilm formation by 17.81%, 69.83%, and 96.57%, respectively. The antibacterial activity of the HCP film was higher than that of flat PANI films, probably due to the higher coating of PANI on the HCP surface. Moreover, sulfonation of the HCP film with H2SO4 might have improved the wettability, thereby enhancing the antibacterial and antibiofilm properties. Our results showed that topographical changes, as well as doping, offer simple and cost-effective ways to modify the structural and functional properties of films.