Solvent and substrate contributions to the formation of breath figure patterns in polystyrene films

Enhancing Sensitivity in Gas Detection: Porous Structures in Organic Field-Effect Transistor-Based Sensors

Gas detection is crucial for detecting environmentally harmful gases. Organic field-effect transistor (OFET)-based gas sensors have attracted attention due to their promising performance and potential for integration into flexible and wearable devices. This review examines the operating mechanisms of OFET-based gas sensors and explores methods for improving sensitivity, with a focus on porous structures. Researchers have achieved significant enhancements in sensor performance by controlling the thickness and free volume of the organic semiconductor layer. Additionally, innovative fabrication techniques like self-assembly and etching have been used to create porous structures, facilitating the diffusion of target gas molecules, and improving sensor response and recovery. These advancements in porous structure fabrication suggest a promising future for OFET-based gas sensors, offering increased sensitivity and selectivity across various applications.

Investigation of Orderliness of Breath Figures on Polydimethylsiloxane

Breath figures, the self-assembled water droplet patterns formed on cold surfaces, are ideally hexagonal. A deviation from the ideal honeycomb pattern can occur due to variation of roughness of the substrate, change in vapor from water to other liquids, etc. The thermodynamics of breath figure formation is complex, and any deviation from ideality is even more difficult to understand. In the absence of a unified theory to understand such patterns and experimental difficulties in monitoring all aspects of formation of breath figures, the patterns formed are studied in terms of their orderliness by determining their Voronoi entropy. We report here the Voronoi entropy calculations of the breath figure fabricated over the smooth and constrained surfaces using polydimethylsiloxane (PDMS) of molecular weight 235 g/mol in two different environments: (a) water and (b) binary mixture of ethanol-propanol over the entire concentration range. Ordered honeycomb patterns are seen on the smooth surfaces, and disordered patterns are seen on constrained surfaces when imaged using confocal microscopy. The latter is attributed to the depinning of the triple-phase contact line, implying that the underlying constraints influence the pore morphology. Contact angle studies of water over the breath figure patterned surfaces indicate the hydrophobic nature of the patterned surfaces.

Metallic Micro-Nano Network-Based Soft Transparent Electrodes: Materials, Processes, and Applications

Soft transparent electrodes (TEs) have received tremendous interest from academia and industry due to the rapid development of lightweight, transparent soft electronics. Metallic micro-nano networks (MMNNs) are a class of promising soft TEs that exhibit excellent optical and electrical properties, including low sheet resistance and high optical transmittance, as well as superior mechanical properties such as softness, robustness, and desirable stability. They are genuinely interesting alternatives to conventional conductive metal oxides, which are expensive to fabricate and have limited flexibility on soft surfaces. This review summarizes state-of-the-art research developments in MMNN-based soft TEs in terms of performance specifications, fabrication methods, and application areas. The review describes the implementation of MMNN-based soft TEs in optoelectronics, bioelectronics, tactile sensors, energy storage devices, and other applications. Finally, it presents a perspective on the technical difficulties and potential future possibilities for MMNN-based TE development.

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.

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.

Biopolymer Honeycomb Microstructures: A Review

In this review, we present a comprehensive summary of the formation of honeycomb microstructures and their applications, which include tissue engineering, antibacterial materials, replication processes or sensors. The history of the honeycomb pattern, the first experiments, which mostly involved the breath figure procedure and the improved phase separation, the most recent approach to honeycomb pattern formation, are described in detail. Subsequent surface modifications of the pattern, which involve physical and chemical modifications and further enhancement of the surface properties, are also introduced. Different aspects influencing the polymer formation, such as the substrate influence, a particular polymer or solvent, which may significantly contribute to pattern formation, and thus influence the target structural properties, are also discussed.

Self-assembled polylactic acid (PLA): Synthesis, properties and biomedical applications

The surface morphology and topography of cell culture substrates play an important role in cell proliferation and growth. Regulation of the surface microstructure allows the development of tissue culture media suitable for different cells. Polylactic acid (PLA) is a biobased and biodegradable (under defined conditions) polymer with low immunogenicity, non-toxicity, and good mechanical properties, which have facilitated their pharmaceutical and biomedical applications. This review summarizes recent advances in the synthesis and self-assembly of surface microstructure based on PLA materials and discusses their biomedical applications such as cell culturing and tissue engineering.

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 μ m 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.

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.

Nanoparticle-Induced Self-Assembly of Block Copolymers into Nanoporous Films at the Air-Water Interface

Herein, we report the cooperative self-assembly of nanoparticles and block copolymers at the air-water interface, which can generate highly uniform and readily transferable composite films with tunable nanoscale architecture and functionalities. Interestingly, the incorporation of nanoparticles significantly affects the self-assembly of block copolymers at the interface. The nanoparticle-induced morphology change occurs through distinct mechanisms depending on the volume fraction of the hydrophobic block. For block copolymers with a relatively small hydrophobic volume fraction, the morphology transition occurs through the nanoparticle-induced swelling of a selective block. When the hydrophobic volume fraction is large enough, added nanoparticles promote the breath figure assembly, which generates uniform honeycomb-like porous structures with unusual nanoscale periodicity. This approach is generally applicable to various types of nanoparticles, constituting a simple one-step method to porous thin films with various functionalities.

Breath figure-derived porous semiconducting films for organic electronics

Porous semiconductor film morphologies facilitate fluid diffusion and mass transport into the charge-carrying layers of diverse electronic devices. Here, we report the nature-inspired fabrication of several porous organic semiconductor-insulator blend films [semiconductor: P3HT (p-type polymer), C8BTBT (p-type small-molecule), and N2200 (n-type polymer); insulator: PS] by a breath figure patterning method and their broad and general applicability in organic thin-film transistors (OTFTs), gas sensors, organic electrochemical transistors (OECTs), and chemically doped conducting films. Detailed morphological analysis of these films demonstrates formation of textured layers with uniform nanopores reaching the bottom substrate with an unchanged solid-state packing structure. Device data gathered with both porous and dense control semiconductor films demonstrate that the former films are efficient TFT semiconductors but with added advantage of enhanced sensitivity to gases (e.g., 48.2%/ppm for NO₂ using P3HT/PS), faster switching speeds (4.7 s for P3HT/PS OECTs), and more efficient molecular doping (conductivity, 0.13 S/m for N2200/PS).

1D Roughness Driven Depinning of Self-Assembly of Liquid Droplets

The conventional hexagonal, uniform breath figure pattern formed over smooth substrates and substrates with constraints of the order of 50 μm is distorted when the underlying constraints are down to 1 μm. This paper explores this phenomenon further and concludes that, in addition to topology-based arguments presented by other authors previously, it is necessary to invoke the depinning effects of the three-phase contact line in order to explain the same. The influence of surface constraints on the self-assembly of liquid droplets is investigated. A semiquantitative explanation for large-scale pattern formation consisting of small-scale closely arranged droplets inside the large-scale distorted ring of droplets is presented in this paper. The scale at which the influence of constraints becomes dominant is also determined in this study. It is seen that the underlying roughness has a larger impact than the nature of polymer on pore size. Comparative studies of pore patterns formed on smooth and constrained substrates are reported. The simulated energy-minimized shapes of the droplets on smooth and constrained substrates are obtained using Surface Evolver.

Formation of Hierarchical Porous Films with Breath-Figures Self-Assembly Performed on Oil-Lubricated Substrates

Hierarchical honeycomb patterns were manufactured with breath-figures self-assembly by drop-casting on the silicone oil-lubricated glass substrates. Silicone oil promoted spreading of the polymer solution. The process was carried out with industrial grade polystyrene and polystyrene with molecular mass M w = 35 , 000 g m o l . Both polymers gave rise to patterns, built of micro and nano-scaled pores. The typical diameter of the nanopores was established as 125 nm. The mechanism of the formation of hierarchical patterns was suggested. Ordering of the pores was quantified with the Voronoi tessellations and calculation of the Voronoi entropy. The Voronoi entropy for the large scale pattern was S v o r = 0.6 - 0.9 , evidencing the ordering of pores. Measurement of the apparent contact angles evidenced the Cassie-Baxter wetting regime of the porous films.

In Search of a Green Process: Polymeric Films with Ordered Arrays via a Water Droplet Technique

As an efficient technique for the preparation of polymeric hexagonal orderly arrays, the breath figure (BF) process has opened a modern avenue for a bottom-up fabrication method for more than two decades. Through the use of the water vapor condensation on the solution surface, the water droplets will hexagonally pack into ordered arrays, acting as a template for controlling the regular micro patterns of polymeric films. Comparing to the top-down techniques, such as lithography or chemical etching, the use of water vapor as the template provides a simple fabrication process with sustainability. However, using highly hazardous solvents such as chloroform, carbon disulfide (CS2), benzene, dichloromethane, etc., to dissolve polymers might hinder the development toward green processes based on this technique. In this review, we will touch upon the contemporary techniques of the BF process, including its up-to-date applications first. More importantly, the search of greener processes along with less hazardous solvents for the possibility of a more sustainable BF process is the focal point of this review.

Controlled Phase Separation in Poly( p-phenyleneethynylene) Thin Films and Its Relationship to Vapor-Sensing Properties

In this paper, we report the synthesis and mesoporous film formation of hydrophobic rodlike poly( p-phenyleneethynylene)s (PPEs) and present porosity-dependent quenching studies using 1,3,5-trinitrotoluene (TNT) vapors. Nonsolvent vapor-induced phase separation was used to induce pore formation during film casting, and the concentration of PPEs in the casting solution was controlled carefully to prevent excimer formation. We found that the structures of the sidechains of the PPEs strongly influence the range of relative humidity at which controlled pore generation occurs, which could be rationalized from interfacial energies calculated from contact angle measurements. Porosity of the PPE films resulted in increased efficiency of fluorescence quenching toward TNT vapors, which previously required very thin films (below 5 nm) for sensing applications. The control of the porous structure as well as film thickness constitutes a promising strategy for enhancing the efficiency of chemosensors and in more general applications requiring fine-tuned polymer-gas interactions.

Antimicrobial Porous Surfaces Prepared by Breath Figures Approach

Herein, efficient antimicrobial porous surfaces were prepared by breath figures approach from polymer solutions containing low content of block copolymers with high positive charge density. In brief, those block copolymers, which were used as additives, are composed of a polystyrene segment and a large antimicrobial block bearing flexible side chain with 1,3-thiazolium and 1,2,3-triazolium groups, PS54-b-PTTBM-M44, PS54-b-PTTBM-B44, having different alkyl groups, methyl or butyl, respectively. The antimicrobial block copolymers were blended with commercial polystyrene in very low proportions, from 3 to 9 wt %, and solubilized in THF. From these solutions, ordered porous films functionalized with antimicrobial cationic copolymers were fabricated, and the influence of alkylating agent and the amount of copolymer in the blend was investigated. Narrow pore size distribution was obtained for all the samples with pore diameters between 5 and 11 µm. The size of the pore decreased as the hydrophilicity of the system increased; thus, either as the content of copolymer was augmented in the blend or as the copolymers were quaternized with methyl iodide. The resulting porous polystyrene surfaces functionalized with low content of antimicrobial copolymers exhibited remarkable antibacterial efficiencies against Gram positive bacteria Staphylococcus aureus, and Candida parapsilosis fungi as microbial models.

Molecular Design for Preparation of Hexagonal-Ordered Porous Films Based on Side-Chain-Type Liquid-Crystalline Star Polymer

Fabrication of regularly porous films by the breath-figure method has attracted much attention. The simple, low-cost technique uses the condensation of water droplets to produce these structures, but the phenomenon itself is complex, requiring control over many interacting parameters that change throughout the process. Developing a unified understanding for the molecular design of polymers to prepare ordered porous films is challenging, but required for further advancements. In this article, the effects of the chemical structure of polymers in the breath-figure technique were systematically explored using side-chain-type liquid-crystalline star polymers. The formation of porous films was affected by the structure of the polymers. Although the entire film surface of poly(11-[4-(4-cyanobiphenyl)oxy]undecyl methacrylate) (P11CB) had a hexagonal ordered porous structure over a certain M_n value, regularly arranged holes did not easily form in poly(methyl methacrylate) (PMMA), even though the main chain of PMMA is similar to that of P11CB. A comparison of P11CB and poly(11-[(1,1'-biphenyl)-4-yloxy]undecyl methacrylate) (P11B) (P11CB without cyano groups) showed that the local polar groups in hydrophobic polymers promoted the formation of ordered porous films. No holes were formed in poly(4-cyanobiphenyl methacrylate) (P0CB) (P11CB without alkyl spacers) films due to its hydrophilicity. The introduction of alkyl chains in P0CB allowed the preparation of honeycomb-structured films by increasing the internal tension. However, alkyl chains in the side chain alone did not result in a porous structure, as in the case of poly(undecyl methacrylate) (P11). Aromatic rings are also required to increase the T_g and improve film formability. In the present study, suitable molecular designs of polymers were found, specifically hydrophobic polymers with local polar groups, to form a regularly porous structure. Development of clear guidelines for the molecular design of polymers is the subject of our current research, which will enable the fabrication of porous films using various functional polymers.

Honeycomb-patterned porous films fabricated via self-organization of Tb complex-loaded amphiphilic copolymers

Amphiphilic copolymers, poly(styrene)-block-Tb complex (PS-b-Tb complex), were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The honeycomb structured porous films were fabricated via dropping the PS-b-Tb complex copolymer solutions on glass substrates by the breath figures method (BFM). The structure and composition of the amphiphilic copolymer PS-b-Tb complex were confirmed by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). The surface morphology and elemental mapping of the highly ordered porous films were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and laser scanning confocal microscopy (LSCM). The results indicated that the solvent type and copolymer concentration can affect the surface morphology of the porous films. The average diameter of the pores in the porous films decreased with the polymer concentration and the molecular weight of the copolymers increased. The FESEM-EDX analysis further verified that the hydrophilic groups (Tb complex groups) were mainly distributed at the pore wall, instead of at the outer surface layer of the films, which was consistent with the LSCM results.

Amphiphilic copolymers PS-b-Tb complex were synthesized by RAFT polymerization, the honeycomb structured porous films were fabricated via BFM, the hydrophilic groups (Tb complex groups) were mainly distributed at the pore wall.

Breath-Figure Self-Assembly, a Versatile Method of Manufacturing Membranes and Porous Structures: Physical, Chemical and Technological Aspects

The review is devoted to the physical, chemical, and technological aspects of the breath-figure self-assembly process. The main stages of the process and impact of the polymer architecture and physical parameters of breath-figure self-assembly on the eventual pattern are covered. The review is focused on the hierarchy of spatial and temporal scales inherent to breath-figure self-assembly. Multi-scale patterns arising from the process are addressed. The characteristic spatial lateral scales of patterns vary from nanometers to dozens of micrometers. The temporal scale of the process spans from microseconds to seconds. The qualitative analysis performed in the paper demonstrates that the process is mainly governed by interfacial phenomena, whereas the impact of inertia and gravity are negligible. Characterization and applications of polymer films manufactured with breath-figure self-assembly are discussed.

Mechanically durable liquid-impregnated honeycomb surfaces

Liquid repellent surfaces typically work by keeping the fouling liquid in a metastable state, with trapped pockets of air between the substrate and the liquid. An alternative method with greater long-term stability utilizes liquid-impregnated surfaces, where the liquid being repelled slides over an immiscible liquid immobilized on a porous surface. Here, we report a method for creating honeycomb surfaces amenable to liquid-impregnation. Polystyrene dissolved in a water-immiscible, volatile solvent was deposited in a humid environment on a variety of substrates to achieve the necessary porosity. Evaporative cooling results in condensation of water in a breath figure array of droplets, forming a sacrificial template for the drying polymer film. These honeycomb surfaces were further functionalized with fluorosilane and dipped in the lubricating liquid to result in a durable, liquid-repellent surface. These surfaces were found to exhibit repellency towards water and oils with extremely low tilt angles due to the smooth liquid–liquid contact between the lubricating liquid and the liquid being repelled.

Assembly of Ultrathin Gold Nanowires into Honeycomb Macroporous Pattern Films with High Transparency and Conductivity

Because of its promising properties, honeycomb macroporous pattern (HMP) film has attracted increasing attention. It has been realized in many artificial nanomaterials, but the formation of these HMPs was attributed to templates or polymer/supermolecule/surfactant assistant assembly. Pure metal HMP film has been difficult to produce using a convenient colloidal template-free method. In this report, a unique template-free approach for preparation of Au HMP film with high transparency and conductivity is presented. Ultrathin Au nanowires, considered a linear polymer analogue, are directly assembled into HMP film on various substrates using a traditional static breath figure method. Subsequent chemical cross-linking and oxygen plasma treatment greatly enhance the stability and conductivity of the HMP film. The resulting HMP film exhibits great potential as an ideal candidate for transparent flexible conductive nanodevices.

Hierarchically Structured Macro with Nested Mesoporous Zinc Indium Oxide Conducting Film

Fabrication of homogeneously distributed (HD) macropores by breath figure process is an active research area. Adopting the process, for the first time, we report the fabrication of HD macro with nested meso (hierarchical) porous nanocrystalline zinc indium oxide conducting sol-gel thin film on glass by dip-coating at 45-50% room relative humidity (RH) from a solution in ethanol-2-butanol (1:1, w/w) medium with a 1:1, Zn:In ratio. In this process, solution composition and RH are found to play key roles on HD macropore generation. The film is highly promising toward visible-light-driven photoelectrochemical water splitting.

From honeycomb- to microsphere-patterned surfaces of poly(lactic acid) and a starch-poly(lactic acid) blend via the breath figure method

BACKGROUND

This study investigated the preparation of ordered patterned surfaces and/or microspheres from a natural-based polymer, using the breath figure and reverse breath figure methods.

METHODS

Poly(D,L-lactic acid) and starch poly(lactic acid) solutions were precipitated in different conditions - namely, polymer concentration, vapor atmosphere temperature and substrate - to evaluate the effect of these conditions on the morphology of the precipitates obtained.

RESULTS

The possibility of fine-tuning the properties of the final patterns simply by changing the vapor atmosphere was also demonstrated here using a range of compositions of the vapor phase. Porous films or discrete particles are formed when the differences in surface tension determine the ability of polymer solution to surround water droplets or methanol to surround polymer droplets, respectively. In vitro cytotoxicity was assessed applying a simple standard protocol to evaluate the possibility to use these materials in biomedical applications. Moreover, fluorescent microscopy images showed a good interaction of cells with the material, which were able to adhere on the patterned surfaces after 24 hours in culture.

CONCLUSIONS

The development of patterned surfaces using the breath figure method was tested in this work for the preparation of both poly(lactic acid) and a blend containing starch and poly(lactic acid). The potential of these films to be used in the biomedical area was confirmed by a preliminary cytotoxicity test and by morphological observation of cell adhesion.

Rhodamine-doped nanoporous polymer films as high-performance anti-reflection coatings and optical filters

We demonstrate a simple and robust procedure for the fabrication of rhodamine-doped nanoporous poly(methyl methacrylate) (PMMA) films, whose optical properties, such as anti-reflection, fluorescence and absorption can be tailored to specific applications. By exploiting phase separation of a binary polymer blend (PMMA and polystyrene), we fabricated foam-like nanoporous films that could be easily and cost-effectively integrated into the fabrication process of optical components. We link film morphology, studied by multifrequency atomic force microscopy (AFM), to the effective refractive index of the films for use as anti-reflection coatings. The film's morphology leads to superior broadband anti-reflection performance compared with homogeneous films. For applications involving optical filters and spectral conversion layers (e.g., for photovoltaic applications), we doped the films with the fluorescent molecule rhodamine, whereby simple variations in the fabrication process enabled us to prepare rhodamine-doped nanoporous PMMA with tunable fluorescence and absorption, without losing the anti-reflective properties. The above combination of optical properties makes the films attractive for a wide range of applications.

Phase Separation of Silicon-Containing Polymer/Polystyrene Blends in Spin-Coated Films

In this Article, two readily available polymers that contain silicon and have different surface tensions, polydimethylsiloxane (PDMS) and polyphenylsilsequioxane (PPSQ), were used to produce polymer blends with polystyrene (PS). Spin-coated thin films of the polymer blends were treated by O2 reactive-ion etching (RIE). The PS constituent was selectively removed by O2 RIE, whereas the silicon-containing phase remained because of the high etching resistance of silicon. This selective removal of PS substantially enhanced the contrast of the phase separation morphologies for better scanning electron microscope (SEM) and atomic force microscope (AFM) measurements. We investigated the effects of the silicon-containing constituents, polymer blend composition, concentration of the polymer blend solution, surface tension of the substrate, and the spin-coating speed on the ultimate morphologies of phase separation. The average domain size, ranging from 100 nm to 10 μm, was tuned through an interplay of these factors. In addition, the polymer blend film was formed on a pure organic layer, through which the aspect ratio of the phase separation morphologies was further amplified by a selective etching process. The formed nanostructures are compatible with existing nanofabrication techniques for pattern transfer onto substrates.

Amino-functionalized breath-figure cavities in polystyrene-alumina hybrid films: effect of particle concentration and dispersion

We report the formation of breath-figure (BF) patterns with amino-functionalized cavities in a BF incompatible polystyrene (PS) by incorporating functionalized alumina nanoparticles. The particles were amphiphilic-modified and the modifier ratio was regulated to achieve a specific hydrophobic/hydrophilic balance of the particles. The influence of the physical and chemical properties of the particles like particle concentration, the hydrophobic/hydrophilic balance, etc., on particle dispersion in solvents having different polarity and the corresponding changes in the BF patterns have been studied. The amphiphilic-modified alumina particles could successfully assist the BF mechanism, generating uniform patterns in polystyrene films with the cavity walls decorated with the functionalized alumina particles, even from water-miscible solvents like THF. The possibility of fabricating free-standing micropatterned films by casting and drying the suspension under ambient conditions was also demonstrated. The present method opens up a simple route for producing functionalized BF cavities, which can be post-modified by a chemical route for various biological applications.

Highly Ordered Honeycomb Film Formation of Linear Polymers by the Breath Figure Technique

Highly ordered, porous honeycomb (HC) films were prepared by the breath figure technique from linear polymers poly(methyl methacrylate) (PMMA) and polystyrene (PS). Typically HC films are difficult to form from such simple linear polymers. The addition of a novel fluorinated polymer (FP) additive with as little as 1 wt-% to PMMA or 5 wt-% to PS was required to obtain regular porous HC films. Through investigation of the influence of the additive on the polymer properties, three parameters based on interfacial tension, polymer solution viscosity, and polymer solidification rate were identified as key factors affecting the ability of polymer systems to form regular porous HC films. A new hypothesis was subsequently developed based on the relationships of these parameters to explain the unusual behaviour associated with HC film formation from linear PMMA and PS with addition of FP additive. This work will provide a new tool to guide the formation of HC films and will greatly broaden the range of polymers used to form HC films in the future.

Breath Figure Method for Construction of Honeycomb Films

Honeycomb films with various building units, showing potential applications in biological, medical, physicochemical, photoelectric, and many other areas, could be prepared by the breath figure method. The ordered hexagonal structures formed by the breath figure process are related to the building units, solvents, substrates, temperature, humidity, air flow, and other factors. Therefore, by adjusting these factors, the honeycomb structures could be tuned properly. In this review, we summarized the development of the breath figure method of fabricating honeycomb films and the factors of adjusting honeycomb structures. The organic-inorganic hybrid was taken as the example building unit to discuss the preparation, mechanism, properties, and applications of the honeycomb films.

Non-Close-Packed Breath Figures via Ion-Partitioning-Mediated Self-Assembly

We report a one-step method of forming non-close-packed (NCP) pore arrays of micro- and sub-micropores using chloroform-based solutions of polystyrene acidified with hydrogen bromide for breath figure (BF) patterning. As BF patterning takes place, water vapor condenses onto the polystyrene solution, forming water droplets on the solution surface. Concurrently, preferential ion partitioning of hydrogen bromide leads to positively charged water droplets, which experience interdroplet electrostatic repulsion. Self-organization of charged water droplets because of surface flow and subsequent evaporation of the droplet templates result in ordered BF arrays with pore separation/diameter (L/D) ratios of up to 16.5. Evidence from surface potential scans show proof for preferential ion partitioning of HBr. Radial distribution functions and Voronoi polygon analysis of pore arrays show that they possess a high degree of conformational order. Past fabrication methods of NCP structures typically require multi-step processes. In contrast, we have established a new route for facile self-assembly of previously inaccessible patterns, which comprises of only a single operational step.

Single-step shaping of fluorescent polymer beads by a reverse breath figure approach

A fast and facile approach is proposed to decorate a substrate with micrometric fluorescent polymer beads of many different materials.

Honeycomb porous films of pentablock copolymer on liquid substrates via breath figure method and their hydrophobic properties with static and dynamic behaviour

The peeled film obtained on the isopropanol substrate through breath figure method exhibits the best hydrophobic properties, and the water droplet impact behavior shows an obvious rebound tendency and a weak maximum spreading diameter.