Superhydrophobic and lipophobic properties of self-organized honeycomb and pincushion structures

This report describes the simple preparation of superhydrophobic and lipophobic surfaces by self-organization. Microporous polymer films of a fluorinated polymer with hexagonally arranged pores were prepared by casting from solution under humid conditions. Hexagonally packed water microdroplets were formed by evaporative cooling on the surface of the casting solution. After solvent evaporation, a honeycomb-patterned polymer film was formed with the water droplet array acting as a template; the water droplets themselves evaporated soon after the solvent. Two porous polymer layers were stacked vertically, separated by pillars at the hexagon vertexes. After peeling off the top layer using adhesive tape, a pincushion-like structure was obtained. Here, we show that superhydrophobic behavior was achieved, with the maximum contact angle, 170 degrees, observed using these pincushion structures. Theoretical calculations fit the experimental results well. The lipophobic properties of the films are also discussed.     

Spontaneous film formation from a polymer solution

An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene terephthalate)s (s-PPPT) and poly(carbonate) (PC) is observed. A liquid film of polymer solution creeps over the surface of water dropped into the polymer solution. By vaporization of the solvent a solid polymer film is formed on the water surface and can be removed. The driving force for the film formation mechanism is assumed by the reduction of the surface tension of water. Experiments verify this mechanism by increasing the film formation speed using a gas stream, by reducing the formation speed through lowering the surface tension by rinsing agents, and by lowering the solubility of the polymer. As expected, no effects are found by variation of the pH-value of water. Necessary conditions for the film formation process are: good solubility of the polar polymers in organic solvents having a high vapor pressure, complete phase separation, solution density higher than water density, and a surrounding gas phase unsaturated with solvent vapor.The thickness of the mechanically stable films is less than 0.5 m. The films are amorphous by microscopical, FT-IR, x-ray, and DTA investigations.     

Fabrication of self-organized chemically and topologically heterogeneous patterns on the surface of polystyrene-b-oligothiophene block copolymer films

A novel fabrication of the chemically and topologically heterogeneous patterns on the surface of polymeric films over an area of more than 1 square centimeter in a single step was demonstrated by using the self-organizing character of polystyrene-b-oligothiophene block copolymers. Hexagonally arranged open pores of a size of approximately 2 mum are spontaneously formed by casting the polymer solution under a moist air flow. The amphiphilic character of the polystyrene-b-oligothiophene block copolymers played the crucial role as a surfactant to stabilize the inverse emulsion of water droplets in the organic solvent, and subsequently the structure of the arranged hydrophilic oligothiophene segments remained on the interiors of the micropores. The chemical composition of the surface of the microporous films was characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS) to prove the chemical heterogeneity. The ToF-SIMS imaging clearly indicated that the oligothiophene forms the aggregated structure on the interior of the open micropores on the surface while the flat area on the surface was covered with the polystyrene.     

Preparation of a unique microporous structure via two step phase separation in the course of drying a ternary polymer solution

A unique porous polymeric film was prepared by drying a ternary polymer solution: a polystyrene (PS), polyethylene glycol (PEG), and toluene solution. Highly ordered micropores, ranging from 5 to 12 mum in diameter, were formed on the film surface, and the rim of each micropore was surrounded by a ring of PEG. The effects of the weight ratio of the polymer blend and molecular weight of the polymer (PEG) on the porous structure were investigated. Based on in situ visual observation and light scattering measurements, the formation mechanism of the porous structure was speculated to be a two step phase separation: the phase separation into PEG-rich and PEG-poor (i.e., PS-rich) phases occurred first at the surface area of the ternary solutions, where polymers were condensed due to solvent evaporation. The PEG-rich phase became droplets and had an ordered structure on the surface. The PEG-poor phase became a matrix where PS and solvent coexisted as a single phase solution. Secondary phase separation then followed in the PEG droplets, which was induced by further solvent evaporation, and formed into solvent-rich and PEG-rich domains within the droplets. Solvent evaporation and secondary phase separation created a cavity structure in each PEG droplet structured on the film surface.     

Crystallization of condensation droplets on a liquid surface

Highly ordered microporous two-dimensional membranes have been obtained from polymer solutions (Widawski et al. (1994) Nature 369: 397–399). Recently, a mechanism for the formation of such membranes was proposed, involving water vapour condensation (induced by the rapid evaporation of the volatile solvent) onto the surface of solutions and the formation of floating water droplets. Unfortunately, the droplets growth process was not observed, and consequently only qualitative information was reported. In the present paper, results of light-scattering experiments with this system are reported. The formation of water droplets growing at the surface of the solution has been observed and the evolution with time of the mean droplet radius has been found to be described by a power law with an exponent of 1/3, proving that no coalescence processes occur. This particular behaviour is attributed to the precipitation of the polymer at the water/solution interface and to the formation of a mechanically resistant polymer layer encapsulating each droplet. In this way, water droplets behave like solid particles, allowing compact sheets to be formed. The presence of important surface currents is believed to promote the formation of “polycrystal” and “monocrystal” patterns. Received: 4 January 1999 Accepted in revised form: 15 February 1999     

两亲性Janus粒子在蜂窝状多孔聚合物膜上的自组装性能

采用具有两亲性的两面体(Janus)粒子实现稳定的粒子界面组装与水滴模板法自组装过程相结合的方法获得了粒子在蜂窝状多孔聚合物薄膜内壁的高效定向修饰.通过与均质粒子组装形貌的对比,证明了Janus粒子因其特殊的界面自组装活性,可以获得高粒子加量条件下的规则多孔结构,解决了使用均质粒子时存在的结构有序性和粒子修饰密度之间的矛盾.而在较低粒子加量的条件下,Janus粒子也展示出与均质粒子极为不同的组装形貌.这一方法的建立,为新型表面功能化材料的制备提供了一个新的思路.     

Formation of a "hard microemulsion" and its role in controllable synthesis of nanoparticles within a functional polymer matrix

Microemulsions are often used in the synthesis of nanoparticles in solution. In this work, we put forward the concept of a "hard microemulsion", which is based on the differential partitioning of water and ethanol solvent molecules inside functional polymer matrices. When the mixture of water and organic solvent enters the functional polymer, the liquid molecules should partition to different regions. Water should concentrate in the microdomains rich in hydrophilic functional groups, forming water-enriched cores, whereas organic solvents should localize near the alkyl polymer skeleton, forming organic liquid enriched outer layers. From a macroscopic view, the swollen polymer matrix is divided into numerous "microdroplets", resembling frozen water-in-oil microemulsions. We define such a structure as a "hard microemulsion". The water-enriched microdroplets may act as templates for synthesizing inorganic nanoparticles. We demonstrate the utility of hard microemulsions for the controllable synthesis of silver and platinum nanoparticles inside different macroreticular functional polymers.     

Unconventional multiple ring structure formation from evaporation-induced self-assembly of polymers

The formation of multiring deposits of poly(2-vinylpyridine) (P2VP) from the evaporation of a P2VP-(2,6-lutidine + water) drop on a glass substrate does not conform to the conventional pinning-depinning mechanism. Instead, ringlike deposits are formed when the droplet undergoes several cycles of spreading and receding where, for each spreading event, a P2VP ridge is formed at the contact line when the polymer flows toward the outward advancing edge. The complex interplay between an outward solutal-Marangoni flow due to a higher concentration of the polymer at the contact line and an inward solvent-Marangoni flow arising from the differences in volatilities and surface tensions of the pure solvent components plays an important role in enhancing the droplet spreading rate. The newly discovered surface patterning mechanism has important implications in the development of novel techniques for inducing self-assembly of functional materials from evaporating drops.     

漆酚醛胺聚合物多孔膜的制备

以漆酚醛胺聚合物(UFDP)为成膜材料,利用水辅助自组装的固体基板展开法和水面展开法制备了漆酚醛胺聚合物多孔膜.研究了在静态(即不在聚合物表面吹扫氮气)高湿度环境下聚合物溶液浓度、环境湿度和固体基板等因素对多孔膜形貌的影响.结果表明,水面展开法更有利于形成单层的多孔膜而固体基板展开法得到的是多层的多孔膜.当UFDP聚合物浓度为6.0 mg/mL,环境相对湿度为90%时,用水面展开法制得的单层多孔膜的孔径分布较均匀.     

Recovery of nanoparticles produced in phosphatidylcholine-based template phases

This paper focuses on the characterization and use of polymer-modified phosphatidylcholine (PC)/sodium dodecyl sulfate (SDS)-based inverse microemulsions as a template phase for BaSO4 nanoparticle formation. The area of the optically clear inverse microemulsion phase in the isooctane/hexanol/water/PC/SDS system is not significantly changed by adding polyelectrolytes, i.e., poly(diallyldimethylammonium chloride) (PDADMAC), or amphoteric copolymers of diallyldimethylammonium chloride and maleamid acid to the SDS-modified inverse microemulsion. Shear experiments show non-Newtonian flow behavior and oscillation experiments show a frequency-dependent viscosity increase (dilatant behavior) of the microemulsions. Small amounts of bulk water were identified by means of differential scanning calorimetry. One can conclude that the macromolecules are incorporated into the individual droplets, and polymer-filled microemulsions are formed. The polymer-filled microemulsions were used as a template phase for the synthesis of BaSO4 nanoparticles. After solvent evaporation the nanoparticles were redispersed in water and isooctane, respectively. The polymers incorporated into the microemulsion are involved in the redispersion process and influence the size and shape of the redispersed BaSO4 particles in a specific way. The crystallization process mainly depends on the type of solvent and the polymer component added. In the presence of the cationic polyelectrolyte PDADMAC the crystallization to larger cubic crystals is inhibited, and layers consisting of polymer-stabilized spherical nanoparticles of BaSO4 (6 nm in size) will be observed.     

Preparation of microporous polymers in the form of particles and a thin film from hyperbranched polyphenylenes

The use of a hyperbranched polymer as a building block for the synthesis of a microporous organic polymer was demonstrated. Hyperbranched polyphenylenes (HBPs) were prepared from (3,5‐dibromophenyl)boronic acid, which contained numerous unreacted bromophenyl end groups. Utilizing metal‐catalyzed coupling reactions between these functional groups, cross‐linked porous polymers were obtained. Although the HBPs did not show porosity, their cross‐linked polymers had highly porous structures with Brunauer–Emmett–Teller surface areas of up to 2030 m²/g. An insoluble porous thin film was fabricated by spin casting of a solution containing a HBP followed by Sonogashira cross‐coupling reaction. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2336–2342     

Self-assembly in evaporated polymer solutions: influence of the solution concentration

Amorphous polymers were dissolved in chlorinated organic solvents and deposited on thin horizontal substrates. The solutions with various concentrations of polymers were deposited and evaporated under ambient conditions in a slow air current. Self-assembled oriented mesoscopically scaled patterns were observed. The patterns were studied with optical and atomic force microscopy. The concentration of the solution exerts a decisive influence on the mesoscopic cell characteristic dimension. Cell dimensions grow linearly with the polymer solution concentration for all kinds of tested polymers, chlorinated solvents and substrates. The dependence could be explained by a physical mechanism, based on the mass transport instability occurring under the intensive evaporation of the solvent. In situ FTIR study of the process was performed first. It was established with FTIR spectroscopy that film porosity is not due to water droplet condensation under evaporation.     

Complex aggregates of silica microspheres by the use of a polymer template

Evaporation of a droplet of silica microsphere suspension on a polystyrene and poly(methyl methacrylate) blend film with isolated holes in its surface has been exploited as a means of particles self-assembly. During the retraction of the contact line of the droplet, spontaneous dewetting combined with the strong capillary force pack the silica microspheres into the holes in the polymer surface. Complex aggregates of colloids are formed after being exposed to acetone vapor. The morphology evolution of the underlying polymer film by exposure to acetone solvent vapor is responsible for the complex aggregates of colloids formation.     

Synthesis and Characterization of Poly(ether-block-amide) Membranes

Poly(ether-block-amide) membranes were made via casting a solution on a nonsolvent (water) surface. In this research, effects of different parameters such as ratio of solvent mixture (n-butanol/isopropanol), temperature, composition of coagulation bath (water) and polymer concentration, on quality of the thin film membranes were studied. The mechanism of membrane formation involves solution spreading, solvent–nonsolvent exchange, and partial evaporation of the solvent steps. Solvent- nonsolvent exchange is the main step in membrane formation and determines membrane morphology. However, at higher temperature of polymeric solution greater portion of solvent evaporates. The results showed that type of demixing process (mutual affinity between solvent and nonsolvent) has important role in film formation. Also, addition of solvent to the nonsolvent bath is effective on membrane morphology. The film quality enhances with increasing isopropanol ratio in the solvent mixture. This behavior can be related to increasing of solution surface tension, reduction of interfacial tension between solution and nonsolvent and delayed solvent-nonsolvent demixing. Uniform films were made at a temperature rang of 60–80 °C and a polymer concentration of 4–7 wt%. Morphology of the membranes was investigated with scanning electron micrograph (SEM). Pervaporation of ethyl butyrate/water mixtures was studied using these membranes and high separation performance was achieved. For ethyl butyrate/water mixtures, It was observed that both permeation flux and separation factor increase with increasing ethyl butyrate content in the feed. Increasing temperature in limited range studied resulted in decreasing separation factor and increasing permeation flux.     

Large-scale controllable patterning growth of aligned organic nanowires through evaporation-induced self-assembly

Organic one-dimensional nanostructures are attractive building blocks for electronic, optoelectronic, and photonic applications. Achieving aligned organic nanowire arrays that can be patterned on a surface with well-controlled spatial arrangement is highly desirable in the fabrication of high-performance organic devices. We demonstrate a facile one-step method for large-scale controllable patterning growth of ordered single-crystal C(60) nanowires through evaporation-induced self-assembly. The patterning geometry of the nanowire arrays can be tuned by the shape of the covering hats of the confined curve-on-flat geometry. The formation of the pattern arrays is driven by a simple solvent evaporation process, which is controlled by the surface tension of the substrate (glass or Si) and geometry of the evaporation surface. By sandwiching a solvent pool between the substrate and a covering hat, the evaporation surface is confined to along the edge of the solvent pool. The geometry of the formed nanowire pattern is well defined by a surface-tension model of the evaporation channel. This simple method is further established as a general approach that is applicable to two other organic nanostructure systems. The I-V characteristics of such a parallel, organic, nanowire-array device was measured. The results demonstrate that the proposed method for direct growth of nanomaterials on a substrate is a feasible approach to device fabrication, especially to the fabrication of the parallel arrays of devices.     

界面上蜂窝状多孔薄膜的构建、性质和应用

综述了以Breath Figure(呼吸图案)法制备聚合物及纳米颗粒蜂窝状多孔结构的研究现状.当潮湿的气流吹到聚合物或纳米颗粒的有机溶液表面时,溶剂蒸发导致水微滴在液体表面冷凝重排成六角阵列结构.溶剂和水微滴蒸发完毕后,聚合物或纳米颗粒在基底上形成具有六角阵列的蜂窝状多孔结构.该技术是自组装领域的一大进展,在生物技术、组织工程、微图像技术、高端分离技术、光催化及医药等领域有望获得重要应用.本文系统阐述了规整蜂窝状孔结构材料的构建方法、构建材料、形成机理以及影响因素(包括湿度、浓度、气流方向和速度、溶剂、基底曲率等),评述了蜂窝状多孔薄膜的性质和应用,并对其在化学和材料科学领域的应用前景作了展望.     

Morphology of microporous poly(vinylidene fluoride) membranes studied by gas permeation and scanning electron microscopy

Microporous poly(vinylidene fluoride) (PVDF) membranes with asymmetric pore structure were prepared by a wet phase inversion process. The polymer was precipitated from a casting solution when immersed in a cold water (gelation) bath. The casting solution was, in most cases, composed of polymer, solvent, and nonsolvent. In this solvent-nonsolvent system, the solvents used were triethylphosphate (TEP) and dimethylsulfoxide (DMSO), and the nonsolvents used were glycerol and ethanol. Mean pore sizes and effective porosity of the microporous membranes were calculated using the gas permeation method. They were studied as a function of evaporation time of wet nascent film, polymer molecular weight, concentration of polymer, and concentration of nonsolvent. The morphology of the membranes was examined by scanning electron microscopy (SEM).     

Formation of organically and inorganically passivated CdS nanoparticles in reverse microemulsions

This paper is focused on the formation of organically and inorganically passivated cadmium sulfide (CdS) nanoparticles in two different types of microemulsions. On the one hand, we used a ternary inverse microemulsion consisting of water, heptanol, and 3-(N,N-dimethyldodecylammonio)propanesulfonate and on the other hand, a poly(ethyleneimine)-based quaternary microemulsion containing water, toluene, pentanol, and sodium dodecylsulfate. UV-vis measurements confirm the formation of CdS-ZnS core-shell nanoparticles in the ternary microemulsion. Using the quaternary microemulsion template phase, polymer capped luminescent CdS nanoparticles can be formed. After a complete solvent evaporation, the nanoparticles are redispersed in water and characterized by means of dynamic light scattering and transmission electron microscopy. From the ternary microemulsion, well-stabilized CdS-ZnS core-shell nanoparticles with diameters of about 5 nm can be redispersed, but from the quaternary microemulsion, only nanoparticle aggregates of about 100 nm.     

Synthesis of polymer materials by low energy electron beam. VIII. Formation mechanism of microporous urethane-acrylamide film

The formation mechanism of microporous film which was obtained by casting a methyl ethyl ketone (MEK)/N,N-dimethlformamide (DMF) solution of an electron beam (EB)-reactive urethane-acrylamide prepolymer was discussed. The porosity and crystallinity increased with increasing DMF content in the solvent mixture. This correlation was explained by a progressive slight coagulation and nucleation of the prepolymer due to the difference in volatility between MEK and DMF. As the result, when the DMF content reached 25 vol%, micropores were formed throughout the film. Such a mechanism was supported by the localization of the acrylamide groups at the surface which was induced by the crystallization and by the interaction of amide groups with DMF. The polymerization of acrylamide groups by EB could fix the microporous morphology.     

Binary Polymer Mixtures in Selective Solvents: Interfacial Structure

Summary: The interaction of a large polymer droplet (formed by a poorly soluble polymer A) with a soluble polymer additive (polymer B) is investigated in the framework of a mean‐field approach. We found that polymer B may tend to adsorb on the surface of the droplet even when it is immiscible with polymer A in the droplet and is soluble in the solvent surrounding the droplet. We calculated the concentration profiles of both polymers A and B near the interface and established conditions for polymer B accumulation at the interface. The dependencies of the surface tension and the interfacial excess of polymer B on its bulk concentration are also calculated. We found that even a very small amount of homopolymer B additive may result in a significant reduction of the interfacial tension (by a factor of 2). The effect is stronger if the additive is more flexible than the insoluble polymer.

The region of parameters where B from dilute solution is adsorbed at the A/solvent interface (II).