利用呼吸图案法制备聚(苯乙烯-b-丙烯腈)有序多孔薄膜

以自制的聚(苯乙烯-b-丙烯腈)(PS-b-PAN)嵌段共聚物为成膜材料, 采用呼吸图案法制备了有序多孔薄膜, 采用扫描电子显微镜(SEM)对薄膜形貌进行了分析, 研究了聚合物浓度、溶剂种类及共聚物结构对薄膜结构的影响. 结果表明, 薄膜表层为多孔结构, 且孔为圆形、以六方阵列形式排列; 薄膜表层下面是蜂窝状结构.以三氯甲烷(CHCl₃)为溶剂时, 在较高浓度下制备的薄膜表层孔间距较大, 蜂窝结构尺寸较小, 且形成了多层结构. 与CHCl₃为溶剂时相比, 挥发速度较快的二硫化碳(CS₂)作溶剂时制备的多孔薄膜有序性较好, 薄膜表层孔径和孔间距均较大, 蜂窝结构尺寸较小. 以没有PAN链段的聚苯乙烯大分子引发剂(PS-Cl)为成膜材料时, 制备的薄膜表层没有形成多孔结构, 而是形成了窝状结构. 同时, 通过对薄膜表层晕的研究证明了多孔薄膜表层缺陷是由水滴处于液膜下较深的位置造成的.     

Effect of humidity and solvent vapor phase on cellulose esters films

In the present study the effect of relative humidity (RH) during spin-coating process on the structural characteristics of cellulose acetate (CA), cellulose acetate phthalate (C-A-P), cellulose acetate butyrate (CAB) and carboxymethyl cellulose acetate butyrate (CMCAB) films was investigated by means of atomic force microscopy (AFM), ellipsometry and contact angle measurements. All polymer solutions were prepared in tetrahydrofuran (THF), which is a good solvent for all cellulose esters, and used for spin-coating at RH of (35 ± 5)%, (55 ± 5)% or (75 ± 5)%. The structural features were correlated with the molecular characteristics of each cellulose ester and with the balance between surface energies of water and THF and interface energy between water and THF. CA, CAB, CMCAB and C-A-P films spin-coated at RH of (55 ± 5)% were exposed to THF vapor during 3, 6, 9, 60 and 720 min. The structural changes on the cellulose esters films due to THF vapor exposition were monitored by means of AFM and ellipsometry. THF vapor enabled the mobility of cellulose esters chains, causing considerable changes in the film morphology. In the case of CA films, which are thermodynamically unstable, dewetting was observed after 6 min exposure to THF vapor. On the other hand, porous structures observed for C-A-P, CAB and CMCAB turned smooth and homogeneous after only 3 min exposure to THF vapor.     

溶剂散逸自组装制备导电各向异性的金属有序阵列

通过溶剂散逸自组装法制备了聚苯乙烯(PS)有序多孔膜. 利用水珠在冷的PS溶液表面凝结形成有序阵列, 使PS以水珠阵列为模板形成有序多孔膜. 将有序多孔膜的上层剥离并附着在可收缩性高分子表面, 并进行离子溅射, 除掉有序多孔膜后在可收缩膜上留下了有序的金属圆盘阵列. 经过收缩, 有序阵列不仅光学性质发生了改变, 而且实现了导电的各向异性.     

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.     

Nanostructure formation in polymer thin films influenced by humidity

The influence of relative humidity (RH) during the film preparation on the surface morphology and on the material distribution of the resulting technical polymer blend films consisting of poly (methyl methacrylate) (PMMA) and poly (vinyl butyral) (PVB) is investigated by atomic force microscopy. Both pure polymers and polymer blends with different compositions of PVB/PMMA dissolved in tetrahydrofuran (THF) were used. Polymer films prepared under dry conditions (RH < 20%) are compared with those that have the same polymer composition but were prepared under increased humidity conditions (RH > 80%). The films consisting of the pure polymers showed a nonporous surface morphology for low‐humidity preparation conditions, whereas high‐humidity preparation conditions lead to porous PVB and PMMA films, respectively. These pores are explained as the result of a breath figure formation. In the case of the polymer blend films containing both polymers, porous or phase‐separated surface structures were observed even at low‐humidity conditions. A superposition of the effects of phase separation and breath figure formation is observed in the case of polymer blend films prepared under high‐humidity conditions. Atomic force microscopy (AFM) images taken before and after the treatment with ethanol as a selective solvent for PVB indicate that PMMA is deposited on top of a PVB layer in the case of the low‐humidity preparation process whereas for high‐humidity conditions the silicon substrate is covered with a PMMA film. Copyright © 2006 John Wiley & Sons, Ltd.     

Polymer surfaces with reversibly switchable ordered morphology

Honeycomb macroporous films fabricated by the "breath figures" method were composed of poly2-vinylpyridine (P2VP) distributed in the holes of polystyrene (PS). The porous films exhibited reversible behavior responding to water and different solvent vapors. When the porous film was treated with water, the honeycomb pattern would change to the hexagonal islandlike pattern. Once heated to remove the water, the honeycomb pattern emerged again. When the porous film was exposed to different solvent vapors, the same reversible process appeared. Carbon disulfide (CS(2)), toluene (TOL), and tetrahydrofuran (THF) solvent vapors induced the honeycomb pattern into the ordered islandlike pattern, and ethanol, chloroform, methyl ethyl ketone (MEK), and dimethylformamide (DMF) solvent vapors made the islandlike pattern come back to the honeycomb pattern. The hygroscopic property of P2VP and the polymer-solvent interaction are the driving force for the reversibly switchable morphology. The appropriate control of the hole depth is very crucial in determining the reversible changes.     

Electroless plating of honeycomb and pincushion polymer films prepared by self-organization

This report describes the fabrication and electroless plating of regular porous and pincushion-like polymer structures prepared by self-organization. Honeycomb-patterned films were prepared by simple casting of polymer solution under applied humid air and pincushion structures by peeling off the top layer of the former films. Silver-deposited honeycomb-patterned films and pincushion films were obtained by simple electroless plating of the respective original structures. XPS revealed Ag deposition on the honeycomb-patterned film. After thermal decomposition or solvent elution of the template polymer, unique metal mesoscopic structures were obtained.     

用含氟丙烯酸酯无规共聚物制备超疏水膜

用微乳液聚合法制备了丙烯酸全氟烷基乙酯和甲基丙烯酸甲酯的无规共聚物,并对其进行了表征.采用溶剂挥发成膜法一步制备了具有超疏水性的该聚合物膜,水滴在该聚合物膜上的静态接触角可达151°~160°,滚动角小于3°.通过扫描电子显微镜观察发现该聚合物膜表面分布了许多乳突状突起和微孔洞,并具有微米和纳米尺度相结合的复合杂化结构.该类超疏水表面的形成是由适度粗糙的表面和低表面能相互结合引起的.探讨了该类超疏水膜的形成机理.     

Formation of ordered mesoporous films from in situ structure inversion of azo polymer colloidal arrays

This work shows that mesoporous polymeric films with spherical and elliptical pores can be obtained by in situ structure inversion of the azo polymer colloid arrays through selective interaction with solvent. The epoxy-based azo polymer contained both the pseudo-stilbene-type azo chromophores and the hydrophilic carboxyl groups. The colloidal spheres of the azo polymer were prepared by gradual hydrophobic aggregation of the polymeric chains in THF-H2O media, induced by a steady increase in the water content. Ordered 2D arrays of the hexagonally close-packed colloidal spheres were obtained by the vertical deposition method. After the solvent (THF) annealing, the ordered 2D arrays were directly transformed to mesoporous films through the sphere-pore inversion. Under the same condition, the 2D arrays composed of the ellipsoidal colloids, which were obtained by the irradiation of a polarized Ar+ laser beam on the colloidal sphere arrays, could be transformed to films with ordered elliptical pores. To our knowledge, this is the first example to demonstrate that mesoporous structures can be directly formed from the colloidal arrays of a homopolymer through structure inversion. This observation can shed new light on the nature of self-assembly processes and provide a feasible approach to fabricate mesoporous structures without the infiltration-removal step. By exploring the photoresponsive properties of the materials, mesoporous film with special pore structure and properties can be expected.     

Structural features of polymer adsorbent LiChrolut EN and interfacial behavior of water and water/organic mixtures

The structural and adsorption characteristics of polymer adsorbent LiChrolut EN and the behavior of adsorbed water and water/organic mixtures were studied using adsorption, microcalorimetry, transmission and scanning electron microscopy, mass spectrometry, infrared spectroscopy, 1H NMR spectroscopy with layer-by-layer freezing-out of liquids (190-273 K), and thermally stimulated depolarization current method (90-265 K). This adsorbent is characterized by large specific surface area (approximately 1500 m2/g) and pore volume (0.83 cm3/g) with a major contribution of narrow pores (R<10 nm) of a complicated shape (long hysteresis loop is in nitrogen adsorption-desorption isotherm). The adsorbent includes aromatic and aliphatic structures and oxygen-containing functionalities and can effectively adsorb organics and water/organic mixtures. On co-adsorption of water and organics (dimethyl sulfoxide, chloroform, methane), there is a weak influence of one on another adsorbate due to their poor mixing in pores. Weakly polar chloroform displaces a fraction of water from narrow pores. These effects can explain high efficiency of the adsorbent in solid-phase extraction of organics from aqueous solutions. The influence of structural features of several carbon and polymer adsorbents on adsorbed nitrogen, water and water/organics is compared on the basis of the adsorption and 1H NMR data.     

Stabilization of self‐assembled microdroplets using short chain alcohols

The condensation of water vapor on a volatile polymeric solution leads to a porous surface after evaporation of both solvent and water. However, the stabilization of the water microdroplet is of great importance, which can be achieved using specific polymer or adding a third substance to the polymer solution. Short chain alcohols (methanol, ethanol, and n‐propanol) are utilized to fabricate a self‐assembled porous honeycomb film of linear, low molecular weight polystyrene using the breath figure technique. A combination of breath figure processing and the effect of alcohol on a water droplet can stabilize the pattern and make pores on the surface of the polymer film. The quality of the porous honeycomb film is strongly dependent on the type of alcohols and the concentration of polymer. In a specific range of polymer and alcohol concentration, pores cover all the surface of the polymer film. This method offers the possibility of producing a honeycomb structure with no trace of additive residual after the fabrication process and avoiding polymer modification. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 709–718     

Recent advances in honeycomb-structured porous polymer films prepared via breath figures

Since its introduction in 1994, the preparation of ordered porous polymer films by the breath figure (BF) method has received a considerable interest. The so-called “honeycomb” (HC) films exhibit a hexagonal array of micrometric pores obtained by water droplet condensation during the fast solvent evaporation performed under a humid flow. The main focus of this feature article is to describe the recent advances in the design of honeycomb polymer films by the BF process. We first review the recent studies related to the honeycomb film formation through the exploration of different parameters such as the relative humidity, the polymer concentration, the drying rate, the substrate or the role of interfacial tension. The influence of the architecture and microstructure of the polymer is examined through examples. In this contribution, a special attention is given to the recent articles focused on the preparation of elaborate functional honeycomb-structured polymer films obtained via the simple BF method. In this context, we review the preparation of hierarchical HC films showing either sub- or super-structure, the formation of hybrid HC films by self-assembly of nanoparticles or in situ generation of the inorganic matter, the fluorescence in HC films introduced either by a fluorescent polymer or by fluorescent chemical groups, the elaboration of biomaterials from HC films decorated by glycopolymer and/or showing sensing ability and finally the design of functional polymeric surfaces with either stimuli-responsive or superhydrophobic properties.     

Honeycomb micropatterning of proteins on polymer films through the inverse microemulsion approach

Here we report the rapid and convenient patterning of proteins on porous polymer film using the inverse microemulsion approach. Following this method, proteins, which were dissolved in water, were transferred into dichloromethane solution of polymers through the formation of inverse microemulsion by mixing the two solutions. The protein-containing microemulsion droplets accumulated automatically into large and stable ones on the surface of organic solution casting on solid substrates, and formed tightly packed microemulsion droplet arrays driven by surface tension. With the evaporation of organic solvent and water, the microemulsion droplet arrays, which act as the template, turn to honeycomb patterned pores bearing proteins in them. The formed protein patterns can be locally applied for the detection of other proteins through specific recognition. The generality and reproducibility for the formation of BSA/PS microporous film and protein patterning by using different polymers and solvents were demonstrated by investigating surfactant addition, polymer and solvent types, and casting volume on the morphology of the microporous films. A preliminary mechanism for the protein patterning is discussed based on the analysis of the experimental results.     

INTERACTION OP POLYVINYL ALCOHOL WITH LECITHIN AT THE AIR/WATER AND OIL/WATER INTERFACES AND ITS EFFECT ON EMULSION STABILITY

The interaction of polyvinyl alcohol (PVA) with lecithin films at the air/water and xylene/water interfaces was studied at pH 3, the isoelectric point of lecithin. Surface and interfacial tension measurements and electro-phoretie mobility data showed that PVA either replaces the lecithin molecules or becomes coadsorbed with it at the interface. This mixed film has no elasticity and very low interfacial viscosity. However, coalescence rate measurements showed that the emulsion formed by the polymer* lecithin is more stable than that formed with either polymer or lecithin alone. The enhanced stability by the PVA-lecithin mixed film was attributed to steric interaction produced by the adsorbed polymer.     

Selective layer-by-layer self-assembly on patterned porous films modulated by Cassie-Wenzel transition

We describe a robust and facile approach to the selective modification of patterned porous films via layer-by-layer (LBL) self-assembly. Positively charged honeycomb-patterned films were prepared from polystyrene-block-poly(N,N-dimethyl-aminoethyl methacrylate) (PS-b-PDMAEMA) and a PS/PDMAEMA blend by the breath figure method followed by surface quaternization. Alginate and chitosan were alternately deposited on the films via LBL self-assembly. The assembly on the PS-b-PDMAEMA film exhibits two stages with different growth rates, as elucidated by water contact angles, fluorescence microscopy, and quartz crystal microbalance results. The assembly can be controlled on the top surface or across all surfaces of the film by changing the number of deposition cycles. We confirm that there exists a Cassie-Wenzel transition with an increase in deposition cycles, which is responsible for the tunable assembly. For the PS/PDMAEMA film, the pores can be completely wetted and the polyelectrolytes selectively assemble inside the pores, instead of on the top surface. The controllable selective assembly forms unique hierarchical structures and opens a new route for surface modification of patterned porous films.     

Surfactant-induced formation of honeycomb pattern on micropipette with curvature gradient

Breath figure (BF) process is a facile method to prepare honeycomb structures by dynamic movements of condensed micrometer-sized water droplets at the interface of volatile fluid. Here, we aim to find answers to understand how the BF process occurs on micropipettes with curvature gradient and to understand the role of the surfactant in obtaining honeycomb patterns. Poly (L-lactic acid) (PLLA) chloroform solution with dioleoylphosphatidylethanolamine (DOPE) as surfactant was utilized. It is found that the honeycomb structure formed on the micropipettes changes remarkably with the gradually increased surface curvature. The variation trends of the arrangement and diameter of pores on the micropipettes with the increasing curvature are similar to the different time stages of BF process: smaller and sparse pores formed at higher curvature are similar to those formed at early stage of BF; regular honeycomb patterns formed at lower curvature are similar to those formed at the late stage of BF. Especially, the "semi-coalescence" hemispherical pores strings are found at high curvatures on PLLA-DOPE films, indicating the surfactant-induced coalescence of water droplets in BF process. The differences of drying speed of polymer solvent on micropipette with gradually increased curvatures make the printing of the pores at different BF stages on polymer film possible. These findings not only strongly support the mechanism of BF array formation, but also elucidate the surfactant-induced coalescence.     

Broad-band antireflection coating at near-infrared wavelengths by a breath figure

We prepared a porous thin film by spin-coating of a cellulose acetate butyrate (CAB) solution in tetrahydrofuran under a humid environment. Due to evaporative cooling during spin-coating, condensed water droplets were formed by a breath figure on the CAB solution, and these developed a porous structure after complete drying. By varying the solution concentration and rotating speeds, two distinct morphologies were generated: top and bottom layers with higher and lower porosities, respectively. We found that the two-layer porous film coated on glass exhibited low reflectance of less than 1% in the near-infrared (NIR) regime corresponding to wavelengths between 900 and 2200 nm. Since the porous structure was very uniform over a large area, the film could be easily employed for broad-band antireflection coating at NIR wavelengths.     

聚苯乙烯-嵌段-聚丁二烯有序多孔膜在可收缩膜上的形变研究和光学性质

利用溶剂散逸自组装法在潮湿的条件下,制备了聚苯乙烯-聚丁二烯嵌段聚合物（PS-b-PB）有序多孔膜。 利用聚乙烯可收缩膜将PS-b-PB多孔膜进行两次收缩,形成小孔径的有序多孔膜。 通过收缩,膜上的孔由圆形变为长方形或者梭形,孔的尺寸从微米级收缩至亚微米级。 利用扫描电子显微镜对膜收缩过程中2种形状产生的机理进行了研究。 结果表明,PS-b-PB结合了聚苯乙烯（PS）和聚丁二烯（PB）两个均聚物的优点,收缩后仍然保持膜结构的平整性,从而将不可见的热场变化转变为可见的光学变化。     

Phase separation of polyphosphazene/poly(lactide‐co‐glycolide) blends prepared under different conditions

Using a mutual solvent technique, blend films of poly[(alaine ethyl ester)_0.62(glycine ethyl ester)_0.38]phosphazene/poly(lactide‐co‐glycolide) (PAGP/PLGA blend) were prepared at different conditions including weight ratios, solvents, environmental humidity, film thickness, and substrates. The morphology and properties of blend films were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDX), X‐ray photoelectron spectrometry (XPS), and solvent selective etching. Compared with dichloromethane and tetrahydrofuran (THF), chloroform was the better solvent to form miscible PAGP/PLGA blend films at relatively anhydrous atmosphere. However, in the humid atmosphere, the hexagonal arrangement of holes appeared on the surface of PAGP/PLGA blend films due to the ordered array of water droplets. A sandwich‐liked structure was formed with the hydrophilic PAGP component at the top and bottom, while the PLGA component in the middle. In addition, the surface morphology of PAGP/PLGA blend films was also influenced by the film thickness and the property of the substrate. Copyright © 2010 John Wiley & Sons, Ltd.     

Breath figure patterns prepared by spin coating in a dry environment

We introduce a novel method for fabricating breath figure patterns on a homopolymer film by spin coating of polymer solutions with various solvents. The homopolymers employed in this study were cellulose acetate butyrate, monocarboxylated end-functional polystyrene, and poly(methyl methacrylate). Breath figure patterns were generated even when a water-miscible solvent such as tetrahydrofuran (THF) was used as a solvent. We even succeeded in generating breath figure patterns by spin coating even under a dry environment (relative humidity less than 30%), when water was directly added into THF solution. With the combination of the spin coating method, pores with a few hundred nanometers to several micrometers have been generated. We found that the pore size becomes larger with increasing water content in THF solution and decreasing rotating speed. This is equivalent to increasing humidity and decreasing evaporation speed, respectively, in the conventional method, which is direct solvent evaporation under a humid environment. Thus, compared with the conventional method for making breath figure patterns, this method would be very convenient for fabricating large-scale films with various pore sizes.