Porous Polymer Structures Research Articles

Triangular Elastomeric Stamps for Optical Applications: Near‐Field Phase Shift Photolithography, 3D Proximity Field Patterning, Embossed Antireflective Coatings, and SERS Sensing

AbstractThe use of a decal transfer lithography technique to fabricate elastomeric stamps with triangular cross‐sections, specifically triangular prisms and cones, is described. These stamps are used in demonstrations for several prototypical optical applications, including the fabrication of multiheight 3D photoresist patterns with near zero‐width features using near‐field phase shift lithography, fabrication of periodic porous polymer structures by maskless proximity field nanopatterning, embossing thin‐film antireflection coatings for improved device performance, and efficient fabrication of substrates for surface‐enhanced Raman spectroscopic sensing. The applications illustrate the utility of the triangular poly(dimethylsiloxane) decals for a wide variety of optics‐centric applications, particularly those that exploit the ability of the designed geometries and materials combinations to manipulate light–matter interactions in a predictable and controllable manner.

Supercritical CO2 in injection molding can produce open porous polyurethane scaffolds – a parameter study

There are several methods of producing open porous polymer structures for medical use. However, very few are applicable to industries and are therefore limited to both number of samples and batch variations. This study presents an industrial microcellular injection molding process, known as MuCell® technology, which was used to produce highly porous scaffolds of thermoplastic polyurethane. A parameter study was performed to quantify and analyze the effect of the processing parameters on the porous structure. Six key parameters (gas content, weight reduction, injection speed, mold temperature, plasticizing pressure, and temperature) were tested with an iteration method. The pore structure was determined with advanced micro Computer Tomography algorithm. All key processing parameters were identified. Gas content and weight reduction showed a more profound effect on the pore morphology than other parameters on the pore structure. It was possible to produce scaffolds with open porosity as high as 71%. The study concludes that MuCell® technology is an accurate and liable production method for large-scale production of open porous thermoplastic polyurethane scaffolds, and supercritical fluid could, therefore, be a potential production method for polymer scaffolds.

Nanosized catalysts as a basis for intensifications of technologies

This investigation of the catalytic properties of noble metal nanoparticles stabilized in hyper crosslinked polystyrene (HPS) matrix shows the prospect for their application in selective hydrogenation, selective oxidation and enantioselective hydrogenation, which represent key stages for the synthesis of the intermediates and final products of pharmaceutical industry. Commercial use of nanosized catalysts allows shortening the synthetic stages, increasing product yields, and improving the environmental safety of the existing industrial processes. In this review, the synthesis, structure and catalytic properties of mono (Pt, Ru, Pd), bi (Pt–Pd, Pt–Ru, Pd–Ru), and trimetallic (Pt–Pd–Ru) nanoparticles stabilized in the pores of a polymeric HPS matrix are discussed. Physicochemical investigations have shown that the formation of metalcontaining nanoparticles depends on the properties of the porous polymeric structure, the nature of the initial metal precursor, and the synthesis conditions. The use of nanosized catalysts is revealed to be effective in the most important field of fine organic synthesis: preparation of materials for medicine, vitamins, and food additives (e.g. in food and pharmaceutical industries).

Development of porous polymer monolith by photoinitiated polymerization

Porous polymer monoliths have been successfully prepared by photoinitiated polymerization of butyl methacrylate (BMA) and ethylene glycol dimethacrylate (EDMA) monomers in porogenic solvent of methanol. Mercury intrusion porosimetry and scanning electron microscope are used to characterize the porous properties; nevertheless, the pore size obtained from both techniques is not comparable. The porous structure of the porous polymers is controlled by the phase separation during the polymerization and crosslinking. By varying the composition of the starting solution such as initiator fraction, BMA/EDMA ratio, porogen fraction, and UV intensity, porous polymers with median pore size from about 140 nm to 3 μm can be obtained, and the pore size distribution for majority of the porous polymers is also narrow. The results present a very positive prospect to microfluidic applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Solvent and Substrate Contributions to the Formation of Breath Figure Patterns in Polystyrene Films

The generation of ordered porous polymer structures by the breath figures (BFs) method has long been described as a complex phenomenon, in which several parameters combine in a fairly unknown way. The type of polymer and solvent, degree of humidity, and additives are just a few examples of the several parameters that have been described as playing a role in the generation of BFs. This work reports a detailed investigation over the role played by the solvent in the process of BFs generation from polystyrene (PS) solutions spread over different substrates, and discusses the geometrical aspects of the pores via a quantitative point of view by using a purposely developed software for image analysis. Results show that thermodynamic affinity between polymer and solvent is the key parameter for BFs formation, along with other solvent characteristics such as water miscibility, boiling point, and enthalpy. According to our findings, the role played by the substrate is strictly related to the type of solvent used in the generation of BFs.

Fabrication and Wettability Patterning of Nano-structured Silicon Surface by using Self-organized Polymer Structures

We demonstrate here a creation of superhydrophobic and superhydrophilic patterned surface by using reactive ion etching (RIE) of silicon with a self-organized porous polymer structures and UV-O3 treatments through the photo-mask. Honeycomb-patterned films of polystyrene and amphiphilic polymer were prepared by casting of their chloroform solution. After UV-O3 treatment, honeycomb-patterned films were fixed on silicon substrates up side down with Poly (vinyl alcohol) solution. After peeling of the bottom layer of the honeycomb-patterned films, porous polymer masks were formed on the silicon substrate. After RIE, the silicon nanospike-array structure was obtained. Water contact angles on the silicon nanospike-array structures were c. a. 165 degree. From the results of X-ray photoelectron spectrum of the silicon nanospike-structures, fluorine was detected. The result suggests that superhydrophobicity was originated by absorbed fluorocarbons on the surface of the silicon nanospike-array structures and their surface structures. After UV-O3 treatment with photo-masks, fluorine was partially removed at irradiation area, and the area shows superhydrophilicity. These results suggest that we can easily design superhydrophobic and superhydrophilic patterned surfaces by UV-O3 treatment through photo-masks.

Plasma Amino Acid Coatings for a Conformal Growth of Titania Nanoparticles

We report on the conformal synthesis of ultrathin films from the amino acid histidine on flat silicon substrates and 3D periodic polymer structures via plasma enhanced chemical vapor deposition. We demonstrate the efficient utilization of this functional amino acid nanocoating for the formation of individual titania nanoparticles with dimensions from 2 to 15 nm depending upon reduction conditions. The titania nanoparticles were grown directly on histidine-functionalized planar and 3D polymer substrates by a wet-chemistry method that showed uniform surface coverage that reached approximately 75%. This approach demonstrates the potential for modifying the optical properties of periodic porous polymeric structures via direct conformal growth of titania nanoparticles.

Buckling instabilities in periodic composite polymeric materials

Although buckling instabilities in elastic solids have been known for a long time, high interest in this phenomenon is relatively recent. The current and prospective applications in flexible electronics, materials with tunable surface properties (adhesion and wettability), responsive photonic and phononic structures, and reinforced nanocomposites led to a surge in the interest in buckling instabilities. In fact, some of the applications, such as flexible electronics and metrology, have advanced at a tremendous pace only within the past few years. In this review, we discuss some of the most recent progress in the fundamental understanding of buckling instabilities in periodic multi-component polymer materials and porous polymer structures. We also discuss how the buckling can be localized to predetermined regions and hence form periodic instability patterns. Finally, we present several recent examples where buckling instabilities have been employed as a patterning tool to realize complex surface arrays of various materials.

Nanosized catalysts in fine organic synthesis as a basis for developing innovative technologies in the pharmaceutical industry

This investigation of the catalytic properties of noble metal nanoparticles stabilized in hypercrosslinked polystyrene (HPS) matrix shows the prospect for their application in regioselective oxidation region- and enantioselective hydrogenation, which represent key stages for the synthesis of the intermediates and final products of pharmaceutical industry. Commercial use of nanosized catalysts allows shortening the synthetic stages, increasing product yields, and improving the environmental safety of the existing industrial processes. In this review, the synthesis, structure and catalytic properties of mono- (Pt, Ru, Pd), bi- (Pt-Pd, Pt-Ru, Pd-Ru), and trimetallic (Pt-Pd-Ru) nanoparticles stabilized in the pores of a polymeric HPS matrix are discussed. Physicochemical investigations have shown that the formation of metal-containing nanoparticles depends on the properties of the porous polymeric structure, the nature of the initial metal precursor, and the synthesis conditions. The use of nanosized catalysts is revealed to be effective in the most important field of fine organic synthesis: preparation of materials for medicine, vitamins, and food additives (e.g., in the food and pharmaceutical industry).

Porous polymer structures obtained via the TIPS process from EVOH/PMMA/DMF solutions

The thermally induced phase separation (TIPS) process was used to study the phase behavior of ternary solutions containing poly(ethylene- co-vinyl alcohol) (EVOH) with 38 and 32 wt.% of ethylene content, poly(methyl methacrylate) (PMMA) and N, N-dimethylformamide (DMF) and to prepare microporous membranes. EVOH/PMMA/DMF solutions, with 0.92 and 0.83 DMF volume fraction and variable volume polymer ratios, were submitted to experiments to determine the cloud temperature ( T cloud ) by optical microscopy and the dynamic crystallization temperature ( Tc d ) by differential scanning calorimetry (DSC), related to liquid–liquid (L–L) and solid–liquid (S–L) phase separation, respectively. L–L phase separation takes place as the temperature decreases, an UCST behavior, followed by S–L phase separation due to EVOH crystallization. At room temperature the ternary solutions show two macroscopic phases, F1 and F2, whose compositions were determined by high resolution thermogravimetric analysis in order to determine the tie lines. The ternary solutions (phases F1 and F2) were slowly dried and the morphology of the resulting membranes were analyzed by scanning electronic microscopy (SEM). The membranes show a bi-layer structure, one dense layer richer in PMMA and another porous layer richer in EVOH. The connected porous structure probably derives from the phase separation through a nucleation and growth mechanism.

Porous polymer coatings: a versatile approach to superhydrophobic surfaces.

We present a facile and inexpensive approach to superhydrophobic polymer coatings. The method involves the in-situ polymerization of common monomers in the presence of a porogenic solvent to afford superhydrophobic surfaces with the desired combination of micro- and nano-scale roughness. The method is applicable to a variety of substrates and is not limited to small areas or flat surfaces. The polymerized material can be ground into a superhydrophobic powder, which, once applied to a surface, renders it superhydrophobic. The morphology of the porous polymer structure can be efficiently controlled by composition of the polymerization mixture, while surface chemistry can be adjusted by photografting. Morphology control is used to reduce the globule size of the porous architecture from micro down to nanoscale thereby affording a transparent material. The influence of both surface chemistry as well as the length scale of surface roughness on the superhydrophobicity is discussed.

Improvement of quantum efficiency of photomultiplier tubes by humidity controlled coatings based on porous polymer structures

Based on spin coating in humidity controlled environment an extremely simple deposition process is established which allows convenient and reproducible coating of photomultiplier tubes (PMTs) to achieve an improvement in photon sensitivity and thereby a higher quantum efficiency. The coatings consisting of a blend of polyacrylate based copolymer with p-terphenyl are obtained from dichloromethane solutions. On the curved PMTs structures due to crystallization of p-terphenyl superposed with pores in the copolymer matrix are present. On flat substrates coatings established under identical conditions exhibit the same porous structure. The origin of the obtained structures is discussed in context of breath figures.

Rational Surface Design for Molecular Dynamics Simulations of Porous Polymer Adsorbent Media

The construction and use of nonflat agarose surfaces in a simulation box, together with the employment of criteria for the immobilization of a set of dextran polymer chains on the nonflat agarose surfaces whose mathematical physics is compatible with that of the criteria used for the immobilization of the same set of dextran polymer chains on flat agarose surfaces, are shown to generate, through the use of molecular dynamics simulations whose simulation box has linear dimensions along the lateral directions that are the same when flat and nonflat agarose surfaces are used, dextran porous polymer structures whose pore sizes at the outermost surface and in the vicinity of the outermost surface of the porous medium can be controlled by an indirect manner through the variation of the parameters that characterize the nonflat surface. The use of a nonflat surface for the generation of desired large pores requires only a small or modest increase in the number of solvent molecules in the simulation box, while the use of a flat surface for the construction of the same desired large pores requires significant increases in the size of the linear dimensions of the flat surface. This increases so substantially the number of solvent molecules that the computational loads become intractable. The results in this work show that through the use of nonflat surfaces porous dextran polymer layers having pores of desired sizes can be effectively constructed, and this approach could be used for the design and construction of polymer-based porous adsorbent media that could effectively facilitate the transport and adsorption of an adsorbate biomolecule of interest that must be separated from a mixture of components. A useful definition about the properties that a porous polymer structure must have in order to become, for an adsorbate biomolecule of interest of known molecular size, a useful adsorbent medium, is presented and is used to (1) evaluate the porous polymer structures generated through the employment of different nonflat surface models and (2) determine and select the nonflat surface model from a set of nonflat surface models that is effective in producing promising porous structures. Then a procedure is presented by which a set of porous polymer media is generated through the use of the selected nonflat surface model, and the desired porous structure from this set is determined and could be considered to be used for the transport and immobilization of the selected affinity groups/ligands and the subsequent transport and adsorption of the desired to be separated adsorbate.

Solidification of Emulsified Polymer Solutions via Phase Inversion (SEPPI): A Generic Way To Prepare Polymers with Controlled Porosity

Porous polymeric structures with controlled porosity were prepared using a new approach involving solidification of emulsified polymer solutions via phase inversion (SEPPI). The new method starts from a polymeric emulsion for which the presence of nanosized particles or surfactants is crucial. Subsequent solidification of such emulsion is realized by simple contact with a polymer nonsolvent. The resulting solids exhibit spherical pores for which the emulsion droplets act as template. The preparation method allows easy control over pore morphology by tuning a number of easily accessible parameters, mainly at the level of the emulsion itself. A wide variety of polymers, including biocompatible and biodegradable polymers, can thus be turned into porous materials. Two typical applications in controlled release and solvent resistant nanofiltration are presented, illustrating the real practical utility of the presented method. Compared with the commonly used methods to prepare porous polymers, the presented met...

Synthesis of the hybrid porous rods and nanosheets composed of the nickel ions and poly( p-phenylenediamine) in aqueous solution

A new kind of metal-organic hybrid materials composed of the nickel ions and poly( p-phenylenediamine) have been synthesized in aqueous solution. Long hybrid rods and large nanosheets have been obtained by using the different ratios of the initial reactants. The synthesized rods and nanosheets have been characterized by SEM, TEM, AFM and XPS. The synthesized rods have been found to have porous polymeric structures. The nanosheets are made up of many small nanoparticles.

Incorporation of an abnormally high amount of poly(ethylene glycol) into poly(ethylene terephthalate) during tensile drawing in liquid media

Tensile drawing of PET via the mechanism of solvent crazing in adsorption-active media containing poly(ethylene glycol) with M < 1 × 106 is accompanied by their penetration into the porous structure of the matrix polymer. In this case, the amount of PEG in PET exceeds its concentration calculated on the assumption that the porous structure is filled with the polymer solution. This excess is evidently due to the adsorption of PEG on the highly developed surface of crazes.

Ultraporous 3D polymer meshes by low‐temperature electrospinning: Use of ice crystals as a removable void template

AbstractWhile electrospinning provides an excellent preparation method for the manufacturing of polymer fibers with defined diameter, controlling the overall porosity of the resulting fiber assemblies has remained elusive, particularly at higher porosities. In this study, the use of a low‐temperature fiber collection device in air with controlled humidity allowed the simultaneous deposition of polymer fibers and ice particles from condensing humidity. The ice particles were intimately embedded within the polymer fibers and served as a pore template thus defining the mesh porosity after drying of the collected fiber assemblies. The amount of water condensation therefore contributes to the control of the mean interfiber distance and the resulting porosity. This simple and well accessible use of ice crystals as void templates gives access to the preparation of biodegradable tissue engineering scaffolds with an up to four times higher porosity if compared to conventional fiber electrospinning. The successful application of low‐temperature electrospinning using polyesters or polyurethanes suggests a broad, material independent applicability of the process for the preparation of highly porous polymer structures. POLYM. ENG. SCI., 47:2020–2026, 2007. © 2007 Society of Plastics Engineers

Synthesis of a Novel Porous Polymer/Ceramic Composite Material by Low-Temperature Atomic Layer Deposition

Highly porous poly(styrene-divinylbenzene) particles (∼85% porosity, 8−10 cm3/g pore volume, 43.5 m2/g surface area, 70 kg/m3 particle density, and ∼600 μm diameter) were synthesized by copolymerization of styrene and divinylbenzene. Conformal alumina films were grown on internal and external polymer particle surfaces at 33 °C by atomic layer deposition (ALD). Analytical characterization revealed that the pore filling mechanism was a uniform coating of the pore walls. ALD provides a controllable method for reinforcing porous polymeric structures while modifying surface properties. Such surface functionalization may promote cell adhesion and proliferation for tissue engineering applications.

Regular silicon pillars and dichroic filters produced via particle-imprinted membranes

We have produced regular silicon pillar arrays and porous gold films on the 100 nm scale without any optical or e-beam lithography. Using particle-assisted wetting we produced a nanoporous polymer membrane on silicon. The membrane incorporated a regular array of pores generated by embedding silica particles in an organic liquid and subsequently removing the particles after polymerization of the liquid. Gold vapor was deposited onto the silicon wafer coated by the porous polymer structure. This process created an array of gold dots on the substrate at the bottom of the pores, and at the same time, a sievelike porous gold layer on top of the polymer matrix. The top layer was lifted off and used as an optical short-pass filter. After removal of the polymer membrane, the remaining gold dot pattern on the substrate served as a mask in a deep reactive ion etching process. We obtain large-area arrays of silicon nanopillars up to 1.5 μm in height and below 200 nm in diameter.

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.