Microcontact printing and selective surface dewetting for large area electronic applications

A universal microstructuring approach was developed, which facilitates the patterning of surfaces by a combination of microcontact printing (mCP) and selective surface dewetting/wetting. Self-assembled monolayers (SAMs) were patterned on glass or silicon substrates by μCP. The regions coated by the SAMs turn hydrophobic, whereas the uncoated regions stay hydrophilic. Such functionalized surfaces facilitate selective deposition of polymers or resists. Polymethyl methacrylate and prepolymer polyurethane were selectively deposited on the hydrophilic regions of the substrate. The hydrophobic regions of the substrate stay uncoated. Subsequently, the resist was used to lift-off metallic microstructures in order to realize micro coils and electrodes for radio frequency information tags. The printed electrodes were used to define drain and source contacts of organic thin film transistors. The device characteristic of the organic transistors will be presented.     

Fabrication of Transferable Perforated Isoporous Membranes on Versatile Solid Substrates via the Breath Figure Method

Isoporous separation membranes have received considerable attention because of the high‐resolution performance and energy‐saving characteristics. Isoporous membranes prepared by the breath figure method rely on special substrates such as water and ice because solid substrates such as polyethylene terephthalate films, which are widely used in commercial processes, often lead to nonthrough pores. In this work, it is found that highly ordered through‐pore membranes can be fabricated on hydrophilic glass surface when using polymers that are able to form ordered membranes at low concentrations. On the basis of this finding, a facile strategy is proposed to fabricate isoporous membranes on various solid substrates by introducing a water‐soluble polymer interlayer. The multifunctional interlayer promotes the spreading of membrane‐forming solutions, enables the formation of through pores, and simplifies the transfer to macroporous supports to form composite membranes. The versatility of the proposed strategy is verified by using different substrates including highly hydrophobic polytetrafluoroethylene film and using different water‐soluble polymers as the interlayer. Furthermore, the high‐resolution separation performance of the isoporous composite membranes has been demonstrated by the filtration of yeasts under gravitational pressure.     

Temperature-Responsive Chromatography Using Poly(N-isopropylacrylamide)-Modified Silica

A new concept in chromatography is proposed that utilizes a temperature-responsive surface with a constant aqueous mobile phase. The surface of the silica stationary phase in high-performance liquid chromatography (HPLC) has been modified with temperature-responsive polymers to exhibit temperature-controlled hydrophilic/hydrophobic changes. Poly(N-isopropylacrylamide) (PIPAAm) was grafted onto (aminopropyl)silica using an activated ester-amine coupling method. These grafted silica surfaces show hydrophilic properties at lower temperatures which, as temperature increases, transform to hydrophobic surface properties. The elution profile of five mixed steroids on an HPLC column packed with this material depends largely on the temperature of the aqueous mobile phase. Retention times increase with increasing temperature without any change in the eluent. Changes in the retention times of hydrophobic steroids were larger than those for hydrophilic steroids. The temperature-responsive interaction between PIPAAm-modified silica and these steroids is proposed to result from changes in the surface properties of the HPLC stationary phase by the transition of hydrophilic/hydrophobic surface-grafted IPAAm polymers. We demonstrate a novel and useful new chromatography system in which surface properties and the resulting function of the HPLC stationary phase are controlled by external temperature changes. This method should be effective in biological and biomedical separations of peptides and proteins using only aqueous mobile phases.     

Rapid pattern transfer of biomimetic surface structures onto thermoplastic polymers

Biomimetic surface structures have profound influences on the development of many emerging devices and systems. In this study, a sequential approach involving sputtering, electroforming and embossing for transferring biological surface structures to thermoplastic polymers were investigated and developed. The surface structure on dung beetles (Phanaeus vindex) was used as a case study. A nickel pattern was fabricated by directly sputtering and electroforming the biological surface of the beetle. The resulting nickel structure was used as an embossing master for rapid feature transfer onto ABS substrates. The replicated surface patterns on the polymer were found to be comparable with those on the dung beetle. Contact angle measurements showed that the originally hydrophilic surface is rendered hydrophobic with the addition of the biomimetic topography.     

Achieving One‐Step Surface Coating of Highly Hydrophilic Poly(Carboxybetaine Methacrylate) Polymers on Hydrophobic and Hydrophilic Surfaces

It is highly desirable to develop a universal nonfouling coating via a simple one‐step dip‐coating method. Developing such a universal coating method for a hydrophilic polymer onto a variety of surfaces with hydrophobic and hydrophilic properties is very challenging. This work demonstrates a versatile and simple method to attach zwitterionic poly(carboxybetaine methacrylate) (PCB), one of the most hydrophilic polymers, onto both hydrophobic and hydrophilic surfaces to render them nonfouling. This is achieved by the coating of a catechol chain end carboxybetaine methacrylate polymer (DOPA‐PCB) assisted by dopamine. The coating process was carried out in water. Water miscible solvents such as methanol and tetrahydrofuran (THF) are added to the coatings if surface wettability is an issue, as for certain hydrophobic surfaces. This versatile coating method was applied to several types of surfaces such as polypropylene (PP), polydimethyl siloxane (PDMS), Teflon, polystyrene (PS), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC) and also on metal oxides such as silicon dioxide.     

Hybrid protein-polymer biomimetic membranes

Protein-functionalized polymers retain dramatically increased stability over lipid membranes and the unique ability to be deposited on solid substrates in the ABA complex. Furthermore, since these polymers can mimic hydrophilic/hydrophobic biological environments in a single molecular chain, direct adsorption of protein-functionalized biomembrane films is enabled, which is a significant advantage over conventional lipid systems. Following the demonstration of protein mutagenesis and nanoscale biomimetic membrane fabrication, monolayer arrays of pore proteins have been deposited onto silicon wafers for applications in sensing nanomolecules such as conjugated quantum dots and colloidal gold beads. Furthermore, we have characterized monolayer surface properties of custom tailored polymers with varied block length for biomimetic membrane applications, as well as developed a multiwell microelectromechanical-system-based membrane testing platform for enhanced versatility in film deposition. We have successfully demonstrated the reconstitution of a genetically engineered OmpF porin in block copolymer-based biomembranes, fabrication of large-area hybrid protein-polymer Langmuir-Blodgett films, as well as protein insertion via macromolecule detection using protein-polymer active materials with the goal of buildup toward a multicomponent microsystem while preserving inherent molecular function.     

Self-assembly of hydrophilic homopolymers: a matter of RAFT end groups

Unusual self-assembly behavior is observed for a range of hydrophilic homopolymers. This self-assembly behavior is contrary to the expected behavior of such hydrophilic polymers and instead mimics more commonly reported amphiphilic block copolymers. It is proposed that the unique combination of hydrophobic end groups at both the α and ω chain end accounts for this unusual self-assembly behavior. Complex internal polymer micelles are spontaneously formed when hydrophilic homopolymer polyelectrolytes and neutral polymers (with a weight fraction of the hydrophobic end groups <10 wt%) are directly dissolved in water. The homopolymers, poly[2-(diethylamino)ethyl methacrylate], poly(N-isopropylacrylamide), and poly(ethoxyethylacrylate) are synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization using S'-1-dodecyl-(S')-(α,α'-dimethyl-α″-acetic acid) trithiocarbonate (DDMAT) and its derivatives as chain transfer agents (CTAs). A range of polyelectrolyte homopolymers with different terminal groups are designed and synthesized, which under acidic aqueous solution direct the self-assembly to form well-defined nanostructures. This assembly behavior was also observed for neutral polymers, and it was determined that the structure of the hydrophobic end groups (and thus choice of RAFT CTA) are very important in facilitating this unusual self-assembly behavior of hydrophilic homopolymers. It is proposed that the functionality of commonly used CTAs such as DDMAT, can affect the solution association of the resultant homopolymers and can in fact afford ABA' type polymers, which can undergo self-assembly to form higher-order nanostructures.     

Controlled Transdermal Mucolytic Delivery System

Bromhexine a mucolytic agent was studied to explore for dermal route of administration. The formulations were based on commercial eudragit polymers and polyvinyl pyrrolidone.

Two systems i.e., Matrix and Pseudolatex were studied for their comparative performance evaluation in in vitro. The various combinations of hydrophobic (Eudragit RL-100) and hydrophilic (PVP 40,000) polymers were used to prepare the both matrix and pseudolatex topical systems. The prepared systems were studied for in vitro diffusion using a Franz diffusion cell. Study revealed that the relative concentration of hydrophobic to hydrophilic polymers determines the drug diffusion and across the skin permeation of the drug. Both the systems were noted to be stable, however, the drug release and across the skin permeability of drug from pseudolatex system recorded to be better and uniform. Preliminary studies on bromhexine are indicative of its potentiality for transdermal preparation and establish the need for in vivo evaluation.     

Surface property change of C doped TiO2 nano-pillars by O2 plasma treatment

TiO2 surface is led to super-hydrophilic surface by modifying to hydroxyl group. The super-hydrophilic surface can be applied to anti-fogging, because of preventing formation of water droplet on the surface. Super-hydrophilic coatings are made of metal oxides, polymers, or their mixtures. In this study, columnar-structured C doped TiO2 nano-pillars were grown on glass substrates by MOCVD method. For change of surface properties, grown columnar-structured C-TiO2 nano-pillars were treated by oxygen plasma. After oxygen plasma treatment, the surface property of grown columnar structured C-TiO2 nano-pillars changed from hydrophobic surface to super hydrophilic surface. For determination of this mechanism, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy, and contact angle analyzer were employed.     

聚氨酯-聚丙烯酸酯共聚乳液的成膜和性能

通过XPS和接触角测试研究了聚氨酯-聚丙烯酸酯共聚乳液在不同基材上的成膜情况，并对共聚胶膜的耐水性和附着力进行了考察．由于该共聚乳液同时存在着亲水组分和疏水组分，所以它在不同的基材上成膜可导致其膜表面的组成成分不同，因而导致其耐水性和附着力也随基材而异。结果表明，亲水性的聚氨酯组分均富集于胶膜内部，但胶膜底层聚氨酯组分的含量却随基材的不同而不同。在憎水且表面张力较高的基材上，共聚胶膜的耐水性良好；共聚胶膜的附着力在表面张力较高的基材上也良好。     

Oral-based controlled release formulations using poly(acrylic acid) microgels

Aim: To investigate the release of hydrophobic and hydrophilic substances from tablets containing Pemulen and Carbopol as excipients. Method: The dissolution patterns of a hydrophobic (diazepam) and a hydrophilic active substance (midodrine-HCl) from different tablet formulations containing a nonmodified polyacrylic microgel (Carbopol 981 F) or a hydrophobically modified polyacrylic microgel (Pemulen®) have been studied. Possible differences in dissolution in phosphate buffer (pH 6.8) and in 0.1 M HCl between tablets produced using wet granulation and direct compression were also investigated. Results: Tablets produced by wet granulation had a greater effect on the release of active substance from the tablets. No major differences were observed in the release patterns of the hydrophilic substance midodrine-HCl from wet granulated tablets based on Carbopol and Pemulen. However, the release pattern of the more hydrophobic drug substance, diazepam, differed considerably between the two polymers. Wet granulation gave reproducible release patterns. The release patterns from the polymers differed considerably at pH 6.8 but were similar at low pH. Conclusions: The release of the diazepam from the hydrophobic polymer Pemulen was very slow, and the release was close to zero order.     

Synthesis and Application of Hethacrylate Polyhers in the Forhulation of Hatrix Tablets

Polymers were prepared by using two types of methacrylate monomers viz. hydrophobic monomers (methymethacrylate, butylmethacrylate) and hydrophilic monomers (2-hydroxy ethyl methacrylate, 2-hydroxy propyl methacrylate) using solution polymerisation method. Characterisation of the physico-chemical properties of the polymers was studied. The polymers were then evaluated as matrix formers for drugs selected on the basis of their aqueous solubility.     

Release profiles of theophylline from microspheres consisting of dextran derivatives and cellulose acetate butyrate: effect of polyion complex formation

The objective of this study was to evaluate the utility of mixtures among oppositely charged dextran derivatives as constituents of a controlled release microsphere. Carboxymethyldextran (CMD) and dextran sulfate (DS) were used as polyanions, and [2-(diethylamino) ethyl] dextran (EA) and [2-hydroxypropyltrimethylammonium] dextran (CDC) as polycations. The microspheres consisting of hydrophilic and hydrophobic polymers were prepared by emulsion-solvent evaporation method. The mixtures, CMD/EA, CMD/CDC, DS/EA, and DS/CDC, were used as hydrophilic polymers, because they can interact with each other to form polyion complexes for the improvement of sustained-release performances. Cellulose acetate butyrate and theophylline were used as a model hydrophobic polymer and a model drug, respectively. The yield of microspheres was excellent (more than 95%). According to observation, by scanning election microscopy (SEM) microspheres were spherical with a rough surface. The in vitro drug release from microspheres was examined in the JP XIV first fluid, pH 1.2, and second fluid, pH 6.8, at 37°C, and 100 rpm. In the DS/CDC system, drug release was depressed by formation of a polyion complex and not affected by pH of dissolution medium. The release rate was modulated by the ratio of hydrophilic and hydrophobic matrix. This particulate system, in which the polyion complex matrix is strengthened by a hydrophobic polymer, is a promising formulation for drug delivery.     

Control of microfluidic flow in amphiphilic fabrics

Woven textile fabrics were designed and constructed from hydrophilic and hydrophobic spun yarns to give planar substrates containing amphiphilic microchannels with defined orientations and locations. Polypropylene fibers were spun to give hydrophobic yarns, and the hydrophilic yarns were spun from a poly(ethylene terephthalate) copolyester. Water wicking rates into the fabrics were measured by video microscopy from single drops, relevant for point-of-care microfluidic diagnostic devices, and from reservoirs. intra-yarn microchannels in the hydrophilic polyester yarns were shown to selectively transport aqueous fluids, with the flow path governed by the placement of the hydrophilic yarns in the fabric. By comparing fluid transport in fabric constructions with systematic variations in the numbers of adjacent parallel and orthogonal hydrophilic yarns, it was found that inter-yarn microchannels significantly increased wicking rates. Simultaneous wicking of an aqueous and hydrocarbon fluid into the hydrophilic and hydrophobic microchannels of an amphiphilic fabric was successfully demonstrated. The high degree of interfacial contact and micrometer-scale diffusion lengths of such coflowing immiscible fluid streams inside amphiphilic fabrics suggest potential applications as highly scalable and affordable microcontactors for liquid-liquid extractions.     

Influence of Si(1 0 0) surface pretreatment on the morphology of TiO2 films grown by atomic layer deposition

The effect of water plasma treatment of both hydrophobic and hydrophilic Si(1 0 0) surfaces has been studied using infrared spectroscopy to monitor the various surface species present. Exposure to a water plasma results in a significant increase in the concentration of H-bonded hydroxyls and hydrides. Both atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM) of TiO₂ films deposited by atomic layer deposition at 300 °C, show that the morphology of the films is dependent on the nature of the initial surface. XTEM of the early stages of growth showed that coatings on hydrophilic substrates deposited as initially amorphous and continuous films, which crystallised with further growth. However, the hydrophobic substrate produced island growth of small, crystalline grains. AFM images of 23-nm thick films showed that films deposited on hydrophobic and hydrophilic Si consisted of 35–100 and 150–350 nm crystallites, respectively. A film on water plasma treated Si, closely resembled that on the hydrophilic surface, indicating that hydroxyl groups are responsible for directing the film growth.     

Sustained Release Tablets of Theophylline

Sustained release tablets of theophylline (anhydrous) were prepared using hydrophilic polymers (Methyl Cellulose, Methocel K₄M and K₁₅M) and hydrophobic polymers (ethyl cellulose, cellulose acetate). In addition water soluble adjuvants were used to modify release rate. With methocel, rapid gelling was observed and release was near zero-order, whereas with hydrophobic polymers release followed Fickian law of diffusion.     

Synthesis and Application of Hethacrylate Polyhers in the Forhulation of Hatrix Tablets

Abstract

Polymers were prepared by using two types of methacrylate monomers viz. hydrophobic monomers (methymethacrylate, butylmethacrylate) and hydrophilic monomers (2-hydroxy ethyl methacrylate, 2-hydroxy propyl methacrylate) using solution polymerisation method. Characterisation of the physico-chemical properties of the polymers was studied. The polymers were then evaluated as matrix formers for drugs selected on the basis of their aqueous solubility.     

Mesoscopic simulations of the phase behavior of aqueous EO19PO29EO19 solutions confined and sheared by hydrophobic and hydrophilic surfaces

The MesoDyn method is used to investigate associative structures in aqueous solution of a nonionic triblock copolymer consisting of poly(propylene oxide) capped on both ends with poly(ethylene oxide) chains. The effect of adsorbing (hydrophobic) and nonadsorbing (hydrophilic) solid surfaces in contact with aqueous solutions of the polymer is elucidated. The macromolecules form self-assembled structures in solution. Confinement under shear forces is investigated in terms of interfacial behavior and association. The formation of micelles under confinement between hydrophilic surfaces occurs faster than in bulk aqueous solution while layered structures assemble when the polymers are confined between hydrophobic surfaces. Micelles are deformed under shear rates of 1 μs(-1) and eventually break to form persistent, adsorbed layered structures. As a result, surface damage under frictional forces is prevented. Overall, this study indicates that aqueous triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) (Pluronics, EO(m)PO(n)EO(m)) act as a boundary lubricant for hydrophobic surfaces but not for hydrophilic ones.     

Steuerung der Benetzungseigenschaften von optisch transparenten Polymeren durch Antireflexstrukturen und dünne Schichten

Controlled wetting of optical polymers by antireflective structures and thin films The wetting behaviour of antireflective structures can be modified by additional coatings to become superhydrophobic or hydrophilic. The sub‐wavelength structures which increase the samples transmission are generated by plasma etching. Bump structures with large aspect ratio show a Lotus‐like behaviour immediately after coating with a thin hydrophobic layer. In case of PMMA the Lotus‐state can only be achieved if a thin silica layer is arranged below the hydrophobic top‐layer.     

Directed collagen patterning on gold-coated silicon substrates via micro-contact printing

The ability to create biologically functional systems from non-biological materials has importance in the arena of tissue engineering and medical device implantation. Directing the immobilization of proteins to specified regions on a substrate has attracted a lot of attention as one potential approach. Functionalization of the surface of gold-coated silicon wafers was accomplished by micro-contact printing a hydrophilic (or hydrophobic) self-assembled monolayer (SAM) atop the gold coating using poly(dimethylsiloxane) (PDMS) stamps. Afterwards, the substrate was soaked in a solution of hydrophobic (or hydrophilic) surfactant molecules which filled in the un-stamped area. The intention was to use carbodiimide coupling to attach fluorescently labeled collagen to COOH-terminated (hydrophilic) regions of the substrate. However, even in the presence of the reagents for this reaction, the collagen preferred to assemble on the hydrophobic regions. The results suggest that micro-contact printing may provide a simple mechanism for patterning collagen onto surfaces simply using selective adsorption. This might be useful for examining directed cell interactions, or to enhance the biocompatibility of inorganic materials used as substrates in tissue engineering or devices that are to be implanted into the body.