Polypyrrole coating of inorganic and organic materials by chemical oxidative polymerisation

Polypyrrole is one of the most frequently studied conducting polymers, having high electrical conductivity and stability, suitable for multi-functionalised applications. Coatings of chemically synthesised polypyrrole applied onto various organic and inorganic materials, such as polymer particles and films, nanoparticles of metal oxides, clay minerals, and carbon nanotubes are reviewed in this paper. Its primary subject is the formation of new materials and their application in which chemical oxidative polymerisation of pyrrole was used. These combined materials are used in antistatic applications, such as anti-corrosion coating, radiation-shielding, but also as new categories of sensors, batteries, and components for organic electronics are created by coating substrates with conducting polymer layers or imprinting technologies.     

Malonic Acid Diazoesters for C−H Insertion Crosslinking (CHic) Reactions: A Versatile Method for the Generation of Tailor‐Made Surfaces

A simple and versatile method for the modification of a broad spectrum of surfaces with thin polymer films through the thermally or photochemically induced generation of surface‐attached polymer networks is reported. The system is based on copolymers containing diazomalonate groups, which can be activated by heat or light. To this end, the copolymers are deposited from solution onto solid substrates by standard techniques of thin‐film deposition (spin coating, dip coating). Upon activation the diazomalonate group decomposes and forms a carbene, which induces C−H insertion crosslinking (CHic) reactions. In the course of this process network formation and covalent surface attachment occur at the same time. The crosslinking process proceeds very rapidly, especially when the carbenes generated in the activation process cannot undergo Wolff‐rearrangement. The presented system can be used for the generation of a wide range of polymer layers and microstructures on a broad spectrum of surfaces.     

Activation of crystalline cellulose surfaces through the chemoenzymatic modification of xyloglucan

Cellulose constitutes an important raw material for many industries. However, the superb load-bearing properties of cellulose are accompanied by poor chemical reactivity. The hydroxyl groups on cellulose surfaces can be reacted but usually not without loss of fiber integrity and strength. Here, we describe a novel chemoenzymatic approach for the efficient incorporation of chemical functionality onto cellulose surfaces. The modification is brought about by using a transglycosylating enzyme, xyloglucan endotranglycosylase, to join chemically modified xyloglucan oligosaccharides to xyloglucan, which has a naturally high affinity to cellulose. Binding of the chemically modified hemicellulose molecules can thus be used to attach a wide variety of chemical moieties without disruption of the individual fiber or fiber matrix.     

Viscoelasticity and water plasticization of polymer-cellulose composite films and paper sheets

Viscoelastic properties of cellulose microfibril—polymer composites and paper sheets were studied with dynamic mechanical analysis as a function of relative humidity in order to assess the bonding properties in cellulosic networks. The amount of associated water in the composites (equilibrium moisture content) was measured by thermogravimetry. Water plasticization was evidenced by DMA both in composite and paper samples. Polymers with high affinity to water, e.g. carboxymethyl cellulose, clearly increased the water plasticization in the composites. The plasticization behavior of paper sheet samples was also influenced by polymers. However, the effect of polymers on the plasticization was different between the composite and the paper samples. The consideration of fiber bonding domain in paper structure as a gel-like layer consisting of cellulose microfibrils, polymers, and associated water can help to unveil some of the complex mechanisms behind the strength in fibrous cellulosic materials.     

Synthesis and properties of water-soluble gold colloids covalently derivatized with neutral polymer monolayers

Citrate-capped gold nanoparticles as well as planar gold surfaces can be efficiently grafted with a covalently attached polymer monolayer a few nanometers thick, by simple contact of the metal surface with dilute aqueous solutions of hydrophilic polymers that are end-capped with disulfide moieties, as shown by UV/vis absorption, dynamic light scattering, and surface plasmon resonance studies. The hydrophilic polymer-coated gold colloids can be freeze-dried and stored as powders that can be subsequently dissolved to yield stable aqueous dispersions, even at very large concentrations. They allow for applying filtrations, gel permeation chromatography, or centrifugation. They do not suffer from undesirable nonspecific adsorption of proteins while allowing the diffusion of small species within the hydrogel surface coating. In addition, specific properties of the original hydrophilic polymers are retained such as a lower critical solution temperature. The latter feature could be useful to enhance optical responses of functionalized gold surfaces toward interaction with various substrates.     

Renewable resources as reinforcement of polymeric matrices: composites based on phenolic thermosets and chemically modified sisal fibers

Lignocellulosic materials can significantly contribute to the development of composites, since it is possible to chemically and/or physically modify their main components, cellulose, hemicelluloses and lignin. This may result in materials more stable and with more uniform properties. It has previously been shown that chemically modified sisal fibers by ClO(2) oxidation and reaction with FA and PFA presented a thin coating layer of PFA on their surface. FA and PFA were chosen as reagents because these alcohols can be obtained from renewable sources. In the present work, the effects of the polymeric coating layer as coupling agent in phenolic/sisal fibers composites were studied. For a more detailed characterization of the fibers, IGC was used to evaluate the changes that occurred at the sisal fibers surface after the chemical modifications. The dispersive and acid-base properties of untreated and treated sisal fibers surfaces were determined. Biodegradation experiments were also carried out. In a complementary study, another PFA modification was made on sisal fibers, using K2Cr2O(7) as oxidizing agent. In this case the oxidation effects involve mainly the cellulose polymer instead of lignin, as observed when the oxidation was carried out with ClO(2). The SEM images showed that the oxidation of sisal fibers followed by reaction with FA or PFA favored the fiber/phenolic matrix interaction at the interface. However, because the fibers were partially degraded by the chemical treatment, the impact strength of the sisal-reinforced composites decreased. By contrast, the chemical modification of fibers led to an increase of the water diffusion coefficient and to a decrease of the water absorption of the composites reinforced with modified fibers. The latter property is very important for certain applications, such as in the automotive industry.     

Treatment in Swelling Solutions Modifying Cellulose Fiber Reactivity – Part 2: Accessibility and Reactivity

The reorganization of cellulose fibers by swelling treatments in alkali solutions results in numerous changes to fiber structure, causing changes of chemical reactivity in the fiber-solution heterogeneous system. An important part of the change in chemical reactivity is the change of fiber accessibility because it results in exclusion of chemicals such as reagents or catalysts from the fiber. In the second of a two-part series of papers, we examine the influence of changes in fiber accessibility and/or reactivity due to treatment in swelling solutions on the performance or behavior of substrates during and after chemical finishing treatments. Changes in fiber accessibility due to alkali treatments are visualized with fluorescence microscopy. The effect of alkali treatments on enzymatic hydrolysis and pad-dry-cure crosslinking treatments of cellulose substrates are discussed as representative examples to demonstrate the effects of swelling processes on fiber reactivity and accessibility. Model calculations indicate that a considerable redistribution of chemicals in substrates occurs during dry-cure operations resulting from molecule-specific exclusion effects. Pilling tests on lyocell knit-fabrics show the impact of preceding alkali processes on the final physical performance of textile fabric highlighting the importance of correct selection of alkali processes to achieve desired behavior.     

Cell attachment and detachment on micropattern-immobilized poly(N-isopropylacrylamide) with gelatin

To investigate by microscopic observation the effects on cell behaviour of immobilized polymers, a micropattern-immobilization technique using a photo-mask was employed. Poly(acrylic acid) or poly(N-isopropylacrylamide-co-acrylic acid) was coupled with azidophenyl groups to form a photo-reactive polymer. The photo-reactive polymer was coated, with or without gelatin, on a cell-culture polystyrene plate and photo-irradiated through a micropatterned photo-mask. Mouse fibroblast STO cells were cultured on the micropattern-immobilized plate. The surface wettability of the immobilized plate was examined by measurement of the contact angle in the cell culture medium. The attachment of cells on the plate was significantly affected by the surface properties. Although the poly(acrylic acid) has the same effect on cell adhesion as a bare polystyrene surface, co-immobilization with gelatin significantly enhanced cell adhesion, while poly(N-isopropylacrylamide) reduced it. However, co-immobilization with gelatin enhanced cell adhesion, and, on the co-immobilized surface, cell detachment was observed by lowering the temperature. Micropattern immobilization was useful for comparing the effects of materials on cell behavior and for constructing biochips.     

Kinetics of adsorption of polyvinylamine on cellulose fibers. I. Adsorption from salt-free solutions

Adsorption of fully hydrolyzed polyvinylamine on cellulose fibers in the short term was investigated by supplying the polymer to the fibers, first instantaneously by pouring the polymer solution into a jar containing the fiber dispersion (jar experiments) and second, at controlled rates (the reactor experiments). In the latter case, the rate of supply of polymer to the fiber dispersion confined in the reactor was monitored by setting the concentration of the solution being injected at a controlled rate. The concentration of the polymer solution exerts a paramount influence on the kinetics of adsorption and on the amount of polymer adsorbed at (or near) fiber surface saturation, while the rate of polymer supply only plays a minor role. The main observation is the emergence of two types of polymer layers corresponding to diffuse and dense layers. The former were characterized by adsorption layers of density smaller than 0.65 mg/g cellulose that are composed of adsorbed polymers having sustained extended flattening in the adsorbed state. The latter reach densities as high as 10 mg/g cellulose when the fiber surface is fully coated, thus indicating that reconformation is limited or even impeded at short terms. The threshold adsorption corresponds more or less to equilibrated layers, since the final coverage determined at adsorption equilibrium did not exceed 0.6 to 0.7 mg/g cellulose.     

Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3‐aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene‐alt‐maleic anhydride) (PSMA), and poly(ethylene‐alt‐maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT‐IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of polymer binding on the spectroscopic properties of stilbene-based fluorescent dyes

Studies utilizing absorption and emission spectrophotometry have been carried out to observe the effect of various polymer substrates on the spectral characteristics of several stilbene-based fluorescent dyes. Poly(vinyl alcohol), cellulose acetate, cellulose fiber, and bovine serum albumin were used as substrates for two common fluorescent whitening agents and for two model compounds. Binding of these molecules to polymers leads to a marked red shift in the absorption spectra and an increase in vibrational structure. These effects are attributed to an increase in molecular planarity induced by the polymer environment. For the case of bovine serum albumin, it is concluded that the dye molecules bind to the protein largely through electrostatic interaction involving the dye sulfonate groups. The spectral characteristics of the dye molecules on wool fibers are interpreted in light of these results.     

Direct visualization of reversible switching of micropatterned polyelectrolyte brushes on gold surfaces using laser scanning confocal microscopy

We apply confocal fluorescence microscopy for real time studies of reversible conformational changes of poly(methacryloyloxyethyl phosphate) (PMEP) brushes chemically grafted onto gold substrates. Oregon green 488 fluorophores chemically attached onto the PMEP polymers were used as reporters for probing the conformational changes. Use of a specially designed liquid flow microchamber allowed dynamic imaging of the brushes under varying environmental conditions. The fluorescence intensities exhibited fully reversible brightness changes on alternation of the solution in the chamber between water and KCl. This reversible quenching behavior is consistent with a conformational change between an extended and a collapsed brush configuration. The fluorescence quenching behavior of the brushes was found to be dependent on ion concentration as well as polymer grafting density and was caused by nonradiative energy transfer to the polymer scaffold and the gold substrate.     

Self-assembled DNA-conjugated polymer for novel DNA chip.

We developed DNA-conjugated polymer for DNA chip fabrication. A 30 mer probe DNA and disulfide bridges were covalently attached to the polymer side chain. The DNA-conjugated polymer can be specifically adsorbed on a gold substrate surface by a self-assembly technique. The interaction between fully matched DNA and DNA-conjugated polymer was investigated by surface plasmon resonance (SPR) technique. The DNA-conjugated polymer-modified gold surface highly recognized fully matched DNA, rather than unmatched DNA. Therefore, DNA-conjugated polymer can be used for novel DNA chip fabrication.     

Vacuum coating of plastic optics

Vacuum technologies for the deposition of optical interference coatings on polymer substrates, based on long-term experience in glass coating, have been under development for about 20 years. A growing market for precision optical elements and consumer optics moulded from thermoplastic polymers requires antireflective properties and hard coatings. Owing to the manifold chemical and physical properties of optical polymers, special efforts are essential for each type of plastic to find polymer-capable coating conditions. The main focus of this article is on evaluating the state of the art in vacuum-coating processes applied to plastics today, and on discussing specific coating techniques and evaluation procedures. A better understanding of the complex interactions between low-pressure plasmas and the various polymer materials will be a key factor in making durable plastic optics for future applications; achieving this will be a challenge to surface scientists.     

Adsorption isotherms of cellulose-based polymers onto cotton fibers determined by means of a direct method of fluorescence spectroscopy

We present a novel method for the measurement of polymer adsorption on fibers by employing fluorescently labeled polymers. The method itself can be used for any compound that either shows fluorescence or can be labeled with a fluorescent dye, which renders it ubiquitously applicable for adsorption studies. The main advantage of the method is that the choice of adsorbent is not limited to flat surfaces, thereby allowing the investigation of fibrous and porous systems. As an example of high interest for application we determined the adsorption isotherms of various polysaccharide-based polymers with different charges and different substituents on cotton fibers. These experiments show that the extent of adsorption depends not only on the charge conditions but also very much on the specific interactions between the polymer and fiber. For instance, the cationic hydroxyethyl cellulose can become bound to an extent similar to that of the anionic alginate, while the anionic carboxymethyl cellulose of similar charge density adsorbs much less under these conditions. This shows that the adsorption of polymers depends subtly on the details of the interaction between the polymer and fiber but can be determined with good precision with our direct fluorescence method.     

Nanotemplating for two-dimensional molecular imprinting

A new 2D molecular imprinting technique based on nanotemplating and soft-lithography techniques is reported. This technique allows the creation of target-specific synthetic recognition sites on different substrates using a uniquely oriented and immobilized template and the attachment of a molecularly imprinted polymer on a substrate. The molecularly imprinted polymer was characterized by AFM, fluorescence microscopy, and ATR-FTIR. We evaluated the rebinding ability of the sites with theophylline (the target molecule). The selectivity of the molecularly imprinted polymer was determined for the theophylline-caffeine couple. The molecularly imprinted polymer exhibited selectivity for theophylline, as revealed by competitive rebinding experiments. Fluorescence microscopy experiments provided complementary proof of the selectivity of the molecularly imprinted polymer surfaces toward theophylline. These selective molecularly imprinted polymers have the potential for chemical sensor applications. Because of its 2D nature, this novel chemical sensor technology can be integrated with many existing high-sensitivity multichannel detection technologies.     

A simple method for creating molecularly imprinted polymer-coated bacterial cellulose nanofibers

Molecularly imprinted polymer-coated bacterial cellulose nanofibers have been prepared by immersing solvent treated-bacterial cellulose into a dilute pre-polymerization mixture solution prior to the polymerization process. The quercetin-imprinted polymer coating bacterial cellulose (QIP-BC) nanofibers show discrete nanoparticles encapsulated along the BC nanofibers. The binding capacity of dried QIP-BC was approximately 3 mg per gram of the polymer. The obtained results indicated that QIP-BC nanofibers provided a three fold higher recognition ability for quercetin than quercetin-imprinted nanospheres. This technique can be easily used to combine two fascinating materials like BC nanofibers and molecularly imprinted polymers (MIPs) to afford promising polymer composites that are useful in various innovative applications in biomedical, pharmaceutical, and industrial sectors.     

Surface‐Grafted conjugated polymers for hybrid cellulose materials

Conjugated polymers were grafted onto cellulose substrates in an effort to create a general method for the synthesis of conjugated polymer/cellulose hybrid materials. In this report, we describe the grafting of poly(fluorene), poly(fluorenevinylene), and a poly(fluorene‐ethynylene‐phenylene) onto modified cellulose paper substrates using Suzuki, Heck, and Sonogashira‐type polymerizations, respectively. The application of these three widely used coupling chemistries to surface‐grafted conjugated polymers on cellulose provides a general route to cellulose‐based hybrid materials tunable with almost any aromatic repeat structure for specific applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Analysis of CMC attachment onto cellulosic fibers by infrared spectroscopy

Infrared spectroscopy has been used to measure the amount of carboxymethyl cellulose (CMC) attached to cellulosic fibers. CMC was attached to an unbleached kraft pulp in aqueous conditions. Isotropic handsheets were then prepared and ATR spectroscopy was used to measure the intensity of the carboxyl vibration, which correlates to the amount of attached CMC that was determined using a wet chemical approach. The ATR method is rather time consuming as several measurement points on the sample have to be averaged, although it is still much faster than the wet chemical approach. Infrared reflection absorption spectroscopy (IRRAS) using polarized light was further used to measure the amount of attached CMC. In this method the intensity of an electromagnetic wave confined to the thin layer is used to correlate the spectroscopy to the amount of CMC on the fiber surface in the paper sample. The measurement time is shorter than with the ATR method. The proposed IRRAS method could be employed as a fast and reliable way to quantify adsorption of chemicals on pulp fibers.