An SKP and EIS investigation of amine adsorption on zinc oxide surfaces

A metal/oxide/polymer ‘interphase’ with mixed organic–inorganic nature insures the high stability and the strength of the adhesive joints in a variety of corrosive environments. To model the interaction of epoxy resin with a metal surface, the interaction of amines of different structure with oxidized zinc surfaces was studied by Scanning Kelvin Probe (SKP), FTIR microscopy in atmospheric conditions, and a.c. and d.c. electrochemical techniques in the aqueous electrolyte. It was shown that bidentate ligand‐ethylendiamine, forming stable chelate complexes reacts with zinc oxide with redeposition of the interphase. In air and water electrolyte, this ligand shifts the potential of Zn/ZnO electrode to the level of the oxide‐free zinc. The amines with low chelating property show low effect on the potential of Zn/ZnO. The SKP was used to measure the potential drop at epoxy resin/zinc interface. On this basis, SKP is proposed as a sensitive nondestructive technique to characterize in situ the interaction of the resin with the metal and the subsequent formation of the interphase in the metal–polymer joints. Copyright © 2010 John Wiley & Sons, Ltd.     

Fabrication of Mussel‐Inspired Highly Adhesive Honeycomb Films Containing Catechol Groups and Their Applications for Substrate‐Independent Porous Templates

Porous surface patterns are used in a wide variety of practical applications. Honeycomb‐patterned porous polymer films are good templates for preparing porous surfaces due to their simple fabrication and the arrangement of pores on the surface. Catechol groups include in adhesive protein of mussels have attracted much attention due to their highly and substrate‐independent adhesive properties. In this paper, highly and substrate‐independent adhesive honeycomb‐patterned porous polymer films are prepared by using amphiphilic copolymer having catechol moieties. Furthermore, porous surface patterns are transferred on various organic or inorganic substrates by wet etching with using adhesive honeycomb films as templates.

     

Mechanism of adhesion of polyurethane/polymethacrylate simultaneous interpenetrating networks adhesives to polymer substrates

Polyether-based polyurethane/poly (methyl methacrylate-co-ethyleneglycol dimethacrylate) interpenetrating polymer networks [PU/P (MMA–co–EGDMA)-IPNs] were synthesized and used as adhesives to adhere vulcanized natural rubber (NR) and soft polyvinyl chloride (PVC). The structure and morphology of the IPN adhesives in bulk and near the adhesive/substrate interfaces were investigated. A new mechanism of adhesion called conjugate interpenetration of networks across interfaces, which is suitable for IPN adhesives and polymer substrates, was put forward. According to this mechanism, while forming simultaneous interpenetrating networks in the adhesive, the monomers in the IPN adhesive can permeate polymer substrates and polymerize in situ to form gradient IPNs, thereby producing conjugate three-component IPNs near the adhesive/substrate interfaces. It is the conjugate interpenetration of the networks across the interfaces that strengthens interfacial combination remarkably and results in high bond strength of IPN adhesives. © 1994 John Wiley & Sons, Inc.     

Folic‐Acid‐Modified Conducting Polymer: Electrochemical Detection of the Cell Attachment

Here, postfunctionalization and bioapplication of a π‐conjugated polymer named 4‐[4H‐dithieno(3,2‐b:2′,3′‐d)pyrrol‐4‐yl]aniline (DTP‐aryl‐NH₂) are reported, which is successfully synthesized via electropolymerization onto the glassy carbon electrode. Folic acid (FA) is used to modify the amino functional polymer via N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride/N‐hydroxysuccinimide chemistry for the further steps. The selective adhesion of folate receptor positive cells on the surface is followed by the electrochemical methods. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to characterize stepwise modification of the electroactive surface. After optimization studies such as scan rate during the polymer deposition, FA amount for the efficient surface targeting, incubation time with the cells etc., analytical characterization is carried out. The surface morphologies at each step are imaged by using fluorescence microscopy.

     

Chemically bonded carbon nanotubes on modified gold substrate as novel unbreakable solid phase microextraction fiber

A new technique is introduced for preparation of an unbreakable fiber using gold wire as a substrate for solid phase microextraction (SPME). A gold wire is used as a solid support, onto which a first film is deposited that consists of a two-dimensional polymer obtained by hydrolysis of a self-assembled monolayer of 3-(trimethoxysilyl)-1-propanthiol. This first film is covered with a layer of 3-(triethoxysilyl)-propylamine. Next, a stationary phase of oxidized multi-walled carbon nanotubes was chemically bound to the surface. The synthetic strategy was verified by Fourier transform infrared spectroscopy and scanning electron microscopy. Thermal stability of new fiber was examined by thermogravimetric analysis. The applicability of the novel coating was verified by its employment as a SPME fiber for isolation of diazinon and fenthion, as model compounds. Parameters influencing the extraction process were optimized to result in limits of detection as low as 0.2?ng?mL^?1 for diazinon, and 0.3?ng?mL^?1 for fenthion using the time-scheduled selected ion monitoring mode. The method was successfully applied to real water, and the recoveries for spiked samples were 104% for diazinon and 97% for fenthion.

Electrochemically Tunable Cell Adsorption on a Transparent and Adhesion‐Switchable Superhydrophobic Polythiophene Film

A superhydrophobic polythiophene film (SSPTH) is prepared by double‐layer electrodeposition on an indium tin oxide (ITO) glass electrode. This film shows not only electroresponsive superhydrophobic features, but also high transparency compared with the usual polythiophene film. The water‐droplet adhesion on the SSPTH film can be switched between sliding and pinned states under the applied potential. More intresetingly, the change in water‐droplet adhesion results in a change in cell adsorption on the SSPTH film. The low‐adhesion (dedoped) SSPTH films can prevent Hela cell adhesion, whereas high‐adhesion (doped) SSPTH films can promote Hela cell adsorption. This controllable cell adhesion on a SSPTH film may be developed as a smart biointerface material.

     

Morphology and properties of waterborne adhesives made from hybrid polyacrylic/montmorillonite clay colloidal dispersions showing improved tack and shear resistance

The morphology and adhesive properties of waterborne films from n-butyl acrylate/methyl methacrylate/montmorillonite clay hybrid polymer latexes which were synthesized by miniemulsion polymerization in the presence of a reactive organoclay ((2-methacryloylethyl) hexadecyldimethylammonium modified montmorillonite, CMA16) were investigated. It was found by cryo-TEM analysis that the hybrid dispersions were a mixture of colloidal particles composed of a small fraction of free montmorillonite clay platelets, polymer latex particles, polymer particles to which one or more clay platelets where adhered onto its surface and a fraction of colloidal material consisted of a clay platelet with a polymer lob adhered to either side, in other words hybrid particles with a dumbbell-like morphology. The films made from these waterborne hybrid dispersions presented a homogeneous dispersion of the clay platelets and exfoliated morphology. The shear adhesion failure temperature (SAFT) and shear resistance of the hybrid latex films synthesized with CMA16 were better than those prepared with a commercial clay (Cloisite 30B), but presented a liquid-like probe-tack performance. When allyl methacrylate (AMA) was added in the formulation, SAFT and shear resistance improved, but the film had a very low energy of adhesion due to the excessively crosslinked matrix. In order to reduce crosslink density and thus improve the adhesion energy, small amounts of chain transfer agent, in this case n-dodecyl mercaptan (n-DDM), were used in the miniemulsion polymerization process. Adhesive films made from these waterborne hybrid dispersions showed excellent SAFT and shear resistance, and good energy of adhesion.      

Patterning Surfaces for Controlled Platelet Adhesion and Detection of Dysfunctional Platelets

Platelets play a fundamental role in thrombus formation and in the pathogenesis of arterial thrombosis. Patterning surfaces for controlled platelet adhesion paves the way for adhesion and activation mechanisms in platelets and detection of platelet functional defects. Here, a new and simple method based on controlled polymerization of 2‐methacryloyloxyethyl phosphorylcholine (MPC) on the surface of styrene‐block‐(ethylene‐co‐butylene)‐block‐styrene (SEBS) is shown. The competition between polymerization and degradation enables platelet adhesion on SEBS to be switched on and off. The adhesive sites of the platelets can be down to single cell level, and the dysfunctional platelets can be quantitatively detected.

     

Thermodynamic analysis of polymer‐solid adhesion: Sticker and receptor group effects

Adhesion of dense linear polymer chains containing a small number of randomly distributed sticker groups (?_X) to a solid substrate containing receptor groups (?_Y) has been analyzed by a single‐chain scaling approach. An entanglement sink probability (ESP) model motivated by vector percolation explains the nonmonotonic influences of sticker concentration (?_X), receptor concentration (?_Y), and their interaction strength (χ) on the adhesion strength G_IC of the polymer‐solid interface. The ESP model quantifies the degree of interdigitation between adsorbed and neighboring chains on the basis of the adsorbed chain domain with an extension of the scaling treatment of de Gennes. Here, the adsorbed chain domain changes thermodynamically with respect to the energy of interaction parameter, r = χ?_X?_Y. This model considers the situation of a blend consisting of a small volume fraction of adhesive molecules as a compatibilizer at the interface, where these molecules promote adhesion by adsorbing to the surface via sticker‐receptor interactions. The percolation model scales solely with r = χ?_X?_Y, and this parameter can be related to both the adhesive potential (G_A) and the cohesive potential (G_C). G_A describes adhesive failure between adsorbed chains and the solid surface and linearly behaves as G_A ～ r = χ?_X?_Y. The cohesive strength between adsorbed and neighboring chains corresponds to G_C ～ r^?0.5～?1.0 = (χ?_X?_Y)^?0.5～?1.0. When the fracture stresses for cohesive and adhesive failure are equal, the model predicts maximum adhesion strength at an optimal value of r* = (χ?_X?_Y)*. Thus, for a given χ value, optimal values ? and ? exist for the sticker and receptor groups, above or below which the fracture energy will not be optimized. Alternatively, if the X‐Y interaction strength χ increases, then the number of sticker groups required to achieve the optimum strength decreases. Significantly, the optimum strength is not obtained when the surface is completely covered with receptor groups (?_Y = 1) but is closer to 30%. For polybutadiene, the optimum value of r* was determined experimentally (Lee, I.; Wool, R. P. J Adhesion 2001, 75, 299), and typically ? ≈ 1–3%, ? ≈ 25–30%. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2343–2353, 2002     

IR laser ablative decomposition of poly(vinyl acetate) loaded with Fe and Cu particles

Pulsed IR laser-induced decomposition of poly(vinyl acetate) (PVAC) loaded with nanometer-sized Cu and micrometer-sized Fe particles results in the formation of gaseous products and deposition of polar crosslinked polymer films which contain metal (Cu and Fe) particles. The main volatile products are hydrocarbons, carbon oxides (CO and CO₂), molecular hydrogen and acetic acid. The deposited polymer films were characterized by FTIR, UV and XP spectra and by electron microscopy and thermogravimetry. They contain reactive conjugated CC bonds and ca. 50% of the initially present acetate groups. Residual reactivity of the CC bonds results in polymer crosslinking and decrease in solubility. The deposited, crosslinked PVAC-based films containing metal particles are less thermally stable than similar films not containing these particles. The reported process reveals feasible ablation of metal particles when embedded in a polymer and makes it possible to fabricate films of metal/polymer composites in which metal particles are completely protected by the polymer.     

Stratified Polymer Brushes from Microcontact Printing of Polydopamine Initiator on Polymer Brush Surfaces

Stratified polymer brushes are fabricated using microcontact printing (μCP) of initiator integrated polydopamine (PDOPBr) on polymer brush surfaces and the following surface initiated atom transfer radical polymerization (SI‐ATRP). It is found that the surface energy, chemically active groups, and the antifouling ability of the polymer brushes affect transfer efficiency and adhesive stability of the polydopamine film. The stickiness of the PDOPBr pattern on polymer brush surfaces is stable enough to perform continuous μCP and SI‐ATRP to prepare stratified polymer brushes with a 3D topography, which have broad applications in cell and protein patterning, biosensors, and hybrid surfaces.

     

Interfacial toughness in polymer‐layered laminar composites

The investigation of the interfacial toughness of polymer layered laminar composites with two different approaches produced results differing by up to an order of magnitude and following opposite trends with respect to the strain rates. The flexural modulus and neutral axis of a constrained epoxy‐adhesive layer bound to a painted metal substrate varied with the thickness of the adhesive layer. The adhesion energy depended on the rate at which the force was transmitted to the adhesion bonds—not just on the strength of the adhesion bonds—and on the concomitant strain hardening at high strain rates. As the strain rate and thickness of the polymer layer increased, the transition from a cohesive mode to an adhesive–cohesive (polymer–polymer interface) mode of debonding led to the observed high adhesion energy. The high adhesion energy and increased strain hardening were attributed to the formation of organic–inorganic composites and nanocomposites within the polymer matrix, which evolved as a result of the interactions between the metal oxide pigments and fillers with the polymer matrix during curing. Scission of the polymer chains at the interface was proposed to be the predominant fracture mechanism; it was based on the high relaxation time (～10¹⁷ s) and the high activation energy (～175 kJ mol^?1). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3822–3835, 2004     

Adhesion and tack of polymers: Influence of mechanical properties and surface tensions

The adhesion of various polymers used as model adhesives, polyisobutylene, polyacrylates etc. has been investigated by means of an apparatus measuring the adhesive failure energyw in dependence on contact time, contact pressure, rate of separation, and temperature. The adhesive failure energy of adhesive joints formed with low contact pressure during a short contact time is called tack. After a sufficiently long contact time and with a high bonding pressure an adhesive joint exhibits its maximum energy of separationw _m .The viscoelastic properties of the model adhesives were characterized by creep experiments in dependence on time and temperature. The surface tension of the polymer adhesives and adherents could be determined by contact angle measurements. Adhesion measurements of polyisobutylene on a number of adherents were carried out in air and in various liquids in order to obtain information about the influence of surface tension on tack and maximum adhesive failure energy. w _m can be written as the product of two terms: the thermodynamic work of adhesionW _A which is related to the surface and interfacial tensions of adhesive and adherent and a dimensionless function dependent on temperature and rate of separation which describes the viscoeleastic properties of the adhesive and which obeys the rate-temperature superposition principle known from linear viscoelasticity. The tack is related to incomplete bond formation and cannot be described in the same manner. It is, however, strongly dependent on the viscoelastic properties of the adhesive showing a maximum at about 50 to 70 °C above the glass transition temperature. It is, moreover, influenced by the compliance in the plateau range above the glass transition which is determined by the entanglement network of the polymer. Wetting of the adherent by the adhesive is a further important condition for high tack values which is fulfilled if the adherent has a higher surface tension than the adhesive.     

Adhesion of an aromatic thermosetting copolyester with copper foils

Copper foils have been widely used in microelectronic devices. Adequate adhesion between copper foils to various substrates, such as Si, SiO₂, polyimide, is crucial to high performance of these devices. The adhesion between a new high temperature adhesive, aromatic thermosetting copolyester (ATSP), and various copper foils, namely, zinc(Zn)‐coated copper foil, copper foil and nickel (Ni)‐coated copper foil was characterized by a 90° peel strength test. It was found that the peel strength of Zn‐coated copper foil to ATSP was 1050 N/m, which was more than three times higher than copper foil and five times that of Ni‐coated copper foil. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS) studies indicated that this higher adhesion results from the stronger mechanical interlocking due to the rougher surface of Zn‐coated copper foil, and from chemical reactions at the interface which occur during the curing process of ATSP on the Zn‐coated copper surface. In contract to the adhesive failure at the ATSP/Cu and ATSP/Ni interfaces, the failure mechanism of ATSP/Zn is both cohesive and adhesive. Copyright © 2004 John Wiley & Sons, Ltd.     

Adhesion of Human U937 Monocytes to Nitrogen‐Rich Organic Thin Films: Novel Insights into the Mechanism of Cellular Adhesion

We present a two‐fold study designed to elucidate the adhesion mechanism of human U937 monocytes on novel N‐rich thin films deposited by plasma‐ and VUV photo‐polymerisation, so‐called “PVP:N” materials. It is shown that there exist sharply‐defined (“critical”) surface‐chemical conditions that are necessary to induce cell adhesion. By comparing the film chemistries at the “critical” conditions, we demonstrate the dominant role of primary amines in the cell adhesion mechanism. Quantitative real‐time RT‐PCR experiments using U937 cells that had adhered to PVP:N materials for up to 24 h are presented. The adhesion induces a transient expression of cytokines, markers of macrophage activation, as well as a more sustained expression of PPARγ and ICAM‐I.

     

Morphology of Electropolymerized Poly(N-Methylaniline) Films

The influence of polymerization conditions on the morphology of thin films of poly-(N-methylaniline) (PNMA) was studied. The films were prepared by electropolymerization on gold and platinum electrodes and studied by optical and electron microscopy. It was demonstrated that the film morphology does not depend on the polymerization rate or on the electrode metal. However, it is sensitive to the kind of counter ion of PNMA. The polymers containing acetate or chloride do not form stable films. Polymer films containing phosphate or sulfate display inhomogeneous structures. A formation of sprouts and nanotubes was observed for PNMA sulfate. The films formed by PNMA perchlorate are smooth and transparent (glass-like structure). A sublayer of 4-aminothiophenol increases the adhesion of polymers to the gold surface.     

Effect of divalent cations on the adhesion rate of cellular surfaces with ionizable groups

The adhesion rate of cells under charge regulation onto a rotating disc with constant potential is investigated theoretically in this paper. In particular, the effect of the presence of divalent carions in the suspension medium on adhesion rate of cells is discussed. By using sheep leucocytes as an illustrative example, it is shown that the presence of divalent cations in the suspension medium has the effect of decreasing the adhesion rate of cells. At a fixed level of ionic strength, the adhesion rate decreases with the increase of the concentration of divalent cations in the suspension medium for the various values of Peclet number andAd parameter given in this paper. For a fixed concentration of cations, the adhesion rate increases with the increase of ionic strength. At high ionic strength, the effect of increasing the concentration of cations on decreasing the adhesion rate of cells is not as high as that at low ionic strength. Applying the concept of Donnan potential, it is found that the magnitude of the electrostatic force between an ion-penetrable cell membrane and a solid surface is much smaller than that for the ion-impenetrable cell membrane.Nomenclature a cell radius (cm) - A Hamaker's constant (erg) - Ad A/kT - C dimensionless cell concentration - D cell diffusion coefficient (cm²/s) - e magnitude of electron charge (statcoul) - F dimensionless interaction force between cell and rotating disc pernkT - h minimum separation distance between cell surface and disc surface (cm) - H dimensionless separation distance between cell surface and disc surfaceh/a - [H ⁺] _r hydrogen ion concentration in the suspension medium (mole dm^–3) - [H ⁺] _s hydrogen ion concentration on the cell surface (mole dm^–3) - Boltzmann's constant (erg K^–1) - K _a dissociation equilibrium constant for acid groups on cell surface (mole dm^–3) - K _b dissociation equilibrium constant for base groups on cell surface (mole dm^–3) - n ionic strength in the suspension medium (ions cm^–3 - Pe Peclet number - q valence of cations - Sa the reciprocal of acidic density on the cell surface (cm²/group) - S _b the reciprocal of basic density on the cell surface (cm²/group) - Sh Sherwood number - T absolute temperature (K) - the fraction of cationic electrolyte in the suspension medium, 01 - reciprocal of Debye length, (cm^–1) - fluid kinematic viscosity (cm²/s) - ×a - l distance between two plate surfaces in Derjuguin's model (cm) - dimensionless total interaction energy between cell surface and disc surface - _vdw dimensionless unretarded van der Waals potential between cell surface and disc surface - _DL dimensionless double-layer interaction potential between cell surface and disc surface - dimensionless electrostatic potential between cell surface and disc surface - rotating speed of the disc (rad/s)     

Study of Adhesion and Fracture of Polymer Laminates by Imaging of Interfaces

The adhesion and fracture of styrene‐acrylonitrile random copolymer and poly(methyl methacrylate) (PMMA/SAN) laminates were studied. They showed a drastic transition from brittle to ductile on varying the acrylonitrile (AN) content in SAN, with changes in the fracture mode from interfacial failure to cohesive fracture. Energy‐filtering transmission electron microscopy (EFTEM) and scanning electron microscopy (SEM) with an in‐lens detector system were employed to study the interface and adhesion of the laminates. The effect of the AN content in SAN on the PMMA/SAN interfacial structures could be revealed by imaging of the interfaces using elemental mapping and electron energy loss spectroscopy (EELS). The in‐lens detector system in the SEM enabled the differentiation of thin interfaces with poor adhesion strength, yielding smooth and flat fracture surfaces, where numerous nanosized fibrils were formed normal to the surfaces.

     

Preparation and characterization of electrostrictive polyurethane films with conductive polymer electrodes

All-polymer electrostrictive soft films were developed for the first time by depositing conductive polymer (polypyrrole) directly on both sides of solution-cast electrostrictive polyurethane elastomer films. The final composite films are flexible with strong adhesion between the polyurethane film and the conductive polymer electrode. The conductivity (sheet resistivity ∼1000 Ω/□), of the polymer electrode is appropriate for its intended use. The compatible interface between the polypyrrole electrode polymer and the electrostrictive polyurethane significantly improves the acoustic and optical transparency of these composite films, compared with using a metal electrode film. The all-polymer films also exhibit comparable dielectric properties to gold-electroded polyurethane films in the temperature range from −40^°C to +80^°C. The temperature range covers the soft segment glass transition temperature of the polyurethane elastomers, which is about −20^°C. The films also show large electric field induced strain responses which are dependent on film thickness and measurement frequency. The electrostrictive characteristics in the all-polymer films show similarities to those of the films with gold electrodes under identical measurement conditions. © 1998 John Wiley & Sons, Ltd.     

Growth of the Bismuth Titanate Films on Textured Oxide Electrode by the Spin Coating-Pyrolysis

Bismuth titanate films were fabricated onto highly oriented LaNiO₃ electrode grown on SrTiO₃(100) and LaAlO₃(012) substrates using spin-coating technique with metal naphthenates as starting materials. (00l)/(h00)-oriented bismuth titanate films on LaNiO₃/SrTiO₃ and LaNiO₃/LaAlO₃ were obtained by pyrolysis at 500°C, followed by annealing at 750°C. In-plane alignment and surface morphology of the films analyzed by pole-figure analysis ( scanning) and field emission scanning electron microscope showed an imperfect epitaxy with polycrystalline structure.An erratum to this article can be found at