1,399 research outputs found

    Composition depth profiling of polystyrene/poly(vinyl ethyl ether) blend thin films by angle resolved XPS

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    Angle resolved XPS (ARXPS) and scanning force microscopy (SFM) are used to study polystyrene/poly(vinyl ethyl ether) 50/50 wt% blend thin films spin cast from toluene solution, as a function of polystyrene molecular weight and film thickness. ARXPS is used to investigate the composition depth profile (CDP) of the blend thin films and SFM to study their surface morphology and miscibility. The CDPs are modelled by an empirical hyperbolic tangent function with three floating parameters. These are determined by non-linear least squares regression, their uncertainties estimated and the curve fit residuals analysed to demonstrate that the hyperbolic tangent CDP is a satisfactory fit to the ARXPS data. Conclusions are drawn regarding the behaviour of the blend thin films as the thickness and polystyrene molecular weight are varied. Flory-Huggins interaction parameters (chi) for the mixtures are calculated based upon the segregation data, and suggest a value of chi = 0.05 to be appropriate for this system. (c) 2009 Elsevier B.V. All rights reserved

    The swelling of weak polyelectrolytes at low salt concentrations in dilute solution

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    The possibility of swelling of single polyelectrolyte chains in dilute aqueous solution by free ions in the presence of a small amount of salt is investigated using a mean-field approach. The swelling of chains by free ions is more likely for larger chains in solutions containing only a small amount of salt. The swollen chains are likely to retain a spherical structure

    The study of cells using scanning force microscopy

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    A reversible water-based electrostatic adhesive

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    \ua9 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH. Commercial adhesives typically fall into two categories: structural or pressure sensitive. Structural glues rely on covalent bonds formed during curing and provide high tensile strength whilst pressure-sensitive adhesives use physical bonding to provide weaker adhesion, but with considerable convenience for the user. Here, a new class of adhesive is presented that is also reversible, with a bond strength intermediate between those of pressure-sensitive and structural adhesives. Complementary water-based formulations incorporating oppositely charged polyelectrolytes form electrostatic bonds that may be reversed through immersion in a low or high pH aqueous environment. This electrostatic adhesive has the advantageous property that it exhibits good adhesion to low-energy surfaces such as polypropylene. Furthermore, it is produced by the emulsion copolymerization of commodity materials, styrene and butyl acrylate, which makes it inexpensive and opens the possibility of industrial production. Bio-based materials have been also integrated into the formulations to further increase sustainability. Moreover, unlike other water-based glues, adhesion does not significantly degrade in humid environments. Because such electrostatic adhesives do not require mechanical detachment, they are appropriate for the large-scale recycling of, e.g., bottle labels or food packaging. The adhesive is also suitable for dismantling components in areas as varied as automotive parts and electronics

    Double-network hydrogels improve pH-switchable adhesion

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    For environmentally-switchable adhesive systems to be reused repeatedly, the adhesive strength must not deteriorate after each adhesion cycle. An important criterion to achieve this goal is that the integrity of the interface must be retained after each adhesion cycle. Furthermore, in order to have practical benefits, reversing the adhesion must be a relatively rapid process. Here, a double-network hydrogel of poly(methacrylic acid) and poly[oligo(ethylene glycol)methyl ether methacrylate] is shown to undergo adhesive failure during pH-switchable adhesion with a grafted (brush) layer of polycationic poly[2-(diethyl amino)ethyl methacrylate], and can be reused at least seven times. The surfaces are attached at pH 6 and detached at pH 1. A single-network hydrogel of poly(methacrylic acid), also exhibits pH-switchable adhesion with poly[2-(diethyl amino)ethyl methacrylate] but cohesive failure leads to an accumulation of the hydrogel on the brush surface and the hydrogel can only be reused at different parts of that surface. Even without an environmental stimulus (i.e. attaching and detaching at pH 6), the double-network hydrogel can be used up to three times at the same point on the brush surface. The single-network hydrogel cannot be reused under such circumstances. Finally, the time taken for the reuse of the doublenetwork hydrogel is relatively rapid, taking no more than an hour to reverse the adhesion

    Slow polymer diffusion on brush-patterned surfaces in aqueous solution

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    A model system for the investigation of diffusional transport in compartmentalized nanosystems is described. Arrays of ā€œcorralsā€ enclosed within poly[oligo(ethylene glycol)methyl ether methacrylate] (POEGMA) ā€œwallsā€ were fabricated using double-exposure interferometric lithography to deprotect aminosilane films protected by a nitrophenyl group. In exposed regions, removal of the nitrophenyl group enabled attachment of an initiator for the atom-transfer radical polymerization of end-grafted POEGMA (brushes). Diffusion coefficients for poly(ethylene glycol) in these corrals were obtained by fluorescence correlation spectroscopy. Two modes of surface diffusion were observed: one which is similar to diffusion on the unpatterned surface and a very slow mode of surface diffusion that becomes increasingly important as confinement increases. Diffusion within the POEGMA brushes does not significantly contribute to the results

    Application of mean-field theory to the spin casting of polystyrene and poly(methyl methacrylate) blend films from toluene

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    The Flory-Huggins free energy of mixing is shown to be appropriate for the analysis of the temporal evolution of a ternary blend of polystyrene and poly (methyl methacrylate) during spin-coating from toluene using an in-situ light scattering technique. For the range of concentrations studied, both the onset of film instability and the observation of a scattering ring occur at the same toluene volume fraction. The success of Flory-Huggins theory indicates that polymer chains retain random walk characteristics during spin-coating. It is also concluded that the thermodynamics of phase separation during film formation is independent of the initial solvent concentration

    Distinct binding interactions of Ī±5Ī²1-integrin and proteoglycans with fibronectin

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    Dynamic single molecule force spectroscopy was performed to monitor the unbinding of fibronectin with the proteoglycans syndecan-4 and decorin, and to compare this with the unbinding characteristics of Ī±5Ī²1-integrin. A single energy barrier was sufficient to describe the unbinding of both syndecan-4 and decorin from fibronectin, while two barriers were observed for the dissociation of Ī±5Ī²1-integrin from fibronectin. The outer (high affinity) barrier in the interactions of fibronectin with Ī±5Ī²1-integrin and syndecan-4 are characterized by larger barrier heights and widths, and slower dissociation rates than those of the inner (low affinity) barrier in the interactions of fibronectin with Ī±5Ī²1-integrin and decorin. These results indicate that syndecan-4 and (ultimately) Ī±5Ī²1-integrin have the ability to withstand deformation in their interactions with fibronectin, while the decorin-fibronectin interaction is considerably more brittle

    1.6 W continuous-wave Raman laser using low-loss synthetic diamond

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    Low-birefringence (Ī”n<2x10āˆ’6), low-loss (absorption coefficient <0.006cmāˆ’1 at 1064nm), single-crystal, synthetic diamond has been exploited in a CW Raman laser. The diamond Raman laser was intracavity pumped within a Nd:YVO4 laser. At the Raman laser wavelength of 1240nm, CW output powers of 1.6W and a slope efficiency with respect to the absorbed diode-laser pump power (at 808nm) of ~18% were measured. In quasi-CW operation, maximum on-time output powers of 2.8W (slope efficiency ~24%) were observed, resulting in an absorbed diode-laser pump power to the Raman laser output power conversion efficiency of 13%
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