How silanization of silica particles affects the adsorption of PDMS chains on its surface

A series of six fumed silica types, with different surface areas in the 50–400 m²/g range, were modified by grafting with trimethylchlorosilane. The grafting reaction was controlled by elemental analyses, surface hydroxyl titration, and combustion techniques. The silica surface energy was determined as a function of silanization degree by inverse gas chromatography (IGC). Adsorption of a series of poly(dimethylsiloxane) elastomers with molecular weights ranging between 4 and 420 kg/mol on silica was followed using flow microcalorimeter (FMC). IGC results show that free adsorption energies of two series of alkanes and siloxanes as well as the dispersive component of the surface energy were found to decrease monotonously with surface silanization and so does the polymer molar heat of adsorption. FMC results indicate, however, that the conformation of the macromolecules on silica depends on the silica surface area but remains unaffected by the surface treatments. A given polymer chain was found to remain adsorbed on the surface preserving its same conformation until its molar heat of adsorption falls bellow a critical value. These findings offer a better monitoring of surface–polymer interactions as it defined a comprehensive relationship between the degree of modifications of the filler surface and polymer adsorption conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Determination of Meloxicam Using Europium Sensitized Luminescence in the Presence of Co-Luminescence Reagents

A sensitive time- resolved luminescence method for the determination of meloxicam (MX) in methanol and in aqueous solution is described. The method is based on the luminescence sensitization of europium (Eu³⁺) by formation of ternary complex with MX in the presence of 1,10- phenanthroline as coligand, Tween-80 as surfactant and gadolinium ion as a co-luminescence reagent. The signal for Eu- MX-1, 10- phenanthroline is monitored at λ_ex = 360 nm and λ_em = 620 nm. Optimum conditions for the formation of the complex in aqueous system were 0.01 M TRIS buffer, pH 8.0, 1,10- phenanthroline (6.0 × 10⁻⁶ M) , Gd³⁺ (7.0 × 10⁻⁶ M), Tween-80 (0.28%) and 1.75 mM of Eu³⁺ which allows the determination of 20–800 ppb of MX with limit of detection (LOD) of 7 ppb. The relative standard deviations of the method range between 0.1 and 1.1% indicating excellent reproducibility of the method. The proposed method was successfully applied for the assay of MX in pharmaceutical formulations, plasma and in urine samples. Average recoveries of 99.8 ± 1.1%, 100.2 ± 0.9% and 100.9 ± 1.1% were obtained for MX in tablet, plasma and urine sample respectively.     

Photocrosslinking of elastomer systems—III Ultraviolet light induced reactions in EPDM and EPR blended with or modified by grafting of derivatives of benzophenone

Photocrosslinking experiments were performed in elastomeric polymer films (EPR or EPDM) that either contained benzophenone or some of its derivatives, or had been previously modified (EPDM) by grafting of benzophenone. This latter modification was performed by a series of Friedel-Crafts reactions. The resulting materials were characterized by i.r. and u.v. spectroscopy in conjunction with physical property measurements. The results allowed relationships between the properties of the photosensitizers in their excited states and their efficiency in the crosslinking processes to be established. The results suggest that each coupled polymer-photoinitiator exhibits a particular behaviour. Thus it appeared that, in the presence of oxygen, the hexadiene branches of the terpolymer can undergo various types of reactions. Moreover, the grafting of the photosensitizer onto the elastomer backbone was shown to enhance considerably the crosslinking reaction. It is possible to conclude that oxygen plays a substantial role in the photocrosslinking. Indeed it always enhances crosslink formation. It can be assumed that the photooxidation of the polymer backbone yields alkoxy and hydroperoxy radicals which can act as crosslink sites.     

Nanosecond kinetics of hydrated electrons upon water photolysis by high intensity femtosecond UV pulses

We report a nanosecond laser study of the transient absorption of hydrated electrons generated by multiphoton ionisation of liquid water upon excitation at 266 and 400 nm by femtosecond pulses with power densities higher than 1 TW/cm². For both wavelengths, as the pump power density increases, the signal amplitude increases and the decay becomes faster proving that more electrons are produced. However, we show that in the nanosecond time range, under pump power densities higher than 1 TW/cm², the distribution of the hydrated electrons is not uniform along the optical pathway of the pump beam in the water sample.     

IMENSE: An e-infrastructure environment for patient specific multiscale data integration,modelling and clinical treatment

Secure access to patient data and analysis tools to run on that data will revolutionize the treatment of a wide range of diseases, by using advanced simulation techniques to underpin the clinical decision making process. To achieve these goals, suitable e-Science infrastructures are required to allow clinicians and researchers to trivially access data and launch simulations. In this paper we describe the open source Individualized MEdiciNe Simulation Environment (IMENSE), which provides a platform to securely manage clinical data, and to perform wide ranging analysis on that data, ultimately with the intention of enhancing clinical decision making with direct impact on patient health care. We motivate the design decisions taken in the development of the IMENSE system by considering the needs of researchers in the ContraCancrum project, which provides a paradigmatic case in which clinicians and researchers require coordinated access to data and simulation tools. We show how the modular nature of the IMENSE system makes it applicable to a wide range of biomedical computing scenarios, from within a single hospital to major international research projects.     

Photocrosslinking of elastomer systems. II. Ultraviolet light-induced reactions in an EPDM modified by grafting of benzoin derivatives

Photocrosslinking experiments were performed on elastomeric polymer films (EPDM) previously modified by grafting a photosensitive initiator (benzoin derivative) onto the macromolecular backbone. This modification was performed by a series of Friedel–Crafts reactions and the resulting materials were characterized by infrared (IR) spectroscopy in conjunction with model reactions. After ultraviolet (UV) irradiation the photocrosslinked samples were studied by IR spectroscopy in conjunction with the measurement of physical properties. It apperared that grafting the photosensitizer onto the elastomer considerably enhances the crosslinking reaction even with a limited quantity of grafted benzoin derivative. Moreover, the results obtained suggest that the structure of the resulting networks is strongly dependent on the crosslinking process used; that is, curing the elastomer with peroxide or UV irradiation either of a blend of elastomer and photosensitizer or of the same elastomer modified by grafting the chromophore.     

Assessing the role of graphene content in the electromagnetic response of graphene polymer nanocomposites

We report experimental results from frequency-domain spectroscopy on graphene (GE) filled polyvinylidene difluoride trifluoroethylene P(VDF-TrFE). The dielectric properties of these polymer nanocomposites (GPN) were investigated over a broad range of frequency (from 10² Hz to a few GHz) and a broad range of temperature (from 150 K to 370 K) by using two measurement techniques: impedance spectroscopy and asymmetrical stripline. Care is needed in relating the GE content to the dielectric properties of GPN since the addition of GE to P(VDF-TrFE) can result in a nonmonotonic permittivity change. At low frequency (<1 MHz) the relaxation spectra is not Debye like but is characterized with a broad relaxation time distribution especially at low temperatures. This effect originates from the freezing process of dipoles and Maxwell-Wagner-Sillars (MWS) interfacial polarization. Additionally, a fit of the effective permittivity versus GE content suggests that our data are in accord with the two-exponent phenomenological percolation equation (TEPPE). These experimental results draw attention to the importance of the large surface area of the GE nanoparticles in controlling the interface between the GE flakes and the polymer phase.