Adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the silica-water interface

in Langmuir (2005), 21(7), 2930-2940

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass ... [more ▼]

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface. [less ▲]

The Vacuum UV Photoabsorption Spectrum of Methyl bromide (CH3Br) and its perdeuterated isotopomer CD3Br: a Rydberg Series Analysis.

in Chemical Physics (2005), 317

The vacuum UV photoabsorption spectrum of CH3Br has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. They were partly ascribed to vibrationless Rydberg transitions. In the ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3Br has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. They were partly ascribed to vibrationless Rydberg transitions. In the high photon energy range of 12-25 eV, very weak diffuse bands are mostly assigned to transitions from the 3a1, 1e and (2a1+1a1) to 3s orbitals. In the 6-12 eV photon energy range, numerous weak to strong bands are observed. The sharpness is very variable over the entire spectral region. In a first step, the interpretation of the spectrum and the assignment of the Rydberg transitions is based on the simple Rydberg formula. The observed features are classified in two groups of four series, each converging to one of the two spin-orbit components of the X2E state of CH3Br+. Rydberg series of nsa1, npa1, npe and nd and possibly nf characters are observed. The same measurements have been made for the first time on CD3Br in the 6-12 eV photon energy range. The observed features are classified into the same Rydberg series characterized by nearly the same delta values. Ionization energies for CD3Br X2E3/2 at 10.565 eV and X2E1/2 at 10.902 eV are deduced. In a second step, we fitted the experimental data to an energy expression taking into account both the exchange interaction and the spin-orbit coupling. Already states with n=6 are found to correspond to Hund's case (c). Constant values of the quantum defects are deduced. [less ▲]

The vacuum UV photoabsorption spectrum of methyl bromide (CH3Br) and its perdeuterated isotopomer CD3Br: a vibrational analysis

in Chemical Physics (2005), 317(1), 87-102

The fine structure of the vacuum UV photoabsorption spectrum of CH3Br and CD3Br has been analyzed in the 6.9-10.2 eV photon energy range. A large number of lines have been observed, classified and ... [more ▼]

The fine structure of the vacuum UV photoabsorption spectrum of CH3Br and CD3Br has been analyzed in the 6.9-10.2 eV photon energy range. A large number of lines have been observed, classified and assigned to the vibrational excitation accompanying a series of Rydberg transitions. The effects of the Jahn-Teller distortion and of the spin-orbit splitting of the ground electronic state of the ion have been considered. The former effect has been evaluated by ab initio calculations, showing that the E-2 state (in the C-3v symmetry group) splits into (2)A' and (2)A" states in the C-s symmetry group. Even though the energy difference of about 1 meV is extremely small, the (2)A' state is energetically the lowest component whereas the (2)A" is found to be a transition state. The Jahn-Teller stabilization energy and the wavenumbers associated with all vibrational modes have been calculated. Experimentally, the entire fine structure could be described in terms of three vibrational modes, i.e., hc omega(4) = 146 +/- 6 meV (1178 +/- 48 cm(-1)), hc omega(5) = 107 +/- 6 meV (863 +/- 48 cm(-1)) and hc omega(6) = 71 +/- 4 meV (572 +/- 32 cm(-1)), respectively, as resulting from an average over all analyzed Rydberg states. In CD3Br the corresponding energies are hc omega(4) = 104 +/- 3 meV (839 +/- 24 cm(-1)), hc omega(5)=82 +/- 4 meV (661 +/- 32 cm(-1)) and hc omega(6) = 62 +/- 4 meV (500 +/- 32 cm(-1)). These values are in fairly good agreement with those predicted by the present ab initio calculations for the ionic ground state. The experimental isotopic ratio rho(i) = [omega/omega(isot)](i) is 1.15 +/- 0.14, 1.31 +/- 0.14 and 1.39 +/- 1.0 and is predicted to be 1.04, 1.34 and 1.36, respectively, for omega(6), omega(5) and omega(4). On the basis of the present study an alternative assignment of the CH3Br+((X) over tilde E-2) photoelectron band structure is proposed. (C) 2005 Elsevier B.V. All rights reserved. [less ▲]

Mixed self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate in aqueous solution

in Langmuir (2004), 20(21), 9019-9028

Interaction of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers with anionic sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. Formation of mixed micelles has ... [more ▼]

Interaction of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers with anionic sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. Formation of mixed micelles has been confirmed by surface tension measurements, whereas the influence of the surfactant on the copolymer self-assembling has been studied by measurement of the 1H NMR self-diffusion coefficients and by small-angle neutron scattering. As a rule, the surfactant decreases the heterogeneity of the micellar structures formed by the copolymer in water. Moreover, increasing the content of SDS results in the increasingly more important extension of the poly(ethylene oxide) (PEO) corona chains and the copolymer micelle deaggregation. The stability of the micelles against SDS increases with the length of the hydrophobic block. Preliminary two-dimensional NMR measurements with nuclear Overhauser enhancement have confirmed the spatial vicinity between SDS and the constitutive blocks of the copolymer. [less ▲]

Self-assembling of poly(-caprolactone)-b-poly(ethylene oxide) diblock copolymers in aqueous solution and at the silica–water interface

in Physica B: Condensed Matter (2004), 350(1-3, suppl. 1), 901-904

Small-angle neutron scattering is used to investigate the self-assembling behaviour of poly( ε-caprolactone)-b-poly(ethylene oxide) diblock copolymers with various block lengths (i) in aqueous solution ... [more ▼]

Small-angle neutron scattering is used to investigate the self-assembling behaviour of poly( ε-caprolactone)-b-poly(ethylene oxide) diblock copolymers with various block lengths (i) in aqueous solution, (ii) in aqueous solution with the addition of sodium dodecyl sulphate (SDS) and (iii) at the silica-water interface. Micelles are observed under our experimental conditions due to the very small critical micellar concentration of these copolymers (0.01 g/l). The poly( ε-caprolactone) core is surrounded by a poly(ethylene oxide) corona. The micellar form factors have been measured at low copolymer concentrations (0.2 wt%) under selected contrast matching conditions. The data have been fitted to various analytical models to extract the micellar core and corona sizes. SDS is shown to induce partial micelle disruption together with an increase of the poly(ethylene oxide) corona extension from 25% (without SDS) to 70% (with SDS) of a completely extended PEOi u chain. Our data at the silica-water interface are compatible with the adsorption of micelles. [less ▲]

The Vacuum UV Photoabsorption Spectroscopy of the Three membered Ring Systems C3H6, C2H4O and C2H4S and their open Chain Isomers.

Book published by Berliner Elektronen Speicherring für Elektronen Synchrotron Strahlung m.b.H - on CD-ROM (2004)

The vacuum UV photoabsorption spectrum of C3H6, C2H4O and C2H4S have been measured using synchrotron radiation and are reported.

Structure of diblock copolymers in aqueous solution in the presence of a classical surfactant

Poster (2003, May 16)

How ergodic is the fragmentation of the pyridine cation? A maximum entropy analysis

in International Journal of Mass Spectrometry (2003), 228(2-3), 389-402

The kinetic energy released to the C4H4+ and HCN fragments produced by the dissociation of the pyridine ion has been determined by a retarding field technique up to an internal energy of 4eV above the ... [more ▼]

The kinetic energy released to the C4H4+ and HCN fragments produced by the dissociation of the pyridine ion has been determined by a retarding field technique up to an internal energy of 4eV above the reaction threshold. This extends our previous study limited to the metastable domain [Int. J. Mass Spectrom. Ion Process. 185/186/187 (1999) 155]. Retarding potential curves resulting from dissociative photoionization using the He(I), Ne(I), and Ar(II) resonance lines have been analyzed by the maximum entropy method. The comparison between the experimentally measured curves and those calculated for the prior (i.e., most statistical) situation reveals the existence of dynamical constraints that prevent phase space from being fully explored. The "ergodicity index" F(E) that measures the efficiency of phase space sampling as a function of the internal energy E of the molecular ion is found to decrease steadily as a function of E and to level off at a value of about 50% when E greater than or equal to 2.5 eV At these high internal energies where phase space exploration no longer decreases, spontaneous intramolecular vibrational energy redistribution (i.e., resulting from the anharmonicity of the molecular vibrations) is thought to contribute to internal energy randomization to a limited extent only. When the lifetime is short, phase space exploration is believed to result instead from the relaxation of the electronic energy via a cascade of non-radiative transitions, which leads to a great diversity of initial conditions, and thus, contributes to statisticity. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Unimolecular Dissociation of Halogenobenzene Cations by Phase space Theory.

in Anton, J.; Cedrequist, H.; Larsson, M. (Eds.) et al 23rd International Conference on Photonic, Electronic and Atomic Collisions: Book of Abstracts. (2003)

The Orbiting Transition State version of the Phase Space Theory (PST) is used to calculate the KER distributions in the dissociation channel of X (X=I,Cl,Br)-loss from C6H5X+. The results are compared to ... [more ▼]

The Orbiting Transition State version of the Phase Space Theory (PST) is used to calculate the KER distributions in the dissociation channel of X (X=I,Cl,Br)-loss from C6H5X+. The results are compared to the experimental distribution and to that obtained by PST. [less ▲]

Alkali cation attachment to derivatized fullerenes studied by matrix-assisted laser desorption/ionization

in Journal of the American Society for Mass Spectrometry (2002), 13(12), 1448-1458

The complexation of alkali metal ions with amphiphilic fullerene derivatives has been investigated by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The ... [more ▼]

The complexation of alkali metal ions with amphiphilic fullerene derivatives has been investigated by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The formation of analyte ions occurs via two competing mechanisms including electron transfer from matrix-derived ions and metal ion attachment. The interplay of these processes has been examined by laser fluence dependent sample activation and by variation of the target composition. The attachment of metal ions has been established as the gentler and thus more efficient route towards the formation of intact analyte ions. Investigations into the metal ion complexation have been conducted to reveal the reactivity order of the alkali metals in these reactions and to elucidate the influence of structural differences of the analytes, as well as to unravel effects caused by the anionic counter ion of the metal. The experimental data have been derived by two complementary approaches. Competing reactants were either studied simultaneously, so that the product distribution would provide direct insight into the reactivity pattern, and/or product distributions were obtained in a large variety of separate experiments and normalized for reliable comparison. It has been found that the extent to which complexation is observed follows the charge density order of the alkali metal ions. The structural features of the fullerene-attached ligands were of profound influence on the attachment of the metal ion, inducing enhanced selectivity for the complexation with less reactive metals. The metal ion attachment is reduced with the use of smaller anionic counter ions. Rationalization of these findings is provided within the framework of the mechanisms of ion formation in MALDI. [less ▲]