The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform

Marta Castillejo - One of the best experts on this subject based on the ideXlab platform.

  • morphological and chemical modifications and plume ejection following uv laser ablation of doped Polymers dependence on Polymer Molecular Weight
    Applied Surface Science, 2007
    Co-Authors: Esther Rebollar, Giannis Bounos, Mohamed Oujja, Savas Georgiou, Marta Castillejo
    Abstract:

    Abstract This work investigates the effect of Polymer Molecular Weight ( M W ) on the morphological and chemical modifications and on the plume ejection of doped polymethyl methacrylate (PMMA), and polystyrene (PS) films following irradiation at 248 nm. Micro-bubbles develop in the irradiated films of the low absorbing PMMA-based substrates. The extent and kinetics of the observed morphological changes are respectively larger and last longer in the low M W Polymer, as evidenced by optical microscopy and real-time monitoring of transmission of a CW laser. The changes observed in the Raman spectra upon irradiation indicate that degradation occurs to a higher extent in larger M W Polymers. Laser induced fluorescence (LIF) probing of the plume reveals the presence of NapH and PhenH products from, respectively, NapI- and PhenI-doped films and a slower ejection process in the plume of low M W Polymer. For highly absorbing PS, a less dramatic dependence on M W is observed. Results are discussed in the framework of the bulk photothermal model, according to which ejection requires a critical number of bonds to be broken.

  • Analysis of plume following ultraviolet laser ablation of doped Polymers: Dependence on Polymer Molecular Weight
    Journal of Applied Physics, 2007
    Co-Authors: Esther Rebollar, Giannis Bounos, Mohamed Oujja, Savas Georgiou, Andreas Kolloch, Marta Castillejo
    Abstract:

    This work investigates the effect of Polymer Molecular Weight MW on the plume characteristics of poly(methyl methacrylate) (PMMA) and polystyrene (PS) films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI) following irradiation in vacuum at 248nm. Laser-induced fluorescence probing of the plume reveals the presence of ArH products (NapH and PhenH from, respectively, NapI- and PhenI-doped films). While a bimodal translational distribution of these products is observed in all cases, on average, a slower translational distribution is observed in the low MW system. The extent of the observed dependence is reduced as the optical absorption coefficient of the film increases, i.e., in the sequence NapI∕PMMA, PhenI∕PMMA, and PS-doped films. Further confirmation of the bimodal translational distributions is provided by monitoring in situ the temporally resolved attenuation by the plume as it expands in vacuum of a continuous wave helium–neon laser propagating parallel to the substrate. Results are di...

  • Influence of Polymer Molecular Weight on the chemical modifications induced by UV laser ablation.
    The journal of physical chemistry. B, 2006
    Co-Authors: Esther Rebollar, Giannis Bounos, Mohamed Oujja, Concepción Domingo, Savas Georgiou, Marta Castillejo
    Abstract:

    This paper investigates the influence of Polymer Molecular Weight (MW) on the chemical modifications of poly(methyl methacrylate), PMMA, and polystyrene, PS, films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI), following irradiation at 248 nm (KrF excimer laser, 20 ns fwhm and hybrid excimer-dye laser, 500 fs fwhm) and at 308 nm (XeCl excimer laser, 30 ns fwhm). The changes of intensity and position of the Polymer Raman bands upon irradiation provide information on cleavage of the Polymer bonds. Degradation of PMMA, which is a weak absorbing system at 248 nm, occurs to a higher extent in the case of a larger MW, giving rise to the creation of unsaturation centers and to degradation products. For highly absorbing PS, no degradation is observed upon irradiation with a KrF laser. Consistently irradiating doped PS at 308 nm, where the absorption is low, induces degradation of the Polymer. Results provide direct support for the bulk photothermal model, according to which ejection requires a cr...

Hamid Mobedi - One of the best experts on this subject based on the ideXlab platform.

Esther Rebollar - One of the best experts on this subject based on the ideXlab platform.

  • morphological and chemical modifications and plume ejection following uv laser ablation of doped Polymers dependence on Polymer Molecular Weight
    Applied Surface Science, 2007
    Co-Authors: Esther Rebollar, Giannis Bounos, Mohamed Oujja, Savas Georgiou, Marta Castillejo
    Abstract:

    Abstract This work investigates the effect of Polymer Molecular Weight ( M W ) on the morphological and chemical modifications and on the plume ejection of doped polymethyl methacrylate (PMMA), and polystyrene (PS) films following irradiation at 248 nm. Micro-bubbles develop in the irradiated films of the low absorbing PMMA-based substrates. The extent and kinetics of the observed morphological changes are respectively larger and last longer in the low M W Polymer, as evidenced by optical microscopy and real-time monitoring of transmission of a CW laser. The changes observed in the Raman spectra upon irradiation indicate that degradation occurs to a higher extent in larger M W Polymers. Laser induced fluorescence (LIF) probing of the plume reveals the presence of NapH and PhenH products from, respectively, NapI- and PhenI-doped films and a slower ejection process in the plume of low M W Polymer. For highly absorbing PS, a less dramatic dependence on M W is observed. Results are discussed in the framework of the bulk photothermal model, according to which ejection requires a critical number of bonds to be broken.

  • Analysis of plume following ultraviolet laser ablation of doped Polymers: Dependence on Polymer Molecular Weight
    Journal of Applied Physics, 2007
    Co-Authors: Esther Rebollar, Giannis Bounos, Mohamed Oujja, Savas Georgiou, Andreas Kolloch, Marta Castillejo
    Abstract:

    This work investigates the effect of Polymer Molecular Weight MW on the plume characteristics of poly(methyl methacrylate) (PMMA) and polystyrene (PS) films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI) following irradiation in vacuum at 248nm. Laser-induced fluorescence probing of the plume reveals the presence of ArH products (NapH and PhenH from, respectively, NapI- and PhenI-doped films). While a bimodal translational distribution of these products is observed in all cases, on average, a slower translational distribution is observed in the low MW system. The extent of the observed dependence is reduced as the optical absorption coefficient of the film increases, i.e., in the sequence NapI∕PMMA, PhenI∕PMMA, and PS-doped films. Further confirmation of the bimodal translational distributions is provided by monitoring in situ the temporally resolved attenuation by the plume as it expands in vacuum of a continuous wave helium–neon laser propagating parallel to the substrate. Results are di...

  • Influence of Polymer Molecular Weight on the chemical modifications induced by UV laser ablation.
    The journal of physical chemistry. B, 2006
    Co-Authors: Esther Rebollar, Giannis Bounos, Mohamed Oujja, Concepción Domingo, Savas Georgiou, Marta Castillejo
    Abstract:

    This paper investigates the influence of Polymer Molecular Weight (MW) on the chemical modifications of poly(methyl methacrylate), PMMA, and polystyrene, PS, films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI), following irradiation at 248 nm (KrF excimer laser, 20 ns fwhm and hybrid excimer-dye laser, 500 fs fwhm) and at 308 nm (XeCl excimer laser, 30 ns fwhm). The changes of intensity and position of the Polymer Raman bands upon irradiation provide information on cleavage of the Polymer bonds. Degradation of PMMA, which is a weak absorbing system at 248 nm, occurs to a higher extent in the case of a larger MW, giving rise to the creation of unsaturation centers and to degradation products. For highly absorbing PS, no degradation is observed upon irradiation with a KrF laser. Consistently irradiating doped PS at 308 nm, where the absorption is low, induces degradation of the Polymer. Results provide direct support for the bulk photothermal model, according to which ejection requires a cr...

Reyhaneh Astaneh - One of the best experts on this subject based on the ideXlab platform.

M.-r. Kula - One of the best experts on this subject based on the ideXlab platform.

  • Electrostatic effects on protein partitioning: simultaneous effect of pH and Polymer Molecular Weight
    Chemical Engineering Science, 1992
    Co-Authors: D. Forciniti, Carol K. Hall, M.-r. Kula
    Abstract:

    Abstract The partition coefficients of lysozyme, chymotrypsinogen A, albumin and catalase in 64 polyethyleneglycol/dextran systems are reported. The measurements were performed at four pHs for each protein. The simultaneous effect of pH changes and Polymer Molecular Weight and concentration on the partition coefficient of each protein is analyzed. The partition coefficient of lysozyme (IP = 10.5) has a minimum value at its isoelectric point and it takes its maximum value at acidic pHs. We observe a change in the aggregational state of lysozyme when the pH is shifted from the acidic to the alkaline ranges. The partition coefficient of chymotrypsinogen A (IP = 9.5) has a minimum at pH 5.6 and increases towards more alkaline or acidic pHs. The partition coefficient of albumin (IP = 4.6) takes its minimum value at pH 5.6. The partition coefficient of catalase (IP = 5.6) takes its maximum value at pH 5.6. The effect of the pH on the partition coefficient of lysozyme and chymotrypsinogen A at high Polymer concentrations is larger than at low total Polymer concentrations but the effect of the pH on the partition coefficient of albumin and catalase at high Polymer concentrations is smaller than at low Polymer concentrations. We find that the partition coefficient of the four proteins studied becomes less sensitive to changes in the pH at high PEG Molecular Weights. Close to the isoelectric point the partition coefficient is less sensitive to changes in the Molecular Weight of the Polymers than at conditions far from the isoelectric point.

  • Influence of Polymer Molecular Weight and temperature on phase composition in aqueous two-phase systems
    Fluid Phase Equilibria, 1991
    Co-Authors: D. Forciniti, Carol K. Hall, M.-r. Kula
    Abstract:

    Abstract In an effort to understand the Molecular Weight and temperature dependence of protein partition coefficients, we have conducted experiments to determine how the binodal curve and the difference in Polymer concentrations between the top and bottom phases (▵ PEG  [PEG] T — [PEG] B and Δ Dx  [Dx] B — [Dx] T ); depend on Polymer Molecular Weight and temperature. We report the equilibrium compositions at 4°, 25° and 40°C for 16 different aqueous two-phase PEG-Dx systems which consist of all possible combinations of the four PEG Molecular Weights (4000, 6000, 10 000, and 20 000) and the four Dx Molecular Weights (10 000, 40 000, 110 000 and 500 000). Four tie lines were measured for each system. We confirm that increasing Polymer Molecular Weight increases the tie line length and depresses the binodals to lower Polymer concentrations, and that this effect will be greater when the ratio of this Molecular Weight increase to the Molecular Weight of the other species is large. The increase in the tie line length and in Δ Dx and Δ PEG with increasing Polymer Molecular Weight tends to level off at high Polymer Molecular Weight and at high total Polymer concentrations. It is shown that the effect of temperature is not symmetric, i.e. changes in temperature produce a change in Δ Dx while Δ PEG remains nearly constant. The effect of Polymer Molecular Weight on both Δ Dx and Δ PEG is magnified with increasing temperature. The results found here suggest a series of experiments which could be used to isolate (or highlight) the effect of the second virial coefficient on the partition coefficient.

  • Protein partitioning at the isoelectric point: influence of Polymer Molecular Weight and concentration and protein size.
    Biotechnology and bioengineering, 1991
    Co-Authors: D. Forciniti, Carol K. Hall, M.-r. Kula
    Abstract:

    We report the partition coefficient, K(p') at the isoelectric point of lysozyme, chymotrypsinogen A, albumin, transferrin, and catalase in 64 different polyethylene(PEG)/ dextran(Dx)/water systems. We study the trends of the partition coefficient with protein type, Polymer concentration, and Polymer Molecular Weight. We find that the partition coefficient decreases with increasing tie line length for lysozyme, albumin, transferrin, and catalase for which K(p) is less than 1, but increases for chymotrysinogen for which K(p) is larger than 1. The effect of the tie line length on the partition coefficient is larger for the large proteins than for the small proteins. The partition coefficient decreases with increasing protein Molecular Weight except for lysozyme suggesting that lysozyme is present as a dimer or a trimer. The partition coefficient decreases with increasing PEG Molecular Weight, but the magnitude of the increase is larger for the smaller PEG Molecular eights and tends to level of at high PEG Molecular Weight. The partition coefficient increases with increasing dextran (Dx) Molecular Weight for chymotrypsinogen but decreases for catalase. The partition coefficients of lysozyme, albumin, and transferrin increase with increasing Dx Molecular Weight from Dx 10(4) to Dx 1.1 x 10(5) and then slightly decrease from Dx 1.1 x 10(5) to Dx 5 x 10(5). The experimental results are analyzed using a statistical thermodynamics model. The experimental results are analyzed using a statistical thermodynamics model. The experiments suggest that protein partitioning at the isoelectric point in aqueous two-phase systems is strongly related to the size of the proteins and Polymers. Finally, the impossibility of obtaining data completely independent of Polymer concentration is emphasized.