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Different Poly (different + poly)
Selected AbstractsThe Effect of Polymer Optoelectronic Properties on the Performance of Multilayer Hybrid Polymer/TiO2 Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 4 2005P. Ravirajan Abstract We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO2 and a conjugated polymer. Three different poly(2-methoxy-5-(2,-ethylhexoxy)-1,4-phenylenevinylene) (MEH-PPV)-based polymers and a fluorene,bithiophene copolymer are compared. We use photoluminescence quenching, time-of-flight mobility measurements, and optical spectroscopy to characterize the exciton-transport, charge-transport, and light-harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic-device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO2/polymer devices as a function of the fabrication route and device design. Including a dip-coating step before spin-coating the polymer leads to excellent polymer penetration into highly structured TiO2 networks, as was confirmed through transient optical measurements of the photoinduced charge-transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip-coated and PEDOT:PSS layers produced a short-circuit current density of about 1,mA,cm,2, a fill factor of 0.50, and an open-circuit voltage of 0.86,V under simulated AM,1.5 illumination (100,mW,cm,2, 1,sun). The corresponding power conversion efficiency under 1,sun was ,,0.4,%. [source] Controlled drug release from gels using surfactant aggregates: I. Effect of lipophilic interactions for a series of uncharged substancesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2001Mattias Paulsson Abstract Gels are often used for the delivery of drugs because they have rheological properties that will give a long residence time. Most pharmaceutical gels consist of ,99% water and a polymer matrix that will not hinder the release of drugs with a small molecular weight. To fully take advantage of the residence time, it is necessary to have a sustained drug release. In this paper it is suggested that surfactant micelles can be used to control the release from gels. The in vitro release under physiological conditions of five parabens from four different poly(acrylic acid) gels (Carbopol 934, 940, 1342) and one gellan gum (Gelrite) gel was measured using a USP dissolution bath modified for gels, and the diffusion coefficients were calculated. The diffusion coefficient of uncharged parabens was generally lower in gels with lipophilic modifications, such as C1342, and the greatest effect was seen for butylparaben, with a diffusion that was 25% lower than that in C934 (lacking lipophilic modification). Addition of surfactant micelles to gels delayed the release of all the uncharged drugs in all types of gels studied. The slowest release was seen for butylparaben in a lipophilically modified gel with micelles present. The diffusion coefficient in such a system was almost 30 times smaller than that in C934 without micelles. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1216,1225, 2001 [source] Biodegradable comb polyesters containing polyelectrolyte backbones facilitate the preparation of nanoparticles with defined surface structure and bioadhesive properties,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002A. Breitenbach Abstract A major challenge in oral peptide and protein delivery remains the search for suitable carrier systems. Therefore, a new concept was investigated combining a modified three-dimensional architecture, increased hydrophilicity of poly(lactic- co -glycolic acid) (PLGA) and charged groups in a single polymer. Biodegradable comb PLGA were synthesized by grafting short PLGA chains onto different poly(vinyl alcohol) (PVA) based backbone polyols, poly(2-sulfobutyl-vinyl alcohol) and poly(diethylaminoethyl-vinyl alcohol). The polyelectrolyte backbones were obtained by etherification of PVA with charge-containing pendent groups. The comb polymer structure could be confirmed by nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, elemental analysis and measurement of intrinsic viscosity. Nanoparticles (NP), as potential mucosal carriers systems, were prepared by controlled precipitation and investigated as a function of polymer composition. The amphiphilic character and the three-dimensional architecture of the novel polyesters allowed the preparation of small nanoparticles even without the use of surfactants. Surface NMR, surface charge and hydrophobicity determination indicate a core,corona-like NP structure, especially in the case of negatively charged polyesters. A structural model is proposed for the NP with an inner polyester core and an outer charged-groups-containing surface, depending on polymer composition and backbone charge density. The higher the polymer backbone charge density, the more pronounced its influence on the nanoparticle surface properties. The possibility of preparing NP without the use of a surfactant, as well as of designing the NP surface characteristics by polymer backbone charge density and polymer hydrophilic,hydrophobic balance, will be a major advantage in protein adsorption, bioadhesion and organ distribution. This makes these biodegradable polymers promising candidates for colloidal protein and peptide delivery. Copyright © 2003 John Wiley & Sons, Ltd. [source] Characterization of different poly(2-ethyl-2-oxazoline)s via matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2009Anja Baumgaertel Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) coupled with CID (collision-induced dissociation) has been used for the detailed characterization of two poly(2-ethyl-2-oxazoline)s as part of a continuing study of synthetic polymers by MALDI-TOF MS/MS. These experiments provided information about the variety of fragmentation pathways for poly(oxazoline)s. It was possible to show that, in addition to the eliminations of small molecules, like ethene and hydrogen, the McLafferty rearrangement is also a possible fragmentation route. A library of fragmentation pathways for synthetic polymers was also constructed and such a library should enable the fast and automated data analysis of polymers in the future. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||