Search results for "Optica"
showing 10 items of 7696 documents
Modeling of Amino Acid Electrodiffusion through Fixed Charge Membranes
2001
Abstract We study theoretically the electrodiffusion of amino acids through fixed charge membranes, calculating the ionic fractions of the amino acid in the membrane as well as its total flux as a function of the relevant experimental parameters (amino acid concentration, salt concentration, and pH of the external solution; membrane fixed charge concentration; and amino acid membrane/solution partition coefficients) under different experimental conditions (symport vs antiport transport, uphill transport, etc.). The theoretical approach employed is based on the Nernst–Planck flux equations in the (Goldman) constant electric field assumption and considers all the species present in the system…
α,ω-Functionalized poly-N-isopropylacrylamides: controlling the surface activity for vesicle adsorption by temperature
2003
The synthesis of alpha,omega-end-functionalized copolymers of N-isopropylacrylamide and N-(3-dimethylaminopropyl)acrylamide was performed. Monomer ratios of 100:0, 96:4, and 81:19 were investigated. The lower critical solution temperature (LCST) of these polymers was determined by cloud-point measurements and by microcalorimetric measurements. The LCST increased from 32 over 37 to 47 degrees C as the hydrophobicity increased with increasing amount of comonomer N-(3-dimethylaminopropyl)acrylamide. The polymers could successfully be adsorbed onto gold surfaces. Finally, vesicle adsorption onto these self-assembled polymer films on flat gold surfaces was investigated as the vesicle solution te…
Adsorption of water vapor by poly(styrenesulfonic acid), sodium salt: isothermal and isobaric adsorption equilibria
2004
Abstract Air conditioning and dehumidifying systems based on sorption on solids are of great interest, especially in humid climates, because they allow reduction of thermal loads and use of chlorofluorocarbons. Previous studies have shown that hydrophilic polymers such as sulfonic polymers can have very high performance in water adsorption from air. The aim of this study was to characterize the water vapor adsorption properties of fully sulfonated and monosulfonated poly(styrenesulfonic acid), sodium salt, and to elucidate the mechanism of adsorption on these materials. Adsorption isotherms have been determined by TGA between 298 and 317 K for pressures ranging from 0.1 to 45 hPa. They have…
Effective conductivity in association with model structure and spatial inhomogeneity of polymer/carbon black composites
1996
The relationship between effective conductivity and cell structure of polyethylene/carbon composites as well as between effective conductivity and spatial distribution of carbon black are discussed. Following Yoshida's model both structures can, in a way, be said to be intermediate between the well known Maxwell-Garnett (MG) and Bruggeman (BR) limiting structures. Using TEM photographs on composites with various carbon blacks we have observed that the larger is Garncarek's inhomogeneity measure H of two-dimensional (2D) representative distribution of the carbon black, the smaller is the effective conductivity of the composite.
Nonlinear optical susceptibilities of polysilanes: exciton effect
1992
Abstract Third-order nonlinear optical susceptibilities of σ-conjugated one-dimensional polymers have been calculated in a tight-binding model by taking account of the formation of excitons due to long-range Coulomb interactions. The spectrum of third-harmonic generation (THG) exhibits peaks due to excitons as well as unbound electron—hole states, in contrast to the linear absorption spectrum which is dominated by the lowest exciton state. The results are in excellent agreement with recent experiments in polysilanes not only for THG but also for linear absorption, two-photon absorption, and electroabsorption in a mutually consistent way.
Heterogeneity at the glass transition: a review
1999
Theoretical concepts and experimental evidence of heterogeneity in glass-forming liquids and polymers are reviewed. The main purpose is to provide an introduction to theoretical developments and recent experiments which have led to rapidly increasing knowledge. Realizing that there is no consensus in regard to the various scenarios of the glass transition starting from rather different assumptions we try to give a balanced overview although we also compare and interrelate some of the approaches. The experimental part describes recent nuclear magnetic resonance, dielectric, and optical experiments from which dynamically distinguishable subensembles can be selected thus proving the existence …
Glassy dynamics in thin polymer films: recent MD results
2002
The influence of a film geometry on the glass transition is investigated via molecular dynamics (MD) simulations of a (non-entangled) polymer melt. The confinement is realized by two identical potential barriers of the form U wall = z -9 , where z denotes the distance of a particle from the wall. Despite the geometric confinement, basic qualitative features of the system dynamics can be well described in the framework of the mode-coupling theory (MCT). Examples are the two-step relaxation of the incoherent intermediate scattering function, the time-temperature superposition property of the late time α-process and the space-time factorization of the scattering function on the intermediate ti…
Characterization of poly(N-alkylanilines) by Raman spectroscopy
2007
Abstract Thin films of poly( N -alkylaniline) were synthesized in acidic aqueous solution and in mixtures of aqueous and organic solvents. The polymer films (alkyl = methyl, ethyl, propyl and butyl) were characterized by Raman spectroscopy with the excitation wavelengths of 514.5, 632.8 and 780 nm. The main Raman bands have been characterized for the leucoemeraldine, emeraldine and pernigraniline oxidation states between −0.2 and 0.8 V (vs. Ag|AgCl). This fundamental study shows that the structure of the half-oxidized emeraldine form contains quinoid units, which supports the commonly accepted oxidation and reduction scheme of poly( N -alkylanilines).
Electropolymerization of N-methylanthranilic acid and spectroelectrochemical characterization of the formed film
2009
Abstract The electropolymerization of N-methylanthranilic acid (NMAA) is reported in this paper. The monomer is substituted both at ortho- and N-position and, to the best of our knowledge, it has not been previously electropolymerized. Electropolymerization of NMAA was done on glassy carbon and optically transparent (indium) tin oxide electrodes. The obtained films, which are probably of an oligomeric nature (oligoNMMA), were characterized with cyclic voltammetry (CV), in situ UV–vis and Raman spectroscopy, ex situ FTIR spectroscopy and scanning electron microscopy (SEM). Our results show that NMAA can be electropolymerized as thin films in 1.0 M HClO4, but the oxidation and reduction peak …
Patterning of Conducting Polymers Using UV Lithography: The in-Situ Polymerization Approach
2012
We report on the in-situ polymerization of 3T with Cu(ClO4)2 inside several host polymers such as Novolak-based negative-tone photoresist, polystyrene (PS), poly(4-vinylphenol) (P4VP), poly(methyl methacrylate) (PMMA), and poly(4-vinylphenol)-co-(methyl methacrylate) (P4VP-co-MMA) to form an interpenetrating polymer network (IPN). Conducting IPN films in the order of 10–4–150 S/cm are obtained depending on the specific IPN composition. Moreover, the convenience of this synthetic approach has been demonstrated using a commercially available negative-tone photoresist based on Novolak as a host polymer. Novolak photoresist was properly formulated with 3T and Cu(ClO4)2 to preserve as far as pos…