We show that fingerprints of the different states of water association can be clearly distinguished in the range of the first overtone of water′s symmetric O‐H stretching in the spectra of water‐saturated [EMIm]+‐based ionic liquids with anions of substantially different hydrophilicity, such as hydrophobic [(CF3SO2)2N]?, moderately hydrophilic [CF3SO3]?, and highly hydrophilic [HSO4]?. 相似文献
Photovoltaic cells composed of thin mesoporous polyaniline films sandwiched between an indium-tin oxide anode and aluminium cathode have been fabricated. The cells show an increase in the photo-generated open-circuit voltage (Voc) from 0.2 V to 0.6 V and stable-in-time Voc generation following the addition of water containing highly hydrated ions, e.g. tap water.We explain the waterpromoted photo-voltaic effect by the polarity of the water environment. Theoretical calculations show that increasing the solvent polarity increases the energy of the electronic transition related to the measured Voc. The stable-in-time Voc generation could be explained by the increase in the lifetime of the excitons as well as by their more efficient dissociation in the interpenetrating network of polyaniline and water. The penetration of water into the mesoporous polyaniline films is promoted by the presence of highly hydrated ions. 相似文献
Polyaniline is among the most intensely investigated polymers because of its exceptional properties affording its current and potential applications. The structure and energy spectra of isolated oligomers and infinite chains in different oxidation states and degrees of protonation have been discussed at length from experimental and theoretical perspectives. The reaction environment effect, however, has received less attention and, particularly, the influence of monomer excess has been completely neglected in theoretical studies. Experimental measurements show that residual aniline is always detected in emeraldine samples obtained at low pH. Upon addition of oxidant to emeraldine PANI samples, post-polymerization due to the presence of excess monomers occurs. This is an indication of the formation of aniline-PANI complexes in the reaction medium. The presence of aniline monomers should affect the PANI chain arrangement and optical/conducting characteristics. Therefore, model clusters of aniline with neutral or singly protonated emeraldine tetramers in explicit water medium and periodic boundary conditions are addressed in this paper using a Monte Carlo/AMBER96/AM1 computational protocol to simulate the absorption spectra. The monomer impact on the structure, energy characteristics, and UV/vis spectra of the polymer are discussed. 相似文献
The kinetics of transport phenomena generated by an electric field and leading to the formation of density gradients in suspensions of charged colloidal silica were studied by using various electrodes. The rate of approach to a steady-state density gradient was found to be much higher when using metallic electrodes (Cu, Fe, and Pt) in comparison with graphite (C) electrodes. Nevertheless, the initial rate with C electrodes was substantially increased by the addition of hydroquinone-quinone because the redox reactions, necessary for electrode-electrolyte current transfer, occur at lower potential compared with the electrolysis of water. On the other hand, the products of oxidation of hydroquinone which accumulate in the system bring about an important decrease of the zeta potential of silica particles and progressive deceleration of their electrophoretic mobility. A detailed study was carried out, by using thin-layer isoperichoric focusing, UV-vis spectrophotometry, and voltamperometry, to explain the observed phenomena which can interfere in electric polarization or focusing field-flow fractionation. Copyright 2000 Academic Press. 相似文献
Unsteady flow in a semi-infinite contracting or expanding pipeis reinvestigated using long series analysis. The proposed seriesmethod is useful in analysing the problem for a moderately largeconstant ( = aa/, where a = a(t), the radius of the pipe isa function of time, a(t) is the velocity of the wall, and iskinematic viscosity). For positive values of (expansion ofthe pipe) accuracy of the series representing shear stress andpressure gradient is increased from = 2.89 to = 6.0 by extractingthe singularity followed by completion of the series. For negativevalues of (contraction of the pipe), we revert the series whichresults into the increase of the region of validity of the transposedseries from = -25.0 to = -2.89. Later we use Padé approximantsfor summing them. Also, the asymptotic solution for large valuesof is obtained and it agrees closely with pure numerical valuesof shear stress at the wall and pressure gradient. 相似文献
Films of polyaniline (PANI) featuring about 80% crystallinity and characterised with strong π‐π stacking alignment parallel to the film surface have been obtained directly after the original synthesis upon simple drying of the aqueous PANI suspension. A strong anisotropy in the growth of the nano‐sized crystals produced during the synthesis results in the formation of micrometer‐length fibrils perpendicular to the film surface in the course of water evaporation. The regular intercalation of water molecules between the PANI chains seems to be crucial for their ordering throughout the synthesis and film formation.