Electrical characterization of poly(amide-imide) for application in organic field effect devices

The admittance spectra and current-voltage (I-V) characteristics are reported of metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) capacitors employing cross-linked poly(amide-imide) (c-PAI) as the insulator and poly(3-hexylthiophene) (P3HT) as the active semiconductor. The capacitance of the MIM devices are constant in the frequency range from 10 Hz to 100 kHz, with tan delta values as low as 7 x 10(-3) over most of the range. Except at the lowest voltages, the I-V characteristics are well-described by the Schottky equation for thermal emission of electrons from the electrodes into the insulator. The admittance spectra of the MIS devices displayed a classic Maxwell-Wagner frequency response from which the transverse bulk hole mobility was estimated to be similar to 2 x 10(-5) cm(2) V(-1)s(-1) or similar to 5 x 10(-8) cm(2) V(-1)s(-1) depending on whether or not the surface of the insulator had been treated with hexamethyldisilazane (HMDS) prior to deposition of the P3HT. From the maximum loss observed in admittance-voltage plots, the interface trap density was estimated to be similar to 5 x 10(10) cm(-2) eV(-1) or similar to 9 x 10(10) cm(-2) eV(-1) again depending whether or not the insulator was treated with HMDS. We conclude, therefore, that HMDS plays a useful role in promoting order in the P3HT film as well as reducing the density of interface trap states. Although interposing the P3HT layer between the insulator and the gold electrode degrades the insulating properties of the c-PAI, nevertheless, they remain sufficiently good for use in organic electronic devices. (c) 2012 Elsevier B.V. All rights reserved.

Properties of a new poly-ether-glycol copolymer.

Triblock copolymers are made of monomer segments, being the central part usually hydrophobic and the outer parts hydrophilic. By varying sizes, molecular weights and monomer types of the segments one obtains different final molecules, with different physico-chemical properties, which are directly related to the performance of the final product. Looking for new products to be used, among other possibilities, in biological applications, a new polymer (Figure 1) was synthesized by the Dow Chemical and studied by Size Exclusion Chromatography, Fourier Transformed Infrared Spectrometry, Small-angle X-ray Scattering (SAXS) and its cloud point was determined by measuring light transmittance. The studies showed low molecular polydispersivety, but different polarities in the macromolecules fractions. Due to the low solubility of Diol in water, a mixture of water/butyl diglycol was used as solvent. An extensive analysis by SAXS was performed for concentrations from 50 wt% to 80 wt% of Diol in solution. Small concentrations showed very low signal to noise ratio, making it impossible to be analysed. The scattering intensity including the form factor of polydisperse non-homogeneous spheres, and the structure factor of interacting hard spheres was fitted to the curves. As the polymer concentration is high, the fitting of form factors of direct and reverse micelles were compared. The results for direct micelles were better up to 80 wt%, whereas at 90 wt% and 95 wt% the curves were better fitted by reverse micelles. It might seem odd that direct micelles are present up to such high concentrations, but it might have been caused by the presence of butyl diglycol, which increases the solubility of Diol in water. The inner and outer radius of the micelles, electron density distribution, and interaction radius of the micelles were obtained. The polydispersivety increases with Diol concentration. Besides, the interaction radius increases with solvent concentration, even when reversed micelles are present. In the last case, accompanied by an increase of inner radius (water content), as there are fewer Diol molecules to involve the water nuclei, which become larger, further apart, and in less number.

The Equilibrium Structure of Lithium Salt Solutions in Ether-Functionalized Ammonium Ionic Liquids

Molecular dynamics simulations have been performed for ionic liquids based on a ternary mixture of lithium and ammonium cations and a common anion, bis(trifluoromethylsulfonyl)imide, [Tf2N](-). We address structural changes resulting from adding Li+ in ionic liquids with increasing length of an ether-functionalized chain in the ammonium cation. The calculation of static structure factors reveals the lithium effect on charge ordering and intermediate range order in comparison with the neat ionic liquids. The charge ordering is modified in the lithium solution because the coordination of [Tf2N](-) toward Li+ is much stronger than ammonium cations. Intermediate range order is observed in neat ionic liquids based on ammonium cations with a long chain, but in the lithium solutions, there is also a nonhomogenous distribution of Li+ cations. The presence of Li+ enhances interactions between the ammonium cations due to correlations between the oxygen atom of the ether chain and the nitrogen atom of another ammonium cation.