Anthracene‐thieno[3,4‐c]pyrrole‐4,6‐dione based donor–acceptor conjugated copolymers for applications in optoelectronic devices

Three novel alternating copolymers of thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) and triisopropylsilylacetylene‐functionalized anthracene were prepared via Suzuki polymerization. Various solubilizing substituents were attached to the TPD moiety in order to ascertain the impact they have upon the optical, electrochemical, and thermal properties of the resulting polymers. All copolymers showed good solubility and thermal stability with decomposition temperatures in excess of 300°C. Optical properties revealed that PTATPD(O), PTATPD(DMO), and PTATPD(BP) displayed optical energy gaps in excess of 2.0 eV. It is speculated that steric repulsion between solubilizing groups on repeat units along polymer chains reduces their planarity and decreases their electronic conjugation. The amorphous nature of the polymers was confirmed with differential scanning calorimetry and powder X‐ray diffraction. The highest occupied molecular orbital levels of the three polymers are unaffected by the different solubilizing chains. However, they exert some influence over the lowest unoccupied molecular orbital (LUMO) levels with PTATPD(BP) and PTATPD(O) displaying the lowest LUMO levels (?3.4 eV). In contrast, PTATPD(DMO) displayed the highest LUMO level (?3.3 eV). © 2015 The Authors. Polymers for Advanced Technologies Published by John Wiley & Sons Ltd.     

A vibrational sum frequency spectroscopy study of the liquid-gas interface of acetic acid-water mixtures: 2. Orientation analysis

Vibrational sum frequency spectroscopy has been used to investigate the surface of aqueous acetic acid solutions. By studying the methyl and carbonyl vibrations with different polarization combinations, an orientation analysis of the acetic acid molecules has been performed in the concentration range 0-100%. The surface tension of acetic acid solutions was also measured in order to obtain the surface concentration. The orientation of the interfacial acetic acid molecules was found to remain essentially constant in an upright position with the methyl group directed toward the gas phase in the whole concentration range. The tilt angle (theta(CH)3) of the symmetry axis of the methyl group with respect to the surface normal was found to be lower than 15 degrees when considering a delta distribution of angles or as narrow as 0 +/- 11 degrees when assuming a Gaussian distribution. Further investigations showed that the C=O bond tilt (theta(C)(=)(O)) of the acetic acid hydrated monomer was constant and close to 55 degrees in the concentration range where it was detected. Finally, the orientation information is discussed in terms of different species of acetic acid, where the formation of a surface layer of acetic acid cyclic dimers is proposed at high acid concentrations.     

Forces between silica surfaces with adsorbed cationic surfactants: influence of salt and added nonionic surfactants

Forces have been measured between silica surfaces with adsorbed surfactants by means of a bimorph surface force apparatus. The surfactants used are the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the nonionic surfactant hexakis(ethylene glycol) mono-n-tetradecyl ether (C(14)E(6)) as well as mixtures of these two surfactants. The measurements were made at elevated pH, and the effect of salt was studied. At high pH the glass surface is highly charged, which increases the adsorption of TTAB. Despite the low adsorption generally seen for nonionic surfactants on silica at high pH, addition of C(14)E(6) has a considerable effect on the surface forces between two glass surfaces in a TTAB solution. The barrier force is hardly affected, but the adhesion is reduced remarkably. Also, addition of salt decreases the adhesion, but increases the barrier force. In the presence of salt, addition of C(14)E(6) also increases the thickness of the adsorbed layer. The force barrier height is also shown to be related to literature values for surface pressure data in these systems.     

Structural subgrid-scale modeling for large-eddy simulation: A review

Accurately modeling nonlinear interactions in turbulence is one of the key challenges for large-eddy simu-lation (LES) of turbulence. In this article, we review recent studies on structural subgrid scale modeling, focusing on evaluating how well these models predict the effects of small scales. The article discusses a priori and a posteriori test results. Other nonlinear models are briefly discussed, and future prospects are noted.     

Crown ethers at the aqueous solution-air interface: 1. Assignments and surface spectroscopy

The surface of aqueous solutions of 4-Nitro Benzo-15-Crown-5 (NB15C5) and Benzo-15-Crown-5 (B15C5) has been studied using the surface sensitive technique vibrational sum frequency spectroscopy (VSFS). The NO, CN, COC and CH vibrational modes of these compounds at the air-water interface as well as OH vibrational modes of the surface water hydrating this compound have been targeted in order to obtain molecular information about arrangement and conformation of the adsorbed crown ether molecules at the air-water interface. The CH(2) vibrational modes of crown ethers have been identified and found to be split due to interaction with ether oxygen. The spectra provide evidence for the existence of a protonated crown complex moiety at the surface leading to the appearance of strongly ordered water species. The interfacial water species are influenced by the resulting charged interface and by the strong Zundel polarizability due to tunneling of the proton species between equivalent sites within the crown ring.