Eric G. Hanson

Effect of Triton X-100 on the stability of aqueous dispersions of copper phthalocyanine pigment nanoparticles

The effect of Triton X-100 on the colloidal dispersion stability of CuPc-U (unsulfonated and hydrophobic) and CuPc-S (surface sulfonated and hydrophilic) particles in aqueous solutions (water and NaNO(3)) was investigated at 25 °C. Its adsorption density was determined from surfactant concentrations analyzed by an HPLC method with a UV detector. The experimental dispersion stability ratios of the particles were determined from dynamic light scattering (DLS) data, with the Rayleigh-Debye-Gans (RDG) light scattering theory. The adsorption densities of Triton X-100 on both the CuPc-U and CuPc-S increase with increasing concentration of surfactant up to the critical micelle concentration (cmc), and then reach a plateau. The maximum adsorption density Γ(m) is higher for the CuPc-U (d(h)=160 nm) than that for the CuPc-S (d(h)=90 nm). The hydrophobic chains are inferred to be adsorbed onto the surfaces, and the hydrophilic ethylene oxide chains are in a coil conformation. The W(app)-values for the CuPc-U dispersions are affected mainly by the surfactant fractional surface coverage θ. Adding NaNO(3) has no significant effect on the dispersion stability. The stabilization mechanism for the CuPc-U is inferred to be primarily steric, as expected. The stability ratios for the CuPc-S in solutions with NaNO(3) are higher than those for CuPc-U, and decrease with increasing concentration of NaNO(3), indicating that the stabilization is affected by the screening of electrostatic repulsive forces. The zeta potential is not a good predictor of the electrostatic stabilization, pointing to the need for new and improved theories.

Benchmark Data for Noncovalent Interactions in HCOOH···Benzene Complexes and Their Use for Validation of Density Functionals

We present benchmark energetic data for the HCOOH···benzene complexes. The benchmark data were determined by a composite approach based on CCSD(T) calculations. Final binding energies (kcal/mol) are in the range of 1.6-4.8 kcal/mol, and they were used as reference data to test density functionals in the literature. Among the tested local density functionals without empirical dispersion corrections, M06-L is the best performing functional, and M06-L/6-31+G(d,p) gives a mean unsigned error (MUE) of only 0.15 kcal/mol. PBEsol and SOGGA also show promising performance. The best local DFT-D methods are BLYP-D and PBEsol-D, and they give an MUE of 0.15 kcal/mol after removing basis set superposition errors by the counterpoise approach. Empirical dispersion corrections greatly improve the descriptions of noncovalent interactions in HCOOH···benzene dimers. The calculated benchmark data and intermolecular potential are useful for the parametrizations of new force fields and coarse-grained models for chemical species such as the acrylic polymers.

Polarization-independent liquid-crystal optical attenuator for fiber-optics applications.

A compact low-power low-voltage polarization-independent electrooptic attenuator has been developed using planar calcite elements and a standard twisted nematic liquid-crystal cell. A dynamic range of 31.5 dB and an insertion loss of 0.87 dB have been demonstrated with the attenuator interposed between a GaAlAs laser and a 0.20-N.A. multimode optical fiber.

Origin of temperature dependence of microbending attenuation in fiber optic cables

Abstract Temperature-induced changes in the attenuation of multimode optical fiber cables are shown to be caused by mismatch between the thermal expansion coefficients of the fiber and the cabling materials. A quantitative theoretical model of low temperature loss, based on the formation of fiber microbends by microvariations in the jacket concentricity, is described. This model applies to tightly jacketed, soft buffered cable designs. An equation relating the low temperature optical attenuation to cable parameters is derived using this model. Good agreement is obtained between this theoretical prediction and experimental results. The theoretical model is used to compare the effectiveness of different cable designs on reducing excess loss at low temperature.

Interpretation of the C1s XPS Signal in Copper Phthalocyanine for Organic Photovoltaic Device Applications

Copper phthalocyanine (CuPc) belongs to a class of small molecules offering particularly interesting advantages when employed in organic electronic devices. Because of its advantageous attributes like high thermal stability, inertness when exposed to acids or alkalis, relatively high electron conductivity, color and light fastness it has been employed in polymer photovoltaic devices as a unipolar dopants complementing the buckminsterfullerene (C60) acceptors and as a conductive buffer. Other organic applications include ambipolar OFETs and non-linear optics structures. X-ray photoelectron spectroscopy (XPS) has been commonly employed to monitor the quality of thin CuPc films. Although XPS analyses of CuPc have been done for over forty years there has not yet been agreement regarding interpretation of the major C1s signal, particularly in the case of non-stoichometric CuPc composition. This work presents systematic studies of the C1s signal of thin film deposits, fabricated using commercially available CuPc materials. It was found that composite C1s CuPc signal consists of five components: two related to the principal C positions within the CuPc macrocycle (C-C in 6-membered ring, C-C-N in 5-membered ring), two associated with shake-up transitions accompanying principal C transitions, and one due to mostly aliphatic impurities. Detailed analysis showed that the magnitude of shake-up peaks was approximately equal 10% to 12% of their principal transitions, in agreement with the theoretical calculations. Correspondingly, the C1s signal originating from the non-CuPc impurities quantitatively agreed with the IR attenuated total reflectance (ATR-IR) measurement of the C-H aliphatic vibrations originating from these impurities present within the CuPc layer. The proposed C1s interpretation has been successfully tested for a large number of commercial CuPc materials and provides a guideline for a routine XPS analysis of the CuPc in organic photovoltaic devices.

Modeling of micro-dielectric barrier discharges

Summary form only given. Arrays of micro-plasmas having dimensions of tens to hundreds of microns are finding use as sources of radicals and charged particles in addition to their conventional use as photon sources. In one variant of these devices, the electrodes are fully or partially covered by dielectrics, and so they operate as dielectric barrier discharges (micro-DBDs). As such, the devices must be pulsed or driven with high frequency (HF) waveforms. When operating at atmospheric pressure in air, the plasma formation and decay times can be as short as tens of ns, and so the plasma may need to be re-ignited with each discharge pulse. In this situation, the physical structure of the micro-DBD and the electron emitting properties are important to its operation.In this presentation, we will discuss the properties of microDBDs sustained in atmospheric pressure N2 and air using results from a 2-d plasma simulation. The micro-DBDs are sandwich structures with openings of tens-of-microns excited with HF voltage waveforms. The model includes solution of Poissons equation, transport of charged and neutral species, radiation transport, electron photo-emission from surfaces, and beam transport of secondary electrons. We found that, depending on the details of the voltage waveform and surrounding structures, the plasma can be expelled from the micro-DBD cavity during one part of the HF cycle, thereby requiring the plasma to be reformed later in the cycle. This expulsion is partly facilitated by the Debye length being larger (in some cases) than the DBD cavity. Long lived neutral species in the plasma can facilitate restart by production of secondary electrons from surfaces. For example, UV photon emission from long lived states continuously provides seed secondary electrons at surfaces until the potential is favorable to generate the plasma.

Surface Molecular Vibrations as a Tool for Analyzing Surface Impurities in Copper Phthalocyanine Organic Nanocrystals

Comparison of the IR spectra of the Cu-phthalocyanine (CuPc) nanocrystals obtained using surface sensitive attenuated total reflectance (ATR) and bulk sensitive transmittance sample configurations revealed small but measurable changes of some vibrational frequencies of the molecules at the surface of nanocrystals with the outermost part of the surface CuPc molecules being the most affected. These changes are caused by electrostatic interactions between the polar components of the molecules on the surface of nanocrystals and external polar molecular species vicinal to the nanocrystals. The external polar species can be either chemically bonded to the CuPc nanocrystals surface or they can reside in its vicinity without forming a chemical bond with the nanocrystal. Molecular modeling (DMOL3 - Materials Studio and Gaussian calculations) of the impact of selected external polar species vicinal to a CuPc molecule on the CuPc molecular vibrations confirmed experimentally observed changes in the vibrational frequencies of the selected CuPc molecular bonding configurations and provided detailed information on the forces involved in these interactions. The population of external polar species vicinal to the CuPc surface can be modified by washing the nanocrystals or by introducing polar molecular additives miscible with the CuPc nanocrystals. Reduction in the number of external polar additives was accomplished by either centrifuging the aqueous dispersion of the nanocrystals or by organic solvent-based Soxhlet extraction, while their number was increased by soaking (followed by drying) the nanocrystals in high and low pH aqueous solutions containing SO 3- and OH- ions. These quantitative and qualitative modifications of the population of external polar species surrounding CuPc nanocrystals were reflected in the corresponding changes of the selected vibrational frequencies of the CuPc surface molecules providing an effective tool for not only recognizing the molecular species vicinal to a nanocrystal but also quantifying their concentration. Some of these modifications can also be observed with a naked eye in the form of noticeable color changes of the CuPc nancrystalline powder. This is due to the extremely high visible extinction coefficient of the CuPc nanocrystals causing that the impinging light is mostly absorbed/reflected within the surface region of the nanocrystals. Changes of the electronic structure within this region, caused by the interactions with the vicinal polar species, shift the vis absorption/reflection spectra changing the observed color of the nanocrystalline powder. Similar results were obtained for other molecular nanocrystals, including yellow chromophore molecules. Preliminary data indicate that the described analytical method of analyzing the molecular polar species vicinal to a molecular nanocrystal could find variety of applications ranging from molecular device fabrication to pharmaceutical materials.

Guest Editorial: Special Section on Nonimpact Printing

This PDF file contains the editorial “Guest Editorial: Nonimpact Printing” for JEI Vol. 2 Issue 03