Modeling reaction kinetics of rigid polyurethane foaming process

A theoretical model was developed to simulate the polyurethane foaming process for a rigid foam. In the model, multiple ordinary differential equations were solved by MATLAB and the model was able to predict temperature profiles by inputting foam recipe information. This initial study on foam modeling focusses on reaction kinetic parameters that were fitted to experimental temperature data as a function of time. The modeling was able to accurately model temperature profiles of single‐polyol polyurethane formulations and was able to accurately predict temperature profiles of mixtures based on pure component kinetic parameters. A primary goal of this work is to expedite the ability to develop new foam formulations by simulation—especially for incorporation of new bio‐based polyols into formulations. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1131‐1138, 2013     

The Role of Semiochemicals in Short-Range Location of Aggregation Sites in Adalia bipunctata (Coleoptera, Coccinellidae)

To survive unfavorable periods, ladybird beetles form conspicuous aggregations in specific microsites, with these locations remaining the same year after year. This constancy of location leads to the hypothesis that semiochemicals are involved in the attraction and aggregation of ladybirds to the microsite. In this study, we identified two types of semiochemicals that could play key roles in the attraction and aggregation formation of the two-spotted ladybird, Adalia bipunctata. We first isolated and identified three alkylmethoxypyrazines from A. bipunctata and tested the behavioral responses of diapausing ladybirds to these chemicals in a four-way olfactometer. This revealed that 2-isobutyl-3-methoxypyrazine, on its own or as part of a two-component mixture with 2-isopropyl-3-methoxypyrazine, elicited a positive behavioral response, causing arrestment of diapausing A. bipunctata. As ladybirds are in contact with each other in aggregations, we investigated the role of cuticular hydrocarbons (CHCs) in driving the cohesion and maintenance of aggregation. When an extract of CHCs from diapausing ladybirds was deposited near an alkylmethoxypyrazine source, ladybirds spent more time in the vicinity of the source. We identified a set of CHCs specific to diapausing A. bipunctata. Alkylmethoxyyrazines and CHCs thus deliver information to diapausing ladybirds searching for an aggregation site, as well as mediating several other behaviors throughout the ladybird’s life cycle. Chemical parsimony is discussed.     

Semivolatile organic compounds in window films from lower Manhattan after the September 11th World Trade Center attacks

The September 11th World Trade Center (WTC) terrorist attacks resulted in the large-scale release of contaminants that were deposited on the environment of New York City (NYC). Six weeks after the attacks, samples of an organic film on window surfaces were collected and analyzed for polybrominated diphenyl ethers (PBDE), polychlorinated biphenyls (PCB), polychlorinated naphthalenes (PCN), polycyclic aromatic hydrocarbons (PAH), and organochlorine pesticides (OCPs). Concentrations dropped by an order of magnitude within 1 km of the WTC and reached background concentrations by 3.5 km. Concentrations within 1 km of the WTC averaged 3280 ng/m2 for sigmaPBDE, 900 ng/m2 for sigmaPCB, 33 ng/m2 for sigmaPCN, and 77100 ng/m2 for sigmaPAH. Congener profiles of the sites nearest the WTC suggested a combination of combustion and evaporative sources of all compounds, whereas the background sites exhibited profiles consistent with evaporative sources. PBDE profiles showed enrichment in lower molecular weight congeners near the WTC, suggesting that these congeners were formed as a result of the combustion conditions. Homologue fractions of PCN combustion markers were approximately 2-9 times greater at near WTC sites compared to background NYC. Gas-phase air concentrations were back-calculated from measured film concentrations using the film-air partition coefficient (KFA), and calculated air concentrations followed spatial trends observed in films.     

Scalable production of graphene sheets by mechanical delamination

Mono- and multilayer graphene sheets have been successfully produced from commercial graphite powder in a wet grinding process under mild milling conditions. The shear forces in the milling chamber lead to a continuous delamination of ultrathin graphene flakes which are dispersed in a liquid medium. To avoid agglomeration of the exfoliated flakes the anionic surfactant sodium dodecyl sulfate was used. By adjusting the process parameters in a way to overcome the weak interlayer forces between the sheets without breaking them leads to the fabrication of thin flakes with high aspect ratios. The presented scalable process allows a high-yield and low-cost production of free-standing graphene sheets for various applications.     

Preparation of the thermally stable conducting polymer PEDOT - Sulfonated poly(imide)

We describe the template polymerization of EDOT with sulfonated poly(amic acid) (SPAA), resulting in a stable conducting polymer aqueous dispersion, PEDOT-SPAA, with particle size ca. 63 nm. In films of PEDOT-SPAA, the sulfonated poly(amic acid) template undergoes imidization within 10 min at temperatures greater than 150 °C, resulting in PEDOT-sulfonated poly(imide) (PEDOT-SPI) with 10-fold conductivity enhancement. This material is highly thermally stable as compared to PEDOT-PSS. Thermal stability is necessary for many processing applications of conducting polymers, including annealing for OPVs and melt-processing of polycarbonate for device encasement. Isothermal TGA experiments were run at 300 °C for PEDOT-PSS and PEDOT-SPAA and we found that PEDOT-SPAA had a smaller slope for degradation. Annealing of films at 300 °C for 10 min caused the conductivity of PEDOT-PSS films to be unmeasurable (<1 × 10⁻⁵ S/cm), while those of PEDOT-SPAA increased 6-fold. Secondary doping of the PEDOT-SPAA system with additives commonly used for PEDOT-PSS was also investigated.     

Poly(thienylenevinylene) prepared by ring-opening metathesis polymerization: Performance as a donor in bulk heterojunction organic photovoltaic devices

Poly(3,4-dioctylthienylenevinylene) (PDOTV) was synthesised by ring-opening metathesis polymerization (ROMP) with controlled molecular weight. PDOTV has been used to fabricate organic photovoltaic devices in combination with phenyl C₆₁-butyric acid methyl ester (PCBM) for the first time. The devices show power conversion efficiency up to 0.18%. Optimal device performance was found at a film thickness of 100 nm and a ratio of PCBM to PTV of 2:1. External quantum efficiency (EQE) measurements, transient absorption spectroscopy and morphology studies were carried out to establish factors governing photovoltaic performance. These results suggest that the efficiency values for the devices were limited by the hole mobility and unexpected phase separation within the blend. Nevertheless, the results show that ROMP is a viable, alternative, synthetic strategy for preparing PTV donors for use in bulk heterojunction OPVs.     

Anodic stripping voltammetry of zinc at boron-doped diamond electrodes in ammonia buffer solution

This paper describes the deposition of zinc(II) with anodic stripping voltammetry on the boron-doped diamond electrode. We illustrate the dependency of several parameters on the magnitude of the oxidation peak and try to optimize the method. The supporting electrolyte was found to influence the oxidation peak magnitude. Compared with acetic acid, the most frequently used supporting electrolyte, ammonia buffer solution leads to a four times higher signal. We assume that the formation of zinc complexes, primarily tetraaminezinc(II), are responsible for the better response. Further factors studied and assessed include buffer pH, buffer concentration, deposition potential, deposition time and scan rate. With the improved conditions, a final detection limit of 5 ppb was accomplished.