Modeling of Precipitation Phase Boundaries in Mixed Surfactant Systems Using an Improved Counterion Binding Model

Anionic surfactants, commonly used in household products and the detergency industry, tend to precipitate with divalent counterions in hard water. The unsightly soap scum thus formed also removes the surfactant from the cleaning action. The current research has improved prediction of the precipitation phase boundary for mixtures of surfactants in hard water in two ways: firstly, an accurate value of the solubility product (K _SP ) has been determined for the calcium salt of 4-octylbenzene sulfonate, and accurate temperature dependent K _SP values have been determined for the calcium salts of dodecyl sulfate and decyl sulfate; secondly, improvements in prediction of the precipitation phase boundary have been achieved using an improved model. The K _SP values of the decyl sulfate and dodecyl sulfate salts strongly increase with increasing temperature, with the shorter chain surfactant having significantly higher K _SP than its longer chain analogue. At 30?°C the K _SP of the 4-octylbenzenesulfonate salt is similar to that of the dodecyl sulfate salt, perhaps due to the similarity in the length of their hydrocarbon tails. A recent counterion binding model proposed by our research group and micellization models have been used to model the precipitation phase boundaries for both single anionic surfactant and binary mixed anionic surfactant systems, improving thermodynamic modeling of the precipitation phase boundary of single and binary mixed anionic surfactant systems. In particular, the improved model of counterion binding has allowed the model to predict the phase boundary accurately over a range of temperatures.     

Experimental study of melting of LDPE/PS polyblend in an intermeshing counter‐rotating twin screw extruder

An experimental study is presented of the melting mechanism in a starve‐fed closely intermeshing counter‐rotating twin screw extruder of a modular Leistritz design. Various polymeric materials, semicrystalline low density polyethylene (LDPE), amorphous polystyrene (PS), and (LDPE/PS) polyblend were investigated at various operating conditions. A “screw pulling‐out” technique was used to investigate polymer behavior along the screw axis. In particular, the solid conveying, melting positions, the extent of starved character along the screw, and the fully filled regions were observed. Polymer samples were stripped off from each screw which was removed from the machine to investigate melting mechanism. Generally, it has been concluded that the melting mechanism revealed by White and Wilczyński for polyolefines has been proved for other polymeric materials under study. This mechanism consists of pellets being dragged into the calendering gap where they are melted due to calendering action. The molten polymer is expelled from the gap and pushes against the pellet bed which is continuously dragged into the gap. The composite modeling of an intermeshing counter‐rotating twin screw extrusion of polyblends has also been discussed. POLYM. ENG. SCI., 52:449–458, 2012. © 2011 Society of Plastics Engineers     

Mechanical and thermal properties of polyphenylene sulfide/multiwalled carbon nanotube composites

Polyphenylene sulfide (PPS)/multiwalled carbon nanotube (MWCNT) composites were prepared using a melt‐blending procedure combining twin‐screw extrusion with centrifugal premixing. A homogeneous dispersion of MWCNTs throughout the matrix was revealed by scanning electron microscopy for the nanocomposites with MWCNT contents ranging from 0.5 to 8.0 wt %. The mechanical properties of PPS were markedly enhanced by the incorporation of MWCNTs. Halpin‐Tsai equations, modified with an efficiency factor, were used to model the elastic properties of the nanocomposites. The calculated modulus showed good agreement with the experimental data. The presence of the MWCNTs exhibited both promotion and retardation effects on the crystallization of PPS. The competition between these two effects results in an unusual change of the degree of crystallinity with increasing MWCNT content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Impact of N on the atomic-scale Sb distribution in quaternary GaAsSbN-capped InAs quantum dots

The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure.     

Observation of the semiconductor–metal transition behavior in monolayer graphene

We have observed that during temperature-dependent four-terminal resistance measurement of monolayer graphene, the resistance exhibits anomalous rising and falling behavior at different temperature regions. At lower temperature region (2–200 K) the resistance decreases gradually, but when the temperature rise further it turn to a sudden increase, and after 280 K it resumes gradual decrease. The rising and falling resistance behavior is characteristic of semiconductor or metal property. Consequently, the resistance transition follows a phase of semiconductor–metal–semiconductor. However, when a perpendicular magnetic field is applied, the resistance shows reverse transition behavior which follows a sequence of metal–semiconductor–metal. The novel transition property is attributed to the competition between the disorder of lattice defects as a short-range scattering in monolayer graphene and the Landau levels interaction. Magneto-transport measurement reveals that the excitonic gap induced by magnetic field in the monolayer graphene show an anomalous thermally activated property.     

Druggability Assessment for Selected Serine Proteases in a Pharmaceutical Industry Setting

Target druggability assessment is an integral part of the early target characterization and selection process in pharmaceutical industry. Here, we investigate a set of five different serine proteases from the blood coagulation cascade. The aim of this study is twofold. Firstly, leveraging the wealth of available in-house high-throughput screening (HTS) data, we analyze HTS hit rates and discuss their predictive value for the development of small molecule (SMOL) candidates. Purely structure-activity relationship (SAR) based druggability ratings are compared with computational protein-structure based druggability assessments. Secondly, we evaluate the impact of using conformational ensembles from molecular dynamics (MD) simulations instead of single static crystal structures as basis for computational druggability assessments. Based on this study, we recommend incorporating molecular dynamics routinely into the early target characterization process, especially if only a single X-ray structure is available.     

New light-sensitive nucleosides for caged DNA strand breaks

Phototriggered bod cleavage has found wide application in chemistry as well as in biology. Nevertheless, there are only a few methods available for site-specific photochemical induction of DNA strand scission despite numerous potential applications. In this study we report the development of new photocleavable nucleotides based on the photochemistry of o-nitrobenzyl esters. The light-sensitive moieties were generated through introduction of o-nitrophenyl groups at the 5'C position of the nucleoside sugar backbone. The newly synthesized, modified nucleosides were incorporated in oligonucleotides and are able to build stable DNA duplexes. In such a way modified oligonucleotides ca cleaved site-specifically upon irradiation with > 360 nm light with high efficiency. Furthermore, we show that these modifications can be bypassed in DNA synthesis promoted by Thermus aquaticus DNA polymerase.     

Compatibility of polysaccharide/maleic copolymer blends. IV. Thermal behavior of hydroxypropyl cellulose‐containing blends

The compatibility of the hydroxypropyl cellulose (HPC) with maleic acid–vinyl acetate copolymer in the solid state was studied by thermogravimetry, thermo‐optical analysis, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy. It was established that physical interactions are prevalent in blends with a high content of HPC, whereas chemical interactions predominate in blends with a medium and low content of HPC. By increasing the temperature, the thermochemical reactions are favored. Thermal properties are dependent on the mixing ratio of the components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2585–2597, 2003     

Microwave-Assisted Batch Extraction of Polyphenols from Sea Buckthorn Leaves

Extraction of polyphenols from sea buckthorn leaves using microwave-assisted extraction (MAE) is described. The influence of different parameters on the extraction process (reactor type, stirring rate, extraction time, temperature, ethanol/water ratio) was studied. The polyphenolic extracts were analyzed in order to determine the total phenolic content (TPC) either by the Folin–Ciocalteu method or by differential pulse voltammetry (DPV), and the concentration of the main polyphenolic compounds by high-performance liquid chromatography (HPLC). The specific microwave energy was also determined. MAE resulted in a shorter extraction time (7.5 versus 30 min for the conventional method). The best results for MAE were obtained at a temperature of 90°C, using a solvent/plant ratio of 20/1 and 50% ethanol in the extraction solvent. The highest values of antioxidant capacity were obtained for polyphenolic extracts resulted from microwave extraction.     

Development of Saturable Absorbers for Laser Passive Q‐Switching near 1.5 μm Based on Transparent Ceramic Co2+:MgAl2O4

We describe the development of a reasonable cost Co²⁺:MgAl₂O₄ transparent ceramic plates fabrication technology that allows the producing of parts functioning as passive laser Q‐switches in the 1.3–1.7 μm domain. The main relevant material characteristics were measured. The absorption band, positioned between 1.2 and 1.7 μm, is typical of the ⁴A₂ (⁴F) → ⁴T₁ (⁴F) transition of Co²⁺ substituting Mg²⁺ ions in their T_d symmetry sites. The measured ground‐state absorption cross section σ_gs = 2.9 × 10^?19 cm², saturation contrast γ = 0.12, and depleted ground‐state recovery time τ₂ = 110–430 ns render such parts suitable for the intended application. The radiative lifetime was estimated as . The spin‐orbit splitting constant was estimated as ξ_SL??150 cm^?1 for the ⁴F parent ground state, and ξ_SL ? –575 cm^?1 for the ⁴P parent excited state. Obtained specimens had a transmission of ~80% (t = 2 mm, λ = 600 nm) and included some opaque, white spots. Further improvement of host optical transmission and resistance to laser damage are necessary.