Thermal treatment of the carbon nanotubes and their functionalization with styrene

In this work we studied the functionalization of commercially available multiwalled carbon nanotubes (MWCNT) (Nanocyl 3100) with polystyrene by the method so called “grafting from”. The nanotubes were used as received and oxidized in air at 400 °C. The functionalization was started using thionyl chloride under reflux, followed by a reaction with ethylene glycol which allowed the inclusion of hydroxyl groups. The reaction of those with 2-chloropropionyl chloride led to the generation of the polymerization initiator. Last, the radical polymerization of the functionalized nanotubes, using styrene as the monomer, led to new materials which were studied with thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) spectroscopy.     

Printable Bioelectronics To Investigate Functional Biological Interfaces

Thin‐film transistors can be used as high‐performance bioelectronic devices to accomplish tasks such as sensing or controlling the release of biological species as well as transducing the electrical activity of cells or even organs, such as the brain. Organic, graphene, or zinc oxide are used as convenient printable semiconducting layers and can lead to high‐performance low‐cost bioelectronic sensing devices that are potentially very useful for point‐of‐care applications. Among others, electrolyte‐gated transistors are of interest as they can be operated as capacitance‐modulated devices, because of the high capacitance of their charge double layers. Specifically, it is the capacitance of the biolayer, being lowest in a series of capacitors, which controls the output current of the device. Such an occurrence allows for extremely high sensitivity towards very weak interactions. All the aspects governing these processes are reviewed here.     

A Safety Strategy for Producing Poly(Acrylic Acid) of Low Molar Mass

The synthesis of poly(acrylic acid) (PAA) of low molar mass under safe conditions is difficult due to the high polymerization rate of acrylic acid (AA) and the fast heat generation. The aqueous‐solution “semibatch” polymerization of non‐ionized AA in almost starved conditions involves high initiator loads when low molar masses are required. This article proposes the simultaneous feeding of AA and nonconventional chain transfer agents (CTA) as a strategy aimed at controlling both the molar masses and the generated heat rate. Three CTAs are investigated: 2‐mercaptoethanol, thioglycolic acid, and isopropyl alcohol. Even when PAA of relatively low molar mass can be produced by adequately selecting the flow rates and concentrations of both AA and CTA, it is found that the nature of CTA can have a significant effect on the polymerizations kinetics. The mechanisms responsible for these effects are discussed with the help of a representative mathematical model.

     

Theoretical characterization of intermolecular vibrational states through the multi-configuration time dependent Hartree approach: the He2,3ICl clusters

Benchmark, full-dimensional calculations on the ground and excited vibrational states for the tetra-, and penta-atomic weakly bound He(2,3)ICl complexes are reported. The representation of the potential energy surfaces includes three-body HeICl potentials parameterized to coupled-cluster singles, doubles, and perturbative triples ab initio data. These terms are important in accurately describing the interactions of such highly floppy systems. The corresponding 6D/9D computations are performed with the multi-configuration time dependent Hartree method, using natural potential fits, and a mode combination scheme to optimize the computational effort in the improved relaxation calculations. For these complexes several low-lying vibrational states are computed, and their binding energies and radial/angular probability density distributions are obtained. We found various isomers which are assigned to different structural models related with combinations of the triatomic isomers, like linear, T-shaped, and antilinear ones. Comparison of these results with recent experimental data is presented, and the quantitative deviations found with respect to the experiment are discussed.     

Analysis of multi-class preservatives in leave-on and rinse-off cosmetics by matrix solid-phase dispersion

Matrix solid-phase extraction has been successfully applied for the determination of multi-class preservatives in a wide variety of cosmetic samples including rinse-off and leave-on products. After extraction, derivatization with acetic anhydride, and gas chromatography–mass spectrometry analysis were performed. Optimization studies were done on real non-spiked and spiked leave-on and rinse-off cosmetic samples. The selection of the most suitable extraction conditions was made using statistical tools such as ANOVA, as well as factorial experimental designs. The final optimized conditions were common for both groups of cosmetics and included the dispersion of the sample with Florisil (1:4), and the elution of the MSPD column with 5 mL of hexane/acetone (1:1). After derivatization, the extract was analyzed without any further clean-up or concentration step. Accuracy, precision, linearity and detection limits were evaluated to assess the performance of the proposed method. The recovery studies on leave-on and rinse-off cosmetics gave satisfactory values (>78% for all analytes in all the samples) with an average relative standard deviation value of 4.2%. The quantification limits were well below those set by the international cosmetic regulations, making this multi-component analytical method suitable for routine control. The analysis of a broad range of cosmetics including body milk, moisturizing creams, anti-stretch marks creams, hand creams, deodorant, shampoos, liquid soaps, makeup, sun milk, hand soaps, among others, demonstrated the high use of most of the target preservatives, especially butylated hydroxytoluene, methylparaben, propylparaben, and butylparaben.     

Natural gas bilevel cash-out problem: Convergence of a penalty function method

This paper studies a special bi-level programming problem that arises from the dealings of a Natural Gas Shipping Company and the Pipeline Operator, with facilities of the latter used by the former. Because of the business relationships between these two actors, the timing and objectives of their decision-making process are different and sometimes even opposed. In order to model that, bi-level programming was traditionally used in previous works. Later, the problem was expanded and theoretically studied to facilitate its solution; this included extension of the upper level objective function, linear reformulation, heuristic approaches, and branch-and-bound techniques. In this paper, we present a linear programming reformulation of the latest version of the model, which is significantly faster to solve when implemented computationally. More importantly, this new formulation makes it easier to analyze the problem theoretically, allowing us to draw some conclusions about the nature of the solution of the modified problem. Numerical results concerning the running time, convergence, and optimal values, are presented and compared to previous reports, showing a significant improvement in speed without actual sacrifice of the solution’s quality.     

Absorption and transport properties of ultra-fine cellulose webs

Characterization of transport and absorption properties of nanofiber webs is a challenge, because in many cases the material is soft and cannot withstand the stresses exerted by the standard instruments. In this paper, we report on development of a new technique for materials characterization. We propose to conduct wicking and permeability experiments for full characterization of the nanowebs. As an example, we used electrospun cellulose acetate nanowebs. The wicking experiments showed very good reproducibility, demonstrating the square-root-of-time dependence of wetting front position vs time. The prefactor depends on a product of capillary pressure and materials permeability. We developed a technique to independently measure the permeability of small samples of nanowebs. Wicking and permeability data allow one to estimate the pore size; SEM micrographs confirmed the obtained estimates of pore radius. In general, the proposed method allows one to characterize the transport and absorption parameters of the nanofibrous materials for which the standard procedures are inapplicable.     

A thermodynamic study of the aggregation process of oxacillin sodium salt in aqueous solution

The aggregation characteristics of oxacillin in aqueous solutions have been examined by means of conductivity measurements over the temperature range 288.15-313.15 K and by static light scattering measurements at 298.15 K. Two critical concentrations were detected in conductivity and light scattering over the concentration range 0-0.35 mol kg^-1. Light scattering measurements indicate the formation of dimers at the first critical concentration (0.024 mol kg^-1) and the subsequent formation of aggregates with an aggregation number of 8 at the second critical concentration (0.104 molkg^-1). The thermodynamic parameters of aggregation were derived from the critical concentration data using a mass-action model that has been modified for application to systems of low aggregation number. Values for the enthalpy of aggregate formation calculated by this method showed that the aggregation became increasingly exothermic with increasing temperature. The values of the two critical concentrations show that this penicillin, oxacillin, is more hydrophobic than other molecules of similar structure.     

Flow-through electrodes. IV. Axial diffusion effects

The simple theory of flow-through electrodes was generalized by analysis of axial diffusion phenomena. The effect of axial diffusion coupled with forced convection on the electrochemical behaviour of flow-through electrodes was analyzed assuming laminar flow through a structurless medium (the analysis is thus applicable also to e.g. capillary bundle models with sufficiently small pores' radii). Diffusional effects involving both reactants and products were considered and the electrochemical kinetic equations allowed for both forward and backward reaction orders with respect to substrates and products. Axial ohmic effects were included.The effect of convection in the pre-electrode chamber was taken into account in establishing the boundary conditions at the electrode entrance. A system of differential equations and boundary conditions describing the model was formulated. The integration was carried out by means of Hamming's method with automatic step size adjustment. The effects of various parameters (flow-rate, exchange current density, conductivity of the electrolyte, etc.) were examined in terms of deviations from the simple model. The regions of large, negligible and small (within 10%) deviations were defined and interpreted.