András Dallos

Pair-wise interactions by gas chromatography V. Interaction free enthalpies of solutes with primary chloro-and and bromoalkanes☆

Abstract Gas chromatographic data of ca. 140 molecular probes were measured on primary chloro and bromo derivatives of a C 78 branched alkane (C 78 H 158 ) as stationary phases. Interaction free enthalpies between solutes and the dipolar chloroalkyl and bromoalkyl groups were nearly the same. Slight differences may be explained by the higher polarizability of the bromo substituent.

Pair-wise interactions by gas chromatography. VII. Interaction free enthalpies of solutes with secondary alcohol groups

A polar type liquid having a secondary alcohol substituent on a branched alkane skeleton, SOH, was used as stationary phase. The molecules of this stationary phase are nearly isomorphous and isochor with those of the branched alkane, C78, elected as standard, i.e., the molecules of both solvents have nearly the same form and the same size. Partition properties of 158 chosen molecular probes were measured by gas chromatography on SOH and on an SOH-C78 mixture having a volume fraction of thetaOH = 0.5. Based on the resulting data an interaction free enthalpy could be calculated, i.e., the additional effect of the secondary alcohol to partition. Comparison with data determined earlier on another member of this solvent family, POH, having a primary alcohol as interacting group gives information about the effect of steric hindrance on polar type solute-solvent interaction free energies.

Combined Computational Approach Based on Density Functional Theory and Artificial Neural Networks for Predicting The Solubility Parameters of Fullerenes

The solubility of organic semiconductors in environmentally benign solvents is an important prerequisite for the widespread adoption of organic electronic appliances. Solubility can be determined by considering the cohesive forces in a liquid via Hansen solubility parameters (HSP). We report a numerical approach to determine the HSP of fullerenes using a mathematical tool based on artificial neural networks (ANN). ANN transforms the molecular surface charge density distribution (σ-profile) as determined by density functional theory (DFT) calculations within the framework of a continuum solvation model into solubility parameters. We validate our model with experimentally determined HSP of the fullerenes C60, PC61BM, bisPC61BM, ICMA, ICBA, and PC71BM and through comparison with previously reported molecular dynamics calculations. Most excitingly, the ANN is able to correctly predict the dispersive contributions to the solubility parameters of the fullerenes although no explicit information on the van der Waals forces is present in the σ-profile. The presented theoretical DFT calculation in combination with the ANN mathematical tool can be easily extended to other π-conjugated, electronic material classes and offers a fast and reliable toolbox for future pathways that may include the design of green ink formulations for solution-processed optoelectronic devices.

Adsorption isotherms of some alkyl aromatic hydrocarbons and surface energies on partially dealuminated Y faujasite zeolite by inverse gas chromatography.

Adsorption isotherm data of some alkyl aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) measured in the temperature range of 423-523K on a partially dealuminated faujasite type DAY F20 zeolite by inverse gas chromatography are presented in this work. The temperature dependent form of Tóths equation has been fitted to the multiple temperature adsorption isotherms of benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene with standard deviations of 4.6, 5.0, 5.9, 4.3, 5.1 and 6.3mmolkg(-1) and coefficients of determinations (r(2)) of 0.977, 0.971, 0.974, 0.975, 0.991 and 0.991, respectively. The gas-solid equilibria and modeling were interpreted on the basis of the interfacial properties of the zeolite, by dispersive, specific and total surface energy heterogeneity profiles and distributions of the adsorbent measured by surface energy analysis.

Simulation of a model nanopore sensor: Ion competition underlies device behavior

We study a model nanopore sensor with which a very low concentration of analyte molecules can be detected on the basis of the selective binding of the analyte molecules to the binding sites on the pore wall. The bound analyte ions partially replace the current-carrier cations in a thermodynamic competition. This competition depends both on the properties of the nanopore and the concentrations of the competing ions (through their chemical potentials). The output signal given by the device is the current reduction caused by the presence of the analyte ions. The concentration of the analyte ions can be determined through calibration curves. We model the binding site with the square-well potential and the electrolyte as charged hard spheres in an implicit background solvent. We study the system with a hybrid method in which we compute the ion flux with the Nernst-Planck (NP) equation coupled with the Local Equilibrium Monte Carlo (LEMC) simulation technique. The resulting NP+LEMC method is able to handle both strong ionic correlations inside the pore (including finite size of ions) and bulk concentrations as low as micromolar. We analyze the effect of bulk ion concentrations, pore parameters, binding site parameters, electrolyte properties, and voltage on the behavior of the device.

Controlling ion transport through nanopores: modeling transistor behavior

We present a modeling study of a nanopore-based transistor computed by a mean-field continuum theory (Poisson-Nernst-Planck, PNP) and a hybrid method including particle simulation (Local Equilibrium Monte Carlo, LEMC) that is able to take ionic correlations into account including the finite size of ions. The model is composed of three regions along the pore axis with the left and right regions determining the ionic species that is the main charge carrier, and the central region tuning the concentration of that species and, thus, the current flowing through the nanopore. We consider a model of small dimensions with the pore radius comparable to the Debye-screening length (Rpore/λD≈ 1), which, together with large surface charges provides a mechanism for creating depletion zones and, thus, controlling ionic current through the device. We report the scaling behavior of the device as a function of the Rpore/λD parameter. Qualitative agreement between PNP and LEMC results indicates that mean-field electrostatic effects predominantly determine device behavior.

Surface Energy Heterogeneity Profiles of Carbon Nanotubes with a Copolymer-Modified Surface Using Surface Energy Mapping by Inverse Gas Chromatography

Abstract The effectiveness and quantitative control of the surface transition of multi-walled carbon nanotubes (MWCNTs) was characterized by inverse gas chromatography (iGC). The surface energy profile of carbon nanotubes compatibilized with an olefin-maleic-anhydride-ester-amide (OMAEA)-type coupling agent was determined by a surface energy analyzer (SEA). The surface energetic heterogeneity with energy distributions of dispersive and specific (acid-base) components of the surface energy of the MWCNTs were determined at various surface coverages. The results of the surface energy mapping showed that surface treatment significantly reduced the dispersive surface energy of MWCNTs and increased the specific surface energy. Furthermore, the surface modification enhanced its Lewis basic character and simultaneously decreased the acidic character of MWCNTs. It has been demonstrated that the surface treatment modified the heterogeneity profiles of the energetic surface of the carbonaceous nanomaterials.

Effects of Ultrasonic Disintegration, Hot-Compressed Liquid Water Pre-Treatment, and Steam Explosion on Solvolysis and Digestibility Of Grain Sorghum Stover

One of the most promising renewable energy crops and biomass feedstock for biogas production in Europe is the C4 plant grain sorghum due to its high photosynthetic efficiency. The release of lignocellulosic material and therefore the acceleration of degradation processes of sorghum stalks and leaves can be achieved using mechanical and thermal pretreatments, which assist to hydrolyse the cell walls and speed the solvolysis of biopolymers. This study is focused on hotcompressed liquid water, steam explosion and ultrasonic pre-treatments of grain sorghum stover. The effectiveness of pre-treatments was evaluated by means of soluble chemical oxygen demand, biochemical oxygen demand, and by the biogas and methane productivities. The results show that the pre-treatments disintegrated the lignocellulosic structure, increased and accelerated the biogas and methane production, and increased the mesophilic anaerobic digestion potential of grain sorghum stover. Our laboratory tests demonstrated that the steam exploded grain sorghum stover possess the highest biogas productivity.

Géza Tarján and József Takács: Essential oils—Manual for gas–liquid chromatography analysis

These data are of great importance, because of the current innovative programs in the perfumery industry and the renaissance of using herbs and essential oils extracted from them as the focus of sustainable developments. essential oils are complex mixtures containing many components. Analyzing and qualifying essential oils requires separation of the components to define their quality and quantity. Gas–liquid chromatography (GLC) is an excellent method for analysing essential oils for quality and purity. Since its introduction in 1952, GLC has been developed greatly in terms of instrumentation. exact, reliable and reproducible results are nowadays guaranteed by columns with good separation characteristics, reliable temperature, pressure and flow controllers even in programmed mode, by specific detectors and by libraries containing chromatograms obtained with specific detectors. The specificity of a qualitative analysis can be improved by increasing the number of identifying processes, especially when the applied processes compensate each other’s limits and deficiencies. That is why sometimes it is worth going back to qualitative identification based on retention data in the isothermal mode which best ensures reproducibility of such measured data in addition to mass spectrometry (MS) which gives specific detection signals. GC-MS is a powerful technique but it does have limitations: