Completely computational model setup for spectroscopic techniques: the ab initio molecular dynamics indirect hard modeling (AIMD-IHM) approach

The spectroscopic quantification of mixture compositions usually requires pure compounds and mixtures of known composition for calibration. Since they are not always available, methods to fill such gaps have evolved, which are, however, not generally applicable. Therefore, calibration can be extremely challenging, especially when multiple instable species, e.g. intermediates, exist in a system. This study presents a new calibration approach that uses ab initio Molecular Dynamics (AIMD)-simulated spectra as to set up and calibrate models for the physics-based spectral analysis method Indirect Hard Modeling (IHM). To demonstrate our approach called AIMD-IHM, we analyze Raman spectra of ternary hydrogen-bonding mixtures of acetone, methanol, and ethanol. The derived AIMD-IHM pure-component models and calibration coefficients are in good agreement with conventionally generated experimental results. The method yields compositions with prediction errors of less than 5% without any experimental calibration input. Our approach can be extended, in principle, to IR and NMR spectroscopy and allows for the analysis of systems that were hitherto inaccessible to quantitative spectroscopic analysis.

Revisiting pure component wax esters as basis of wax-based oleogels

Current research on wax-based oleogels indicates wax esters to be the key component in many natural waxes. This necessitates understanding the properties of pure wax esters to unravel the gelling mechanism in wax-based oleogels. Therefore, wax esters with different carbon numbers and symmetries were studied and characterized regarding their thermal (DSC) and viscoelastic (oscillatory rheology) behavior. Pure wax esters and binary mixtures of wax esters were studied as such and in oleogels formed in combination with medium chained triglyceride oil at WE-inclusion levels of 10 % (w/w). Interpretation of the observations was based on detailed analysis of pre-existing data on crystallographic (SAXS) and thermal properties. It is found that all observations concerning single pure WE’s obey a systematic framework linking molecular make up, crystal structure and behavior. The study on the gelling of four different binary mixtures of wax esters revealed that substantial chain length differences do have the expected consequence of separate crystallization. Mixtures of wax esters with only limited chain length difference reconfirmed earlier speculations on mixing and crystal structure. Applying mixtures of wax esters only differing in their position of the ester bond indicated ideal mixing behavior in the solid phase of the gels. Actually, the data revealed that despite these expected observations in both systems, additional thermal events occur at specific mixing ratios. Their supposed relation to compound formation certainly needs further confirmation. Rheological analysis confirmed that sequential crystallization results in highest firmness values for the systems studied.

Binary adsorption of [Pb(II) + Co(II)] from aqueous solution using thiolated saw dust

Technology advancement contributed to an increase in industrial activities, resulting in the introduction of metal ions into water resources at concentrations well above the WHO limits. Heavy metals are highly toxic and carcinogenic; usually occur as multicomponent mixtures in aquatic environment. In present study, batch experiments have been conducted to study the dependence of varying concentration, time, pH and temperature on the uptake of Pb(II) as pure component under equilibrium conditions using thiolated saw dust. Saw dust has been chemically modified with thioglycolic acid and characterised using proximate and FTIR analyses, degree of thiolation has also been determined. To determine the effect of presence of Co(II) ions on the uptake of Pb(II) ions, batch experiments for [Pb(II) + Co(II)] mixture have been carried out for concentration ratios of 1:0, 1:1, 1:2, 1:3, 1:4 of Pb:Co at pH 5 and data has been interpreted using Langmuir competitive isotherm shows that adsorption of Pb(II) has been suppressed by the presence of Co(II) ions in the binary solution, hence the adsorption process is antagonistic in nature. Study also indicates the possibility of simultaneous removal of both metal ions using low cost bioadsorbent, which is economical specially for application in small scale industries.

Modelling the Diffusion Coefficients of Dilute Gaseous Solutes in Hydrocarbon Liquids

In this work, we present a model, based on rough hard-sphere theory, for the tracer diffusion coefficients of gaseous solutes in non-polar liquids. This work extends an earlier model developed specifically for carbon dioxide in hydrocarbon liquids and establishes a general correlation for gaseous solutes in non-polar liquids. The solutes considered were light hydrocarbons, carbon dioxide, nitrogen and argon, while the solvents were all hydrocarbon liquids. Application of the model requires knowledge of the temperature-dependent molar core volumes of the solute and solvent, which can be determined from pure-component viscosity data, and a temperature-independent roughness factor which can be determined from a single diffusion coefficient measurement in the system of interest. The new model was found to correlate the experimental data with an average absolute relative deviation of 2.7 %. The model also successfully represents computer-simulation data for tracer diffusion coefficients of hard-sphere mixtures and reduces to the expected form for self-diffusion when the solute and solvent become identical.

Relaxation Dynamics of Ethanol and N-Butanol in Diesel Fuel Blends from Terahertz Spectroscopy

Binary blends of ethanol-diesel, n-butanol-diesel, ethanol-biodiesel, and n-butanol-biodiesel have been analyzed with terahertz time-domain spectroscopy in a full range of concentrations and at room temperature. The real and imaginary parts of the complex dielectric constant of the blends were obtained from the spectra and fitted to the Debye model at low volume concentrations (up to 7.5% for ethanol in diesel and up to 20% for butanol in diesel, ethanol in biodiesel, and butanol in biodiesel blends), considering the number of relaxation processes recommended in the literature for each pure component (single for diesel, double for biodiesel, and triple for alcohols). The results indicate that the faster relaxation time in low alcohol mixtures is longer than in pure alcohols. This relaxation time increases as the alcohol content increases. The excess of the real and of imaginary parts of the dielectric constant were individually determined. The analysis of such excess and of its different contributions (volume, contrast, and interactions) suggests that the intermolecular interactions between the different components of the blends dominate the relaxation dynamics in each pseudo-binary system. Ethanol was found to move blends further away from ideal behavior than n-butanol. In fact, these latter blends showed the most ideal behavior, suggesting that the length of the alcohol carbon chain plays an important role. This information allows a possible link between the nonlinear behavior of the physicochemical properties of the blends (e.g., viscosity and surface tension) and the molecular interactions between their constituent molecules. This relation could have direct application for monitoring the fuel composition and quality in the vehicle control systems.

On Using the BMCSL Equation of State to Renormalize the Onsager Theory Approach to Modeling Hard Prolate Spheroidal Liquid Crystal Mixtures

Modifications to the traditional Onsager theory for modeling isotropic–nematic phase transitions in hard prolate spheroidal systems are presented. Pure component systems are used to identify the need to update the Lee–Parsons resummation term. The Lee–Parsons resummation term uses the Carnahan–Starling equation of state to approximate higher-order virial coefficients beyond the second virial coefficient employed in Onsager’s original theoretical approach. As more exact ways of calculating the excluded volume of two hard prolate spheroids of a given orientation are used, the division of the excluded volume by eight, which is an empirical correction used in the original Lee–Parsons resummation term, must be replaced by six to yield a better match between the theoretical and simulation results. These modifications are also extended to binary mixtures of hard prolate spheroids using the Boublík–Mansoori–Carnahan–Starling–Leland (BMCSL) equation of state.