Size Of Alkanes Research Articles

Interfacial Rheological and Emulsion Properties of Self-Assembled Cyclodextrin-Oil Inclusion Complexes.

To investigate the effect of the molecular size of alkanes and the cavity size of cyclodextrins (CDs) on the formation of interfacial host-guest inclusion complexes, the interfacial tension (IFT) of CD (α-CD, β-CD, γ-CD) solutions against oils (hexadecane, dodecylbenzene) was determined by interfacial dilational rheology measurements. The results show that the "space compatibility" between CDs and oil molecules is crucial for the formation of interface host-guest inclusion complexes. Hexadecane with a smaller molecular size can form host-guest inclusion complexes with small cavities of α-CD and β-CD, dodecylbenzene with a larger molecular size can form interfacial aggregates with the medium-sized cavity of β-CD easily, and the polycyclic aromatic hydrocarbon molecules in kerosene can form inclusion complexes with the large cavity of γ-CD. The formation of interfacial inclusion complexes leads to lower IFT values, higher interfacial dilational modulus, nonlinear IFT responses to the interface area oscillating, and skin-like films at the oil-water interface. What's more, the phase behavior of Pickering emulsions formed by CDs with different oils is explored, and the phenomena in alkane-CD emulsions are in line with the results in dilatation rheology. The interfacial active host-guest structure in the kerosene-γ-CD system improves the stability of the Pickering emulsion, which results in smaller emulsion droplets. This unique space compatibility characteristic is of great significance for the application of CDs in selective host-guest recognition, sensors, enhanced oil recovery, food industries, and local drug delivery.

Testing secondary organic aerosol models using smog chamber data for complex precursor mixtures: influence of precursor volatility and molecular structure

Abstract. We use secondary organic aerosol (SOA) production data from an ensemble of unburned fuels measured in a smog chamber to test various SOA formation models. The evaluation considered data from 11 different fuels including gasoline, multiple diesels, and various jet fuels. The fuels are complex mixtures of species; they span a wide range of volatility and molecular structure to provide a challenging test for the SOA models. We evaluated three different versions of the SOA model used in the Community Multiscale Air Quality (CMAQ) model. The simplest and most widely used version of that model only accounts for the volatile species (species with less than or equal to 12 carbons) in the fuels. It had very little skill in predicting the observed SOA formation (R2 = 0.04, fractional error = 108%). Incorporating all of the lower-volatility fuel species (species with more than 12 carbons) into the standard CMAQ SOA model did not improve model performance significantly. Both versions of the CMAQ SOA model over-predicted SOA formation from a synthetic jet fuel and under-predicted SOA formation from diesels because of an overly simplistic representation of the SOA formation from alkanes that did not account for the effects of molecular size and structure. An extended version of the CMAQ SOA model that accounted for all organics and the influence of molecular size and structure of alkanes reproduced the experimental data. This underscores the importance of accounting for all low-volatility organics and information on alkane molecular size and structure in SOA models. We also investigated fitting an SOA model based solely on the volatility of the precursor mixture to the experimental data. This model could describe the observed SOA formation with relatively few free parameters, demonstrating the importance of precursor volatility for SOA formation. The exceptions were exotic fuels such as synthetic jet fuel that expose the central assumption of the volatility-dependent model that most emissions consist of complex mixtures with similar distribution of molecular classes. Despite its shortcomings, SOA formation as a function of volatility may be sufficient for modeling SOA formation in chemical transport models.

A quantum chemical study of the processes during the evaporation of real-life Diesel fuel droplets

Evaporation rate (γ) of molecules from Diesel fuel molecular clusters and nanodrops is analysed using the solvation model SMD within quantum chemistry, the kinetic gas theory, and experimental or extrapolation data on temperature dependence of the enthalpy of evaporation and liquid density. The SMD/HF or SMD/DFT with the same 6-31G(d,p) basis set is used to estimate changes in the Gibbs free energy during the transfer of a molecule from a liquid medium into a gas phase (using the Gibbs free energy of solvation, ΔGs). The kinetic gas theory is used to estimate the collision rate of molecules/clusters/nanodrops in the gas phase. This rate depends on partial pressures, temperature, sizes and masses of molecules and clusters/nanodrops. Such solvents as n-dodecane, tetraline, benzene, and isopropyltoluene are used to analyse the effects of surroundings on the evaporation rate of the components of Diesel fuel: normal, iso and cyclic alkanes, 1–3 ring aromatics, tetralines and indanes (in the C12–C20 range). Compounds C14–C16 give the main contribution to Diesel fuel under consideration, and all cyclic organics have the C1–C6 aliphatic side groups. An increase in the molecular size of alkanes from n-octane to n-heptacosane or in the aromaticity of compounds results in a strong decrease in the γ values.

Studies on molecular transport of n‐alkanes through poly(tetrafluoroethylene‐co‐propylene) elastomeric membrane

AbstractMolecular transport of a series of n‐alkanes through commercial TFE elastomer (FA 150L) has been studied in the temperature range 30–50 °C using sorption‐gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes and temperature. The diffusion coefficients at 30°C varied from 4.53 × 10−8 cm2/s (n‐heptane) to 0.18 × 10−8 cm2/s (n‐hexadecane). The liquid concentration profiles have also been computed using analytical solution of Fick's equation with the appropriate initial and boundary conditions and these were presented as a function of penetration depth of molecular migration and time of immersion. These results have been discussed in terms of molecular size of alkanes as well as temperature. In all the liquid penetrants, the transport phenomenon was found to follow the anomalous behavior. From the temperature dependence of diffusion and permeation coefficients, the Arrhenius activation parameters have been estimated. These parameters do not exhibit any systematic variation with the size of the penetrants. The resulting low diffusion coefficients, contribute to the superior barrier performance of the membrane, is due, in part, to the high glass transition temperature of Aflas™ TFE elastomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2228–2235, 2006