Diffusion of fructose in water: a molecular dynamics study

Present work carries the molecular dynamics (MD) simulation to study the self-diffusion coefficients of fructose (C6H12O6) and SPC/E (Extended Simple Point Charge) water (H2O) along with their binary diffusion coefficients at different temperature (298.15 K, 303.15 K, 308.15 K and 312.15 K). A dilute solution of 3 molecules of fructose (solute, mole fraction 0.0018) and 1624 molecules of water (solvent, mole fraction 0.9982) has been taken for making it relevant to the previously reported experiment. The structural analysis of the mixture has been estimated by using the radial distribution function (RDF) of its constituents. Mean square displacement (MSD) and Einstein’s relation have been used to find the self-diffusion coefficients of both the solute and solvent. Furthermore, Darken’s relation finds the binary diffusion coefficients. The temperature dependence of diffusion coefficients follows the Arrhenius behavior which further calculates activation energy of diffusion. The results from the present work agree well with the previously reported experimental values.

Technical note: Determination of binary gas-phase diffusion coefficients of unstable and adsorbing atmospheric trace gases at low temperature – arrested flow and twin tube method

Gas-phase diffusion is the first step for all heterogeneous reactions under atmospheric conditions. Knowledge of binary diffusion coefficients is important for the interpretation of laboratory studies regarding heterogeneous trace gas uptake and reactions. Only for stable, nonreactive and nonpolar gases do well-established models for the estimation of diffusion coefficients from viscosity data exist. Therefore, we have used two complementary methods for the measurement of binary diffusion coefficients in the temperature range of 200 to 300 K: the arrested flow method is best suited for unstable gases, and the twin tube method is best suited for stable but adsorbing trace gases. Both methods were validated by the measurement of the diffusion coefficients of methane and ethane in helium and air as well as nitric oxide in helium. Using the arrested flow method the diffusion coefficients of ozone in air, dinitrogen pentoxide and chlorine nitrate in helium, and nitrogen were measured. The twin tube method was used for the measurement of the diffusion coefficient of nitrogen dioxide and dinitrogen tetroxide in helium and nitrogen.

Technical note: Determination of binary gas phase diffusion coefficients of unstable and adsorbing atmospheric trace gases at low temperature – Arrested Flow and Twin Tube method

Gas phase diffusion is the first step for all heterogeneous reactions under atmospheric conditions. Knowledge of binary diffusion coefficients is important for the interpretation of laboratory studies regarding heterogeneous trace gas uptake and reactions. Only for stable, nonreactive and non polar gases well-established models for the estimation of diffusion coefficients from viscosity data do exist. Therefore, we have used two complementary methods for the measurement of binary diffusion coefficients in the temperature range of 200 K to 300 K: the arrested flow method is best suited for unstable gases and the twin tube method is best suited for stable but adsorbing trace gases. Both methods were validated by measurement of diffusion coefficients of methane and ethane in helium and air and nitric oxide in helium. Using the arrested flow method the diffusion coefficients of ozone in air, dinitrogen pentoxide and chlorine nitrate in helium and nitrogen were measured. The twin tube method was used for the measurement of the diffusion coefficient of nitrogen dioxide and dinitrogen tetroxide in helium and nitrogen.