Journal articles: 'Molecular diffusion coefficient'

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Miyamoto, Shuichi, and Kazumi Shimono. "Molecular Modeling to Estimate the Diffusion Coefficients of Drugs and Other Small Molecules." Molecules 25, no. 22 (November 16, 2020): 5340. http://dx.doi.org/10.3390/molecules25225340.

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Diffusion is a spontaneous process and one of the physicochemical phenomena responsible for molecular transport, the rate of which is governed mainly by the diffusion coefficient; however, few coefficients are available because the measurement of diffusion rates is not straightforward. The translational diffusion coefficient is related by the Stokes–Einstein equation to the approximate radius of the diffusing molecule. Therefore, the stable conformations of small molecules were first calculated by molecular modeling. A simple radius rs and an effective radius re were then proposed and estimated using the stable conformers with the van der Waals radii of atoms. The diffusion coefficients were finally calculated with the Stokes–Einstein equation. The results showed that, for the molecules with strong hydration ability, the diffusion coefficients are best given by re and for other compounds, rs provided the best coefficients, with a reasonably small deviation of ~0.3 × 10−6 cm2/s from the experimental data. This demonstrates the effectiveness of the theoretical estimation approach, suggesting that diffusion coefficients have potential use as an additional molecular property in drug screening.

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Wei, Qing Hua, Ya Nen Wang, Ming Ming Yang, Wei Hong Chai, and Ying Feng Zhang. "Molecular Dynamics Study of H₂O Molecular Diffusion Behavior in PAM/PVA Polymer Blends." Advanced Materials Research 1119 (July 2015): 268–72. http://dx.doi.org/10.4028/www.scientific.net/amr.1119.268.

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The theoretical method of molecular dynamics was applied to study H2O molecular diffusion behavior in PAM/PVA Polymer blends, investigated the effects of component ratios, temperatures and water contents on diffusion coefficient. Results show that with the increase of PVA content in blend systems, the H2O molecule diffusion coefficient first increased and then decreased. This indicates there is an optimum component ratio to make the H2O molecule diffusion coefficient maximum. There is a certain influence of temperature on H2O molecular diffusion in PAM/PVA blend system, the higher the temperature, the bigger the H2O molecular diffusion coefficient. When the less H2O molecules contained in system, there is a less impact on the diffusion coefficient. As the number of H2O molecules reaches a certain amount, the effect on the diffusion coefficient is more obvious.

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Islam, Md Shafiqul, Sayem Ahmeed, and Sumon Kumar Ghosh. "Diffusion study of chloride and binding of water in concrete pore by molecular dynamics simulation using LAMMPS." Challenge Journal of Concrete Research Letters 12, no. 3 (September 15, 2021): 88. http://dx.doi.org/10.20528/cjcrl.2021.03.002.

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As for the communication between concrete and the particles, the surface shows Cl− shock and Na adsorption. With expanded particle focus, the solid adsorption capacity for Cl− is upgraded as a result of a detailed overview of the dynamic molecular simulation studies examining the chloride diffusion coefficient. Different characteristics of the diffusion process, including molecular models, system-size effects, temperature, and pressure conditions, and the type of protection, are discussed. This paper focus on Molecular Dynamic Simulation to determine the diffusion coefficient of chloride ion and water molecules in concrete. The diffusion coefficient for NaCl salt obtained 6.60178x10-10m2/s and the diffusion coefficient for CaCl2 salt obtained 7.29305x10-10m2/s. So, the average chloride diffusion coefficient 6.9475x10-10m2/s. Diffusion coefficient obtained from graph 5.562x10-10m2/s. Diffusion coefficients for water molecules for NaCl solution are 6.125x10-10m2/s, 6.85x10-10m2/s, 1.044x10-10m2/s, 8.525x10-10m2/s, 6.25x10-10m2/s. diffusion coefficient of water molecules in CaCl2 solution are 4.5x10-10m2/s, 6.725x10-10m2/s, 1.254x10-10m2/s, 7.725x10-10m2/s, 1.3x10-10m2/s. Average value obtained for water molecule diffusion are 4.545x10-10m2/s, 7.4062x10-10m2/s and 1.149x10-10m2/s. This diffusion of chloride effects the binding of water in concrete pore.

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Bhandari, Dipendra, and N. P. Adhikari. "Molecular dynamics study of diffusion of krypton in water at different temperatures." International Journal of Modern Physics B 30, no. 11 (April 28, 2016): 1650064. http://dx.doi.org/10.1142/s0217979216500648.

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Molecular dynamics study of diffusion of two krypton atoms in 300 SPC/E water molecules at temperatures 293, 303, 313, 323 and 333 K has been carried out. Self-diffusion coefficient of krypton and water along with their mutual diffusion coefficients are estimated. Self-diffusion coefficient for krypton is calculated by using Mean Square Displacement (MSD) method and Velocity Autocorrelation (VACF) method, while that for water is calculated by using MSD method only. The mutual diffusion coefficient is estimated by using the Darken’s relation. The diffusion coefficients are found to follow the Arrhenius behavior. The structural properties of the system have been estimated by the study of solute–solute, solvent–solvent, and solute–solvent Radial Distribution Function (RDF).

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Xu, Bo, and Zhenqian Chen. "Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study." Indoor and Built Environment 28, no. 2 (October 16, 2017): 175–85. http://dx.doi.org/10.1177/1420326x17736908.

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To provide a microcosmic theoretical support for the reduction of formaldehyde in building material, the diffusion process was investigated by molecular dynamics simulation. In addition, the diffusion model of formaldehyde molecules in crystalline and amorphous cellulose was built, and diffusion coefficients at different temperatures and electric fields were studied. The simulation temperature was from 293 to 393 K and electric field was from 0 to 400 kV/m. Diffusion coefficient increased with greater temperature and electric field both in crystalline and amorphous region. However, the diffusion coefficient in amorphous region could be ignored for it was two orders of magnitude lower than diffusion coefficient in crystalline region. The relationship between diffusion coefficient and temperature, and the relationship between diffusion coefficient and electric field were obtained by simulation, verified by the experiment. Temperature was shown to have a significant contribution to formaldehyde diffusion than electric field. Compared with experimental studies, the molecular dynamics simulation could only analyse the diffusion coefficient qualitatively because of the difference between micro-scale and macro-scale.

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Xiaoming, Du. "Molecular Dynamics Study of Hydrogen on Alkali-Earth Metal Cations Exchanged X Zeolites." International Journal of Chemical Engineering 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/701057.

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The self-diffusion of hydrogen in Ca2+-, Mg2+- and Ba2+-exchanged X zeolites (Mg46X, Ca46X, and Ba46X) has been studied by molecular dynamics (MD) simulations for various temperatures and loadings. The results indicate that in the temperature range of 77–298 K and the loading range of 1–80 molecules/cell, the self-diffusion coefficients are found to range from1.2×10-9 m2·s−1to2.3×10-7 m2·s−1which are in good agreement with the experimental values from the quasielastic neutron scattering (QENS) and pulse field gradients nuclear magnetic resonance (PFG NMR) measurements. The self-diffusion coefficients decrease with loading due to packing of sorbate-sorbate molecules which causes frequent collusion among hydrogen molecules in pores and increases with increasing temperature because increasing the kinetic energy of the gas molecules enlarges the mean free path of gas molecule. The mechanism of diffusion of hydrogen molecules in these zeolites is transition diffusion. Knudsen diffusion occurs at low loading and the molecular bulk diffusion occurs at higher loading. For given temperature and loading, the self-diffusion coefficients decrease in the orderBa46X<Mg46X<Ca46X, due to the different sizes and locations of the divalent cations. Moreover, the effect of concentration of molecular hydrogen on self-diffusion coefficient also is analyzed using radial distribution function (RDF).

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Green, Peter F., and Edward J. Kramer. "Diffusion in Polymer Alloy Melts." MRS Bulletin 12, no. 8 (December 1987): 42–47. http://dx.doi.org/10.1557/s0883769400066744.

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AbstractDiffusion in polymer alloys or blends can be used to extract information on the fundamentals of the dynamics of individual polymer chains in the melt and the thermodynamics of the interaction between unlike polymer species. The dynamics of individual chains are available from measurements of the tracer diffusion coefficients, D*, of the various species while the thermodynamics of interaction, represented by the Flory parameter, x, can be obtained from measurements of the mutual diffusion or interdiffusion coefficient, D. We will show that these quantities can be measured conveniently by forward recoil spectrometry (FRES), an ion beam analysis technique that can determine the concentration versus depth profile of polymers labeled with deuterium diffusing into unlabeled polymer matrices.For high enough molecular weight of the matrix, the tracer diffusion coefficient of both species in the blend scale as D0N−2, where N is the number of monomer segments per diffusing chain; the constant D0, however, can differ by more than 104 for chemically different molecules diffusing in the same blend, suggesting that conventional concepts of chain dynamics in melts, such as monomer friction coefficients, need to be reexamined. The mutual diffusion coefficient is controlled by the faster species in the blend (the one with the larger D*N product) in agreement with what was found in metallic alloys (but in sharp disagreement with the “slow” theory of mutual diffusion which predicts that the slower species controls). Since the combinatorial (ideal) entropy of mixing of polymers is low, the thermodynamic driving force for diffusion is dominated by enthalpy and excess entropy of mixing (x) to a degree unprecedented for atomic or small molecule systems. This means that one can observe not only a thermodynamic “slowing down” of diffusion when x becomes positive as one nears the spinodal but also a large thermodynamic “speeding up” of diffusion when x is negative. Measurements of mutual diffusion turn out to be one of the most sensitive methods available for measuring x.

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Nejad, Marjan A., and Herbert M. Urbassek. "Adsorption and Diffusion of Cisplatin Molecules in Nanoporous Materials: A Molecular Dynamics Study." Biomolecules 9, no. 5 (May 27, 2019): 204. http://dx.doi.org/10.3390/biom9050204.

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Using molecular dynamics simulations, the adsorption and diffusion of cisplatin drug molecules in nanopores is investigated for several inorganic materials. Three different materials are studied with widely-varying properties: metallic gold, covalent silicon, and silica. We found a strong influence of both the van der Waals and the electrostatic interaction on the adsorption behavior on the pore walls, which in turn influence the diffusion coefficients. While van der Waals forces generally lead to a reduction of the diffusion coefficient, the fluctuations in the electrostatic energy induced by orientation changes of the cisplatin molecule were found to help desorb the molecule from the wall.

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Szmyt, Wojciech, Carlos Guerra, and Ivo Utke. "Diffusion of dilute gas in arrays of randomly distributed, vertically aligned, high-aspect-ratio cylinders." Beilstein Journal of Nanotechnology 8 (January 9, 2017): 64–73. http://dx.doi.org/10.3762/bjnano.8.7.

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In this work we modelled the diffusive transport of a dilute gas along arrays of randomly distributed, vertically aligned nanocylinders (nanotubes or nanowires) as opposed to gas diffusion in long pores, which is described by the well-known Knudsen theory. Analytical expressions for (i) the gas diffusion coefficient inside such arrays, (ii) the time between collisions of molecules with the nanocylinder walls (mean time of flight), (iii) the surface impingement rate, and (iv) the Knudsen number of such a system were rigidly derived based on a random-walk model of a molecule that undergoes memoryless, diffusive reflections from nanocylinder walls assuming the molecular regime of gas transport. It can be specifically shown that the gas diffusion coefficient inside such arrays is inversely proportional to the areal density of cylinders and their mean diameter. An example calculation of a diffusion coefficient is delivered for a system of titanium isopropoxide molecules diffusing between vertically aligned carbon nanotubes. Our findings are important for the correct modelling and optimisation of gas-based deposition techniques, such as atomic layer deposition or chemical vapour deposition, frequently used for surface functionalisation of high-aspect-ratio nanocylinder arrays in solar cells and energy storage applications. Furthermore, gas sensing devices with high-aspect-ratio nanocylinder arrays and the growth of vertically aligned carbon nanotubes need the fundamental understanding and precise modelling of gas transport to optimise such processes.

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Andryuschenko, Vladimir, and Valery Rudyak. "Self-Diffusion Coefficient of Molecular Fluid in Porous Media." Defect and Diffusion Forum 312-315 (April 2011): 417–22. http://dx.doi.org/10.4028/www.scientific.net/ddf.312-315.417.

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The paper deals with the molecular-dynamics simulation of the self-diffusion of fluid molecules in porous media using the hard-sphere potential. A study is made of the velocity autocorrelation functions of the molecules and dependences of the self-diffusion coefficient on the pore sizes, po-rosity, fluid density, and adsorption time.

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Acharya, Khimananda, Rajendra Prasad Koirala, and Nurapati Pantha. "Diffusion of oxytocin in water: a molecular dynamics study." BIBECHANA 18, no. 1 (January 1, 2021): 108–17. http://dx.doi.org/10.3126/bibechana.v18i1.29316.

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Classical molecular dynamics simulation is performed to estimate the diffusion coefficient of oxytocin in water at different temperatures, 288 K, 300 K, 313 K, 323 K, using GROningen Machine for Chemical Simulations (GROMOCS). The simulation is carried out using GROMOS43A1 force field and extended simple point charge (SPC/E) water model. The stability of the system is evaluated from energy profile of potential and kinetic energy, which assures well equilibrated molecular system. The self-diffusion coefficient of oxytocin and water is obtained from Einstein’s relation and binary diffusion coefficient is obtained from Darken’s relation. As temperature increases the diffusion coefficient also increases as per expectation. The diffusion coefficients of water from the present calculations agree well with the previously reported values, within the 10% of deviation. Furthermore, the activation energy has been studied using Arrhenius Plot. BIBECHANA 18 (2021) 108-117

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Deng, Yuan Wang, Liang Yin, and Wei Han. "Molecular Dynamic Simulations of Diffusion Behavior of Diesel Cold Start Emissions." Advanced Materials Research 785-786 (September 2013): 1262–66. http://dx.doi.org/10.4028/www.scientific.net/amr.785-786.1262.

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Hydrocarbon trap is an effective way to solve the diesel cold start emissions. Zeolites used as hydrocarbon adsorbents are paid more and more attention. In order to study the diffusion of diesel cold start emissions in zeolites, molecular dynamics(MD) in canonical ensemble are employed to simulate the diffusion of ethylene and propylene in MCM-22 in different ways, the mean square displacement (MSD) plot, diffusion coefficient for pure and mixed components are obtained-. The simulation results show that, propylene (C3H6) and ethylene (C2H4) have different diffusion coefficients in MCM22 zeolite at the same temperature; for the same gas, it also has different diffusion coefficients at different temperatures. In addition, the diffusion coefficient increases with temperature rise, thus temperature rise is beneficial to accelerate diffusion process.

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Pushpa, S. A., P. Goonetilleke, and N. C. Billingham. "Diffusion of Antioxidants in Rubber." Rubber Chemistry and Technology 68, no. 5 (November 1, 1995): 705–16. http://dx.doi.org/10.5254/1.3538767.

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Abstract Migration of compounding ingredients such as antioxidants is a problem that has been recognized by rubber compounders. The literature is almost void of quantitative data in this area. Therefore an investigation of the diffusion of some commonly used phenolic antioxidants in three different rubber vulcanizates was carried out. The antioxidants were chosen so that they included a wide range of molecular weights as well as structural differences to enable us to study the effect of size and molecular nature on diffusion in the medium of rubber. The effect of crosslink density on diffusion was studied by using rubber vulcanizates of three different crosslink densities. BHT (butylated hydroxytoluene), the smallest antioxidant in the series, shows the highest diffusion coefficient. As the molecular weight of the diffusant increases the diffusion coefficient decreases. The molecules of polar nature, such as Antioxidant 754 (2,6-di-t-butyl-4-hydroxymethyl phenol), show higher diffusion coefficient compared to the nonpolar molecule of the same size, such as BHT. The crosslink densities of vulcanizates effect the diffusion of antioxidants in that there is an optimum value at which the diffusion coefficient is highest.

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Sapkota, D., and N. P. Adhikari. "Diffusion coefficient and solvation free energy of sucrose in water: a molecular dynamics study." Journal of Nepal Physical Society 7, no. 4 (December 31, 2021): 1–9. http://dx.doi.org/10.3126/jnphyssoc.v7i4.42924.

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In this work, we have carried out Molecular Dynamics Simulation technique to study the diffusion coefficients, radial distribution functions and solvation free energy of sucrose (C12H22O11) at different temperatures ranging from 298.15 K to 318.15 K. We have taken 2 molecules of sucrose in 1343 molecules of extended simple point charge (SPC/E) water model. The self-diffusion coefficients are obtained by applying linear best fit to the mean squaredisplacement (MSD) plot and binary diffusion coefficients are obtained by using Darken’s relation. Arrhenius equation has been used to show a linear relationship between natural logarithm of binary diffusion coefficient and reciprocal of temperature. The structural analysis of the solution has been carried out with the help of radial distribution functions (RDFs) of its constituents. The solvation free energy of sucrose is studied at 300 K by using free energy perturbation method like Bennett Acceptance Ratio (BAR). The results of binary diffusion coefficients obtained from this simulation work agree very well with the previously reported experimental data.

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Graaff, R., and J. J. Ten Bosch. "Diffusion coefficient in photon diffusion theory." Optics Letters 25, no. 1 (January 1, 2000): 43. http://dx.doi.org/10.1364/ol.25.000043.

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Vlasov, M. N., and M. C. Kelley. "Specific features of eddy turbulence in the turbopause region." Annales Geophysicae 32, no. 4 (April 15, 2014): 431–42. http://dx.doi.org/10.5194/angeo-32-431-2014.

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Abstract. The turbopause region is characterized by transition from the mean molecular mass (constant with altitude) to the mean mass (dependent on altitude). The former is provided by eddy turbulence, and the latter is induced by molecular diffusion. Competition between these processes provides the transition from the homosphere to the heterosphere. The turbopause altitude can be defined by equalizing the eddy and molecular diffusion coefficients and can be located in the upper mesosphere or the lower thermosphere. The height distributions of chemical inert gases very clearly demonstrate the transition from turbulent mixing to the diffusive separation of these gases. Using the height distributions of the chemical inert constituents He, Ar, and N2 given by the MSIS-E-90 model and the continuity equations, the height distribution of the eddy diffusion coefficient in the turbopause region can be inferred. The eddy diffusion coefficient always strongly reduces in the turbopause region. According to our results, eddy turbulence above its peak always cools the atmosphere. However, the cooling rates calculated with the eddy heat transport coefficient equaled to the eddy diffusion coefficient were found to be much larger than the cooling rates corresponding to the neutral temperatures given by the MSIS-E-90 model. The same results were obtained for the eddy diffusion coefficients inferred from different experimental data. The main cause of this large cooling is the very steep negative gradient of the eddy heat transport coefficient, which is equal to the eddy diffusion coefficient if uniform turbulence takes place in the turbopause region. Analysis of wind shear shows that localized turbulence can develop in the turbopause region. In this case, eddy heat transport is not so effective and the strong discrepancy between cooling induced by eddy turbulence and cooling corresponding to the temperature given by the MSIS-E-90 model can be removed.

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WU, SIZHU, JUN YI, LISHU ZHANG, LIQUN ZHANG, and JAMES E. MARK. "THE STUDY ON THE GAS PERMEABILITIES OF THE ETHYLENE/1-HEXENE COPOLYMER BY MOLECULAR DYNAMICS SIMULATION." International Journal of Modern Physics B 22, no. 31n32 (December 30, 2008): 5859–64. http://dx.doi.org/10.1142/s0217979208051285.

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In this research, molecular dynamics(MD) simulations were used to study the transport properties of small gas molecules in poly(ethylene-co-1-hexene) copolymer. The condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) forcefield was applied. The diffusion coefficients were obtained from MD (NVT ensemble). The results indicated that the diffusion coefficient of oxygen increased with increasing 1-hexene content in copolymer membrane.

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Nagai, Tetsuro, Akira Yoshimori, and Susumu Okazaki. "Dynamic Monte Carlo calculation generating particle trajectories that satisfy the diffusion equation for heterogeneous systems with a position-dependent diffusion coefficient and free energy." Journal of Chemical Physics 156, no. 15 (April 21, 2022): 154506. http://dx.doi.org/10.1063/5.0086949.

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A series of new Monte Carlo (MC) transition probabilities was investigated that could produce molecular trajectories statistically satisfying the diffusion equation with a position-dependent diffusion coefficient and potential energy. The MC trajectories were compared with the numerical solution of the diffusion equation by calculating the time evolution of the probability distribution and the mean first passage time, which exhibited excellent agreement. The method is powerful when investigating, for example, the long-distance and long-time global transportation of a molecule in heterogeneous systems by coarse-graining them into one-particle diffusive molecular motion with a position-dependent diffusion coefficient and free energy. The method can also be applied to many-particle dynamics.

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Chen, Gengbiao, and Zhiwen Liu. "Effect of Modification on the Fluid Diffusion Coefficient in Silica Nanochannels." Molecules 26, no. 13 (July 1, 2021): 4030. http://dx.doi.org/10.3390/molecules26134030.

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The diffusion behavior of fluid water in nanochannels with hydroxylation of silica gel and silanization of different modified chain lengths was simulated by the equilibrium molecular dynamics method. The diffusion coefficient of fluid water was calculated by the Einstein method and the Green–Kubo method, so as to analyze the change rule between the modification degree of nanochannels and the diffusion coefficient of fluid water. The results showed that the diffusion coefficient of fluid water increased with the length of the modified chain. The average diffusion coefficient of fluid water in the hydroxylated nanochannels was 8.01% of the bulk water diffusion coefficient, and the diffusion coefficients of fluid water in the –(CH2)3CH3, –(CH2)7CH3, and –(CH2)11CH3 nanochannels were 44.10%, 49.72%, and 53.80% of the diffusion coefficients of bulk water, respectively. In the above four wall characteristic models, the diffusion coefficients in the z direction were smaller than those in the other directions. However, with an increase in the silylation degree, the increased self-diffusion coefficient due to the surface effect could basically offset the decreased self-diffusion coefficient owing to the scale effect. In the four nanochannels, when the local diffusion coefficient of fluid water was in the range of 8 Å close to the wall, Dz was greater than Dxy, and beyond the range of 8 Å of the wall, the Dz was smaller than Dxy.

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Sharma, Keshav, and Narayan P. Adhikari. "Temperature dependence of diffusion coefficient of nitrogen gas in water: A molecular dynamics study." International Journal of Modern Physics B 28, no. 14 (April 25, 2014): 1450084. http://dx.doi.org/10.1142/s0217979214500842.

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We have carried out the molecular dynamics (MD) simulation to study the structural properties and to estimate the diffusivity of molecular nitrogen ( N 2) gas (solute) in extended simple point charge model (SPC/E) water (solvent) with N 2 mole fraction of 0.018 at different temperatures. For the structural properties of the system, we have determined radial distribution function (RDF). The solute–solute, solute–solvent and solvent–solvent RDF have been evaluated. Self-diffusion coefficient of N 2 was estimated by evaluating mean-squared displacement (MSD) and velocity autocorrelation function (VACF) separately. The diffusion coefficients obtained from the two methods agree within 3%. The results are in agreement with the experimentally determined values within 10%. The self-diffusion coefficient of water ( H 2 O ) was also estimated by evaluating MSD. Mutual diffusion coefficient of the system have also been estimated invoking Darken's relation. The temperature dependance of the diffusion coefficients were found to follow Arrhenius relation.

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Valencia, Drochss P., and Felipe J. González. "Estimation of diffusion coefficients by using a linear correlation between the diffusion coefficient and molecular weight." Journal of Electroanalytical Chemistry 681 (August 2012): 121–26. http://dx.doi.org/10.1016/j.jelechem.2012.06.013.

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Martelli, Fausto, Sacha Abadie, Jean-Pierre Simonin, Rodolphe Vuilleumier, and Riccardo Spezia. "Lanthanoids(III) and actinoids(III) in water: Diffusion coefficients and hydration enthalpies from polarizable molecular dynamics simulations." Pure and Applied Chemistry 85, no. 1 (July 1, 2012): 237–46. http://dx.doi.org/10.1351/pac-con-12-02-08.

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By using polarizable molecular dynamics (MD) simulations of lanthanoid(III) and actinoid(III) ions in water, we obtained ionic diffusion coefficients and hydration enthalpies for both series. These values are in good agreement with experiments. Simulations thus allow us to relate them to microscopic structure. In particular, across the series the diffusion coefficients decrease, reflecting the increase of ion–water interaction. Hydration enthalpies also show that interactions increase from light to heavy ions in agreement with experiment. The apparent contradictory result of the decrease of the diffusion coefficient with decreasing ionic radius is tentatively explained in terms of dielectric friction predominance on Stokes’ diffusive regime.

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Li, Yuhui, Camille Bishop, Kai Cui, J. R. Schmidt, M. D. Ediger, and Lian Yu. "Surface diffusion of a glassy discotic organic semiconductor and the surface mobility gradient of molecular glasses." Journal of Chemical Physics 156, no. 9 (March 7, 2022): 094710. http://dx.doi.org/10.1063/5.0079890.

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Surface diffusion has been measured in the glass of an organic semiconductor, MTDATA, using the method of surface grating decay. The decay rate was measured as a function of temperature and grating wavelength, and the results indicate that the decay mechanism is viscous flow at high temperatures and surface diffusion at low temperatures. Surface diffusion in MTDATA is enhanced by 4 orders of magnitude relative to bulk diffusion when compared at the glass transition temperature Tg. The result on MTDATA has been analyzed along with the results on other molecular glasses without extensive hydrogen bonds. In total, these systems cover a wide range of molecular geometries from rod-like to quasi-spherical to discotic and their surface diffusion coefficients vary by 9 orders of magnitude. We find that the variation is well explained by the existence of a steep surface mobility gradient and the anchoring of surface molecules at different depths. Quantitative analysis of these results supports a recently proposed double-exponential form for the mobility gradient: log D( T, z) = log Dv( T) + [log D0 − log Dv( T)]exp(− z/ξ), where D( T, z) is the depth-dependent diffusion coefficient, Dv( T) is the bulk diffusion coefficient, D0 ≈ 10−8 m2/s, and ξ ≈ 1.5 nm. Assuming representative bulk diffusion coefficients for these fragile glass formers, the model reproduces the presently known surface diffusion rates within 0.6 decade. Our result provides a general way to predict the surface diffusion rates in molecular glasses.

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Neumann, Gerhard, and C. Tuijn. "Diffusion Mechanisms: The Vacancy Diffusion Coefficient." Solid State Phenomena 88 (November 2002): 19–20. http://dx.doi.org/10.4028/www.scientific.net/ssp.88.19.

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LIAO, RUIJIN, MENGZHAO ZHU, XIN ZHOU, FUZHOU ZHANG, JIAMING YAN, WENBIN ZHU, and CHAO GU. "MOLECULAR DYNAMICS STUDY OF THE DISRUPTION OF H-BONDS BY WATER MOLECULES AND ITS DIFFUSION BEHAVIOR IN AMORPHOUS CELLULOSE." Modern Physics Letters B 26, no. 14 (May 14, 2012): 1250088. http://dx.doi.org/10.1142/s0217984912500881.

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Hydrolysis is an important component of the aging of cellulose, and it severely affects the insulating performance of cellulosic materials. The diffusion behavior of water molecules in amorphous cellulose and their destructive effect on the hydrogen bonding structure of cellulose were investigated by molecular dynamics. The change in the hydrogen bonding structure indicates that water molecules have a considerable effect on the hydrogen bonding structure within cellulose: both intermolecular and intramolecular hydrogen bonds decreased with an increase in ingressive water molecules. Moreover, the stabilities of the cellulose molecules were disrupted when the number of intermolecular hydrogen bonds declined to a certain degree. Both the free volumes of amorphous cells and water molecule-cellulose interaction affect the diffusion of water molecules. The latter, especially the hydrogen bonding interaction between water molecules and cellulose, plays a predominant role in the diffusion behavior of water molecules in the models of which the free volume rarely varies. The diffusion coefficient of water molecules has an excellent correlation with water molecule-cellulose interaction and the average hydrogen bonds between each water molecule and cellulose; however, this relationship was not apparent between the diffusion coefficient and free volume.

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Ye, Wenyu, Jian Hao, Yufeng Chen, Mengzhao Zhu, Zhen Pan, and Fei Hou. "Difference Analysis of Gas Molecules Diffusion Behavior in Natural Ester and Mineral Oil Based on Molecular Dynamic Simulation." Molecules 24, no. 24 (December 5, 2019): 4463. http://dx.doi.org/10.3390/molecules24244463.

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Natural ester, as a new environmentally green insulating oil, has been widely used in transformer. In an oil-immersed transformer, the normal aging, thermal failure, and discharge failure could easily lead to the decomposition of the oil-paper insulation system and produce different kinds of gases. Studying gas dissolution in natural ester and mineral oil could provide assistance in applying criteria to make a diagnosis of different kinds of faults in the transformer. In this paper, the molecular dynamics method was used to investigate the diffusion behavior of seven fault characteristic gases (including H2, CO, CH4, C2H2, CO2, C2H4, C2H6) in natural ester and mineral oil. The simulation parameters of free volume, interaction energy, mean square displacement, and diffusion coefficient were compared between the natural ester and mineral oil. Meanwhile, the influence of temperature on the diffusion of gas molecules in two kinds of oils was also analyzed. Results showed that the free volume, the interaction energy, and the relative molecular mass of gas molecules were the factors influenced by the diffusion of gas molecules in natural ester and mineral oil. The order of the diffusion coefficients of gas molecules in natural ester was as follows: H2 > CH4 > CO > C2H2 > C2H4 > CO2 > C2H6 and that in mineral oil was as follows: H2 > CH4 > CO> C2H2 > C2 H4 > C2H6 > CO2. By comparing the diffusion behavior of gas molecules in natural ester and mineral oil, it was found that the smaller free volume and higher interaction energy of gas molecules in natural ester were the major reasons for the gas molecules to be more difficult to diffuse in natural ester. The rising temperature could enhance the free volume and reduce the interaction energy between gas molecules and oil. The diffusion coefficient of gas molecules increased exponentially with the follow of temperature. However, the temperature didn’t affect the ordering of diffusion coefficient, free volume, and interaction energy of gas molecules in natural ester and mineral oil.

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Pogorelova, E. S., E. G. Kulapina, and N. M. Makarova. "Features of Alkylpyridinium Homologues Diffusion through PVC Molecular Sieves." Izvestiya of Saratov University. Chemistry. Biology. Ecology 12, no. 4 (2012): 28–34. http://dx.doi.org/10.18500/1816-9775-2012-12-4-28-34.

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The process of alkylpyridinium homologous transfer through polyvinylchloride plasticized nanofiltration membranes (molecular sieves) under self-diffusion and direct current conditions. Quantitative characteristics of membrane transport: the coefficients of permeability, diffusion, the distribution coefficient, ion flux, were calculated. The dependences of the volume properties of nanofiltration membranes from the hydrocarbon radical length in the alkylpyridinium homologous in membrane solutions and pore formers were shown.

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Kharlamov, G. V. "Simulating diffusion in the conditions of vapor-liquid phase transition by the molecular dynamics method." Journal of Physics: Conference Series 2057, no. 1 (October 1, 2021): 012114. http://dx.doi.org/10.1088/1742-6596/2057/1/012114.

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Abstract The molecular dynamics calculations of diffusion coefficients in binary Lennard-Jones systems have been carried out. The parameters of Lennard-Jones potentials correspond to argon and krypton atoms. The universal dependence of the reduced diffusion coefficient of krypton atoms on density for the homogeneous systems of low and middle densities is found. The deviations of the diffusion coefficients from the universal function are observed for the systems in the vapor – liquid phase transition region. The simulations have shown that almost all krypton atoms have situated inside the liquid phase of argon. Special numerical experiments have shown that the nanodroplets of argon are formed as a result of homogeneous nucleation and then the krypton atoms are captured by these droplets. This phenomenon decreases the diffusion coefficient of krypton atoms greatly.

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29

Pokharel, Sunil, Nurapati Pantha, and N. P. Adhikari. "Diffusion coefficients of nitric oxide in water: A molecular dynamics study." International Journal of Modern Physics B 30, no. 27 (October 17, 2016): 1650205. http://dx.doi.org/10.1142/s0217979216502052.

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Self-diffusion coefficients along with the mutual diffusion coefficients of nitric oxide (NO) and SPC/E water (H2O) as solute and solvent of the mixture, have been studied within the framework of classical molecular dynamics level of calculations using GROMACS package. The radial distribution function (RDF) of the constituent compounds are calculated to study solute–solute, solute–solvent and solvent–solvent molecular interactions as a function of temperature. A dilute solution of five NO molecules (mole fraction 0.018) and 280 H2O molecules (mole fraction 0.982) has been taken as the sample. The self-diffusion coefficient of the solvent is calculated by using mean square displacement (MSD) where as that for solute (NO) is calculated by using MSD and velocity auto-correlation function (VACF). The results are then compared with the available experimental values. The results from the present work for water come in good agreement, very precise at low temperatures, with the experimental values. The diffusion coefficients of NO, on the other hands, agree well with the available theoretical studies, and also with experiment at low temperatures (up to 310 K). The results at the higher temperatures (up to 333 K), however, deviate significantly with the experimental observations. Also, the mutual diffusion coefficients of NO in water have been calculated by using Darken’s relation. The temperature dependence of the calculated diffusion coefficients follow the Arrhenius behavior.

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30

Challa, Sudarsana R., Shi-Qing Wang, and Jack L. Koenig. "In situ Diffusion Studies Using Spatially Resolved Infrared Microspectroscopy." Applied Spectroscopy 50, no. 11 (November 1996): 1339–44. http://dx.doi.org/10.1366/0003702963904764.

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Spatially resolved infrared microspectroscopy is used in conjunction with the contact method to conduct in situ diffusion experiments of photocured polymer-dispersed liquid crystals (LCs). The system analyzed consists of a low-molecular-weight liquid crystal (E7) diffusing into a photopolymerizable monomer (NOA65). The measured concentration profiles were generated by monitoring the hydroxyl band of the monomer as a function of time and spatial position. The diffusion coefficients were calculated from least-squares fitting of the data. The system followed Fick's second law of diffusion. The diffusion coefficient for this system is (1.97 ± 0.2)(10−8) cm2/s. The morphology of the system after polymerization exhibited three distinct regions: nematic LC molecularly mixed in the cross-linked network of the polymer, nematic LC droplet gradient in the polymer matrix, and polymer fibers scattered in the continuous nematic LC.

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31

Malomuzh, M. P. "Nature of Self-Diffusion in Fluids." Ukrainian Journal of Physics 63, no. 12 (December 9, 2018): 1076. http://dx.doi.org/10.15407/ujpe63.12.1076.

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The nature of the self-diffusion in low-molecular fluids is discussed. The particular attention is paid to atomic fluids (such as argon), liquid metals, and associated fluids (such as water). The self-diffusion coefficient in the fluids of all indicated types is considered to be the sum of two components: one of them is associated with the transfer of molecules by hydrodynamic vortex modes, and the other is generated by the circulatory motion of local molecular groups. The both components have a collective nature, they are genetically related to each other and differ only by their scales: the former is mesoscopic, the latter is nanoscopic. Manifestations of the collective vortical transport of molecules as specific features in the time dependence of the root-mean-square displacement of molecules are discussed. Sound arguments are proposed concerning the inadequacy of the activation mechanism of thermal molecular motion in low-molecular liquids. The immanent contradiction of exponential temperature dependences for the viscosity and self-diffusion coefficients is proved. In all cases, the preference is given to qualitative arguments.

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32

Zhang, Guoling, Guogang Yang, Shian Li, Qiuwan Shen, Hao Wang, Zheng Li, Yang Zhou, and Weiqiang Ye. "Effects of Hydration and Temperature on the Microstructure and Transport Properties of Nafion Polyelectrolyte Membrane: A Molecular Dynamics Simulation." Membranes 11, no. 9 (September 8, 2021): 695. http://dx.doi.org/10.3390/membranes11090695.

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To investigate the effects of temperature and hydration on the microstructure of polymer electrolyte membrane and the transport of water molecules and hydronium ions, molecular dynamics simulations are performed on Nafion 117 for a series of water contents at different temperatures. The interactions among the sulfonate groups, hydronium ions, and water molecules are studied according to the analysis of radial distribution functions and coordination numbers. The sizes and connectivity of water clusters are also discussed, and it is found that the hydration level plays a key role in the phase separation of the membrane. However, the effect of the temperature is slight. When the water content increases from 3.5 to 16, the size of water clusters in the membrane increases, and the clusters connect to each other to form continuous channels for diffusion of water molecules and hydronium ions. The diffusion coefficients are estimated by studying the mean square displacements. The results show that the diffusion of water molecules and hydronium ions are both enhanced by the increase of the temperature and hydration level. Furthermore, the diffusion coefficient of water molecules is always much larger than that of hydronium ions. However, the ratio of the diffusion coefficient of water molecules to that of hydronium ions decreases with the increase of water content.

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33

Ye, Anping, Xiaoying Shen, Ping Guo, Shaoping Wang, and Zhongzhao Cheng. "Research on Molecular Diffusion Coefficient of Gas-Oil System." Open Journal of Yangtze Oil and Gas 01, no. 01 (2016): 23. http://dx.doi.org/10.4236/ojogas.2016.11002.

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HONDA, Kota, Akiko KANEKO, and Yutaka ABE. "Molecular dynamics study onmolecular diffusion coefficient in CO2 hydrate." Proceedings of Conference of Kanto Branch 2020 (March 13, 2020): 17G09. http://dx.doi.org/10.1299/jsmekanto.2020.17g09.

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Konev, D. V., T. A. Kravchenko, A. I. Kalinichev, M. Yu Chaika, and V. A. Krysanov. "The Diffusion Coefficient of Molecular Oxygen in Macroporous Sulfocationite." Russian Journal of Physical Chemistry 82, no. 3 (March 2008): 452–58. http://dx.doi.org/10.1134/s0036024408030230.

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36

Green, Peter F., and Edward J. Kramer. "Temperature dependence of tracer diffusion coefficients in polystyrene." Journal of Materials Research 1, no. 1 (February 1986): 202–4. http://dx.doi.org/10.1557/jmr.1986.0202.

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The temperature dependence of the tracer diffusion coefficient D* of long deuterated polystyrene (d-PS) chains of molecular weight M>Mc, where Mc is the critical molecular weight for entanglement, diffusing into highly entangled PS matrices, each of molecular weight P = 2×107, is studied using forward recoil spectrometry. It is found that the temperature dependence of D*/T, reflected primarily in the monomeric friction coefficient, is accurately described by a Vogel equation. The constants that are used to fit these results are independent of M and are the same as those used to fit the temperature dependence of the zero shear rate viscosity of polystyrene.

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37

Zhai, Yanqin, Peng Luo, Jackson Waller, Jeffrey L. Self, Leland W. Harriger, Y. Z, and Antonio Faraone. "Dynamics of molecular associates in methanol/water mixtures." Physical Chemistry Chemical Physics 24, no. 4 (2022): 2287–99. http://dx.doi.org/10.1039/d1cp04726d.

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The nanoscopic mutual diffusion coefficient, DMn, of a methanol/water mixture is smaller than the single particle diffusion coefficient of either methanol or water, indicating the existence of dynamic associates of water and methanol molecules.

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38

Fourteau, Kévin, Florent Domine, and Pascal Hagenmuller. "Macroscopic water vapor diffusion is not enhanced in snow." Cryosphere 15, no. 1 (January 28, 2021): 389–406. http://dx.doi.org/10.5194/tc-15-389-2021.

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Abstract. Water vapor transport in dry snowpacks plays a significant role for snow metamorphism and the mass and energy balance of snowpacks. The molecular diffusion of water vapor in the interstitial pores is usually considered to be the main or only transport mechanism, and current detailed snow physics models therefore rely on the knowledge of the effective diffusion coefficient of water vapor in snow. Numerous previous studies have concluded that water vapor diffusion in snow is enhanced relative to that in air. Various field observations also indicate that for vapor transport in snow to be explained by diffusion alone, the effective diffusion coefficient should be larger than that in air. Here we show using theory and numerical simulations of idealized and measured snow microstructures that, although sublimation and deposition of water vapor onto snow crystal surfaces do enhance microscopic diffusion in the pore space, this effect is more than countered by the restriction of diffusion space due to ice. The interaction of water vapor with the ice results in water vapor diffusing more than inert molecules in snow but still less than in free air, regardless of the value of the sticking coefficient of water molecules on ice. Our results imply that processes other than diffusion play a predominant role in water vapor transport in dry snowpacks.

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Semenov, Ivan. "EXPERIMENTAL ESTIMATION OF THE DIFFUSION COEFFICIENT IN LIQUID SOLUTIONS." Modern Technologies and Scientific and Technological Progress 2022, no. 1 (May 16, 2022): 51–52. http://dx.doi.org/10.36629/2686-9896-2022-1-51-52.

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The paper describes a method for experimental evaluation of molecular diffusion in aqueous solutions. The method is based on solving the equation of non-stationary molecular diffusion in dimensionless form

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40

Torres, Juan F., Atsuki Komiya, Junnosuke Okajima, and Shigenao Maruyama. "Measurement of the Molecular Mass Dependence of the Mass Diffusion Coefficient in Protein Aqueous Solutions." Defect and Diffusion Forum 326-328 (April 2012): 452–58. http://dx.doi.org/10.4028/www.scientific.net/ddf.326-328.452.

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This paper reports the measurement of the binary mass diffusion coefficient for proteins with a wide range of molecular size. The diffusion coefficient is obtained by conducting diffusion experiments in the dilute region. Transient concentration profiles were measured by a phase shifting interferometer and subsequently compared with a numerical calculation based on Ficks law to determine the diffusion coefficient. Distilled water was used as solvent in free diffusion experiments conducted at T = (25 ± 1.0)°C. The method was validated by measuring the diffusion coefficient of aqueous NaCl, Sucrose, and BSA, which values have been extensively reported in the literature. The values of the diffusion coefficient for seven proteins: aprotinin (6.5 kDa), α-lactalbumin (14.2 kDa), lysozyme (14.3 kDa), trypsin inhibitor (20.1 kDa), ovalbumin (44.2 kDa), bovine serum albumin (66.7 kDa), and phosphorylase b (97.2 kDa), were determined in the dilute region of 0-3 mg/ml. The results are compared with the Stokes-Einstein equation. The influence of the molecular structure and pH on the diffusion coefficient is discussed.

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Rudyak, Valery, and A. A. Belkin. "Nonclassical Properties of Molecular Diffusion in Liquids and Dense Gases." Defect and Diffusion Forum 273-276 (February 2008): 560–65. http://dx.doi.org/10.4028/www.scientific.net/ddf.273-276.560.

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The diffusion of molecules in liquids and dense gases is demonstrated to be nonclassical for long time intervals. This means that the time dependence of the mean-square displacement of molecules is nonlinear. This result was obtained by molecular dynamics simulations over a wide range of density of the medium. The problem of plateau values of the diffusion coefficient is discussed. Nonclassical diffusion equations are derived and discussed.

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42

Valencia, Drochss P., and Felipe J. González. "Understanding the linear correlation between diffusion coefficient and molecular weight. A model to estimate diffusion coefficients in acetonitrile solutions." Electrochemistry Communications 13, no. 2 (February 2011): 129–32. http://dx.doi.org/10.1016/j.elecom.2010.11.032.

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43

Zhang, Le, and A. Z. Szeri. "Transport of neutral solute in articular cartilage: effects of loading and particle size." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 461, no. 2059 (June 2005): 2021–42. http://dx.doi.org/10.1098/rspa.2005.1461.

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We investigate the influence that matrix structure, size of diffusing molecules and type and intensity of mechanical loading have on the transport of neutral solutes in articular cartilage. Although this type of investigation has been performed in the past, earlier researchers assumed a constant diffusion coefficient. By contrast, our diffusion coefficient depends on the local deformation of the matrix, and thus varies both in space and in time during an experiment. We derive a three-dimensional formulation of the problem based on mixture theory and utilize the commercial finite-element code ABAQUS to study it numerically. We also make use of the Cohen–Turnbull–Yasuda model to correlate the decrease of the diffusion coefficient with the increase in tortuosity, owing to the presence of the matrix. Under appropriate circumstances, the equations derived here reduce to the classical convection/diffusion equation and the equations of the biphasic cartilage model. Even though we chose axisymmetric sample geometry for the present calculations, the model can easily be applied to irregular three-dimensional samples. Our results reinforce and refine previously published studies. The neutral solute's rate of diffusion is reduced under static compression, due to the strain dependence of the diffusion coefficient; an increase in static compression leads to a decrease in the rate of transport of solutes of all sizes. Dynamic loading, on the other hand, augments solute transport due to convection, depending on particle size. The transport of small molecular size solute is moderately enhanced, but only within the surface layer; however, the rate of transport of large molecule solute is greatly increased, even in the deep layer of the cartilage.

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44

Cao, Qingyu, Yidong Xu, Jianke Fang, Yufeng Song, Yao Wang, and Weiguo You. "Influence of Pore Size and Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores: A Molecular Dynamics Simulation." Materials 13, no. 3 (February 4, 2020): 700. http://dx.doi.org/10.3390/ma13030700.

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The transport properties of chloride ions in cement-based materials are one of the major deterioration mechanisms for reinforced concrete (RC) structures. This paper investigates the influence of pore size and fatigue loading on the transport properties of NaCl in C-S-H nanopores using molecular dynamics (MD) simulations. Molecular models of C-S-H, NaCl solution, and C-S-H nanopores with different pore diameters are established on a microscopic scale. The distribution of the chloride ion diffusion rate and the diffusion coefficient of each particle are obtained by statistically calculating the variation of atomic displacement with time. The results indicate that the chloride ion diffusion rate perpendicular to C-S-H nanopores under fatigue loading is 4 times faster than that without fatigue loading. Moreover, the diffusion coefficient of water molecules and chloride ions in C-S-H nanopores increases under fatigue loading compared with those without fatigue loading. The diffusion coefficient of water molecules in C-S-H nanopores with a pore size of 3 nm obtained from the MD simulation is 1.794 × 10−9 m2/s, which is slightly lower than that obtained from the experiment.

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45

Liu, Zi Yuan, Sheng Li Chen, Peng Dong, and Xiu Jun Ge. "Diffusion of Heavy Oil in SiO₂ Model Catalyst and FCC Catalyst." Advanced Materials Research 550-553 (July 2012): 158–63. http://dx.doi.org/10.4028/www.scientific.net/amr.550-553.158.

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Through the measured effective diffusion coefficients of Dagang vacuum residue supercritical fluid extraction and fractionation (SFEF) fractions in FCC catalysts and SiO2model catalysts, the relation between pore size of catalyst and effective diffusion coefficient was researched and the restricted diffusion factor was calculated. The restricted diffusion factor in FCC catalysts is less than 1 and it is 1~2 times larger in catalyst with polystyrene (PS) template than in conventional FCC catalyst without template, indicating that the diffusion of SFEF fractions in the two FCC catalysts is restricted by the pore. When the average molecular diameter is less than 1.8 nm, the diffusion of SFEF fractions in SiO2model catalyst which average pore diameter larger than 5.6 nm is unrestricted. The diffusion is restricted in the catalyst pores of less than 8 nm for SFEF fractions which diameter more than 1.8 nm. The tortuosity factor of SiO2model catalyst is obtained to be 2.87, within the range of empirical value. The effective diffusion coefficient of the SFEF fractions in SiO2model catalyst is two orders of magnitude larger than that in FCC catalyst with the same average pore diameter. This indicate that besides the ratio of molecular diameter to the pore diameter λ, the effective diffusion coefficient is also closely related to the pore structure of catalyst. Because SiO2model catalyst has uniform pore size, the diffusion coefficient can be precisely correlated with pore size of catalyst, so it is a good model material for catalyst internal diffusion investigation.

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Terentjev, E. M., and M. A. Osipov. "Viscosity Coefficients of a Nematic Mixture: Statistical Theory Approach." Zeitschrift für Naturforschung A 46, no. 9 (September 1, 1991): 733–38. http://dx.doi.org/10.1515/zna-1991-0901.

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AbstractA statistical theory of the rotational diffusion of a molecule in a two-component anisotropic mixture is developed, based on the Fokker-Planck approximation for the one-particle orientational distribution function. The friction constant of the molecular rotation is determined from the threeparticle correlation function, which takes into account interactions A-A, A-B, B-A and B-B between two sorts of molecules. The Leslie coefficients obtained possess a complicated dependence on mixture concentration together with a dependence on temperature and the molecular parameters of the components. In particular, the rotational viscosity coefficient γj is proportional to a polynomial of third-order in concentrations cA and cB with coefficients proportional to exp{JAca + JBcB} √(JACA + JB bcB )

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47

Wang, Junmei, and Tingjun Hou. "Application of molecular dynamics simulations in molecular property prediction II: Diffusion coefficient." Journal of Computational Chemistry 32, no. 16 (September 22, 2011): 3505–19. http://dx.doi.org/10.1002/jcc.21939.

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48

Lang, I., M. Scholz, and R. Peters. "Molecular mobility and nucleocytoplasmic flux in hepatoma cells." Journal of Cell Biology 102, no. 4 (April 1, 1986): 1183–90. http://dx.doi.org/10.1083/jcb.102.4.1183.

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Fluorescence microphotolysis (photobleaching) was used to measure, in single polyethylene glycol-induced polykaryons of hepatoma tissue culture cells, nucleocytoplasmic flux and intracellular mobility for a series of dextrans ranging in molecular mass from 3 to 150 kD and for bovine serum albumin. For the dextrans, the cytoplasmic and the nucleoplasmic translational diffusion coefficients amounted to approximately 9 and approximately 15%, respectively, of the value in dilute buffer. The diffusion coefficients depended inversely on molecular radius, suggesting that diffusion was dominated by viscosity effects. By application of the Stokes-Einstein equation, cytoplasmic and nucleoplasmic viscosities were derived to be 6.6 and 8.1 cP, respectively, at 23 degrees C. Between 10 and 37 degrees C nucleoplasmic diffusion coefficients increased by approximately 45-85%, whereas cytoplasmic diffusion coefficients were virtually independent of temperature. In contrast to that of the dextrans, diffusion of bovine serum albumin was more restricted. In the cytoplasm the diffusion coefficient was approximately 1.5% of the value in dilute buffer; in the nucleus albumin was largely immobile. This indicated that albumin mobility is dominated by association with immobile cellular structures. Nucleocytoplasmic flux of dextrans depended inversely on molecular mass with an exclusion limit between 17 and 41 kD. This agrees with previous measurements on primary hepatocytes (Peters, R., 1984, EMBO [Eur. Mol. Biol. Organ.] J. 3:1831-1836), suggesting that in both cell types the nuclear envelope has properties of a molecular sieve with a functional pore radius of approximately 55 A.

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Sala, Filip A., Marzena M. Sala-Tefelska, and Maksymilian J. Bujok. "Influence of temperature diffusion on molecular reorientation in nematic liquid crystals." Journal of Nonlinear Optical Physics & Materials 27, no. 01 (March 2018): 1850011. http://dx.doi.org/10.1142/s021886351850011x.

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In this paper, the theoretical analyses of optically induced molecular reorientation are presented in a nematic liquid crystal cell. Due to the absorption of the light beam, the temperature of the cell increases, which induces change of anisotropy and the Frank elastic coefficients. In our analyses, a simple model is used. It is based on the Frank–Oseen elastic theory to describe molecular reorientation and on a heat diffusion equation to model thermal effects. Molecular reorientation, its width and maximum value, and extraordinary refractive index are analyzed versus various values of absorption coefficient, rate of change of elastic coefficient, and thermal conductance. It appears that thermal effects do not influence the width of the molecular reorientation. The nonlocality is nearly unaffected by the increase of temperature. However, the maximum molecular reorientation might increase with temperature, in most cases, the extraordinary refractive index decreases with temperature. Only for unlikely high rates of change of elastic coefficients, the refractive index increases with temperature. Moreover, the transition between liquid crystal and isotropic phases is also discussed. The range of input beam width for which the material lasts in a liquid crystal state is also presented. Simulations are performed for parameters corresponding to two liquid crystals: low birefringent 1550 and 6CHBT of a medium birefringence.

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Nikonova, V., and V. Obukhovsky. "Finding and analysis of the partial mutual diffusion coefficients for binary solutions with chloroform using the complex-associative model." Bulletin of Taras Shevchenko National University of Kyiv. Series: Physics and Mathematics, no. 1-2 (2020): 97–100. http://dx.doi.org/10.17721/1812-5409.2020/1-2.16.

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In the article within the complex-associative model of liquid systems the nonlinear diffusion for a number of binary solutions, such as acetone-chloroform, tetrachlorethane-chloroform, diethyl ether-chloroform and benzene-chloroform, is considered: Real binary solutions are replaced by ideal three-component ones, which consist of averaged two associates of substance and solvent and an effective averaged complex, which is the result of quasi-chemical reactions of molecular solutions. The coefficient of mutual diffusion, which nonmonotonically depends on the concentration of the solvent, is represented as a matrix of partial coefficients of mutual diffusion, which are constant values and represent the material parameters of the considered solutions. The method of analytical calculation of numerical values of such quantities when considering the simplest type of one averaged complex is developed. It is shown that the partial coefficients are constant values and the analysis of their values for the considered solutions depending on the structure of the molecules of the substance, enthalpy and temperature is carried out. Based on the proposed approach, the deviation of the calculated «Fick’s» coefficient of mutual diffusion through the matrix of partial coefficients in comparison with experimental data is less than 2.5%.

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Journal articles on the topic 'Molecular diffusion coefficient'

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