Diffusion Of Organic Molecules Research Articles

Effect of Confinement on the Density and Diffusivity of Organic Molecules in Single-Digit Nanopores Relative to Bulk Fluid Behavior

Effect of Confinement on the Density and Diffusivity of Organic Molecules in Single-Digit Nanopores Relative to Bulk Fluid Behavior

Insight of organic molecule dissolution and diffusion in cross-linked polydimethylsiloxane using molecular simulation

Polymeric membranes have gained an immense importance for the pervaporation (PV) of biofuels. The PV performance is influenced by several complex elements and significant understanding is empirically fairly difficult. Furthermore, it is essential to specify membrane swelling in different solvents prior to the PV. A molecular dynamics simulation protocol was applied to examine the swelling of cross-linked PDMS membranes in 1-butanol, ethanol, acetone, and water, the dissolution of organic molecule in dilute aqueous solution in PDMS, the PV through these swollen membranes and dissolution rate of guest molecules in membranes. The agglomeration effects of water as well as organic molecules inside cross-linked PDMS membrane during sorption and diffusion processes were also investigated. The effects of predicted cross-linked PDMS on separation performance of membranes, interactions of the guest molecules on the swelling degree and diffusion coefficients follow the experimental trend. The predicted dissolution and diffusion, the diffusion selectivity and mean square displacement of different agglomerated forms of water and alcohol molecules through cross-linked membrane fairly matches the reported experimental results. Moreover, their reliability on the interaction between solvent and polymer, void size distribution and temperature were investigated. The micro level insights into the swelling of cross-linked polymer membranes, dissolution and diffusion of organic molecules and understanding of mass transfer were provided by simulation, which are valuable for making new membranes for high PV performance.

Diffusion of Organic Molecules as a Function of Temperature in a Sucrose Matrix (a Proxy for Secondary Organic Aerosol).

Knowledge of diffusion coefficients as a function of temperature in secondary organic aerosol (SOA) or proxies of SOA is needed to predict atmospheric chemistry, climate, and air quality. We determined diffusion coefficients as a function of temperature of a fluorescent organic molecule in a sucrose matrix (a proxy for SOA). Diffusion coefficients were a strong function of temperature (e.g., at water activity = 0.43, diffusion coefficients decreased by a factor of ∼40 as the temperature decreased by 20 K). Interestingly, the apparent activation energy for diffusion of the fluorescent organic molecule was similar to the apparent activation for diffusion of water in the sucrose matrix. On the basis of these measurements, the mixing time of organic molecules by diffusion in some types of SOA particles will often be >1 h in the free troposphere, if a sucrose matrix is an accurate proxy for these types of SOA.

Template‐free Fabrication of ZnS/TiO2 Photocatalyst with Macrochannels

Constructing a porous structure in photocatalysts is an effective strategy for improving the photocatalytic activity because of its enhanced molecule transfer capability and light capturing efficiency. In this work, a hierarchical macro‐/mesoporous ZnS/TiO2 composite with macrochannels was successfully synthesized without using templates by the simple dropwise addition of an ethanol solution of tetrabutyl titanate and zinc acetate into a sodium sulfide aqueous solution, which was then calcined at 450°C. Compared with pure TiO2, the ordered porous ZnS/TiO2 composite exhibited an enhanced photocatalytic activity on methylene blue removal under UV‐light irradiation. The results indicate that the macro‐/mesoporous structure, the large specific surface area, and the heterostructure combination between ZnS and TiO2 play a synergistic effect on the enhanced photocatalytic activity via improving the light absorption and the diffusion of organic molecules, providing more reactive sites for the photocatalytic reaction and improving the separation of photogenerated electron–hole pairs, respectively. Radical trapping experiments demonstrated that holes (h+) and superoxide anion radicals (O2−) play an important role in the photocatalytic oxidation process.

Titan’s missing ethane: From the atmosphere to the subsurface

The second most abundant component of the present-day Titan atmosphere, methane (CH4), is known to undergo photolytic conversion to ethane (C2H6) that accumulates as a liquid on Titan’s surface. Condensation temperature of ethane is higher than that of methane, so that ethane “rain” may be expected to occur before the liquefaction of methane. At present, the partial pressure of ethane in the atmosphere is 1E−5bar, much lower than 1E−1bar of CH4. Estimated 8.46E17kg or 1.37E6km3 of C2H6 have been produced on Titan since accretion. The Titan surface reservoirs of ethane are lakes and craters, of estimated volume of 50,000km3 and 61,000km3, respectively. As these are smaller than the total volume of liquid ethane produced in the course of Titan’s history, the excess may be stored in the subsurface of the crust, made primarily of water ice. The minimum porosity of the crust needed to accommodate all the liquid ethane would be only 0.9% of the uppermost 2km of the crust. The occurrence of CH4 and liquid C2H6 on Titan has led to much speculation on the possibility of life on that satellite. The aggregation of organic molecules in a “primordial soup or bullion” depends in part on the viscosity of the medium, diffusivity of organic molecules in it, and rates of polymerization reactions. The temperatures on Titan, much lower than on primordial Earth, are less favorable to the “Second Coming of life” on Titan.

An all-atom force field developed for Zn4O(RCO2)6 metal organic frameworks

An all-atom force field is developed for metal organic frameworks Zn₄O(RCO₂)₆ by fitting to quantum mechanics data. Molecular simulations are conducted to validate the force field by calculating thermal expansion coefficients, crystal bulk and Young's moduli, power spectra, self-diffusion coefficients, and activation energies of self-diffusions for benzene and n-hexane. The calculated results are in good agreement with available experimental data. The proposed force field is suitable for simulations of adsorption or diffusion of organic molecules with flexible frameworks.

Macroporous Oxide Platforms Templated by Non‐Close‐Packed Spherical Copolymer Aggregates

Exclusive organic templating of macroporous oxide films is reported by using non-close and lose packing of spherical copolymer aggregates, in combination with facile control of condensation degree/density of inorganic oxide frameworks. Unique macroporous oxide films, mainly titania showing highly porous, crystalline, and versatile properties, can be fabricated with continuous design from unusual 3-D net-shape to tunable spherical macrostructures, which expands the preparation of other inorganic oxide films (silica, alumina, and zirconia) and possibly adapts the use of other assembled organic polymers. The macroporous structures are helpful for effective accommodation of bulky biomoleculeshigh and diffusivity of organic molecules (useful for photocatalysts). Unusual structural variation, expansion of spherical voids, is also observed, being useful for fine tuning of optical property.

Role of van der Waals forces in the adsorption and diffusion of organic molecules on an insulating surface

The adsorption and diffusion of 3,4,9,10-perylene-tetracarboxylic-dianhydride PTCDA molecules on a nanostructured KBr 001 surface were investigated by combining noncontact atomic force microscopy NCAFM and first-principles calculations. Atomically resolved measurements demonstrate trapping of PTCDA molecules in intentionally created rectangular monolayer-deep substrate pits and a preferential adsorption at kink sites. In order to understand the experimental results, we found that it was essential to include a firstprinciples treatment of the van der Waals interactions. We show that at some sites on the surface, 85% of the molecular binding is provided by van der Waals interactions, and in general it is always the dominant contribution to the adsorption energy. It also qualitatively changes molecular diffusion on the surface. Based on the specificity of the molecular interaction at kink sites, the species of the imaged ionic sublattice in the NC-AFM measurements could be identified.

Adsorption of 1-heptanol on bismuth single-crystal plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for the quantitative study of 1-heptanol (1-HepOH) adsorption on the bismuth single-crystal plane|aqueous Na2SO4 solution interface. The adsorption isotherms, Gibbs energies of adsorption, $$ \Delta G_{\rm A}^ {\circ} $$ , the limiting surface excess, Γmax, and other adsorption parameters have been determined. The adsorption of 1-HepOH on Bi single-crystal planes is mainly physical and is limited by the rate of diffusion of organic molecules to the electrode surface. Comparison of the adsorption data for 1-HepOH with other alcohols shows that the adsorption characteristics depend on the structure of the hydrocarbon chain. The adsorption activity of adsorbates at the bismuth|solution interface increases in the sequence 1-propanol<1-butanol<1-pentanol<1-hexanol<1-heptanol as the adsorption activity at the air|solution interface increases. For all the compounds studied, the adsorption activity increases in the sequence of planes as $$ (111) < (001) < (01\overline 1 ) $$ .

Organic secondary ion mass spectrometry: sensitivity enhancement by gold deposition.

Hydrocarbon oligomers, high-molecular-weight polymers, and polymer additives have been covered with 2-60 nmol of gold/cm2 in order to enhance the ionization efficiency for static secondary ion mass spectrometry (s-SIMS) measurements. Au-cationized molecules (up to -3,000 Da) and fragments (up to the trimer) are observed in the positive mass spectra of metallized polystyrene (PS) oligomer films. Beyond 3,000 Da, the entanglement of polymer chains prevents the ejection of intact molecules from a "thick" organic film. This mass limit can be overcome by embedding the polymer chains in a low-molecular-weight matix. The diffusion of organic molecules over the metal surfaces is also demonstrated for short PS oligomers. In the case of high-molecular-weight polymers (polyethylene, polypropylene, PS) and polymer additives (Irganox 1010, Irgafos 168), the metallization procedure induces a dramatic increase of the fingerprint fragment ion yields as well as the formation of new Aucationized species that can be used for chemical diagnostics. In comparison with the deposition of submonolayers of organic molecules on metallic surfaces, metal evaporation onto organic samples provides a comparable sensitivity enhancement. The distinct advantage of the metal evaporation procedure is that it can be used for any kind of organic sample, irrespective of thickness, opening new perspectives for "real world" sample analysis and chemical imaging by s-SIMS.

Diffusion of Organic Molecules in the Excited Triplet States Detected by the Transient Grating with a High Wavenumber

Diffusion constants of organic molecules in the excited triplet states are measured in solution by using the transient grating technique with a high wavenumber, which is about 1 order of magnitude larger than that commonly used so far. Using this high wavenumber grating system under two different experimental conditions, we can detect the diffusion process of molecules in the T1 states as long as the lifetime is longer than 300 ns. Contrary to the previously observed slow diffusion of many transient radicals, diffusion coefficients (D) of all molecules in the T1 states of this study (benzophenone, 4,4‘-dimethylbenzophenone, phenazine, anthracene, fluorenone, 2-nitrofluorenone, benzil, 1-nitronaphthalene, C60, and Michler's ketone) are close to those in the ground state but most of them (except C60) are slightly (≤5−10%) but certainly larger than D in the ground states. D of C60 in the T1 state is found to be the same as that in the ground state.

Microwave irradiation effect on diffusion of organic molecules in polymer

Microwave irradiation effects on diffusion of some small organic molecules in polyethylene, polyvinylchloride, and silicone rubber were investigated using general weight-gain method. To eliminate the development of hot spots and inhomogeneous temperature distribution that occur often during microwave heating, sorption/diffusion solutions were well mixed with a magnetic stirrer at atmospheric pressure. The deviations of the diffusion rates between microwave and conventional diffusions were shown to be below 2.1%. This result reveals that previously reported nonthermal effects of microwave to promote diffusion do not exist in the examined diffusant/polymer systems.

Adsorption of propanol on bismuth single-crystal-plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for the quantitative study of 1-pentanol (n-PenOH) adsorption at the bismuth single-crystal plane | aqueous Na2SO4 solution interface. The adsorption isotherms, Gibbs energies of adsorption ΔGA∘, the limiting surface excess Γmax and other adsorption parameters, dependent on the crystallographic structure of the electrodes, have been determined. The adsorption of n-PenOH on Bi single-crystal planes is mainly physical and is limited by the rate of diffusion of organic molecules to the electrode surface. Comparison of the adsorption data for n-PenOH with 1-propanol (n-PrOH), 1-butanol (n-BuOH), cyclohexanol (CH) and 1-hexanol (n-HexOH) shows that the adsorption characteristics depend on the structure of the hydrocarbon group. The adsorption activity of adsorbates at the bismuth | solution interface increases in the sequence n-PrOH < n-BuOH < CH ≤ n-PenOH < n-HA as the adsorption activity at the air | solution interface increases. For all the compounds studied, the adsorption activity increases in the sequence of planes (111)<(001)<(011¯).

Diffusion of organic molecules through epoxy/acrylic copolymer films

The diffusion coefficients of limonene, myrcene, linalool and pine oil through films of a comb copolymer with advanced bisphenol A-epichlorohydrin epoxy as the backbone and poly(styrene- co-acrylic acid) grafts were determined by means of inverse gas chromatography. In the case of pine oil, the six isomers present in the supplied product were characterised by distinct diffusion coefficients. Diffusion coefficients were found to increase in line with the molar volume of the organic molecule: limonene < pine oil < linalool < myrcene.

Dynamics of articular joints visualised by MRI: Joint flexion, cartilage-compression and solute-perfusion

Since articular cartilage is avascular, the continued viability of the chondrocytes, and hence of the cartilage structure, depends on the mass transport of nutrients from the synovial fluid into the cartilage and of proteoglycan from the chondrocytes. Although those processes have been studied for isolated specimens (Maroudas 1970, Urban 1992, Burstein et al. 1993), in an intact joint the effects of joint flexion and extension, and of the associated waves of cartilage compression, can be expected to enhance what would otherwise be a passive, diffusive process. In anticipation of making such studies we demonstrate here in-vivo the visualisation by Magnetic Resonance Imaging (MRI) of joint flexion/extension and of cartilage compression, and ex-vivo the perfusive diffusion of organic molecules through an intact articular joint.

ChemInform Abstract: Computer Simulations in Zeolite Chemistry

Recent developments in molecular modelling techniques have provided us with a new and powerful tool for the simulation and better understanding of the complex chemistry of zeolites. The range of applications include cation distributions, acid strengths of catalytic sites, intergrowth phenomena, derivation of new structures, molecular adsorption and selective diffusion of organic molecules through zeolite frameworks. A perspective summary of a number of simulation methods and their specific areas of applicability is given in this article.

Diffusion of organic molecules through wood

AbstractThe diffusion of alcohols, glycerol, phenol, formic, acetic and butyric acids through four species of Indian timbers in the water‐saturated condition has been studied and the results reported. In contrast to several inorganic ions, Fick's law is obeyed by the organic molecules in the concentrations studied. As is to be expected, the diffusion in the axial direction is several times that in the other directions. The speed of diffusion decreases rapidly with the molecular weight of the substance and the density of the wood. While in the case of the alcohols the logarithm of the diffusion constant varies as the molecular weight with the acids the diffusion constant is proportional to the molecular weight.

Loci of Emulsion Polymerization: The Diffusion of Organic Molecules from Emulsion Droplets through an Aqueous Phase into Soap Micelles

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Loci of Emulsion Polymerization: Diffusion of Organic Molecules from Emulsion Droplets through an Aqueous Phase into Polymer Latex Particles

Loci of Emulsion Polymerization: Diffusion of Organic Molecules from Emulsion Droplets through an Aqueous Phase into Polymer Latex Particles