Kinetics Of Condensation Research Articles

Biomimetic Silicification of Fibrous Chitin from Diatoms

Poly-N-acetyl-d-glucosamine (p-GlcNAc, chitin) is a biopolymer found in various organisms and in forms such as sheets, membranes, and fibers. Its presence in numerous calcium-based biominerals is well-known. Recently, chitin was even found in silica-based biominerals. While it is well-established that various proteins and even long-chain polyamines are involved in silica biomineralization events, the role of polysaccharides is rather poorly understood. Furthermore, silica-chitin nanocomposites and silica-coated chitin constructs are increasingly important, e.g., in materials science and for biomedical applications. Therefore, we have investigated the interaction between p-GlcNAc in fibers and silicic acid/silica species in vitro, using 13C and 29Si NMR as well as Raman spectroscopy, in combination with microscopic techniques. Furthermore, the kinetics of silica condensation in the presence/absence of p-GlcNAc fibers could be analyzed using the molybdenum blue test.

Energy relaxation in one-dimensional polariton condensates

We study the kinetics of polariton condensation accounting for the condensation process as well as the energy relaxation of condensed polaritons due to their scattering with phonons and excitons. By assuming a Boltzmann kinetic description of the scattering process, we show that intra-condensate relaxation can be accounted for by an additional time-dependent term in the Gross-Pitaevskii equation. As an example, we apply the formalism to the experimental results recently obtained in polariton microwires [E. Wertz, et al., Nature Phys. 6, 860 (2010)]. In the presence of a local non-resonant optical pump, a dynamic balance between spatially dependent relaxation and particle loss develops and excites a series of modes, roughly equally spaced in energy. Upon comparison, excellent agreement is found with the experimental data.

Multiproxy analysis of a new terrestrial and a marine Cretaceous–Paleogene (K–Pg) boundary site from New Zealand

An integrated study of palynology, Mössbauer spectroscopy, mineralogy and osmium isotopes has led to the detection of the first K–Pg boundary clay layer in a Southern Hemisphere terrestrial setting. The K–Pg boundary layer was independently identified at centimetre resolution by all the above mentioned methods at the marine K–Pg boundary site of mid-Waipara and the terrestrial site of Compressor Creek (Greymouth coal field), New Zealand. Mössbauer spectroscopy shows an anomaly of Fe-containing particles in both K–Pg boundary sections: jarosite at mid-Waipara and goethite at Compressor Creek. This anomaly coincides with a turnover in vegetation indicated by an interval dominated by fern spores and extinction of key pollen species in both sections. In addition to the terrestrial floristic changes, the mid-Waipara section reveals a turnover in the dinoflagellate assemblages and the appearance of global earliest Danian index species. Geochemical data reveal relatively small iridium enrichments in the boundary layers of 321 pg/g at mid-Waipara and 176 pg/g at Compressor Creek. Unradiogenic 187Os/ 188Os values of the boundary clay reveal the presence of a significant extraterrestrial component. We interpret the accumulation of Fe nano-phases at the boundary as originating from both the impactor and the crystalline basement target rock. The goethite and jarosite are interpreted as secondary phases formed by weathering and diagenesis. The primary phases were probably controlled by the initial composition of the vapor plume and condensation kinetics rather than condensation thermodynamics. This investigation indicates that identification of Fe in nano-phases by Mössbauer spectroscopy is an accurate and cost-effective method for identifying impact event horizons and it efficiently complements widely used biostratigraphic and geochemical methods.

Condensation of alkoxysilanes in alcoholic media: II. Oligomerization of aminopropylmethyldiethoxysilane and co‐oligomerization with dimethyldiethoxysilane

AbstractIn the context of the preservation of cultural heritage, the treatment of paper by an aminoalkylalkoxysilane, or its mixture with dimethyldiethoxysilane (DMDES), gave encouraging results. The condensation experiments presented here, carried out in alcohol medium using aminopropylmethyldiethoxysilane (AMDES) alone or with DMDES, were followed using 1H NMR, 29Si NMR and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI TOF) spectroscopies. The aim was to determine whether DMDES and AMDES could copolymerize under the conditions used. An exchange reaction was observed for AMDES in ethanol in the absence of water, under conditions where no exchange took place for DMDES. In methanol, this reaction proceeded much more rapidly and the reactivity of methoxysilyl groups was higher than that of ethoxysilyl groups. In the same solvent, in the presence of water, hydrolysis, cyclization and oligomerization were observed using NMR and MALDI TOF spectroscopies. In ethanol, a kinetic study of a mixture of DMDES and AMDES showed that the condensation of the two monomers proceeded at comparables rates and MALDI‐TOF analysis gave evidence that mixed oligomers were produced, containing from one to four AMDES units. It was concluded that the co‐oligomerization did not lead to a mixture of homo‐oligomers, which would be due to different hydrolysis and condensation kinetics, but induced the formation of co‐oligomers. Copyright © 2010 Society of Chemical Industry

Experimental and computational study on hydrolysis and condensation kinetics of γ-glycidoxypropyltrimethoxysilane (γ-GPS)

Since the amount of silanol units in the hydrolysis solution directly determines the interfacial adhesive strength and corrosion resisting property of self-assembled silane films, therefore, it is very essential to have a deep understanding of hydrolysis behaviors of SCAs (silane coupling agents). Conductivity measurement, RA-IR measurement and density functional theory (DFT) calculation was applied to the study of the hydrolysis and condensation kinetics of γ-glycidoxypropyltrimethoxysilane (γ-GPS) under near-neutral and acidic conditions. The results indicated that a critical point existed at about 50 h, dividing the entire hydrolysis period into two stages: Stage 1 (S1) and Stage 2 (S2). In S1, the first step hydrolysis reaction prevailed, while the second and third step hydrolysis reactions only played minor roles. The pH value of the hydrolysis solution imposed little influence on the reactions occurring in the solution. However, in S2, pH value exerted a significant influence on the hydrolysis and condensation reactions, based on which there was an optimum pH value range. The results of DFT calculation were consistent with the experimental measurements. Hitherto, a validate method was proposed to simulate the reactions occurring in the hydrolysis solution.

Abiotic CC bond formation under environmental conditions: Kinetics of the aldol condensation of acetaldehyde in water catalyzed by carbonate ions (CO3 2− )

The role of CC bond-forming reactions such as aldol condensation in the degradation of organic matter in natural environments is receiving a renewed interest because naturally occurring ions, ammonium ions, NH+4, and carbonate ions, CO32−, have recently been reported to catalyze these reactions. While the catalysis of aldol condensation by OH− has been widely studied, the catalytic properties of carbonate ions, CO32−, have been little studied, especially under environmental conditions. This work presents a study of the catalysis of the aldol condensation of acetaldehyde in aqueous solutions of sodium carbonate (0.1–50 mM) at T = 295 ± 2 K. By monitoring the absorbance of the main product, crotonaldehyde, instead of that of acetaldehyde, interferences from other reaction products and from side reactions, in particular a known Cannizzaro reaction, were avoided. The rate constant was found to be first order in acetaldehyde in the presence of both CO32− and OH−, suggesting that previous studies reporting a second order for this base-catalyzed reaction were flawed. Comparisons between the rate constants in carbonate solutions and in sodium hydroxide solutions ([NaOH] = 0.3–50 mM) showed that, among the three bases present in carbonate solutions, CO32−, HCO3−, and OH−, OH− was the main catalyst for pH ≤ 11. CO32− became the main catalyst at higher pH, whereas the catalytic contribution of HCO3− was negligible over the range of conditions studied (pH 10.3–11.3). Carbonate-catalyzed condensation reactions could contribute significantly to the degradation of organic matter in hyperalkaline natural environments (pH ≥ 11) and be at the origin of the macromolecular matter found in these environments. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 676–686, 2010

Erratum: “Fluctuation-induced spreading of size distribution in condensation kinetics” [J. Chem. Phys. 131, 164514 (2009)

Erratum: “Fluctuation-induced spreading of size distribution in condensation kinetics” [J. Chem. Phys. 131, 164514 (2009)

A model of aerosol evaporation kinetics in a thermodenuder

Abstract. Aerosol thermodenuders provide a measure of particle volatility. The information provided by a thermodenuder is fundamentally related to the kinetics of evaporation and condensation within the device. Here, a time-dependent, multi-component model of particle and gas-phase mass transfer in a thermodenuder is described. This model empirically accounts for the temperature profile along the length of a typical thermodenuder and distinguishes between the influence of the heating section and of the adsorbent denuder section. It is shown that "semi-volatile" aerosol is particularly sensitive to the inclusion of an adsorbent denuder in the model. As expected, the mass loss from evaporation of particles as they pass through the thermodenuder is directly related to the compound vapor pressure, although the assumptions regarding the enthalpy of vaporization are shown to also have a large influence on the overall calculated mass thermograms. The model has been validated by comparison with previously measured mass thermograms for single-component aerosols and is shown to provide reasonable semi-quantitative agreement. The model that has been developed here can be used to provide quantitative understanding of aerosol volatility measurements of single and multi-component aerosol made using thermodenuders that include adsorbent denuder sections.

On the evaporation of ammonium sulfate solution

Aqueous evaporation and condensation kinetics are poorly understood, and uncertainties in their rates affect predictions of cloud behavior and therefore climate. We measured the cooling rate of 3 M ammonium sulfate droplets undergoing free evaporation via Raman thermometry. Analysis of the measurements yields a value of 0.58 +/- 0.05 for the evaporation coefficient, identical to that previously determined for pure water. These results imply that subsaturated aqueous ammonium sulfate, which is the most abundant inorganic component of atmospheric aerosol, does not affect the vapor-liquid exchange mechanism for cloud droplets, despite reducing the saturation vapor pressure of water significantly.

Fluctuation-induced spreading of size distribution in condensation kinetics

One of the major results of condensation theory is the time independence of the size distribution shape (in terms of a certain invariant size) at the stage of regular growth of particles. This property follows directly from the simplified Zeldovich equation in the continuous form, where the fluctuation term is neglected. We show that the time invariance is broken by the fluctuation-induced spreading of the size spectrum. We first analyze the linear kinetic equations for the distributions p(i)(t) with the growth rates of the form i(alpha). Exact solutions demonstrate the increase in dispersion with time as sqft[t] at alpha=0 and the time-independent dispersion at alpha=1. From the asymptotic analysis of the continuous Zeldovich equation with fractional alpha, it is shown that the distribution spreading always occurs at alpha<1/2. We then study the general case of homogeneous condensation in an open system with pumping. Asymptotical solutions for the size distribution have the form of a diffusionlike Gaussian. In the case of constant material influx, the spectrum width increases with mean size z as sqrt[z] irrespective of alpha. We present a diagram of different growth scenarios and show that the time spreading occurs in the majority of condensing systems. Some numerical estimates for the effect of spectrum spreading are also presented.

Water Vapor Absorption in Porous Media Polluted by Calcium Nitrate Studied by Time Domain Nuclear Magnetic Resonance

Nuclear magnetic resonance relaxation analysis of liquid water (1)H nuclei in real porous media, selected for their similar composition (carbonate rocks) and different pore space architecture, polluted with calcium nitrate, is presented to study the kinetics of water condensation and salt deliquescence inside the pore space. These phenomena are responsible for deterioration of porous materials when exposed to environmental injury by pollution in a humid atmosphere. The theory is well described for simple pore geometries, but it is not yet well understood in real porous media with wide distributions of pore sizes and connections. The experiment is performed by following in time the formation of liquid water inside the pore space by T(1) and T(2) relaxation time distributions. The distributions allow one to see the effects of both the salt concentration and the pore space structure on the amount of water vapor condensed and its kinetics. It is shown that, for a given lithotype, even with different amounts of pollutant, the rate-average relaxation time T(1ra) tends to increase monotonically with NMR signal, proportional to the amount of liquid water. T(1ra) is often inversely associated with surface-to-volume ratio. This suggests a trend toward the filling of larger pores as amounts of liquid water increase, but it does not indicate a strict sequential filling of pores in order of size and starting with the smallest; in fact, relaxation time distributions show clearly that this is not the case. Increased amounts of salt lead to both markedly increased rates and markedly increased amounts of water absorption. NMR measurements of amounts of water, together with relaxation time distributions, give the possibility of information on the effect of pollution in porous materials exposed to humid atmospheres but sheltered from liquid water, even before the absorption of large amounts of moisture and subsequent damage. These phenomena are of importance also in other fields, such as the exploitation of geothermal energy.

Kinetic study of the condensation of salicylaldehyde with diethyl malonate in a nonpolar solvent catalyzed by secondary amines

AbstractThe kinetics of condensation between salicylaldehyde and diethylmalonate in a toluene solution in the presence of secondary amines (i.e., piperidine and 4‐piperidinopiperidine) as catalysts was investigated. It was found that the reaction proceeds via the Knoevenagel mechanism, and the kinetic model was numerically verified. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 589–598, 2009

Catalytic condensation of glycolaldehyde and glyceraldehyde with formaldehyde in neutral and weakly alkaline aqueous media: Kinetics and mechanism

The kinetics of glycolaldehyde and glyceraldehyde condensation with formaldehyde in a neutral aqueous medium in the presence of homogeneous phosphates and in a weakly alkaline medium in the presence of MgO was studied. The temperature dependences of the observed kinetic constants and the apparent activation energies of the reactions were determined. A reaction scheme for the interaction of lower monosaccharides with formaldehyde was derived from analyses of the reaction products.

Dynamic Effective Mass of Granular Media

We develop the concept of frequency dependent effective mass, M[over ](omega), of jammed granular materials which occupy a rigid cavity to a filling fraction of 48%, the remaining volume being air of normal room condition or controlled humidity. The dominant features of M[over ](omega) provide signatures of the dissipation of acoustic modes, elasticity, and aging effects in the granular medium. We perform humidity controlled experiments and interpret the data in terms of a continuum model and a "trap" model of thermally activated capillary bridges at the contact points. The results suggest that attenuation of acoustic waves in granular materials can be influenced significantly by the kinetics of capillary condensation between the asperities at the contacts.

Temperature Dependence of Nanoscale Friction Investigated with Thermal AFM Probes

AbstractMeasurements of nanoscale friction between silicon AFM tips featuring an in-situ solid state heater and silicon substrates (both with native oxide) were performed. The temperature of the heater was varied between room temperature and approximately 650 °C. For these temperatures and the silicon substrate, the temperatures at the point of contact are estimated to range from room temperature to approximately 120±20 °C. Experiments were carried out in ambient atmosphere (˜30% relative humidity) and under dry nitrogen. Tests under constant load revealed that in the presence of ambient, friction increased with heater temperature whereas it did not change in dry nitrogen. For experiments carried out for different tip velocities (40 to 7800 nm/s), friction decreased with velocity in ambient and did not change in dry nitrogen. Both trends can be explained by thermally-assisted formation of capillary bridges between tip and substrate and the kinetics of capillary condensation under ambient conditions.

From Hollow Nanosphere to Hollow Microsphere: Mild Buffer Provides Easy Access to Tunable Silica Structure

A facile synthesis method for producing silica hollow spheres from nano- to microsize level is realized by adjusting the hydrolysis and condensation kinetics of silane precursors in a mild buffer solution (NaH2PO4−Na2HPO4, pH ≈ 7.0) in the presence of F127 (EO106PO70EO106) surfactant. Characterization using transmission electron microscopy, field-emission scanning electron microscopy, and nitrogen sorption techniques reveals that the silica hollow nanospheres with outer diameter of about 12 nm can be obtained with tetramethoxysilane as silane precursor. Silica hollow nanospheres (∼20 nm) can also be prepared using tetraethoxysilane (TEOS) as silane precursor with the addition of hydrolysis and condensation catalyst NH4F. Using TEOS as the silane precursor without F−, the formation of silica hollow microspheres (0.5∼8 μm) was observed. Time-resolved in situ UV-Raman results show that TEOS does not hydrolyze at room temperature, and the hydrolysis of TEOS occurs immediately at room temperature when NH4F was...

Kinetics of homogeneous nucleation and condensation of n-butanol at high supersaturation

We have measured rate constants for the homogeneous nucleation and condensation of n-butanol in a supersonic nozzle. Because our setup works at stagnation pressures of up to 10 bars we could extend the temperature range for which nucleation data is available by approximately 50 K to values between 263 K and 277 K. We observe peak nucleation rates of the order of 5 × 10 24 m − 3 s − 1 , a typical value expected in supersonic nozzles. We find that our data can be very well described by Hale's scaling formalism but that this formalism slightly underpredicts the scaled nucleation rate at our temperatures. This is in contrast to a trend observed earlier by others. We suspect this to be due to our high temperatures ( T / T C ≈ 0.5) as Hale's scaling formalism that is applicable only at T / T C < 0.5. A value for the sticking probability ζ = 1.29 × 10 − 3 is found in our analysis. This rather low value is obtained because of the neglection of the Kelvin effect necessary for a fast numerical implementation of the specific method chosen to analyze our data. The same concept will be applied to study the kinetics of the homogeneous nucleation and condensation of zinc in future.

An estimate of the equilibrium speciation of sulfur vapor over solid sulfur and implications for planetary atmospheres

Sulfur allotropes have been observed in planetary atmospheres and are believed to have been present in the ancient Earth atmosphere. The vapor pressures of sulfur allotropes, especially S2, S3, and S4, are poorly known at typical atmospheric temperatures, but have generally been assumed to be high enough to represent significant gas phase abundances in model calculations. Here I present estimates of the speciation of the equilibrium vapor pressure over solid sulfur, which would seem to imply that the vapor pressures of most allotropes are too low at typical atmospheric temperatures for gas phase formation reactions to be important. However, consideration of the kinetics of condensation shows that gas phase sulfur allotrope reactions can be important under certain conditions. The implications for the mechanism of sulfur isotope mass-independent fractionation on early Earth are discussed. Implications for the presence of sulfur allotropes in Venusian clouds, the distribution of S2 in the atmosphere of Jupiter following the comet Shoemaker-Levy 9 impacts, and the observation of S2 in volcanic plumes on Io are also presented.

Kinetics of binary condensation on the droplet growing in diffusion regime

A relaxation equation determining the regular tendency of the concentration of binary solution in the growing droplet to the stationary value, at which there is a self-similar solution to the problem of the condensation in a binary mixture, is derived. An analytical solution of the relaxation equation is obtained and it is demonstrated that the stationary value of concentration is achieved via the power law. The time interval that elapses from the emergence of the droplet until the diffusion regime of droplet growth and derived relaxation equation become effective is revealed. The stationary value of concentration is found for the model of ideal solution.

Studies to aid process development for the manufacture of neopentyl glycol from isobutyraldehyde: aldol condensation followed by hydrogenation

AbstractIn our present research and investigations, attempts were made to study aldol condensation of isobutyraldehyde with formaldehyde, and the subsequent hydrogenation of resultant hydroxypivaldehyde (aldol product) to neopentyl glycol. The kinetics of aldol condensation were studied using a weak basic anion‐exchange resin catalyst, Indion‐860, after screening other heterogeneous catalysts. The initial rate data were analyzed using a power‐law model to aid process design. Further, subsequent hydrogenation of resultant hydroxypivaldehyde was studied using 5% Ru/Al2O3 catalyst. The selectivity towards neopentyl glycol was &gt; 99%. The kinetic data were analyzed using a power‐law model. A dual‐site Langmuir–Hinshelwood‐type model suggesting molecular adsorption (nondissociative) of hydrogen and surface reaction as the rate‐controlling step provided the best fit of the experimental data. The catalyst could be recycled with good selectivity. Copyright © 2008 Curtin University of Technology and John Wiley &amp; Sons, Ltd.