Polarizable Gas Research Articles

Design and simulation of a plasmonic density nanosensor for polarizable gases.

In this paper, an optical method of measuring the mass density of polarizable gases is proposed using a plasmonic refractive index nano-sensor. Plasmonic sensors can detect very small changes in the refracting index of arbitrary dielectric materials. However, attributing them to a specific application needs more elaboration of the material's refractive index unit's (RIU) relation with the introduced application. In a gaseous medium, the optical properties of molecules are related to their dipole moment polarizability. Hence, the theoretical index-density relation of Lorentz-Lorenz is applied in the proposed sensing mechanism to interpret changes in the gas' refractive index and to changes in its density. The proposed plasmonic mass density sensor shows a sensitivity of 348.8nm/(gr/cm3) for methane gas in the visible light region. This sensor can be integrated with photonic circuits for gas sensing purposes.

Effect of 2-MeIM/Zn Molar Ratio on CO2 Permeability of Pebax/ZIF-8 Mixed Matrix Membranes

The impact of controlling molar ratio of ZIF-8 precursors on Pebax 1657 and Pebax 2533 based Mixed Matrix Membranes (MMMs) on the CO2 permeability and CO2 /N2 ideal selectivity was investigated. Three types of ZIF-8 were synthesized by controlling molar ratio of 2-methylimidazole and zinc nitrate hexahydrate as 2/1, 8/1, and 32/1. The SEM images and XRD patterns of ZIF-8 showed that particle sizes and crystallinity peaks were decreased as molar ratio of ZIF-8 increased. The CO2 permeability of Pebax MMM was improved by filling with the ZIF-8 particles compared to the pure Pebax. At equivalent temperatures, the highest CO2 permeability was shown in Pebax 1657/ZIF-8 with the ZIF8 precursors’ molar ratio of 32/1 and Pebax 2533/ZIF-8 with the molar ratio of 2/1. As molar ratio of ZIF-8 precursors increases, CO2 permeability of Pebax 1657 was increased by excessive sorption of CO2 by imidazolium ions in ZIF-8, whereas CO2 permeability of Pebax 2533 was decreased by decreasing pore size and particle size of ZIF-8. The CO2 permeability was higher in Pebax 2533/ZIF-8 compared to Pebax 1657/ZIF-8, because Pebax 2533 has more concentrations of polar groups in the polymer matrix than Pebax 1657. However, the CO2 /N2 ideal selectivity was higher in Pebax 1657/ZIF-8 compared to Pebax 2533/ZIF-8 because diffusivity of Pebax 1657 compared to Pebax 2533 is lower for nonpolar gases, such as N2 , and the solubility is higher for polarizable gases like CO2 . As increasing temperature, Pebax/ZIF-8 MMMs showed enhancement of CO2 and N2 permeability but decreased in CO2 /N2 ideal selectivity.

Enhanced Stability toward Humidity in a Family of Hybrid Ultramicroporous Materials Incorporating Cr2O72– Pillars

Dichromate (Cr2O72–) pillared pcu hybrid ultramicroporous materials, while previously shown to exhibit benchmark selectivity for small polarizable gases, sometimes suffer from poor stability when exposed to moisture, which could limit their potential application in gas separation systems. In attempting to improve their stability toward humidity, we have crystal engineered two new families of DICRO-L-M-i materials of formula [M(L)2(Cr2O7)]n (M = Ni2+, Co2+; L = 5: 1,4-bis(4-pyridyl)xylene; 6: 1,4-bis(4-pyridyl)durene). Evaluating these materials in combination with a previously reported analogue, DICRO-4-Ni-i, in terms of their stability toward humidity has revealed a relationship between increasing the number of methyl groups on the dipyridyl organic linkers and a greater stability toward humidity.

Ballistic Evaporation and Solvation of Helium Atoms at the Surfaces of Protic and Hydrocarbon Liquids.

Atomic and molecular solutes evaporate and dissolve by traversing an atomically thin boundary separating liquid and gas. Most solutes spend only short times in this interfacial region, making them difficult to observe. Experiments that monitor the velocities of evaporating species, however, can capture their final interactions with surface solvent molecules. We find that polarizable gases such as N2 and Ar evaporate from protic and hydrocarbon liquids with Maxwell-Boltzmann speed distributions. Surprisingly, the weakly interacting helium atom emerges from these liquids at high kinetic energies, exceeding the expected energy of evaporation from salty water by 70%. This super-Maxwellian evaporation implies in reverse that He atoms preferentially dissolve when they strike the surface at high energies, as if ballistically penetrating into the solvent. The evaporation energies increase with solvent surface tension, suggesting that He atoms require extra kinetic energy to navigate increasingly tortuous paths between surface molecules.

Chalcogels: Porous Metal−Chalcogenide Networks from Main-Group Metal Ions. Effect of Surface Polarizability on Selectivity in Gas Separation

We report the synthesis of metal-chalcogenide gels and aerogels from anionic chalcogenide clusters and linking metal ions. Metal ions such as Sb(3+) and Sn(2+), respectively chelated with tartrate and acetate ligands, react in solution with the chalcogenide clusters to form extended polymeric networks that exhibit gelation phenomena. Chalcogenide cluster anions with different charge densities, such as [Sn(2)S(6)](4-) and [SnS(4)](4-), were employed. In situ rheological measurements during gelation showed that a higher charge density on the chalcogenide cluster favors formation of a rigid gel network. Aerogels obtained from the gels after supercritical drying have BET surface areas from 114 to 368 m(2)/g. Electron microscopy images coupled with nitrogen adsorption measurements showed the pores are micro (below 2 nm), meso (2-50 nm), and macro (above 50 nm) regions. These chalcogels possess band gaps in the range of 1.00-2.00 eV and selectively adsorb polarizable gases. A 2-fold increase in selectivity toward CO(2)/C(2)H(6) over H(2) was observed for the Pt/Sb/Ge(4)Se(10)-containing aerogel compared to aerogel containing Pt(2)Ge(4)S(10). The experimental results suggest that high selectivity in gas adsorption is achievable with high-surface-area chalcogenide materials containing heavy polarizable elements.

Gas permeation of poly(amide-6- b-ethylene oxide) copolymer

Block copolymers exhibit a different gas permeation behavior from that of homopolymers. In the diffusion process, the fraction of impermeable regions in the block copolymer decreases the diffusivity and the permeability. As the amount of impermeable regions in the block copolymer increases, the flow paths for the gas diffusion are restricted. Poly(amide-6- b-ethylene oxide) (PEBAX ®) copolymer consists of a regular linear chain of rigid polyamide for hard segment interspaced with flexible polyether for soft segment. PEBAX ® copolymer shows a typical permeation behavior of rubbery polymers. The permeability of CO 2 increases with the pressure originating from the increment of the sorbed CO 2 amounts. PEBAX ® copolymer shows the high permeability and the high selectivity for polarizable/nonpolar gas pairs. Particularly, the selectivity of CO 2 over N 2 is 61 and that of SO 2 over N 2 is 500. For small and nonpolar gases (i.e. He, H 2, O 2 and N 2), the permeability decreases with increasing the molecular size or volume of gases. On the other hand, for polarizable and larger gases (i.e. CO 2 and SO 2), it shows the high permeability. The high permeability and permselectivity of PEBAX ® copolymer are attributed of polarizable gases to polyether segment in PEBAX ®.

Diffuse Reflectance and Photoacoustic Fourier Transform Infrared Spectra of Silica Surfaces under Polarizable Gases

It has been reported that the use of an infrared transparent polarizable gas such as xenon enhances the FT-IR photoacoustic signal of some species adsorbed on a sample surface. Diffuse reflectance and photoacoustic FT-IR methods were used to obtain spectra of silica surfaces under helium, nitrogen, and xenon. Absence of the reported effect with both techniques is shown, and a tentative explanation for these results is given.

Characterization of Kevlar fiber surfaces using a newly developed infrared photoacoustic technique

AbstractA newly developed infrared photoacoustic technique has been used to obtain information about the orientation of the surface functional groups of Kevlar‐49R fibers. This method involves the use of a highly polarizable gas in the photoacoustic cell and comparison of the spectra with a non‐polarizable coupling gas. A highly polarizable inert gas, xenon, enhances the surface modes oriented parallel to the surface and suppresses the intensity of the perpendicular modes. This method shows differences in the structure of the skin and the core of the fibers. The polymer chains in the skin are oriented parallel to the surface, and in the core they are almost radially oriented.

Determination of the Orientation of Silanes on Silica Surfaces by Fourier Transform Infrared Photoacoustic Spectroscopy

Fourier transform infrared photoacoustic spectroscopy has been used for quantitative surface analysis of silica treated with trifunctional coupling agents such as γ-Methacryloxypropyltriethoxysilane (γ-MPS), γ-Glycidoxypropyltrimethoxysilane (γ-GPS), and γ-Aminopropyltri-ethoxysilane (γ-APS). The calibration curves are obtained for several characteristic bands of the coupling agents. Using a highly polarizable gas in the photoacoustic cell and comparing the spectra with a nonpolarizable coupling gas, it is possible to evaluate orientation of the coupling agents on the silica surface. The type of orientation is a function of the extent of surface coverage. At low surface coverage, coupling agents tend to take a perpendicular orientation with respect to the surface, and increasing surface coverage leads to parallel orientation. Increasing the coupling agent concentration also causes orientational changes of the species which form chemical bonds with the silica surface (hydroxyl, water, and carbonyl groups).

Enhancement of the Surface Modes in Photoacoustic FT-IR Spectroscopy Using a Highly Polarizable Inert Gas

Fourier transform infrared photoacoustic spectroscopy has been used for the analysis of surface functionality and adsorbed species. Using a highly polarizable gas in the photoacoustic cell and comparing the spectra with a nonpolarizable coupling gas, one can obtain useful information regarding the species present and their orientation with respect to the surface. A highly polarizable inert gas, xenon, enhances those surface modes which are preferentially oriented parallel to the surface and suppresses the intensity of the perpendicular modes. The two types of modes for adsorbed molecules on the oxide surfaces such as silica hare been demonstrated. The intensities of the carbon monoxide mode (parallel to the surface) are greatly enhanced and those of adsorbed water (perpendicular) are suppressed. Surface hydroxyls show less intensity in xenon than helium, reflecting preferentially perpendicular orientation with respect to the surface. This method requires only a routine photoacoustic setup and the use of polarizable and nonpolarizable gases.

Study of a gas-solid dielectric interface by means of surface depolarization thermocurrents

The method of thermally stimulated currents (TSC), with a special configuration of electrodes, was used to study interfacial reactions on a soda glass surface exposed to a highly polarizable gas such as carbon dioxide. Two well-developed peaks were observed at −100 and −120 °C, which were completely absent from the volume response of the same material. The peaks disappeared on prolonged heat treatment of the specimen in vacuum. The results were interpreted in terms of polarization phenomena introduced near the surface of the glass by the presence of highly polarizable molecules.

The Clustering of Ions and the Mobilities in Gaseous Mixtures

It is shown by direct analysis that the deviations from Blanc's law for mobilities of ions in mixtures of gases observed when a strongly polarizable gas is mixed with one less polarizable cannot be ascribed to a statistical clustering effect as proposed by Loeb. Analysis involving the assumption that the ion undergoes labile clustering of the simplest type indicates that the observed results can be completely accounted for within the realms of simple theory. Thus assuming that the active gas can attach a single molecule to the ion and that this attachment molecule may be detached with different probabilities by collisions with the two types of gas molecules leads to an equation for the resultant mobilities which will cover practically all cases observed. The forces assumed can be dielectric but may also be secondary valence or van der Waals' forces. It is indicated how, with appropriate experimental procedures possible under modern techniques, most of the constants required for the solution of the equation can be directly determined or computed.

The variation of the mobility of gaseous ions with temperature II-caesium and sodium ions in helium

In a recent paper Professor Tyndall and the writer described experiments on the variation with temperature of the mobility of positive ions of helium moving in helium gas. Owing to lack of knowledge of the precise effects of the phenomenon of electron transfer, it was not possible to deduce from the results the forces between an ion and a neutral atom of this gas. But it was pointed out that if alkali ions were used instead of helium ions, electron transfer between the atoms and ions would not occur. In that case the main objection to a treatment based on a classical which had already been proposed. Further it was suggested that the most marked variation of mobility with temperature might be expected for a relatively large ion moving in a weakly polarizable gas. In the work described below, it was this condition that determined the choice of caesium ions in helium. Sodium ions also have been studied mainly for purposes of comparison. Experimental Fig. 1 is a scale diagram of the apparatus. In principle, the apparatus is similar to experimental tubes employed previously with the alkali ions in this laboratory; but it was necessary to modify the old design so that the enclosed gas could be maintained at various temperatures ranging between that of liquid nitrogen, and about 250° C. A Kunsman sources S, run at a dull red heat, was used as emitter of ions, and this had to be placed as far as conveniently possible from the section M in which the ionic speeds were measured, so that it would not affect the temperature of the gas in that region. According the apparatus was arranged as in the figure, with the source S at the upper end the measuring section M at the lower end, the ions being carried across the intervening space by means of a uniform electric field maintained by six guard rings. The measurement of the speed of an ion in the gas at any chosen temperature was made in the manner previously described.

Emission of metallic ions from oxide surfaces. I.—Identification of the ions by mobility measurements

In two recent papers an account was given of the determination of the mobility of ions of the alkali metals in various gases. It was shown that in argon, krypton, xenon and nitrogen the experimental results could be represented with considerable accuracy by the relation K = A/√ρ (D - 1)·(1 + m /M) ½ cm./sec./unit electrostatic field, (1) where K is the speed of an ion of mass M in a gas of molecular weight m , density ρ and dielectric constant D, at a pressure of 760 mm. of mercury and a temperature of 20°C. For a given gas A is a constant; it changes slightly from one gas to another, the extreme values being 0·48 for nitrogen and 0·56 for xenon. The equation is very similar to one deduced by Langevin using a simple atomic model. In his equation A depends upon the “size” and polarizability of the gas molecules, but for the particular case of a highly polarizable gas it approaches a limiting value of 0·51. The experimental facts summarized above suggest that in the more polarizable gases the “size” of the ions has little influence on their mobility. This view was confirmed by further experiments in nitrogen which showed that the mobility of even large clustered ions like (Na + , NH 3 ) and (Na + , 2NH 3 ) is also given by the same relation which holds for the simple alkali ions.