Polar Vapors Research Articles

Specific and non-specific interactions on non-porous carbon black surfaces

The interactions which occur between methanol, ethanol or propanol and the surfaces of non-porous carbon blacks with increasing levels of oxygen chemistry have been studied using adsorption isotherm analysis and immersion calorimetry. Surface oxygen has been controlled by ozone treatment and characterised using X-ray photoelectron spectroscopy, which gives a direct and quantitative measure of surface composition from first-principles, and has not yet been extensively employed in detailed carbon adsorption studies. Nitrogen adsorption at 77 K and heat of immersion − h i (mJ m −2) data for toluene, show that the physical structure of the carbon blacks is not modified by ozone treatment. A systematic shift to higher adsorption values, due to increasing specific hydrogen bonding interactions between the alcohol –OH groups and surface oxygen, is observed in all of the alcohol isotherms as the total oxygen content of the carbon surfaces ([O] T/at.%) increases. This effect is most significant for methanol confirming that the mechanism of adsorption is dominated by hydrogen bonding and therefore dependant on the surface concentration of oxygen sites. It is also observed for ethanol and propanol but is less marked due to the increasing non-specific, dispersion, interactions of the alkyl chain with the non-polar carbon surface. This description is in agreement with the data obtained for the specific enthalpies of immersion − h i (mJ m −2) into the alcohols and into water or toluene which allow a semi-quantitative assessment off the relative polar and dispersion contributions to the overall interactions as functions of both carbon surface oxygen composition and the molecular structure of the alcohols. An overall correlation is observed between adsorption behaviour, [O] T/at.%, the resulting − h i values and the characteristic energy E (kJ mol −1) of the DRK equation. It is also observed that the values of the affinity coefficient β DRK increase directly as a function of [O] T indicating that this latter parameter may provide a basis for predicting the adsorption isotherms of certain polar vapours on non-porous carbon surfaces. The effects of carbon surface chemistry on the character of adsorption isotherms, which change from Type III for the base N330 (and for a graphitized carbon black N234G) to Type II for the oxidised N330 materials, is discussed and the resulting effects on the surface area parameters S DRK and S BET (m 2 g −1) are considered.

Response behavior of an epoxy resin/amine curing agent/carbon black composite film to various solvents

A novel polymer based sensitive film was prepared from thermosetting epoxy resins (EP) filled with carbon blacks. The curing reaction of amine curing agents with epoxy resins and the response of the curing resultants to solvent vapors were dealt with. The influence of the types and content of carbon blacks and curing agents, and curing temperatures and time on curing reactions and response selectivity of the conductive films were investigated. The structural characterization was conducted on a Fourier transform infrared spectrophotometer (FTIR). The results indicated that the conductive films showed high response selectivity to polar solvent vapors, especially to chloroform vapor, while no response was observed in non-polar solvent vapors. The responsivity of the film increased with the decreased carbon black contents. The film filled with acetylene carbon black gave an optimal response, with responsivity of about 700 times. The response performances were improved with the amount of curing agents increased, and an optimal response appeared at the amount of the curing agent of 8%. The film's responsivity was remarkably enhanced, the reversibility property, however, rapidly declined in the order of diethyleneltriamine < triethylenetetramine < ethylenediamine. The curing reaction tended to complete with the curing temperature elevated and the curing time prolonged. But the response performance dropped because of over cross-linking as the temperature was too high or the time was too long.

Analysis of gas sensing behaviors of carbon black/waterborne polyurethane composites in low concentration organic vapors

Conductive composite comprised of carbon black and waterborn polyurethane was prepared by latex blending. It exhibited sensitivity to non-polar solvent vapors and polar solvent vapors as a result of the microphase separation structure of polyurethane. By studying the electrical response and absorption behaviors of the composite in low vapor pressure, a model based on Flory-Huggins principle was proposed to discuss the specific performance of the composite, including selective sensitivity, influences of vapor pressure and test temperature. Interaction between solvent and matrix polymer was proved to determine the maximum magnitude of response of the composite.

Investigation into the vapor sensing behavior and mechanism of a reactive hydroxyl-terminatedpolybutadiene liquid rubber/carbon black conductive film

An electrically conductive composite of polyurethane pre-polymers was prepared by anintramolecular hydrogen transfer reaction using a reactive hydroxyl-terminatedpolybutadiene (HTPB) liquid rubber oligopolymer as a reactant, toluene diisocyanate(TDI) as a curing agent and carbon black (CB) as a conductive filler. The influence of thecomponent ratios, types of carbon black particles, curing temperatures and chain-extendingagents such as glycerine and triethanolamine on the responsiveness and reversibility ofHTPB/TDI/CB composite films was investigated. The structural characterization of thecuring materials was conducted on a FT-IR spectrometer. The experimental resultsindicated that a higher response behavior of HTPB/TDI/CB composite films occurred innon-polar solvent vapors than with polar solvent vapors. The response intensity of thecomposite films enhanced with increased TDI content and the introduction ofchain-extending agents. The responsivity of the films to benzene vapor reached106 times the original value, but the responsive time and recovery time were prolonged athigher curing temperatures. The response mechanism for the films was elucidated based onthe relationship between soft chain segments and hard chain segments.

Novel Contamination and Gas Sensor Materials from Amphiphilic Polymer-Grafted Carbon Black

The responses of electric resistance of composites prepared from amphiphilic polymer-grafted carbon blacks to contamination in solution and solvent vapor were investigated. The electric resistance of the composite prepared from poly(N-isopropylacrylamide) (PNIPAM)-grafted carbon black drastically increased when the composite was dipped in n-hexane containing contamination, such as methanol, THF, dioctyl phthalate, and chloroform, and returned to the initial resistance when it was transferred to dry air. The logarithm of the electric resistance of the composite was linearly proportional to chloroform concentration in n-hexane. The electric resistance of the composite drastically increased in organic polar solvent vapor, such as methanol, THF, and chloroform and returned to the initial resistance when it was transferred to dry air. But the response to non-polar solvent vapor, such as n-hexane, was very small. The logarithm of electric resistance of the composite was linearly proportional to humidity. In addition, electric resistance of the composite prepared from poly(diethylacrylamide) (PDEAA)-grafted carbon black also drastically increased when the composite was dipped in n-hexane containing contamination, such as methanol, trichloroethane, THF, chloroform, and benzene, and returned to the initial resistance when it was transferred to dry air. Based on the results, it was found that the composites could be used as a novel contamination sensor in n-hexane and gas sensor.

Selective gas nanosensors with multisize CdSe nanocrystal/polymer composite films and dynamic pattern recognition

We introduce a concept for selective chemical sensing based on different size semiconductor nanocrystals incorporated into a preselected polymer matrix. When CdSe nanocrystals of different sizes (2.8 and 5.6nm diam) were incorporated into a polymer film, each size of the nanocrystals demonstrated a distinct photoluminescence response pattern (excitation at λ=407nm) upon exposure to polar and nonpolar vapors in air at atmospheric pressure. When this composite response was processed using a multivariate analysis, a single film with different size CdSe nanocrystals served as a selective sensor.

Decadal and inter-hemispheric variability in polar mesospheric clouds, water vapor, and temperature

Variability in polar mesospheric clouds (PMCs), temperature, and water vapor over decadal time scales and also between hemispheres was examined using measurements from the Halogen Occultation Experiment (HALOE) covering 1991 to present. HALOE measurements were compared to results from a zonally averaged chemical/dynamics model (CHEM2D). HALOE indicates decadal cycles in temperature, water vapor, and PMCs that are correlated with the 11-year solar cycle. During solar cycle 23, variations in temperature and water vapor were nearly identical in the north and south. Temperatures varied by roughly 5 K at 85 km to 1 K at 30 km, with colder temperatures during solar minimum. Water vapor varied by roughly 30% at 85 km to less than 1% at 30 km, with more water vapor during solar minimum. Solar cycle variations in PMC extinction were roughly 23% in both the south and north, with brighter PMCs occurring during solar minimum. The overall picture given by HALOE is consistent with expectations, where a cooler and wetter mesosphere during solar minimum corresponds to brighter PMCs. CHEM2D confirms the solar cycle variations in temperature indicated by HALOE, but underestimates the observed solar cycle changes in H 2O. Comparing southern and northern HALOE measurements reveals warmer temperatures in the south throughout the mesosphere. CHEM2D results show the same pattern, although the model appears to overestimate the magnitude of these north-south differences. HALOE indicates that water vapor is nearly identical in the north and south, while CHEM2D predicts a wetter southern mesosphere. HALOE measurements show that northern PMCs are 30% brighter than southern clouds on average, a difference that must be related to the cooler northern summer mesosphere.

Ionic liquid high temperature gas sensors

An ionic liquid piezoelectric gas sensor was demonstrated for detection of polar and nonpolar organic vapors at high temperature with fast linear and reversible response.

Dipole Moment of Condensing Monomers: A New Parameter Controlling the Ion-Induced Nucleation

Many chemically active, hazardous, and toxic substances have a high dipole moment, and they interact strongly with the charged particles and molecular ion clusters. A new nucleation model considering the contribution of the dipole-charge interaction to the ion-induced nucleation rates is developed, with the dipole moment of the condensing monomers as a new parameter. It is shown that in the polar vapors the influence of the dipole-charge interaction on the nucleation rates may be much stronger than the Thomson effect. The new model is an extension of the classical ion-induced nucleation theory, and can explain the deviation between the experimental data and the predictions of the classical ion-induced nucleation theory.

Formation of binary ion clusters from polar vapours: effect of the dipole-charge interaction

Abstract. Formation of binary cluster ions from polar vapours is considered. The effect of vapour polarity on the size and composition of the critical clusters is investigated theoretically and a corrected version of classical Kelvin-Thomson theory of binary ion-induced nucleation is derived. The model predictions of the derived theory are compared to the results given by classical binary homogeneous nucleation theory and ion-induced nucleation theory. The calculations are performed in wide range of the ambient conditions for a system composed of sulfuric acid and water vapour. It is shown that dipole-charge interaction significantly decreases the size of the critical clusters, especially under the atmospheric conditions when the size of critical clusters is predicted to be small.

Uptake of neutral polar vapor molecules by charged clusters/particles: Enhancement due to dipole‐charge interaction

Recently proposed ion‐mediated nucleation theory suggests that the enhanced uptake of neutral polar molecules by the charged clusters as a result of dipole‐charge interaction may be critical to the nucleation of particles in the atmosphere. A rigorous parameterization of the enhancement effect of dipole‐charge interaction on the growth of charged clusters is presented and the important parameters controlling this enhancement factors are explored. The interaction of polar gas molecules with charges significantly enhances the growth rate of small charged clusters/particles. Polar molecules with higher dipole moment and smaller molecular size have larger enhancement factor. The enhancement factor decreases with increasing particle size and is roughly inversely proportional to temperature when the charged particles are small. At T of 300 K, the enhancement factor reaches up to 10 for the uptake of sulfuric acid molecules by ions with diameter of ∼0.5 nm but decreases quickly to 2 for uptake by a charged particle of ∼2 nm in diameter. For the uptake by molecular ions, the enhancement factor can reach as high as 20 for water molecules in the mesopause and as high as 15 for sulfuric acid in the polar stratosphere. The enhancement factors for the uptake of water dimers by charged clusters are consistently higher (up to 20–25%) than the corresponding enhancement factors for monomers. The hydration of sulfuric acid molecules in the atmosphere may affect the enhancement factor and hence ion‐mediated nucleation rate, which remains to be investigated.

Carbon nanotube/PMMA composite thin films for gas-sensing applications

The design and development of composite thin films of polymethylmethacrylate (PMMA)with multiwalled carbon nanotubes (CNTs) and surface-modified multiwalledcarbon nanotubes (f-CNTs) for gas-sensing applications are presented in thispaper. The responses of these composites for different organic vapors wereevaluated by monitoring the change in the resistance of thin films of compositewhen exposed to gases like dichloromethane, chloroform, acetone, methanol, ethylacetate, toluene and hexane. It was observed that the f-CNT/PMMA compositeshowed a higher response. There was an increase in resistance of the order of102–103, due to surface modification, when exposed to dichloromethane, chloroform and acetone.The sensing mechanism is explained on the basis of volume expansion and polar interactionof various vapors on the CNT surface.

Water vapor enhancement in the polar summer mesosphere and its relationship to polar mesospheric clouds

Polar mesospheric water vapor exhibits a strong seasonal cycle, with summer mixing ratios dramatically higher than in winter. It is generally accepted that vertical transport from ∼50 km altitude towards the mesopause is one driver behind this change, however, upwelling alone cannot explain observed H2O changes. H2O near 83 km increases from 1 ppmv in winter to over 8 ppmv in summer, and upwelling accounts for roughly half of this increase. It has been suggested that evaporation of polar mesospheric clouds (PMCs) should produce a layer of enhanced water vapor. This idea was explored using particle measurements from the Halogen Occultation Experiment (HALOE) to derive the equivalent gas phase H2O contained in PMCs. Comparing these estimates to HALOE water vapor measurements suggests that PMC evaporation is a large component in H2O enhancement near 83 km during summer.

Gaseous adsorption properties of a silica-pillared layered manganese oxide

Adsorptions of N 2, H 2O, and organic vapors including CH 2Cl 2, CCl 4, c-C 6H 12, C 6H 6, n-C 6H 14, and n-C 9H 20 on a silica-pillared layered manganese oxide (SiHMnO) and nonane-preadsorbed SiHMnO were examined. It is found that SiHMnO has a microporosity with a wide pore width distribution showing different pore wall affinities. Micropores with smaller width preferentially accommodate the nonane preadsorbate while the surface hydrophilicity of pore wall leads to an easier detachment of the adsorbed nonane molecules. H 2O adsorption influences both the porosity and the surface properties by accelerating a sufficient hydrolysis of the remained TEOS molecules in SiHMnO. Examinations using Dubinin–Radeshkevich (DR) equation and isosteric heat of adsorption of organic molecules provide evidences that the wall surface of micropores with smaller and larger width have less affinity toward nonpolar and polar organic vapors, respectively.

Gas sensitive porous silicon devices: responses to organic vapors

Geometrically scaled PS-based structures were fabricated in order to develop gas sensing devices by exploring porous silicon (PS) electrical characteristics. The electrical behavior of PS devices respond to polar organic vapors (as acetone and ethanol) reversibly in a reproducible way. Devices were fabricated with three different perimeters, maintaining a constant area (5.76 mm 2) and constant PS porosity (60%) throughout samples, in order to evaluate their electrical impedance depending on the area/perimeter ratio. Electrical impedance was measured from 10 kHz to 10 MHz in acetone, ethanol and vacuum (as reference) environments. The results obtained show the general aspect for impedance variation as expected for disordered materials such as amorphous semiconductors or polymers. Measured impedance is fitted proportionally to (2 πf) s , where f is the excitation frequency. The exponential factor “ s” was found to be around −0.55 for ethanol and −0.45 for acetone, whereas in vacuum s equals −0.97, thus providing a method for identifying polar molecules. The parameter “ s” for the tested environments is independent of device geometry.

Fullerene C60-cryptand coated surface acoustic wave quartz crystal sensor for organic vapors

A fullerene C60-cryptand 22 (C60-di-propylamine-cryptand 22) coated surface acoustic wave (SAW) quartz crystal gas detection system with 250 MHz oscillator and a computer interface for signal acquisition and data processing was prepared to detect various organic vapors. The C60-cryptand 22 coated SAW quartz crystal sensor exhibited sensitivity to both polar and nonpolar organic molecules. The C60-cryptand 22 was demonstrated as a better and more sensitive coating material than fullerene C60 or cryptand 22 for polar organic molecules. Comparison of C60-cryptand 22 coated SAW crystal and quartz crystal microbalance (QCM) sensors was also made and the SAW sensor exhibited much better response than the piezoelectric sensor for organic molecules with the same concentrations. The C60-cryptand 22 coated SAW crystal sensor could be repeatedly reused for the detection of most of organic vapors, e.g. alcohols, aldehydes, ketones, ethers, alkanes and alkenes. The selectivity of the C60-cryptand 22 coated SAW crystal sensor for various polar organic vapors seem to be in the order: alcohols>aldehydes>ketones>ethers. For nonpolar organic molecules, the C60-cryptand 22 coated SAW crystal sensor showed sensitivity for alkenes, e.g. hexene and benzene than for alkanes, 1-hexane and cyclohexane. Effects of molar mass, steric structures and isomers of organic molecules on the SAW frequency responses were also investigated. The SAW detection system showed the good detection limit of 0.1–3.0 mg/ml for these organic molecules. The C60-cryptand 22 coated SAW crystal sensor was successfully applied as a quite sensitive gas chromatography (GC) detector for various organic compounds. The C60-cryptand 22 coated surface acoustic wave GC detector compared well with the commercial thermal conductivity detector (TCD) for various organic molecules, e.g. organic halides, alcohols, alkenes and ketones.

Study of sorption/desorption of water and organic vapors on poly(ethylene maleate)‐based sensor‐coating materials using an automated gravimetric analyzer

AbstractHydrophobic comonomers bisphenol‐A and hexafluorobisphenol‐A were incorporated as diol components in the sensor‐coating material poly(ethylene maleate) (PEM), resulting in modified polymers, HCPEM and HFPEM, respectively. To assess the suitability of these polymers as sensor interfaces, the sorption/desorption isotherms and kinetics of water and a range of volatile organic vapors were obtained over the entire relative pressure range of 0.1 to 1.0, using an automated intelligent gravimetric sorption analyzer. The extent and rate of sorption of organic vapors were higher in the modified polymers compared to those of the parent polymer. Sorption hysteresis was observed at high relative pressures, especially with water and other hydrogen‐bonded polar organic vapors. Polarizable vapors like toluene and benzene were sorbed more than nonpolarizable cyclohexane vapors. The sorption results were interpreted in terms of semiempirical models based on concepts of thermodynamic interaction parameter, partition coefficient, and linear solvation energy relationship. The study reveals the potential of sorption/desorption isotherms and kinetics in characterizing the sorption properties of coating materials that are used as an interface in acoustic wave sensors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1760–1767, 2003

Carbon black/polystyrene composites as candidates for gas sensing materials

Amorphous polymer-based composites consisting of polystyrene and carbon black were developed in the current work as candidates for gas sensing materials. With the help of polymerization filling, i.e., in-situ polymerization of styrene in the presence of carbon black, the composites were provided with low percolation threshold. The experimental results indicated that the composites have selective sensitivity as characterized by high electrical responsivity to the vapors of non-polar and low polar solvents, and low responsivity to high polar solvent vapors as well. Besides conductivity of the composites, absorption characteristics of both the matrix and the fillers exert importance influence on the gas sensitivity of the composites. Therefore, composites’ performance can be tailored by changing filler concentration, molecular weight and molecular weight distribution of matrix polymer, etc. In regard to the fact that most conducting polymer composites as vapor sensing materials are based on crystalline polymer matrices, the approach reported by this paper provides another feasible way to develop new candidates.

Variability of polar stratospheric water vapor observed by ILAS

We present an analysis of polar stratospheric water vapor from measurements of the Improved Limb Atmospheric Spectrometer (ILAS) onboard the Advanced Earth Observing Satellite (ADEOS). The variability of water vapor is examined using contemporaneous potential vorticity fields to separate the vortex from the extravortex air. The overall water vapor distribution from the ILAS measurements agrees qualitatively with the water vapor climatology in the UARS reference atmosphere (covering 1992–1999), and the space‐time variability is consistent with the known stratospheric circulation. Quantitatively, comparisons between ILAS and Halogen Occultation Experiment (HALOE) equivalent latitude zonal means show agreement to within 5% in the lower stratosphere (400–800 K potential temperature or 15–30 km). In the upper stratosphere (800–1800 K potential temperature or 30–45 km), however, ILAS data have a 10% to 20% high bias compared to the 8‐year (1992–1999) UARS climatology and to HALOE data for the same time period. The ILAS data, covering the time period November 1996 to June 1997, were measured during a winter‐spring period when the Arctic polar stratosphere was anomalously cold. The ILAS water vapor data suggest an Arctic vortex that is more isolated and persistent in the spring than that seen in the UARS climatology. The spatial and temporal extent of the Arctic vortex this year was very similar to that of the Antarctic vortex. This feature is supported by HALOE data for the same measurement period. Using a trajectory model, we show that the NH vortex in spring 1997 was significantly more isolated compared to other years in the decade, and this explains the unusual confinement of high water vapor within the Arctic vortex observed by ILAS.

Determination of surface heterogeneity profiles on graphite by finite concentration inverse gas chromatography

Inverse gas chromatography (IGC) is an established tool in the determination of the adsorption potential distribution function. This function reflects the energetic heterogeneity profile of a surface and therefore provides interesting information on the nature and population of different surface sites. IGC is shown to be a fast and accurate technique for the determination of the adsorption potential distribution function of two different graphite samples. In this paper the adsorption of acidic and basic organic vapours is studied. Unlike heterogeneity profiles determined by nitrogen measurements, experiments with polar vapours can provide additional information on the adsorption mechanism and polar sorption sites. The heterogeneity profiles of all probes used are significantly different from one another and allow discreet energy levels to be distinguished. Chemically different probes reveal different adsorption mechanisms for the graphite surface.