Sorption Of Organic Vapors Research Articles

A Dynamic Three-Dimensional Covalent Organic Framework.

A guest-induced reversible crystal-structure transformation is identified in a new 3D covalent organic framework (COF) by comprehensive analyses using powder X-ray diffraction, organic vapor sorption isotherm, and 129Xe NMR spectroscopy. The revolving imine bond in interpenetrating 3D networks is uncovered as the key to the dynamic behavior, the potential applications of which are illustrated by gas separation and heterogeneous catalysis, thus paving the way to the design of stimuli-responsive and multifunctional COF materials.

Kinetic and equilibrium sorption of organic liquids and vapors in Matrimid

This work examines the kinetic and equilibrium sorption characteristics of a variety of chemical penetrants in the polyimide polymer Matrimid. Liquid equilibrium sorption for dense films with thicknesses of 50µm for a large variety of organic species including alkanes, alcohols, acetates, furans, and ionic liquids is presented. Vapor equilibrium sorption isotherms and kinetic sorption behavior for water and C1-C6 alcohols as a function of chemical activity from 0 to 0.9 were measured using a quartz crystal microbalance with films ranging in thickness from 0.07 to 2.0µm. Diffusion coefficients and relaxation parameters were calculated according to the diffusion-relaxation model for penetrants in glassy polymers. Diffusion coefficients at infinite dilution for water and C1-C6 alcohols are given as a function of van der Waals molar volume and a clear dependency is shown ranging from 2E-11 to 6.5E-13cm2/s for water and hexanol, respectively, for 0.26µm thick films. Diffusion coefficients for all studied vapor penetrants displayed a marked dependence on thickness spanning approximately two orders of magnitude for each respective vapor penetrant over the range 0.1–1.0µm. Penetrant-induced relaxation behavior accounts for the majority of mass sorption at chemical activities of 0.2 and above for the C1-C6 alcohol vapors.

Structural studies on inclusion compounds and solvent sorption behavior of gradually elongated wheel-and-axle-type diol hosts featuring lateral benzo[b]thiophene units

Based on the wheel-and-axle design strategy, a series of six new clathrate hosts featuring two di(benzo[b]thien-2-yl)hydroxymethyl units attached to both ends of a central linear building element of varying length have been synthesized and their capability to form crystalline inclusion compounds with a fixed range of organic solvents are reported. X-ray crystal structures of relevant inclusion compounds have been determined and are comparatively discussed involving structural modification of the host molecules. Organic vapor sorption behavior of the host compounds coated as solid films on the quartz crystal of a QCM device has been studied. Significant differences in the affinities towards solvent vapors dependent both on structural and polarity properties of host and solvent are observed, indicating potential application as mass sensitive materials.

Humidity Tolerant Organic Vapor Detection Using a Superhydrophobic Quartz Crystal Microbalance

The organic vapor sensitivity of a quartz crystal microbalance (QCM) with an epoxy resin–carbon soot coating designed to be tolerant to humidity is reported. This is achieved using nonengulfed, but attached, hydrophobic carbon soot nanoparticles, coated in an irregular surface topography composed of islands and cavities. The root mean square roughness ( $R_{\mathrm {{rms}}}$ ) of 130 nm, together with the hydrophobic soot, convert the epoxy surface to a superhydrophobic (SH) one with high static contact angle ( $\sim 151^{\circ }$ ) and low contact angle hysteresis ( $\sim 1.1^{\circ }$ ). The frequency shift of the SH QCM at 100% relative humidity is $\sim 7$ times lower compared with an uncoated device, and thus indicating low water vapor adsorption due to superhydrophobicity. In addition, the SH QCM shows between three and six times higher gas sensitivity and lower detection limit compared with the conventional polymer coated QCMs. These results correlate well with the $R_{\mathrm {{rms}}}$ and surface topography of the coating, which ensure enhanced sensing area. Furthermore, the sensor demonstrates reproducibility, reversibility, and fast response-recovery time ( $\sim 10$ s) to ethanol, methanol, and isopropanol vapor. These experiments reveal that superhydrophobicity increases the organic vapor sorption at the expense of water vapor sorption, and thus allowing operation of the QCM gas sensors in an uncontrolled humidity environment.

Applicability of the one-step DVS method for the determination of amorphous amounts for further different hydrophilic and hydrophobic drugs

In a former publication the authors showed that low amounts of amorphous content (LOQ of 0.5%) in a hydrophobic model API (Ciclesonide) can be measured with an individually adjusted one-step dynamic organic vapor sorption (DVS). In this investigation the applicability is tested on various APIs which differ in lipophilicity (poor water solubility) and hygroscopicity (absorption of water).The vapor sorption method proved to be applicable in almost all cases. Moisture sorption isotherms were determined for all five investigated crystalline and amorphous APIs. However, it was necessary to select the parameters individually for each API. The used solvents (water, methanol, isopropanol and methylene chloride) and the humidity-levels (0.05 p/p0 until 0.5 p/p0) were chosen carefully because otherwise the amorphous amounts switch to their crystalline counterparts and are not detectable. The production of fully amorphous samples (absence of crystalline material measured by DSC, mDSC and XRPD) was optimized over several trials. As successfully methods proved ball-milling, freeze-drying, spray-drying and/or quench cooling. In the next step these fully amorphous amounts were blended with crystalline starting material to calibration curves (Turbula blender, influence of electrostatic charge to homogeneity) for the calculation of amorphous content.In summary, the following presented methods were used to determine and quantify low amorphous amounts (between 1.5% and 17.0%) in jet-milled powders (grinding pressure of 8bar, 1–3 grinding cycles), respectively.

Determination of specific surface of activated mesocarbons by sorption of organic vapors

The determination of specific surface of activated mesocarbons prepared from coal tar pitch by sorption of organic vapors and the operating factors affecting their performances were investigated. Proposed paper deals with alternative experimental method based on weight registration during adsorption of pure vapors of volatile organic compounds VOCs on tested samples. Thermogravimeter TGA-HP50 was used for sorption experiments where activated mesocarbon microbeads were the sorbent and vapors of benzene, toluene, acetone and cyclohexane were used as adsorbate. Primary data were actual weight of the tested sorbent and absolute pressure of organic vapor. Experimental data were fitted by Langmuir model of adsorption isotherm. Specific surface was determined from evaluated parameters. Obtained results were compared with results from standard nitrogen S-BET method. Specific surfaces evaluated from both methods are comparable. The influence of important parameters such as chemical activation, extraction and addition of catalytic agents on activated mesocarbons was studied too. Coal tar pitch as raw material was thermally treated together with Lewis acid (FeCl3). Final solid sorbents were prepared by chemical activation of pyridine-insoluble (PI) matters using potassium hydroxide. Weight ratio of activated agent (potassium hydroxide) to PI matters was 1:5, and temperature of activation was 850 °C. It was found that three samples which were activated had greater specific surface area than the one (B) that was not activated, also as they are appropriate for adsorbing the selected adsorptives.

Measurement of low amounts of amorphous content in hydrophobic active pharmaceutical ingredients with dynamic organic vapor sorption

Today, a variety of devices for dry powder inhalers (DPIs) is available and many different formulations for optimized deposition in the lung are developed. However, during the production of powder inhalers, processing steps may induce changes to both, the carrier and active pharmaceutical ingredients (APIs). It is well known that standard pharmaceutical operations may lead to structural changes, crystal defects and amorphous regions. Especially operations such as milling, blending and even sieving generate these effects. These disorders may induce re-crystallization and particle size changes post-production which have a huge influence on drug delivery and product stability.In this study, pilot tests with a polar solvent (water) and hydrophilic drug (Salbutamol sulfate) were performed to receive a first impression on further possible implementation of hydrophobic samples with organic solvents. Thereafter, a reliable method for the accurate detection of low amounts of amorphous content is described up to a limit of quantification (LOQ) of 0.5% for a hydrophobic model API (Ciclesonide). The organic vapor sorption method which is a gravimetric method quantifies exactly these low amounts of amorphous content in the hydrophobic powder once the suitable solvent (isopropanol), the correct p/p0 value (0.1) and the exact temperature (25°C) have been found. Afterward it was possible to quantitate low amorphous amounts in jet-milled powders (0.5–17.0%).In summary, the data of the study led to a clearer understanding in what quantity amorphous parts were generated in single production steps and how variable these parts behave to fully crystalline material. Nevertheless it showed how difficult it was to re-crystallize hydrophobic material with water vapor over a short period. For the individual samples it was possible to determine the single humidity at which the material starts to re-crystallize, the behavior against different nonpolar solvents and the calculation of the reduction of the glass transition temperature (Tg) according to the Gordon–Taylor equation.

Thermodynamic study on dynamic water and organic vapor sorption on amorphous valnemulin hydrochloride

The sorption of water and organic vapors on valnemulin hydrochloride was determined by dynamic vapor sorption at 25 °C. The adsorption-desorption behavior of water vapor and a series of organic vapors was investigated to probe the structural changes in valnemulin hydrochloride before and after sorption. The isothermal adsorption equilibrium data was evaluated using Guggenheim-Anderson-deBoer (GAB) and Brunauer-Emmett-Teller (BET) models. The BET model is applicable only at low relative pressures (0.1⩽RP⩽0.4) while the GAB model is applicable in the whole range of RPs (0.1⩽RP⩽0.9). The sorption kinetics at high RPs was determined by fitting the sorption data to the Avrami equation and the sorption content vs. time relationship could be predicted by the Avrami equation. Finally, the possible sorption mechanism of valnemulin hydrochloride was also discussed. Open image in new window

Rapid and Fully Automated Measurement of Water Vapor Sorption Isotherms: New Opportunities for Vadose Zone Research

Eminent environmental challenges such as remediation of contaminated sites, the establishment and maintenance of nuclear waste repositories, or the design of surface landfill covers all require accurate quantification of the soil water characteristic (SWC) at low water contents. Furthermore, several essential but difficult‐to‐measure soil properties, including clay content and specific surface area, are intimately related to water vapor sorption. Until recently, it was a major challenge to measure detailed water vapor sorption isotherms accurately within a reasonable time frame. This priority communication illustrates potential applications of a new, fully automated, and rapid Vapor Sorption Analyzer (VSA) to pertinent issues in vadose zone research. Detailed vapor sorption isotherms for 25 variably textured soils were measured with the VSA within 1 to 3 d. Links between generated isotherms and pesticide volatilization, toxic organic vapor sorption kinetics, and soil water repellency are illustrated. Several methods to quantify hysteresis effects and to derive soil clay content and specific surface area from VSA‐measured isotherms are presented. Besides above mentioned applications, potential relationships to percolation threshold for solute diffusion in unsaturated soil and to soil cation exchange capacity are discussed to stimulate new and much‐needed vadose zone research.

Organic vapor sorption method of isostructural solvates and polymorph of tenofovir disoproxil fumarate

Tenofovir disoproxil fumarate (TDF) is a prodrug of tenofovir that belongs to a class of antiretroviral drugs, a nucleotide reverse transcriptase inhibitor. An acetonitrile solvate of TDF I, another new solvated form of TDF, was prepared and solid state characterization of its form was conducted using powder X-ray diffraction, FT-IR spectroscopy, and organic vapor sorption isotherm. During the characterization work, it was discovered that (1) TDF I can form solvates and polymorph with a wide variety of organic solvents as well as water and (2) to different extents, these solvates undergoes anisotropic lattice contraction/expansion during desolvation/solvation process suggesting the formation of isostructural solvates of TDF. Solvents used in this study include ethanol, isopropyl alcohol, acetonitrile, cyclohexane, toluene, and water. Four new solvates using ethanol, isopropyl alcohol, acetonitrile, and toluene vapor and one polymorph using water vapor were discovered. Their solid state characterizations were conducted using powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and Fourier transform infrared spectroscopy. A variety of isostructural solvates and a polymorph of TDF was produced by an organic vapor sorption method, showing varying physicochemical properties. This study demonstrates an alternative crystallization method to obtain isostructural solvates.

Vapor and Liquid Sorption in Matrimid Polyimide: Experimental Characterization and Modeling

The sorption of organic vapors of different chemical nature, molecular weight and polarity in glassy Matrimid 5218 polyimide films is measured and modeled in the entire activity range up to saturated vapor conditions. Experimental isotherms show several different peculiarities according to the nature of the solute component, consistent with the glassy character of the polymeric matrix. These features range from high vapor solubility coefficient at infinite dilution to swelling and plasticization of the polymer matrix depending on temperature and solute affinity. The various behaviors are then discussed by means of a thermodynamic model for properties of glassy polymeric phases. Indeed, the Non-Equilibrium Lattice Fluid (NELF) model is used to interpret the Vapor–Liquid-Equilibrium below Tg, while the corresponding equilibrium Lattice Fluid model was considered to the same purpose for the case of plasticization conditions in the system. This representation is able to describe consistently all different observed features and allows for a predictive procedure to reproduce solubility isotherms over a wide activity range.

Thermodynamics of Sorption in an Amorphous Perfluorinated Copolymer AF1600 Studied by Inverse Gas Chromatography

Detailed investigation of infinite dilution sorption of organic vapors (C7−C16 n-alkanes, toluene, octafluorotoluene, p-fluorotoluene, 2,3,4,5,6-pentafluorotoluene, perfluorooctane) in perfluorinated copolymer AF1600 (random copolymer of 35 mol % perfluoroethylene and 65 mol % 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole) was performed by inverse gas chromatography (IGC). C13−C16 n-alkanes were studied in the temperature range including both glassy and rubbery states of the polymer, while sorption of other solutes was investigated only in the glassy state of the perfluorinated copolymer. Retention diagrams of C13−C16 n-alkanes showed breakpoints at ∼150 °C which corresponds to Tg of AF1600. Thermodynamic analysis of IGC data in rubbery and glassy states was performed based on the model developed earlier which included evaluation of Flory−Huggins interaction parameter χ and glassy state structual parameters: excess free volume φV0, polymer cohesion energy ε22, and entropy depression term s12. It was shown that aliphatic and aromatic hydrocarbons were poor solvents for glassy AF1600. Positive χ values substantially increased when the length of the alkane increases. Fluorinated hydrocarbons were, however, good solvents for AF1600, and their quality improved with the increase in fluorination degree. On the basis of the cohesion energy of AF1600 (−17.76 kJ/mol) evaluated by CAChe 7.5 molecular modeling package, excess free volume of AF1600 in the glassy state was found to be close to 0.12 and slightly dependent on temperature. The entropy effect of sorption in glassy polymer was highly negative with entropy depression proportional to molar volume of solute.

ChemInform Abstract: Soil Infrastructure, Interfaces & Translocation Processes in Inner Space (“Soil‐it‐is”): Towards a Road Map for the Constraints and Crossroads of Soil Architecture and Biophysical Processes

AbstractReview: 70 refs.

Characterization and Anisotropic Lattice Expansion/Contraction of Polymorphs of Tenofovir Disoproxil Fumarate

Tenofovir disoproxil fumarate (TDF) is a nucleotide reverse transcriptase inhibitor that is used to treat HIV/AIDS. According to the literature, TDF is known to have three polymorphic forms: I, A, and B. Crystals of all three polymorphs were grown following literature procedures and characterized in the solid state using optical microscopy, single crystal X-ray crystallography, powder X-ray diffraction, Fourier transform infrared spectroscopy, Raman, solid-state NMR, differential scanning calorimetry, thermogravimetric analysis, and organic vapor sorption isotherms. In the course of the analysis, we found that (1) the stoichiometric composition of TDF form A (TD/FA = 2:1) is different from that of TDF forms B and I (TD/FA = 1:1), and therefore TDF form A should not be regarded as a polymorph of TDF form I or TDF form B, (2) TDF forms B and I are actually desolvated forms, (3) anisotropic lattice contraction/expansion occurs between (i) hemimethanolate of TDF form B (TDF form B-MeOH) at low temperature and...

Soil Infrastructure, Interfaces & Translocation Processes in Inner Space ("Soil-it-is"): towards a road map for the constraints and crossroads of soil architecture and biophysical processes

Abstract. Soil functions and their impact on health, economy, and the environment are evident at the macro scale but determined at the micro scale, based on interactions between soil micro-architecture and the transport and transformation processes occurring in the soil infrastructure comprising pore and particle networks and at their interfaces. Soil structure formation and its resilience to disturbance are highly dynamic features affected by management (energy input), moisture (matric potential), and solids composition and complexation (organic matter and clay interactions). In this paper we review and put into perspective preliminary results of the newly started research program "Soil-it-is" on functional soil architecture. To identify and quantify biophysical constraints on soil structure changes and resilience, we claim that new approaches are needed to better interpret processes and parameters measured at the bulk soil scale and their links to the seemingly chaotic soil inner space behavior at the micro scale. As a first step, we revisit the soil matrix (solids phase) and pore system (water and air phases), constituting the complementary and interactive networks of soil infrastructure. For a field-pair with contrasting soil management, we suggest new ways of data analysis on measured soil-gas transport parameters at different moisture conditions to evaluate controls of soil matrix and pore network formation. Results imply that some soils form sponge-like pore networks (mostly healthy soils in terms of agricultural and environmental functions), while other soils form pipe-like structures (agriculturally poorly functioning soils), with the difference related to both complexation of organic matter and degradation of soil structure. The recently presented Dexter et al. (2008) threshold (ratio of clay to organic carbon of 10 kg kg−1) is found to be a promising constraint for a soil's ability to maintain or regenerate functional structure. Next, we show the Dexter et al. (2008) threshold may also apply to hydrological and physical-chemical interface phenomena including soil-water repellency and sorption of volatile organic vapors (gas-water-solids interfaces) as well as polycyclic aromatic hydrocarbons (water-solids interfaces). However, data for differently-managed soils imply that energy input, soil-moisture status, and vegetation (quality of eluded organic matter) may be equally important constraints together with the complexation and degradation of organic carbon in deciding functional soil architecture and interface processes. Finally, we envision a road map to soil inner space where we search for the main controls of particle and pore network changes and structure build-up and resilience at each crossroad of biophysical parameters, where, for example, complexation between organic matter and clay, and moisture-induced changes from hydrophilic to hydrophobic surface conditions can play a role. We hypothesize that each crossroad (e.g. between organic carbon/clay ratio and matric potential) may control how soil self-organization will manifest itself at a given time as affected by gradients in energy and moisture from soil use and climate. The road map may serve as inspiration for renewed and multi-disciplinary focus on functional soil architecture.

Thermodynamics of the sorption of organic vapors in a carbosilane dendrimer and a hyperbranched polymer

Fluorinated derivatives of the carbosilane G6 dendrimer and the hyperbranched polymer of the same chemical structure are synthesized and characterized via the method of inverse gas chromatography. For various organic compounds (n-alkanes, aromatic hydrocarbons, partially fluorinated and perfluorinated organic compounds), the following thermodynamic parameters of their interaction with the above polymers are defined: solubility coefficient S, the sorption enthalpy, the partial molar enthalpy of mixing, the Flory-Huggins parameter, and the solubility parameter. The thermodynamic behavior of vapors in the dendrimer is similar to that in the hyperbranched polymer. For a dendrimer and a hyperbranched polymer, a linear correlation between the logarithm of S and T cr 2 is established, where T cr is the critical temperature of a probe. For both polymers, the partial enthalpy of mixing of n-alkanes is shown to be independent of the dimensions of the probe molecules. This behavior is typical of the vapor sorption in linear polymers at temperatures above the glass transition temperature.

Impact of polymer processing on sorption of benzaldehyde vapor in amorphous and semicrystalline polypropylene

AbstractIn this study, organic vapor sorption properties of different polypropylene (PP) forms (resin, sheet, thermoformed sheet, and atactic PP) at 25°C were investigated. The sorption of benzaldehyde at five vapor activities was studied by using a continuous gravimetric method. The sorption of benzaldehyde vapor in PP exhibited different behaviors among resin, sheet, and polyhedron thermoformed sheet. The experimental results demonstrated that the extrusion and thermoforming processes used for forming these parts had a great impact on the sorption behavior because of the changes in surface and bulk morphologies, especially at high vapor activities. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.

Use of a magnetic suspension microbalance to measure organic vapor sorption for evaluating the impact of polymer converting process

A gravimetric analyzer consisting of a magnetic suspension balance was set up to study the sorption kinetics of benzaldehyde in various forms of polypropylene (PP), including resin, sheet and thermoformed container. Instrument noise was determined throughout the experiments over a maximum of 4000 min or until equilibrium was reached. The sorption of benzaldehyde by PP resin exhibited Fickian sorption kinetics at low vapor activities (0.1–0.5). However, at high vapor activities (0.7 and 0.9), a two-stage sorption involving Fickian diffusion during the initial sorption, followed by a protracted polymer relaxation, which enhanced the sorption capacity, was observed. The converting process of PP resin into sheets and thermoformed containers had a significant impact on the benzaldehyde sorption profile. Benzaldehyde exhibited a much higher solubility in extruded sheet and thermoformed container than in the resin.

Model of Vapor-Induced Resistivity Changes in Gold−Thiolate Monolayer-Protected Nanoparticle Sensor Films

An investigation of the modulation of charge transport through thin films of n-octanethiolate monolayer-protected gold nanoparticles (MPN) induced by the sorption of organic vapors is presented. A model is derived that allows predictions of MPN-coated chemiresistor (CR) responses from vapor-film partition coefficients, and analyte densities and dielectric constants. Calibrations with vapors of 28 compounds collected from an array of CRs and a parallel thickness-shear-mode resonator are used to verify assumptions inherent in the model and to assess its performance. Results afford insights into the nature of the vapor-MPN interactions, including systematic variations in apparent film swelling efficiencies, and show that the model can predict CR responses typically to within 24%. Using CRs of different dimensions, vapor sensitivities are found to be virtually independent of the MPN film volume over a range of 104 (device-area x MPN layer thickness). Sensitivities vary inversely with analyte vapor pressure similarly for the two sensor types, but the CR sensor affords significantly greater signal-to-noise ratios, yielding calculated detection limits in the low-part-per-billion concentration range for several of the analytes tested. The implications of these results for implementing MPN-coated CR arrays as detectors in microanalytical systems are considered.

Dynamics of CO2-Plasticized Electron Transport in Au Nanoparticle Films: Opposing Effects of Tunneling Distance and Local Site Mobility

The electron-transport properties of unlinked and linked solid-state films of very small “Au38” nanoparticles (monolayer protected clusters, or MPCs) remarkably change in opposing directions upon contact with increasing pressures of CO2 gas (0∼6.6 MPa). Electronic conductivities (σEL) of dropcast, unlinked Au MPC films increase up to 31-fold with increasing CO2 pressure, while σEL of dithiol-linked Au MPC films decreases with increasing CO2 pressure. In conductivity by electron hopping between electron donor and acceptor Au MPC cores, the organic protecting ligands serve as a solvent shell whose properties influence the dynamics of electron transport. Exposure of Au MPC films to CO2 and consequent swelling by CO2 (or organic vapor) sorption into the monolayers changes two key factors: core edge-to-edge electron tunneling distances (dHOP) and a previously underappreciated effect of dimension and/or frequency of local core thermal motions. Swelling induces increases in both, but depending on which factor i...