Organic Solvent Vapors Research Articles

Microcapsules Fabricated from Liquid Marbles Stabilized with Latex Particles

Millimeter- and centimeter-sized "liquid marbles" were readily prepared by rolling water droplets on a powder bed of dried submicrometer-sized polystyrene latex particles carrying poly[2-(diethylamino)ethyl methacrylate] hairs (PDEA-PS). Scanning electron microscopy studies indicated that flocs of the PDEA-PS particles were adsorbed at the surface of these water droplets, leading to stable spherical liquid marbles. The liquid marbles were deformed as a result of water evaporation to adopt a deflated spherical geometry, and the rate of water evaporation decreased with increasing atmospheric relative humidity. Conversely, liquid marbles formed using saturated aqueous LiCl solution led to atmospheric water absorption by the liquid marbles and a consequent mass increase. The liquid marbles can be transformed into polymeric capsules containing water by exposure to solvent vapor: the PDEA-PS particles were plasticized with the solvent vapor to form a polymer film at the air-water interface of the liquid marbles. The polymeric capsules with aqueous volumes of 250 μL or less kept their oblate ellipsoid/near spherical shape even after complete water evaporation, which confirmed that a rigid polymeric capsule was successfully formed. Both the rate of water evaporation from the pure water liquid marbles and the rate of water adsorption into the aqueous LiCl liquid marbles were reduced with an increase of solvent vapor treatment time. This suggests that the number and size of pores within the polymer particles/flocs on the liquid marble surface decreased due to film formation during exposure to organic solvent vapor. In addition, organic-inorganic composite capsules and colloidal crystal capsules were fabricated from liquid marbles containing aqueous SiO2 dispersions.

Novel THTBN/MWNTs-OH polyurethane conducting composite thin films for applications in detection of volatile organic compounds

Novel polyurethane (PU) conducting composite thin films based on tetrahydroxyl-terminated poly(butadiene-co-acrylonitrile) (THTBN) and hydroxyl-functionalized multi-walled carbon nanotubes (MWNTs-OH), were prepared via an in-situ coupling reaction route between hydroxyl groups and isocyanate groups. The chemical and crystal structures were characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD). The morphologies and the dispersion behavior of THTBN/MWNTs-OH were examined by scanning electron microscope (SEM), transmission electron microscopy (TEM) and UV–Vis measurements. The influence of MWNTs-OH loading amount on conducting properties and response to some volatile organic compounds (VOCs) especially benzene and toluene was investigated. The experimental results indicated that MWNTs-OH was tightly encapsulated by PU moieties and homogeneously dispersed in the PU moieties. The as-prepared THTBN/MWNTs-OH PU conducting thin films exhibited strong and selective response to nonpolar benzene and toluene vapors, and the response depends on the loading of MWNTs-OH and VOC vapor concentrations. The improvement in dispersity and sensing properties were closely correlated with the chemical linkage of MWNTs-OH in the THTBN matrices through bridging molecules HDI. The developed PU conducting thin films had fast response and reversibility, significant reproducibility and long-term stability. Therefore, they had a possibility as a candidate of volatile organic solvent vapor sensors.

Electrical conductivity of insulating polymer nanoscale layers: environmental effects

As electronic devices are scaled down to submicron sizes, it has become critical to obtain uniform and robust insulating nanoscale polymer films. For that reason, we address the electrical properties of grafted polymer layers made of poly(glycidyl methacrylate), polyacrylic acid, poly(2-vinylpyridine), and polystyrene with thicknesses of 10-20 nm. It was found that layers insulating under normal ambient conditions can display a significant increase in conductivity as the environment changes. Namely, we demonstrated that the in-plane electrical conductivity of the polymer grafted layers can be changed by at least two orders of magnitude upon exposure to water or organic solvent vapors. Conductive properties of all polymer grafted films under study could also be significantly enhanced with an increase in temperature. The observed phenomenon makes possible the chemical design of polymer nanoscale layers with reduced or enhanced sensitivity to the anticipated change in environmental conditions. Finally, we demonstrated that the observed effects could be used in a micron-sized conductometric transducing scheme for the detection of volatile organic solvents.

Occupational exposure to airborne chemical substances in paintings conservators

This paper presents the results of the quantitative study of the airborne chemical substances detected in the conservator's work environment. The quantitative tests were carried out in 6 museum easel paintings conservation studios. The air test samples were taken at various stages of restoration works, such as cleaning, doubling, impregnation, varnishing, retouching, just to name a few. The chemical substances in the sampled air were measured by the GC-FID (gas chromatography with flame ionization detector) test method. The study results demonstrated that concentrations of airborne substances, e.g., toluene, 1,4-dioxane, turpentine and white spirit in the work environment of paintings conservators exceeded the values allowed by hygiene standards. It was found that exposure levels to the same chemical agents, released during similar activities, varied for different paintings conservation studios. It is likely that this discrepancy resulted from the indoor air exchange system for a given studio (e.g. type of ventilation and its efficiency), the size of the object under maintenance, and also from the methodology and protection used by individual employees. The levels of organic solvent vapors, present in the workplace air in the course of painting conservation, were found to be well above the occupational exposure limits, thus posing a threat to the worker's health.

A Flexible Multifunctional Sensor Based on Carbon Nanotube/Polyurethane Composite

A sensor was made of a polymer composite composed of electrically-conductive carbon nanotubes embedded in elastic polyurethane. The composite was prepared using a polyurethane filter membrane, enmeshing it, and melding together with carbon nanotubes. Testing has shown that the composite can be elongated as much as 400% during which the electrical resistance is increased 270 times. The composite is also sensitive to compression and to organic solvent vapors. These properties indicate the composite could have applications as a highly-deformable strain and chemical vapors sensing element and also as flexible electromagnetic shielding or protection against lightning. As an example of the use of the composite as a strain sensor, the pressure variation between a shoe and floor during walking and knee flexion during cycling has been monitored.

CuS-doped CuO nanoparticles sensor for detection of H2S and NH3 at room temperature

Low-cost sensors based on CuS–CuO nanoparticles were fabricated in spray technology and were used as gas sensors for H2S and NH3. The devices had good responses to H2S and NH3 at room temperature. The sensor based on CuS prepared with H2S at 323K and CuS to CuO molar ratio of 1:15 had the highest response value 3139 to 1.88% H2S at operating voltage 8V. The sensor based on CuS prepared with H2S at room temperature and CuS to CuO molar ratio of 1:20 showed a good linear response to H2S gas from 0.85 to 4.25% at 2V operating voltage. The sensor based on CuS prepared with H2S at room temperature and CuS to CuO molar ratio of 1:20 had the highest response value 218 to 9.88% NH3 at operating voltage 2V. The linearity interval of the sensor response to NH3 gas was from 2.88 to 9.88% at 2V operating voltage. No response to NO2, SO2, water vapor and organic solvent vapors was observed. The response and recovery times were satisfactory. Temperature and operating voltage significantly affected the response of the sensors to H2S and NH3.

Plasma Treatment as a Way of Increasing the Selectivity of Carbon Nanotube Networks for Organic Vapor Sensing Elements

Multi-walled carbon nanotubes networks (MWCNTs) were used as a layer for organic vapor detection. The sensor detects volatile organic compounds (VOC). The gas sensing by MWCNTs is measured by means of macroscopic electrical resistance. The selected solvents had different polarities and volume fractions of saturated vapors. The electrical resistance of MWCNTs increases when exposed to organic solvent vapors, and a reversible reaction is observed when the MWCNT is removed from the vapors. The MWCNTs were modified by means of plasma treatment. For modifications RF plasma in O2 at 50 Pa and an afterglow configuration were used. The modified MWCNTs show an increase in sensitivity caused by creating carboxylic groups on the surface of the carbon nanotubes. It leads, for example, to enhancement of the sensitivity from usual 30 % for heptane at RT to more than 200% after plasma treatment in O2 for 10s.

Investigation of the Conformational Changes of a Conducting Polymer in Gas Sensor Active Layers by Means of Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS).

Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) was employed to observe the changes in the molecular conformation of poly(2-phenyl-1,4-xylylene) (PPPX) films that occurred after exposure to organic solvent vapors. The PPPX films were supported on solid matrixes by casting, spin-coating, and Langmuir-Blodgett (LB) techniques. The results show that the polymer is sensitive to the solvent vapors, which affect some of the vibration dipole moments, as detected by PM-IRRAS. The sensitivity depends on the method employed to immobilize the polymer, with more significant changes in films formed using techniques that result in a less systematically organized conformation. This feature enables the use of surface vibration spectroscopy to detect organic solvent vapors and may be applied in an artificial nose.

Detailed FT-IR spectroscopy characterization and thermal analysis of synthesis of barium titanate nanoscale particles through a newly developed process

BaTiO3 nanopowders were prepared at lower temperature and in shorter time span through a newly developed process. To reach an in-detail understanding of mechanism of the process, thermal analysis were performed using DTA/TGA and FT-IR techniques aided by in-depth discussions. The results indicated that thermal evolution of sol–gel-powder transformation consists of following steps: the vaporization of volatile organic solvents, the deformation of gel structure and pyrolysis of the Ba–Ti organic precursors, the decomposition of BaCO3 into BaO and CO2, reaction of resulted BaO with TiO2 to form BaTiO3. The results also elucidated the reaction pattern and formation mechanism of BaTiO3 nanopowders from gel-derived precursor.

Sensing behavior of CdS nanoparticles to SO2, H2S and NH3 at room temperature

The sensors based on the semiconductor CdS nanoparticles were fabricated in spray technology. The properties of the sensors response to SO2, H2S, NH3, NO2, water vapor and some organic solvent vapors were studied systematically. The sensors exhibited a good response to SO2, H2S and NH3 at room temperature. The sensor based on CdS prepared with Na2S at 353K displayed a linear response to NH3 from 0.3 to 6.0% and to SO2 from 0.5 to 1.7%. The sensor based on CdS prepared with H2S at 353K displayed a linear response to NH3 from 0.08 to 1.1% and to SO2 from 0.25 to 1.5%. All the sensor response and recovery times were less than 54s and 70s respectively. Temperature and operating voltage significantly affected the response of the sensor.

Organic solvent vapor effects on phase transition of α and β tegafur upon grinding with solvent additives

Solvent effects on α tegafur (5-fluoro-1-(tetrahydro-2-furyl)uracil) phase transition to β tegafur during grinding with solvent additive, as well as phase transition in samples exposed to 95% relative solvent vapor pressure has been studied in this research. Samples containing 0.5% and 0.1% of β tegafur in α and β tegafur mixture, as well as samples of pure α tegafur were ground with different solvent additives, and conversion degrees depending on the solvent were determined using PXRD method. Samples with α and β tegafur weight fraction of 1:1 were exposed to 95% relative solvent vapor pressure, and phase transition rates were determined. Solubility of α tegafur, solvent sorption and desorption behavior on α and β tegafur have been examined. It was found that the conversion degree of α tegafur to β tegafur mainly depends on solubility of α tegafur in the relevant solvent, and the conversion degree to β tegafur is higher in such solvents, where solubility of α tegafur is higher. The samples ground in a ball mill with solvent additive had a trend of phase transition dynamics from α tegafur to β tegafur similar to the samples exposed to 95% relative solvent vapor pressure.

Facile synthesis of soluble nonlinear polymers with glycogen-like structures and functional properties from “simple” acrylic monomers

A facile approach for the synthesis of hyperbranched polyacrylates is developed. Tetraphenylethene-containing di- and tetra-acrylates are synthesized by esterification of bis(4-hydroxylphenyl)diphenylethene and tetrakis(4-hydroxylphenyl)ethene with acryloyl chloride and polymerized using azobisisobutyronitrile in refluxing THF, furnishing high molecular weight (Mw up to 87 100) polyacrylates with glycogen-like structures and closed-loops in nearly quantitative yields (isolation yield up to 99%). All the polymers are soluble in common organic solvents and are thermally stable with degradation temperatures up to 357 °C under nitrogen. Whereas the monomers and polymers are nonemissive or faintly emissive in solutions, they become strong emitters in the aggregated state, demonstrating a phenomenon of aggregation-induced or enhanced emission. The emission of the monomer and polymer spots on the TLC plates can be turned “off” and “on” continuously and reversibly by wetting and dewetting processes by vapors of organic solvents. The polymers are photosensitive and UV irradiation of their films through copper masks crosslinks the exposed parts, generating fluorescent negative photoresist patterns. The polymers possess good optical transparency and show high refractive indices (RI = 1.6825–1.5653) in a wide wavelength region (400–1700 nm) with low chromatic dispersion. The emission of the polymer nanoaggregates can be quenched efficiently by picric acid with large quenching constants up to 2.07 × 105 M−1, suggesting that they are sensitive fluorescent sensors for explosive detection. The fluorescent polymers become weakly emissive when hydrolyzed under appropriate conditions, implicative of their utility in controlled drug delivery.

Characteristics of a Real Time Monitor Using the Interference Enhanced Reflection Method for Organic Vapors

Performance and sensor characteristics of a monitor for volatile organic compounds (VOC monitor) using the interference enhanced reflection (IER) method were investigated for 52 organic solvent vapors that are designated as class 1 and class 2 organic solvents by the Ordinance of Organic Solvent Poisoning Prevention in Japan. Test vapors were prepared by injecting 1 to 3 μl of liquid solvent into a 20 l Tedlar(®) bag and perfectly vaporizing them. The vapor concentration was simultaneously measured with the monitor and a gas chromatograph (GC) equipped with flame ionization detector, and both values were compared. The monitor could detect all the solvent vapors that we used. Linear response was obtained between the concentration measured by the monitor and those by the GC. The monitor could detect 1/10 of the administrative control level for 37 of 52 solvent vapors, including toluene and xylenes. For 15 vapors, on the other hand, the monitor could not be used for the working environment measurement because the sensor response was low or the regression lines did not pass through the origin.

Performance Tests of Three Types of Air-sampling Bags on Organic Solvent Vapor Retention

Performance of two new air sampling bags [the transparent bag (TP bag) and the semi-transparent bag (ST bag)] was examined as possible surrogates for the traditional PVF bag (the Ref bag). Solvent vapor mixture of butyl acetate, chloroform, ethyl acetate, isopropyl alcohol and toluene at administrative control levels were introduced to each bag (n=5 for each of the three types), and the decay in the concentrations (by%) was followed by use of a gas auto-sampler - FID-GC system. A trend of time-dependent decay was noted for all types including the Ref bag. When the performance was compared, the TP bag was equal to or even better than the Ref bag. In contrast, the performance of the ST bag was comparable to that of the other two types of bags with regard to toluene and chloroform when the storage time was short, but poorer than others for the other three solvents throughout the test period. The TP bag may be a bag of choice when the storage time is extended (e.g., up to 48 h) although this bag is physically less robust and requires careful handling. The ST bag may be used when analysis will be completed within 24 h.

Colloidal monolayer at the air/water interface: Large-area self-assembly and in-situ annealing

Nanosphere lithography (NSL) has been proved to be an inexpensive, inherently parallel, high-throughput, and materials-general technique for the fabrication of ordered nanoparticle arrays. In this work, we present the fabrication of large-area and exclusively single layer polystyrene colloidal crystal using an air/water interface self-assembly method. The interstice size in the floating colloidal monolayer can be manipulated by a subsequent in-situ annealing with a saturated organic solvent vapor. As a result, large-area, transferrable, and high-crystalline-integrity colloidal masks with controllable interstice sizes for NSL application are achieved.

Diffusion, Swelling and Electrical Properties of Polyisoprene/Multiwall Carbon Nanotube Composites in Organic Solvent Vapours

Polyisoprene/nanostructured carbon composites have been fabricated utilizing multiwall carbon nanotubes and carbon black nanoparticles as electrically conductive filler materials. Simultaneous measurements of (1) absorbed mass of organic solvent vapours (OSV), (2) swelling predicted elongation of sample and (3) electrical resistance changes versus the time of the presence of polyisoprene/multiwall carbon nanotube composites (PCNTC) in the OSV ambience were carried out by an in-house computerized setup. Non-Fickian anomalous diffusion has been found for all PCNTC samples as well as for reference samples of polyisoprene/high structure carbon black composites (PCBC). Obtained results indicate that the filler material content can play a substantial role in vapour diffusion into the composite. An advanced tunneling-percolation model was developed and used for describing of the OSV sensing effect in PCNTC and PCBC.

Increased sensitivity of multiwalled carbon nanotube network by PMMA functionalization to vapors with affine polarity

AbstractMultiwalled carbon nanotube network (MWCNT‐N)/poly(methyl methacrylate) (PMMA) composite is prepared by solution radical polymerization. The entangled multiwall carbon nanotube network (MWCNT‐N) is obtained by vacuum filtration and functionalized by allyl isocyanate to form polymerizable vinyl groups on a nanotube surface. The solution polymerization binds PMMA covalently to these groups and yields MWCNT‐N/PMMA composite manifesting electrical conduction and selective chemical vapor sensing. The latter property is evaluated in terms of affinity of organic solvent vapor and PMMA polarities. It is found that the affinity of acetone polarity with polarity of PMMA improves significantly the sensitivity of the composite to this solvent while the sensitivity to methanol is the same and to iso‐pentane even decreased in comparison with the corresponding property of MWCNT‐N. The composite selective response is favorable for a possible composite use as a sensing element and/or vapor switch. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Interaction of l‐leucyl‐l‐leucyl‐l‐leucine thin film with water and organic vapors: receptor properties and related morphology

The ability of highly ordered tripeptide structures to keep or change their morphology in contact with organic vapors was studied. A thin film of tripeptide L-leucyl-L-leucyl-L-leucine (LLL) was prepared having microcrystals and nanocrystals on its surface, which are stable upon vacuum drying but become objects of selective morphology change after a contact with vapors of organic solvents. Fine separate LLL crystals and their agglomerates of submicron and larger dimensions were observed by atomic force microscopy and scanning electron microscopy. After saturation with guest vapors, these crystals can remain intact or change their morphology with the increase in size or complete destruction depending on the guest molecular structure. The crystals completely lose their shape after the binding of pyridine vapors. The other studied guests produce much smaller transformations or have no effect on crystal morphology despite being sorbed by solid LLL, which was shown using quartz crystal microbalance sensor. The observed size-exclusion effect for guest sorption by LLL was found to be broken by the same guests that can change the initial crystal shape. This helps to explain the morphology changes of LLL crystals after the guest sorption and release.

Investigation on the electrical response behaviors of multiwalled carbon nanotube/polyurethane composite in organic solvent vapors

A conducting composite was fabricated from the polyurethane (PU) filled with multiwalled carbon nanotubes (MWCNTs). In the organic vapors condition, the electric resistance of the composite exhibited a drastic increase when compared with its initial resistance. This is because of the matrix swelling induced by the solvent absorption that expands the gap between the fillers. We compared the electrical response behaviors with the organic vapor absorption behaviors of the composite. The non-Fickian (case II) diffusion theory was used to calculate the diffusion rate of organic vapor in the composite. The response rate equation of the composite depending on its organic vapor absorption behavior was then deduced. This equation is better able to explain the experimental phenomena of the selective sensitivity, the influence of vapor pressure and the test temperature. Furthermore, the experiment results showed that the Flory–Huggins interaction parameter and the acid–base interactions of the low permittivity of the organic vapors can determine the maximum magnitude of the response.

Novel HTPB/MWNTs-COOH PU Conductive Polymer Composite Films for Detection of Hazardous Organic Solvent Vapors

A novel polyurethane (PU) conducting composite film was developed by a simple coupling reaction route. The morphologies and structural characterization were conducted by means of FTIR, UV-vis, XRD, TEM, TGA and POM. The influence of the MWNTs-COOH loading amount and curing temperature on response was investigated. The results indicated that the films displayed strong and selective response to some non-polar organic solvent vapor, and have long-term stability. The film loading 15.5 wt% conductive filler exhibited higher response. As the curing temperature is increased, the response is increased, demonstrating the potential for developing a new class of stable and sensitive sensors.