Controlling Microstructure-Transport Interplay in Poly(ether-block-amide) Multiblock Copolymer Gas Separation Membranes.

In this study, we investigated the effect of morphology on the gas-transport properties of a poly(ether-block-amide) (PEBA) multiblock copolymer. We annealed the copolymer samples and varied the annealing temperature to evaluate the influence of changes in the microstructure on the gas transport properties of PEBA. In addition, we used time-resolved attenuated total reflection Fourier transform infrared spectroscopy to evaluate the diffusion coefficient of CO2 in PEBA based on the Fickian model. The effect of the annealing temperature on the microphase-separated structure of the multiblock copolymer is discussed in detail. Furthermore, the gas diffusivity was significantly affected by the purity of the soft domains. The annealed sample demonstrated a 38% increase in CO2 permeability while maintaining a high CO2/N2 permselectivity of approximately 53. The findings of this study provide valuable insight into the design and optimization of PEBA membranes for gas separation applications.

Membrane thinning for efficient CO2 capture.

Enhancing the fluxes in gas separation membranes is required for utilizing the membranes on a mass scale for CO2 capture. Membrane thinning is one of the most promising approaches to achieve high fluxes. In addition, sophisticated molecular transport across membranes can boost gas separation performance. In this review, we attempt to summarize the current state of CO2 separation membranes, especially from the viewpoint of thinning the selective layers and the membrane itself. The gas permeation behavior of membranes with ultimate thicknesses and their future directions are discussed.

A Nano-Thin Film-Based Prototype QCM Sensor Array for Monitoring Human Breath and Respiratory Patterns.

Quartz crystal microbalance (QCM) sensor array was developed for multi-purpose human respiration assessment. The sensor system was designed to provide feedback for human respiration. Thorough optimization of measurement conditions: air flow, temperature in the QCM chamber, frequency measurement rate, and electrode position regarding to the gas flow-was performed. As shown, acquisition of respiratory parameters (rate and respiratory pattern) could be achieved even with a single electrode used in the system. The prototype system contains eight available QCM channels that can be potentially used for selective responses to certain breath chemicals. At present, the prototype machine is ready for the assessment of respiratory functions in larger populations in order to gain statistical validation. To the best of our knowledge, the developed prototype is the only respiratory assessment system based on surface modified QCM sensors.

Cellulose Nanocrystals Crosslinked with Sulfosuccinic Acid as Sustainable Proton Exchange Membranes for Electrochemical Energy Applications.

Nanocellulose is a sustainable material which holds promise for many energy-related applications. Here, nanocrystalline cellulose is used to prepare proton exchange membranes (PEMs). Normally, this nanomaterial is highly dispersible in water, preventing its use as an ionomer in many electrochemical applications. To solve this, we utilized a sulfonic acid crosslinker to simultaneously improve the mechanical robustness, water-stability, and proton conductivity (by introducing -SO3-H+ functional groups). The optimization of the proportion of crosslinker used and the crosslinking reaction time resulted in enhanced proton conductivity up to 15 mS/cm (in the fully hydrated state, at 120 °C). Considering the many advantages, we believe that nanocellulose can act as a sustainable and low-cost alternative to conventional, ecologically problematic, perfluorosulfonic acid ionomers for applications in, e. fuel cells and electrolyzers.

Respiratory monitoring by porphyrin modified quartz crystal microbalance sensors.

A respiratory monitoring system based on a quartz crystal microbalance (QCM) sensor with a functional film was designed and investigated. Porphyrins 5,10,15,20-tetrakis-(4-sulfophenyl)-21H,23H-porphine (TSPP) and 5,10,15,20-tetrakis-(4-sulfophenyl)-21H, 23H-porphine manganese (III) chloride (MnTSPP) used as sensitive elements were assembled with a poly(diallyldimethyl ammonium chloride) (PDDA). Films were deposited on the QCM resonators using layer-by-layer method in order to develop the sensor. The developed system, in which the sensor response reflects lung movements, was able to track human respiration providing respiratory rate (RR) and respiratory pattern (RP). The sensor system was tested on healthy volunteers to compare RPs and calculate RRs. The operation principle of the proposed system is based on the fast adsorption/desorption behavior of water originated from human breath into the sensor films deposited on the QCM electrode.

"Artificial Wood" Lignocellulosic Membranes: Influence of Kraft Lignin on the Properties and Gas Transport in Tunicate-Based Nanocellulose Composites.

Nanocellulose membranes based on tunicate-derived cellulose nanofibers, starch, and ~5% wood-derived lignin were investigated using three different types of lignin. The addition of lignin into cellulose membranes increased the specific surface area (from 5 to ~50 m2/g), however the fine porous geometry of the nanocellulose with characteristic pores below 10 nm in diameter remained similar for all membranes. The permeation of H2, CO2, N2, and O2 through the membranes was investigated and a characteristic Knudsen diffusion through the membranes was observed at a rate proportional to the inverse of their molecular sizes. Permeability values, however, varied significantly between samples containing different lignins, ranging from several to thousands of barrers (10-10 cm3 (STP) cm cm-2 s-1 cmHg-1cm), and were related to the observed morphology and lignin distribution inside the membranes. Additionally, the addition of ~5% lignin resulted in a significant increase in tensile strength from 3 GPa to ~6-7 GPa, but did not change thermal properties (glass transition or thermal stability). Overall, the combination of plant-derived lignin as a filler or binder in cellulose-starch composites with a sea-animal derived nanocellulose presents an interesting new approach for the fabrication of membranes from abundant bio-derived materials. Future studies should focus on the optimization of these types of membranes for the selective and fast transport of gases needed for a variety of industrial separation processes.

Critical Role of the Molecular Interface in Double-Layered Pebax-1657/PDMS Nanomembranes for Highly Efficient CO2/N2 Gas Separation.

In this work, we deposited a CO2-selective block copolymer, Pebax-1657, as a selective layer with a thickness of 2-20 nm on the oxygen plasma-activated surface of poly(dimethylsiloxane) (PDMS) used as a gutter layer (thickness ∼400 nm). This double-layered structure was subsequently transferred onto the polyacrylonitrile (PAN) microporous support and studied for CO2/N2 separation. The effect of interfacial molecular arrangements between the selective and gutter layers on CO2 permeance and selectivity has been investigated. We have revealed that the gas permeance and selectivity do not follow the conventional theoretical predictions for the multilayer membrane (resistance in series transport model); specifically, more selective CO2/N2 separation membranes were achieved with ultrathin selective layers. Detailed characterization of the chemical structure of the outermost membrane surface suggests that nanoscale blending of the ultrathin Pebax-1657 layer with O2 plasma-activated PDMS chains on the surface takes place. This nanoblending at the interface between the selective and gutter layers played a critical role in enhancing the CO2/N2 selectivity. CO2 permeances in the developed thin-film composite membranes (TFCM) were between 1200 and 3500 gas permeance units (GPU) and the respective CO2/N2 selectivities were between 72 and 23, providing the gas separation performance suitable for CO2 capture in postcombustion processes. This interpenetrating polymer interface enhanced the overall selectivity of the membrane significantly, exceeding the separation ability of the pristine Pebax-1657 polymer.

Study of Gases Permeation in Necklace-Shaped Dimethylsiloxane Polymers Bearing POSS Cages.

The transport of small gases (H2, CO2, N2, O2) through a series of novel membranes based on necklace-shaped inorganic polymers (DMS@POSS), in which a polyhedral oligomeric silsesquioxane (POSS) cage unit and soft chains of oligo-dimethyl siloxane (DMS) were alternately connected, was investigated. The influence of the DMS chain length and crosslinking density of the DMS@POSS on membrane properties were studied. The membranes revealed characteristic structure-property relation towards both glass transition and gases transport. Specifically, clear dependence of properties from the length of DMS units (or overall siloxane content) was revealed. Gas transport properties, when compared to state-of-art polydimethylsiloxane and commercial silicone rubber, demonstrated significantly higher selectivity of DMS@POSS for carbon dioxide (in CO2/N2), hydrogen (in H2/N2) and oxygen (in O2/N2) but lowered permeability, proportional to the amount of POSS in the material. With a precise control over mechanical and thermal properties compared to conventional silicone rubbers, described materials could be considered as materials of choice in niche gas separation or other applications.

Thickness Effect on CO2/N2 Separation in Double Layer Pebax-1657®/PDMS Membranes.

The effect of thickness in multilayer thin-film composite membranes on gas permeation has received little attention to date, and the gas permeances of the organic polymer membranes are believed to increase by membrane thinning. Moreover, the performance of defect-free layers with known gas permeability can be effectively described using the classical resistance in series models to predict both permeance and selectivity of the composite membrane. In this work, we have investigated the Pebax®-MH1657/PDMS double layer membrane as a selective/gutter layer combination that has the potential to achieve sufficient CO2/N2 selectivity and permeance for efficient CO2 and N2 separation. CO2 and N2 transport through membranes with different thicknesses of two layers has been investigated both experimentally and with the utilization of resistance in series models. Model prediction for permeance/selectivity corresponded perfectly with experimental data for the thicker membranes. Surprisingly, a significant decrease from model predictions was observed when the thickness of the polydimethylsiloxane (PDMS) (gutter layer) became relatively small (below 2 µm thickness). Material properties changed at low thicknesses-surface treatments and influence of porous support are discussed as possible reasons for observed deviations.

Characterization of polymer-polymer type charge-transfer (CT) blend membranes for fuel cell application.

The data presented in this article are related to polymer-polymer type charge-transfer blend membranes for fuel cell application. The visible spectra of the charge-transfer (CT) blend membranes indicated formation of CT complex in the blend membranes, and behavior of CT complex formation by polymers was clarified by Job plot of the visible spectra. The effect of fluorine for membrane property and fuel cell performance of CT blend membranes were evaluated by 19F NMR and overvoltage analysis, respectively.

Macroscale Superlubricity of Multilayer Polyethylenimine/Graphene Oxide Coatings in Different Gas Environments.

Friction and wear decrease the efficiency and lifetimes of mechanical devices. Solving this problem will potentially lead to a significant reduction in global energy consumption. We show that multilayer polyethylenimine/graphene oxide thin films, prepared via a highly scalable layer-by-layer (LbL) deposition technique, can be used as solid lubricants. The tribological properties are investigated in air, under vacuum, in hydrogen, and in nitrogen gas environments. In all cases the coefficient of friction (COF) significantly decreased after application of the coating, and the wear life was enhanced by increasing the film thickness. The COF was lower in dry environments than in more humid environments, in contrast to traditional graphite and diamond-like carbon films. Superlubricity (COF < 0.01) was achieved for the thickest films in dry N2. Microstructural analysis of the wear debris revealed that carbon nanoparticles were formed exclusively in dry conditions (i.e., N2, vacuum), and it is postulated that these act as rolling asperities, decreasing the contact area and the COF. Density functional theory (DFT) simulations were performed on graphene oxide sheets under pressure, showing that strong hydrogen bonding occurs in the presence of intercalated water molecules compared with weak repulsion in the absence of water. It is suggested that this mechanism prevents the separation graphene oxide layers and subsequent formation of nanostructures in humid conditions.

In vitro detection of small molecule metabolites excreted from cancer cells using a Tenax TA thin-film microextraction device.

We developed a new device for the in vitro extraction of small molecule metabolites excreted from cancer cells. The extraction device, which was biocompatible and incubated with cancer cells, consists of a thin Tenax TA film deposited on the surface of a cylindrical aluminum rod. The Tenax TA solid phase was utilized for the direct extraction and preconcentration of the small molecule metabolites from a cell culture sample. The device fabrication and the metabolite extraction were optimized, tested, and validated using HeLa cell cultures. Comparison of metabolic profiles with the control measurement from the culture medium enabled detection of metabolites that were consumed or produced by the cell culture. Tentative identification and semi-quantitative investigation of the excreted metabolites were performed by GC-MS analysis. The proposed approach can be a valuable tool for the characterization of low-volatile cancer cell metabolites that are not covered by use of conventional methods based on headspace solid phase microextraction.

Titania nanocoating on MnCO3 microspheres via liquid-phase deposition for fabrication of template-assisted core-shell- and hollow-structured composites.

A novel class of core-shell- and hollow-structured MnCO3/TiO2 composites was synthesized by titania nanocoating on MnCO3 microspheres via two-step liquid-phase deposition at room temperature. Morphological change from core-shell to hollow microparticles was possible in the prepared samples by controlling prereaction time of MnCO3 and [NH4]2TiF6. Upon the prereaction process, the core of the core-shell MnCO3/TiO2 became highly porous, and a honeycomb-like surface that resembled the orientation of self-assembled MnCO3 nanocrystals was developed. The MnCO3 core was completely removed after 6 h prereaction. Calcination at 600 °C resulted in the transformation of both core-shell- and hollow-structured composites to Mn2O3/TiO2 anatase microspheres that retained their original morphologies. X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and electron probe microanalysis were employed for microsphere characterization. As the first trial for application of the synthesized materials, solid-extraction of organics from aqueous media was examined using methylene blue (MB). Both types of Mn2O3/TiO2 composites showed very fast adsorption of MB with high extraction values of 5.2 and 6.4 µmol g(-1) for the core-shell and hollow structures, respectively. Current work provides a new approach for facile fabrication of titania-metal oxide nanocomposites with unique morphological features and promising application possibilities.

Self-assembly and imprinting of macrocyclic molecules in layer-by-layered TiO2 ultrathin films.

Alternate TiO2 gel ultrathin films assembled with a macrocyclic carboxylic acids of tetrakis-4-carboxyphenyl porphine (TCPP) or tetra-4-carboxylphthalocyanine cobalt (II) (Co-TCPc) were prepared by the surface sol-gel process. To confirm the film growth and imprinting effect, quartz crystal microbalance (QCM) and UV-vis spectroscopy measurements were employed. The binding of TCPP was 1.2-14.3 times more selective compared to structurally related macrocyclic guest molecules. Among other findings, tetrakis-4-carboxymethyloxyphenyl porphine (TCMOPP) that has a spacer (-O-CH2-) between the phenyl rings and carboxylic acid moieties of TCPP showed a significantly lower binding efficiency equal to 0.07, regardless of its similar molecular structure to the template molecule. Structural difference of porphyrin and phthalocyanine analogs could be also selectively discriminated: the TCPP imprinted film showed ca. 13 times higher selectivity for recognition of TCPP itself from the mixture of TCPP and Co-TCPc. Characterization by AFM demonstrated that the TiO2/TCPP film has highly uniform surface and ultrathin thickness, while both TEM and SEM studies confirmed the immobilized structures of TCPP inside the film.

TD-GC-MS Investigation of the VOCs Released from Blood Plasma of Dogs with Cancer.

An analytical TD-GC-MS method was developed and used for the assessment of volatile organic compounds (VOCs) released from the blood plasma of dogs with/without cancer. VOCs released from 40 samples of diseased blood and 10 control samples were compared in order to examine the difference between both sample groups that were showing qualitatively similar results independent from the disease's presence. However, mild disturbances in the spectra of dogs with cancer in comparison with the control group were observed, and six peaks (tentatively identified by comparison with mass spectral library as hexanal, octanal, toluene, 2-butanone, 1-octen-3-ol and pyrrole) revealed statistically significant differences between both sample groups, thereby suggesting that these compounds are potential biomarkers that can be used for cancer diagnosis based on the blood plasma TD-GC-MS analysis. Statistical comparison with the application of principal component analysis (PCA) provided accurate discrimination between the cancer and control groups, thus demonstrating stronger biochemical perturbations in blood plasma when cancer is present.

Simultaneous monitoring of humidity and chemical changes using quartz crystal microbalance sensors modified with nano-thin films.

Quartz crystal microbalance (QCM) electrodes modified with nano-thin films were used to develop a system for measuring significant environment changes (smoke, humidity, hazardous material release). A layer-by-layer approach was used for the deposition of sensitive coatings with a nanometer thickness on the electrode surface. The QCM electrode was modified with self-assembled alternate layers of tetrakis-(4-sulfophenyl) porphine (TSPP) (or its manganese derivative, MnTSPP) and poly(diallyldimethylammonium chloride) (PDDA). The QCM sensors, which had been reported previously for humidity sensing purposes, revealing a high possibility to recognize significant environmental changes. Identifying of the origin of environmental change is possible via differential signal analysis of the obtained data. The sensors showed different responses to humidity changes, hazardous gas (ammonia) or cigarette smoke exposure. Even qualitative analysis is not yet available; it has been shown that ventilation triggers or alarms for monitoring smoke or hazardous material release can be built using the obtained result.

Remarkable enantioselectivity of molecularly imprinted TiO2 nano-thin films.

TiO(2) nano-thin films with imprinted (R)- and (S)-enantiomers of propranolol, 1,1'-bi-naphthol, and 2-(4-isobutylphenyl)-propionic acid were fabricated on quartz plates by spin-coating their solutions with Ti(O-(n)Bu)(4) in a toluene-ethanol mixture (1:1, v/v). After template removal, the imprinted films showed better binding for original templates than to the corresponding enantiomers. The assessment of template incorporation, template removal, and re-binding was conducted through UV-vis measurements. Significant enhancement of enantioselectivity was achieved by optimization of the film thickness and by heat-treatment of the imprinted films. After subtraction of non-specific binding, the optimized films provided chiral recognition with the enantioselectivity of almost 100% for (R)-propranolol and 95% for (S)-propranolol.