Water Vapor Adsorption Isotherms Research Articles

Effects of operative conditions on products obtained of starch-oil mixtures by single-screw extrusion.

d. The aim of the study was to evaluate the fat binding and physicochemical properties of the products under conditions of potato starch extrusion containing rapeseed or linseed oil and rapeseed oil with glycerol. The study dealt with the extrudates of potato starch produced with the addition of rape seed or linseed oil and rapeseed oil and glycerol at 22% humidity. The extrudates were obtained at two screw speeds: 80 rpm and 100 rpm. Extrudates containing rapeseed oil and glycerol (R6G) were obtained at a temperature distribution of 115/130/150°C, while those with the participation of rapeseed oil and linseed oil were obtained at 120/135/128°C. Water solubility index (WSI), water absorption index (WAI), specific surface area (SBET) and quantity of fat permanently bound were determined for the products obtained. When oils were added, the solubility of extrudates decreased as compared to the control samples (starch without oil; S). Rapeseed oil added to the starch mixture at the levels of 3 g and 6 g in had no sig- nificant effect on the solubility of the product and amounted to: 80.3–82.6% and 78–79.6%. The largest decrease in solubility (WSI, 55.4–57.1%) was demonstrated for samples with 6% addition of rapeseed oil and 10 g glycerol. For these samples (R6G), a significant increase in the index WAI (376–397%) was recorded. Extrudates obtained with the addition of 3 g of rapeseed oil absorbed slightly more water than those with 6 g of oil added. The specific surface area (SBET 230–256 m2/g) determined from the water vapor adsorption isotherm indicates no statistically significant difference at α = 0.05 for products with rapeseed oil, linseed oil, and controls. A significant increase in the specific surface area (SBET 284–347 m2/g) was observed for samples with 6g rapeseed oil and 10 g glycerol added. For samples with 3 g of rapeseed oil, the amount of bound fat was 1.9–2.1 g/100 g of starch and for 6% the starch percentage was 2.96–3.5 g/100 g. The water solubility of starch extrudates with the addition of oils decreases with an increase   in screw speed. Starch extrudates with linseed oil and rapeseed oil plus added glycerol are characterized by an increase in water-absorption capacity with respect to the control extrudates. The products obtained with the addition of rapeseed oil and glycerol exhibit a significant increase in their specific surface area. The quan- tity of fat permanently bound during extrusion depended on: the oil type, its percentage in the mixture and the screw speed. The linseed oil was the least absorbed in the starch structure, but rapeseed oil binding increased with the increase in its level in the mixture.

Thickness and stability of water film confined inside nanoslits and nanocapillaries of shale and clay

Characteristics of water film thickness and stability within nanopores are topics of great interest for evaluation of initial fluid storage in unconventional reservoirs. Although related researches with thin film on flat substrates have been carefully and extensively considered, the thickness and stability of liquid films affected by nanoscale confinement in nanostructured materials, such as clay minerals and tight rocks, have raised lots of questions.In this work, an approach by considering fluid/pore-wall interactions (surface forces) was developed to describe the phase behavior of thin water film transition into liquid condensation. The calculated results reveal that the instability mechanisms of adsorbed films differs inside slits and capillaries. In slit pores, the coalescence of flat wetting films forms under the action of attractive forces by opposite slit surfaces. Whereas in capillaries, collapse of curved wetting films occurs due to the integrative action of surface force and cylindrical capillary force. Due to the additional capillary action, the total surface interactions inside capillaries are higher than that inside silts, which leads to an easier condensation and thicker film thickness in capillaries.Meanwhile, the phase behavior of adsorbed water film within nanoporous montmorillonite and shale were investigated by water vapor (H2O) adsorption isotherms. Specially, the water distribution characteristics inside single nanopore rather than the whole porous media were also investigated based on the difference of pore size distribution (PSD) between dry and moist samples, and these PSD information was obtained by low temperature (77K) nitrogen (N2) sorption analysis. Our experimental results directly demonstrated the evidence of water condensation in hydrophilic clay samples, e.g., pores <6–7nm would be totally blocked by capillary water. However, a “partial condensation” phenomenon was found in shale samples, e.g., the shale nanopores could not been entirely filled by water even under a high-moisture condition (RH=0.98), which was mainly caused by hydrophobic repulsion of organic minerals. This surface repulsion could prevent water from condensing and likely result in a monolayer water film adsorbed inside these hydrophobic organic nanopores, e.g. graphite. Therefore, in an actual shale system with initial moisture, the storage of water inside organic pores can be neglected while these inorganic micropores blocked by condensate may be unavailable for gas storage or transport.

Methodology for determining the thermodynamic properties of smectite hydration

This study proposes an improved methodology for extracting the thermodynamic hydration properties of clay minerals from adsorption isotherms performed at two temperatures, by removing the capillary water contribution. The work focuses on Na-smectite. Its thermodynamic hydration properties were extracted as follows: (i) experimental measurement of water vapor adsorption isotherms at two temperatures (25 °C and 45 °C); (ii) removal of the capillary water contribution; (iii) calculation of the thermodynamic properties. The values obtained from the adsorption branch compare favorably with calorimetric measurements. We parameterized a strict regular solid solution model similar to that developed by Ransom and Helgeson (1994). From this we see how the thermodynamic properties of hydration evolve, so we can explain and sort the values obtained by previous authors. The calculation process, based on structural constraints from the literature, considers only half of the total adsorbed water as structurally related to the mineral, when relative humidity conditions are close to 100%. The approach proposed in this work enables generalization to other types of clay minerals and implementation of thermodynamic databases with thermodynamic properties that are intrinsic to each clay mineral and independent from contextual constraints.

Reduction in Crystal Size of Flexible Porous Coordination Polymers Built from Luminescent Ru(II)-Metalloligands

In this study, we examined the reduction in crystal size of the porous coordination polymers (PCPs) {Sr4(H2O)9][4Ru]2·9H2O]} (Sr2[4Ru]) and [Mg(H2O)6]{[Mg2(H2O)3[4Ru]·4H2O} (Mg2[4Ru]) composed of a luminescent metalloligand [Ru(4,4′-dcbpy)]4–([4Ru]; 4,4′-dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) using a coordination modulation method. Scanning electron microscopy measurements clearly show that the sizes of crystals of Sr2[4Ru] and Mg2[4Ru] were successfully reduced to the mesoscale (about 500 nm width and 10 nm thickness for Sr2[4Ru] (abbreviated as m-Sr2[4Ru]) and about 1 μm width and 30 nm thickness for Mg2[4Ru] (abbreviated as m-Mg2[4Ru])) using lauric acid as a coordination modulator. Interestingly, the nanocrystals of m-Sr2[4Ru] formed flower-like aggregates with diameters of 1 μm, whereas flower-like aggregates were not formed in m-Mg2[4Ru]. Water vapor adsorption isotherms of these nanocrystals suggest that the water adsorption behavior of m-Sr2[4Ru], which has a three-dimensional lattice structure containing small pores, is significantly different from that of the bulk Sr2[4Ru] crystal, as shown by the vapor adsorption isotherm. In contrast, m-Mg2[4Ru], which has a two-dimensional sheet structure, had an adsorption isotherm very similar to that of the bulk sample. These contrasting results suggest that the dimensionality of the coordination framework is an important factor for the guest adsorption behavior of nanocrystalline PCPs.

Sr-, Zn- and Cd-exchanged zeolitic materials as water vapor adsorbents for thermal energy storage applications

This paper reports the characterization of Sr-, Zn- and Cd-exchanged zeolitic materials as water vapor adsorbents, in order to evaluate the influence of the extraframework species on their adsorption properties. Both synthetic and natural substrates are taken into account. Water vapor adsorption isotherms on each ion-exchanged sample have been obtained at 298, 318, 338, and 358K and have then been modeled using the Dubinin-Astakhov equation. Focusing on the possible implementation of such adsorbents in thermodynamic cycles, an estimation of their specific heat storage densities has been expressed. Results revealed that adsorbents of natural origin are not suitable for a valid employment in thermodynamic cycles, while FAU-type zeolite X samples exchanged with Sr2+ or divalent transition metal ions (i.e., Zn2+ or Cd2+) show a significant potential as heat storage media. The same trend of the specific heat storage density with the cationic content of the adsorbent can be identified for both series of synthetic and naturally originating materials (i.e., Zn>Sr>Cd>Na), confirming how ion exchange allows effective tuning of zeolitic substrates when employed in thermodynamic cycles based on the reversible adsorption of water vapor.

Surface fractal dimension, water adsorption efficiency, and cloud nucleation activity of insoluble aerosol.

Surface porosity affects the ability of a substance to adsorb gases. The surface fractal dimension D is a measure that indicates the amount that a surface fills a space, and can thereby be used to characterize the surface porosity. Here we propose a new method for determining D, based on measuring both the water vapour adsorption isotherm of a given substance, and its ability to act as a cloud condensation nucleus when introduced to humidified air in aerosol form. We show that our method agrees well with previous methods based on measurement of nitrogen adsorption. Besides proving the usefulness of the new method for general surface characterization of materials, our results show that the surface fractal dimension is an important determinant in cloud drop formation on water insoluble particles. We suggest that a closure can be obtained between experimental critical supersaturation for cloud drop activation and that calculated based on water adsorption data, if the latter is corrected using the surface fractal dimension of the insoluble cloud nucleus.

FIBROUS CHEMISORBENTS-AMPHOLYTE BASED ON THE COMPLEX COMPOUND OF NICKEL(II) CHLORID AND MONOETHANOLAMINE

The water vapor adsorption by complex compounds of nickel(II) chloride and monoethanolamine with different molar ratio metal : ligand, deposited on a fibrous carrier from nonwoven web on the basis of polyester fiber has been investigated under static conditions. Water vapor adsorption isotherms were analyzed in the framework of Brunauer-Emmett-Teller (BET) adsorption theory, monolayer capacitance values and the heats of water molecules adsorption in the first layer were determined. Sulphur dioxide and ammonia chemisorptions under static and dynamic conditions with obtained chemisorbents has been investigated. It was found the process of chemisorption of sulfur dioxide can take place only in the presence of «free» water formed on the fiber surface after formation of the monolayer, when the value of water vapor relative pressure of reaches P/PS = 0,25÷0,30. Under these conditions the destruction of the donor-acceptor bond in the cation complex between the nickel ions and monoethanolamine molecules within the domestic sphere of aminocomplexes takes place followed by the formation of more stable «onium» sulphites, hydrosulphites and pyrosulphite. It is found in the case of ammonia chemisorption by above mentioned material prewetting of the sample does not significantly increase ammonia absorption. In this case the displacement of the water molecules from inner-aquaaminocomplexes composition and replacing it with an equivalent amount of ammonia molecules take place to form a mixedligand complex of the composition: [Ni(HOCH2CH2NH2)n(NH3)6‑2n]Cl2. It is shown that the designed fibrous chemisorbent carries out a combined air purification both on sulfur dioxide and ammonia and may be used for the equipment of personal respiratory protection – lightweight respirators for dust and gases.

EFFECT OF THE TIME OF ACID-THERMAL MODIFICATION OF CLINOPTILOLITE ON ITS STRUCTURE-ADSORPTION CHARACTERISTICS

Literary data concerning the influence of different factors of acid treatment on values of specific surface area (Ssp) of clinoptilolite mined from various deposits are presented and analyzed. These data are compared with our results showing how the time of interaction of natural Ukrainian clinoptilolite with boiling nitric acid affects its structure-adsorption properties. Following IUPAC classification, water vapor ad/desorption isotherms for natural clinoptilolite from Sokirnitskoe deposit and its acid-modified forms belong to IVa type. Values of the specific surface area (Ssp) for the clinoptilolite samples were estimated using the BET equation and by measuring the thermal desorption of argon by the gas chromatographic method. Ssp values estimated by the use of BET equation from water vapor adsorption isotherms and those determined by chromatographic method from thermal desorption of argon are higher for all H-CLI samples than for N-CLI. Values of the monolayer capacity for the clinoptilolite samples have been found to increase in the order N-CLI < H‑CLI‑0.5 < H-CLI-1 < H-CLI-3 ≈ H‑CLI-6 ≈ H-CLI-9 and whereas their C(Q1) parameter have been found to change in the reverse order. Both natural and acid-modified clinoptilolite samples have nonuniform porous structures with prevalence of meso- and macropores. The minimum Ssp value was revealed for natural clinoptilolite and its acid-thermal modification resulted in an increase in the specific surface area.

Multifunctional solar wall for dehumidification, heating and removal of formaldehyde: Part 1. System description, preparation and performance of SiO2/TiO2 adsorbent

This article proposes a novel multifunctional solar wall that can realize heating and removal of formaldehyde in winter and dehumidification and removal of formaldehyde in summer. Multifunctional materials focusing on the dehumidification and the removal of low-concentration indoor gaseous contaminant simultaneously are of great interest for the improvement of building environment and energy conservation in building. SiO2/TiO2 composite adsorbents with different TiO2 content for the adsorption of formaldehyde and dehumidification were prepared by the sol–gel method. The porous properties of the composite adsorbents were investigated by ASAP2010 volumetric adsorption analyzer. The water vapour adsorption isotherms at 25 °C and breakthrough curves of formaldehyde at typical indoor pollutant concentrations i.e. 0.7 ppm and 1.4 ppm, respectively were measured. The kinetic adsorption curves of water vapour and formaldehyde on composite adsorbents were measured and linear driving force (LDF) model was applied. Also the kinetic adsorption rate constants obtained by the fittings of the kinetic adsorption curves based on LDF model were analyzed. Results showed that composite adsorbents had excellent water vapour adsorption capacity under the low and medium humidity compared with commercial silica gel. The introduction of TiO2 increased the polarity of composite adsorbents. And composite adsorbent with a certain amount of TiO2 (SiO2: TiO2 = 90: 10, mole ratio) possessed high kinetic adsorption rate constant under the low relative humidity. Furthermore, the introduction of TiO2 improved formaldehyde adsorption capacity under typical indoor concentration levels, which suggested that composite adsorbents were efficient in capturing the trace amount of indoor formaldehyde.

Stability of an Al-Fumarate MOF and Its Potential for CO2 Capture from Wet Stream

In this work, a new aluminum fumarate MOF was investigated regarding its water stability and CO2 adsorption in the presence and absence of water. The adsorption equilibrium isotherms were measured at 303, 323, and 348 K for CO2 and at 288 and 313 K for water vapor. Water vapor adsorption isotherms are type IV and were fit using the Langmuir-Ising model. The adsorption capacity of CO2 at 303 K and 1.0 bar was 2.1 mmol/g and remained constant after exposure to humidity and regeneration. The isosteric heats of adsorption were 21 and 44 kJ/mol for CO2 and H2O, respectively. Fixed bed experiments were performed at 303 K to determine breakthrough curves of CO2, water vapor, and the CO2/water vapor mixture. Binary breakthrough indicated a reduction of only 17% in CO2 adsorption capacity for a stream with 14% RH. The remarkable stability of this MOF suits it for such applications as CO2 capture and thermal storage with water.

Anhydrous ethanol recovery from wet air in TSA systems – Equilibrium and column studies

An experimental and theoretical study of two combined temperature swing adsorption (TSA) systems for the recovery of anhydrous ethanol from wet air using activated carbon Sorbonorit 4 (ACS4) and zeolite molecular sieve 3A (ZMS3A) are developed. Adsorption isotherms of ethanol and water vapors on ACS4 and ZMS3A in the temperature range of 20–140°C and water from liquid ethanol on ZMS3A at temperatures of 20–60°C were measured. The data were analyzed using multi-temperature Toth, Sips, hybrid Langmuir-Sips, inhomogeneous DA and the excess surface work models. The results demonstrate selective water adsorption on ZMS3A with higher adsorption capacity in the liquid (28.02mol/kg) than in the gas phase (10.67mol/kg), and higher adsorption of ethanol (7.21mol/kg) than water vapor on ACS4 up to relative pressure 0.6. The influence of the inlet concentration in the gas (2.8–8.4g/m3 for ethanol) and liquid phase (45–141kg/m3 for water–ethanol mixture) on the adsorption dynamic was studied in two fixed-bed columns with ACS4 and ZMS3A. The characteristic parameters of breakthrough curves and maximum temperature rise in the column were determined. The Thomas model was successfully employed to predict the breakthrough curves for both gas and liquid phase. The energy requirement for ethanol electrothermal desorption from ACS4 bed (151–235kJ/mol) was lower than for hot purge gas regeneration of wet ZMS3A bed (423kJ/mol). These values were several times larger than the isosteric heat of adsorption (13–71kJ/mol) which represents minimum energy requirement for desorption.

Adsorption characteristics of AQSOA zeolites and water for adsorption chillers

In this article, the authors presented the characterization and property evaluation of AQSOA zeolites by various experimental methods including X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), N2 adsorption/desorption isotherms and thermo gravimetric analysis (TGA). The amount of H2O uptakes on AQSOA-Z01 and AQSOA-Z02 were measured for the temperatures of 298K, 313K and 338K. It was found that the water vapor adsorption isotherm of AQSOA-Z01 was characterized by S-shape with hydrophobic behavior at the beginning of adsorption or low pressures. The enthalpies of adsorption (Qst) for AQSOA zeolites+water were calculated employing Clausius Clapeyron relations via experimentally measured adsorption isotherms data. The Qst derived from various adsorption isotherm models were also added for comparison purposes. It was found that the porous structure of AQSOA-Z01 exhibits a high H2O vapor uptakes and delivered 0.1kg of water per kg of zeolite for one adsorption–desorption cycle even at the desorption temperature of 65°C.

Preparation of hydrophilic activated carbon through alkaline hydrolysis of ester for effective water-vapor adsorption

Hydrophilic activated carbon was prepared by a novel ethyl acetate hydrolysis method. Surface area analysis, spectroscopies, and microscopy were used to examine characteristic differences between raw and hydrophilic activated carbons. Results showed that hydrophilic groups were introduced onto the surface of activated carbon through ethyl acetate hydrolysis in an alkaline environment. The modified activated carbon exhibited higher water vapor adsorption capacity because the hydrophilic groups on its surface bound with water molecules through H-bonding. Adsorption isotherms of water vapor were well fitted by an adsorption model. The optimal temperature for thermal regeneration was determined to be 398 K.

THE THEORY OF DEVELOPMENT OF SUPPORTED METAL-COMPLEX CATALYSTS

Some results of the investigations for the purpose of development of supported metal-complex catalysts for phosphine and carbon monoxide oxidation as well as for ozone decomposition are summarized. The activity of such catalysts has been found to depend not only on a nature of a central atom and ligands but also on a nature of supports. The theoretical model explaining mechanisms of surface complex formation taking into account the influence of physicochemical and structural-adsorption properties of the supports (SiO2, Al2O3, carbon materials, zeolites, dispersed silicas, lamellar aluminosilicates, etc.) has been proposed. For quantitative description of the support effect, such a thermodynamic parameter as the adsorbed water activity assignable with the help of water vapor adsorption isotherms has been introduced. Successive stability constants of the surface metal complexes have been calculated by the kinetic method and, hence, compositions and partial catalytic activity of the latter have been determined. Taking into account the competitive adsorption of metal ions on the supports, some schemes of formation of surface bimetallic complexes have been suggested. The compositions of the supported metal-complex catalysts have been optimized to meet requirements of their use in respirators and plants for air purification from foregoing gaseous toxicants.

Structural and thermodynamic characterization of modified cellulose fiber-based materials and related interactions with water vapor

In this study, the surface characteristics, water vapor interactions, and state of water adsorbed on unmodified and coated paper samples were investigated in an attempt to obtain a better understanding of the fundamental principles related to thermodynamics of this process, as well as to provide essential insight that could be used for further improvement of the papers’ barrier properties. Based on the BET measurement, the coated paper samples showed higher specific surface areas than unmodified paper; however, their mean pore diameters are smaller. The BJH method was used for pore size distribution analysis. Hydrophobic properties of the paper samples were determined from experimental isotherms, e.g., monolayer moisture content, and these results have been related to the water vapor transfer rates (WVTRs) showing a complex nature of these relations. The highest peak corresponding to the modified samples with smaller pore sizes was found to be in the range of 1–30nm, while it was in the 30–100nm pore size range for unmodified paper. The net isosteric heats of sorption for different unmodified and modified paper samples were determined from water vapor adsorption isotherms measured at 15, 25, and 35°C. The net isosteric heats of sorption decreased with an increase of moisture content after reaching the maximum values at 12.53, 15.25, 14.71, 23.2, and 22.77kJ/mol for unmodified, zein grafted, calendered coated, PLA, and PHBV coated papers, respectively. The state of adsorbed water and water-vapor interaction on paper surface were also studied by TGA–DSC and FT-IR spectroscopic techniques. The FT-IR results revealed the formation of water vapor clusters due to poly-layer formation at the higher relative humidity. This has a profound effect on the equilibrium properties, e.g., the intensity of interactions between water molecules and the paper surface decreases as the relative humidity (moisture content) increases. Percentage of bound and unbound water formation and also the dehydration energy at various relative humidities were determined for the paper samples using the TGA–DSC technique.

Hierarchical MOF-xerogel monolith composites from embedding MIL-100(Fe,Cr) and MIL-101(Cr) in resorcinol-formaldehyde xerogels for water adsorption applications

Shaping of otherwise powdery metal-organic frameworks is recognized as a more-and-more important issue to advance them to the application stage. Monolithic MOF composites were synthesized using micro-to-mesoporous MIL-100(Fe,Cr) and MIL-101(Cr) as thermally and chemically stable MOFs together with a mesoporous resorcinol-formaldehyde based xerogel as binding agent. The monolithic bodies could be loaded with up to 77 wt% of powdery MIL material under retention of the MIL surface area and porosities (from N2 adsorption) by pre-polymerization of the xerogel solution. The obtained monoliths are mechanically stable and adsorb close to the expected water vapor amount according to the MIL weight percentage. There is no loss of BET surface area, porosity and water uptake capacity especially for the MIL-101(Cr) composites. Water vapor adsorption isotherms show that the 77 wt% MIL-101(Cr) loaded composite even features a slightly increased water vapor uptake compared to pure MIL-101(Cr) up to a relative vapor pressure of P·P0−1=0.5. These hydrophilic monolithic composites could be applied for heat transformation application such as thermally driven adsorption chillers or adsorption heat pumps.

HKUST-1 Thin Film Layer-by-Layer Liquid Phase Epitaxial Growth: Film Properties and Stability Dependence on Layer Number

The layer-by-layer epitaxial growth of HKUST-1 (Cu3(btc)2 where btc = 1,3,5-benzenetricarboxylate) thin films is measured by quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray diffraction (XRD), and scanning electron microscopy (SEM) as a function of the number of layers (20–80 layers) for −OH and −COOH functionalized surfaces. Up to approximately 40 layers, the film growth proceeds by a layer-by-layer mode controlled by the chemical functionalization of the surface. For example, on hydroxylated SiO2, film growth is in the preferred [222] direction. Beyond 40 layers, for both −COOH and −OH functionalized surfaces, the crystallite grain size increases and ∼50–100 nm octahedral crystals are formed. Independent of the surface functional groups (−COOH and −OH), the octahedral crystals form with the {200} planes oriented parallel to the surface. By monitoring changes in mass and dissipation, the QCM data provides evidence for the change in growth behavior. The stability of the films, determined by measuring CO2 adsorption isotherms, depends on film properties (morphology and grain size) as well as film age. For films deposited on hydroxylated SiO2 surfaces, CO2 uptake decreases rapidly within a few days after film synthesis with the 40 layer films ({222} planes) exhibiting a more pronounced decrease than the 80 layer films ({200} planes, octahedral crystals). The decrease in CO2 uptake is attributed to the differing propensities for water uptake in thin films of different morphologies as evidenced by water vapor adsorption isotherms and Raman spectral changes.

Cassava starch films containing acetylated starch nanoparticles as reinforcement: Physical and mechanical characterization

This paper reports the use of acetylated starch nanoparticles (NPAac) as reinforcement in thermoplastic starch films. NPAac with an average size of approximately 500nm were obtained by nanoprecipitation. Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) indicated that NPAac are more thermally stable and essentially amorphous when compared with acetylated starch. Thermoplastic starch films with different proportions of NPAac (0.5, 1.0, 1.5, 10.0%, w/w) were obtained and characterized by scanning electron microscopy (SEM), water vapor permeability (WVP), adsorption isotherms, TGA and mechanical tests. The inclusion of reinforcement caused changes in film properties: WVP was lowered by 41% for film with 1.5% (w/w) of NPAac and moisture adsorption by 33% for film with 10% (w/w) of NPAac; and the Young's modulus and thermal stability were increased by 162% and 15%, respectively, for film with 0.5% (w/w) of NPAac compared to the starch film without the addition of NPAac.

Changing water affinity from hydrophobic to hydrophilic in hydrophobic channels.

The behavior of water at hydrophobic interfaces can play a significant role in determining chemical reaction outcomes and physical properties. Carbon nanotubes and aluminophosphate materials have one-dimensional hydrophobic channels, which are entirely surrounded by hydrophobic interfaces. Unique water behavior was observed in such hydrophobic channels. In this article, changes in the water affinity in one-dimensional hydrophobic channels were assessed using water vapor adsorption isotherms at 303 K and grand canonical Monte Carlo simulations. Hydrophobic behavior of water adsorbed in channels wider than 3 nm was observed for both adsorption and desorption processes, owing to the hydrophobic environment. However, water showed hydrophilic properties in both adsorption and desorption processes in channels narrower than 1 nm. In intermediate-sized channels, the hydrophobic properties of water during the adsorption process were seen to transition to hydrophilic behavior during the desorption process. Hydrophilic properties in the narrow channels for both adsorption and desorption processes are a result of the relatively strong water-channel interactions (10-15 kJ mol(-1)). In the 2-3 nm channels, the water-channel interaction energy of 4-5 kJ mol(-1) was comparable to the thermal translational energy. The cohesive water interaction was approximately 35 kJ mol(-1), which was larger than the others. Thus, the water affinity change in the 2-3 nm channels for the adsorption and desorption processes was attributed to weak water-channel interactions and strong cohesive interactions. These results are inherently important to control the properties of water in hydrophobic environments.

Specific Surface Area of Clay Using Water Vapor and EGME Sorption Methods

Specific surface area (SSA) is a valuable intrinsic property of clayey soils that can be directly related to more general properties and engineering behavior, including plasticity, cation exchange capacity, and swelling behavior, among many others. Laboratory methods available for estimating SSA, however, remain somewhat complicated and are not routinely used in geotechnical practice. This paper evaluates and compares methods for determining SSA using the conventional ethylene glycol monoethyl ether (EGME) method and various approaches involving sorption of water vapor under controlled humidity conditions. Surface areas estimated from water vapor adsorption and desorption isotherms are comparable for non-expansive clays with SSA values less than about 100 m2/g. Measurements are appreciably different for soils containing expansive clay minerals, where the SSA estimated via Brunauer–Emmett–Teller (BET) analysis of desorption isotherms is consistently about twice the SSA determined from adsorption isotherms. Surface areas estimated from water vapor and EGME methods are comparable at SSAs less than 100 m2/g, but measurements obtained using water vapor for larger SSAs are consistently about half of the EGME-based values. Simplified one-point methods for estimating SSA using water vapor sorption compare well with BET-based methods for SSAs less than 150 m2/g. Recommendations are provided for applying water vapor and EGME sorption methods in geotechnical practice.