Limited Water Content Research Articles

Modelling of morphology and proton transport in PFSA membranes

Computational modelling studies of the structure of perfluorosulfonic acid (PFSA) ionomer membranes consistently exhibit a nanoscopic phase-separated morphology in which the ionic side chains and aqueous counterions segregate from the fluorocarbon backbone to form clusters or channels. Although these investigations do not unambiguously predict the size or shape of the clusters, and whether or not the channels percolate the matrix or if the connections between them are more transient, the sequence of co-monomers along the main chain appears strongly to influence the domain size of the ionic regions, with more blocky sequences giving rise to larger domain sizes. The fundamental insight that substantial rearrangement of the sulfonic acid terminated side chains and fluorocarbon backbone takes place during swelling or shrinkage is borne out by both molecular and mesoscale simulations of model PFSA polymers, along with ab initio electronic structure calculations of minimally hydrated oligomeric fragments. Molecular-level modelling of proton transport in PFSA membranes attests to the complexity of the underlying mechanisms and the need to examine the chemical and physical processes at several distinct time and length scales. These investigations have revealed that the conformation of the fluorocarbon backbone, flexibility of the sidechains, and degree of aggregation and association of the sulfonic acid groups under minimally hydrated conditions collectively control the dissociation of the protons and the formation of Zundel and Eigen cations. The former appear to be the dominant charge carriers when the limiting water content allows only for the formation of a contact ion pair with the tethered sulfonate anion. As the water content increases, solvent-separated Eigen ions begin to appear, indicating that the dominant mechanism for diffusion of protons occurs over a region approximately 4 A away from the sulfonate groups. Finally, both the vehicular and Grotthuss shuttling mechanisms contribute to the mobility of the protons but, surprisingly, they are not always correlated, resulting in a lower overall diffusion coefficient. In summary, as the preceding observations indicate, the state of computational modelling of PFSA membranes has progressed sufficiently over the last decade to enable its use as a powerful predictive tool with which to guide the process of designing novel membrane materials for fuel cell applications.

Developmental profiles in tick water balance with a focus on the new Rocky Mountain spotted fever vector, Rhipicephalus sanguineus

Recent reports indicate that the common brown dog tick, or kennel tick, Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) is a competent vector of Rocky Mountain spotted fever in the U.S.A. This tick is of concern to public health because of its high frequency of contact, as it has a unique ability to thrive within human homes. To assess the moisture requirements necessary for survival, water balance characteristics were determined for each developmental stage, from egg to adult. This is the first time that water relations in ticks have been assessed throughout the complete lifecycle. Notably, R. sanguineus is differentially adapted for life in a dry environment, as characterized by a suppressed water loss rate distinctive for each stage that distinguishes it from other ticks. Analysis of its dehydration tolerance limit and percentage body water content provides no evidence to suggest that the various stages of this tick can function more effectively containing less water, indicating that this species is modified for water conservation, not desiccation hardiness. All stages, eggs excepted, absorb water vapour from the air and can drink free water to replenish water stores. Developmentally, a shift in water balance strategies occurs in the transition from the larva, where the emphasis is on water gain (water vapour absorption from drier air), to the adult, where the emphasis is on water retention (low water loss rate). These results on the xerophilic-nature of R. sanguineus identify overhydration as the primary water stress, indicating that this tick is less dependent upon a moisture-rich habitat for survival, which matches its preference for a dry environment. We suggest that the controlled, host-confined conditions of homes and kennels have played a key role in promoting the ubiquitous distribution of R. sanguineus by creating isolated arid environments that enable this tick to establish within regions that are unfavourable for maintaining water balance.

NMR imaging investigation of rice cooking

The visualization and quantification of the cooking of rice by NMR imaging is reported for Japonica rice ( Oryza sativa. L. Japonica cv. Nipponbare) as a test sample. Rice was cooked in a vial for various times and then studied at room temperature by NMR imaging. The multi slice multi echo method was employed to obtain two-dimensional proton images. Images using only the first echo clearly revealed the changes in the water content of the rice grains during cooking. T 2 images were obtained from the same experiments but using the first 16 echoes and converted to images of the water distributions using an empirical T 2 vs. water content calibration determined from a series of reference water/rice starch mixtures. The total limiting water content within the rice grains was calculated and it agreed with that calculated from the known water/rice ratio used, indicating that both the concentration and distributions of water within the rice grains during cooking obtained from the NMR imaging were quantitatively reliable.

The Non‐Limiting and Least Limiting Water Ranges for Soil Nitrogen Mineralization

A better understanding of factors controlling N mineralization would improve our ability to estimate fertilizer requirements more accurately. Net N mineralization approaches a small reaction rate at low and high water contents, giving rise to lower and upper limiting water contents and the least limiting water range (LLWR). Within the LLWR, there is a range in water contents in which mineralization is largely independent of water content, that is, the non‐limiting water range (NLWR). An incubation study was conducted to determine the LLWR and NLWR for five soils with different properties, and two relative compaction levels with and without the addition of a legume crop residue. These soils were incubated for 1 and 3 mo at eight water contents. Net N mineralization increased with incubation time and legume addition and varied curvilinearly with water‐filled pore space (WFPS). Logistic functions were generated to establish the relationships between net N mineralization and WFPS (%) and to calculate LLWR and NLWR. The mean NLWR was 32.2% after 1 mo and decreased to 18.1% after 3 mo whereas the mean LLWR was 55% after 1 mo and increased to 70.8% after 3 mo. The LLWR increased with organic C or total N but decreased with the addition of legume residue. The NLWR decreased with clay content and with the addition of legume after 3 mo. Emissions of N2O were greatest at water contents near the upper limit of the LLWR. Use of the NLWR to differentiate soils on the basis of the sensitivity of N mineralization to variation in water content is illustrated.

Limiting Compression Curves

Abstract Depending upon the initial water content of the soil sample, a family of compression curves is possible. Identification of characteristic limiting water contents for any fine grained soil system, along with the unique mechanisms controlling them, helps obtain the limiting compression curves. In the present note, it has been demonstrated that the compression curve obtained with its origin at the free swell limit of the soil represents the global upper bound compression curve, and that the compression curve obtained after the soil has reached equilibrium under cyclic consolidation represents the global lower bound compression curve. The compression curve obtained with its origin at the settling limit water content of the soil is the stress-free reference state curve as well as the upper bound compression curve for the homogeneous soil sample.

Gelatinisation of sago starch in the presence of sucrose and sodium chloride as assessed by differential scanning calorimetry

The inhibitory effect of sucrose and sodium chloride on sago starch gelatinisation was investigated by differential scanning calorimetry (DSC). The temperature of gelatinisation of starch in the presence of low levels of water and high levels of sucrose was found to increase in the presence of sucrose, whereas the gelatinisation enthalpy was unaffected. The gelatinisation temperature range was not as broad in the presence of sucrose as without sucrose. Furthermore, the shape of the gelatinisation endotherm was changed by the addition of sucrose. The double endotherm obtained in limited water:starch systems was changed into a single endotherm, similar to the endotherm obtained in excess water:starch systems at a higher temperature. DSC was also used to examine the effects of water and sodium chloride content on the phase transitions of sago starch. Samples were adjusted to starch:water ratios of 2:3 and 3:2 in sodium chloride concentrations of 0.0, 1.0, 2.0, 3.0, 4.0, 5.0 M. The gelatinisation temperatures of sago starch increased and then decreased as the sodium chloride concentration increased. Sodium chloride created similar effects on the endotherms in excess water content and on the first endotherm with limited water content. In the presence of sucrose and sodium chloride, gelatinisation shifted to higher temperatures, and enthalpy associated with the endothermic process decreased. The extent of temperature shift and enthalpy change was dependent on the water to starch to solutes ratios.

STUDY OF SAGO STARCH (METROXYLON SAGU) GELATINIZATION BY DIFFERENTIAL SCANNING CALORIMETRY

Differential scanning calorimetry (DSC), at various heating rates (1-30C/ min) and water:starch ratios (0.1:1-4:1), was used to study gelatinization phenomena of sago starch. The results showed that the gelatinization temperature and enthalpy (ΔH) of starches in excess water were 60-77C and 15.5-15.8 J/g, respectively. ΔH of gelatinization remained substantially the same at excess water contents, but decreased significantly beyond a water:starch ratio of 1.3:1. A single endothermic transition (G) that transformed into a double endotherm (G and M 1 ) and only M 1 occurred, respectively, at excess, intermediate and limited water contents. At 50% water content, evidence of the M 1 endotherm was observed, and 85C represented the effective conclusion temperature (T m ) at the end of melting for sago starch. The experimental data were treated thermodynamically by applying an equation describing phase transitions of semi-crystalline polymers. The calculated value for the melting point of the undiluted polymer (T m o ) was 432 K (R 2 =0.96).

Settling Behaviour and Clay Mineralogy

Sedimentary soils are formed due to the process of settling of soil particles in suspension. The settling process is physico-chemical in nature as the soil contains chemically active clay minerals. The extent to which the clay mineralogy affects the settling process depends upon the initial water content of the soil-water suspension. For montmorillonitic soils, the limiting water content at which the nature of settling changes from a discrete free type to a flocculated free type increases with an increase in the soil plasticity and decreases with an increase in the soil plasticity for kaolinitic soils. While the diffuse double layer repulsion controls this kind of behaviour of montmorillonitic soils, the behaviour of kaolinitic soils can be attributed to the fabric effect.

Liquid Limit Determination of Class F Coal Ash

Abstract Large production of coal ash, a waste material, demands its bulk utilization. Bulk utilization of these ashes is possible only through geotechnical applications such as embankment construction, as a back-fill material, a subbase material, and the like. Hence their physical and engineering properties need to be determined for effective utilization. Liquid limit is one of the important physical properties. The existing popular methods of liquid limit de termination of soils, namely Casagrande's percussion method and the falling cone method, have limitations for their use in nonplastic materials like coal ash. In this paper, a new method has been proposed to determine the liquid limit of coal ash. The proposed method is based on the premise that at its liquid limit water content, soil/coal ash does not imbibe or give out any water under a particular vertical stress under the Ko condition. This vertical stress is found to be 0.9 kPa. Experimental results are presented to substantiate the proposed method.

Differential scanning calorimetry: gelatinisation of sago starch in the presence of sucrose and sodium chloride

The effect of sucrose and sodium chloride (NaCl) on sago starch gelatinisation was investigated by differential scanning calorimetry (DSC). The gelatinisation of starch in the presence of low levels of water and high levels of sucrose was studied. The gelatinisation temperature was found to increase in the presence of sucrose, whereas the gelatinisation enthalpy was unaffected. The gelatinisation temperature range was not as broad in the presence of sucrose as without sucrose. Furthermore, the shape of the gelatinisation endotherm was changed by the addition of sucrose. The double endotherm obtained in limited water–starch systems was changed into a single endotherm, similar to the endotherm obtained in excess water–starch systems at higher temperature. DSC was also used to examine the effects of water and NaCl content on the phase transitions of sago starch. Samples were adjusted to starch–water weight ratios of 2:3 and 3:2 in NaCl concentrations from 1 to 5 M. The gelatinisation temperature of sago starch increased and then decreased as the NaCl concentration increased. NaCl created similar effects on the endotherms with excess water content and on the first endotherm with limited water content. © 1999 Society of Chemical Industry

Fracture Properties of Short-Dough Biscuits: Effect of Composition

The mechanical properties of short-dough biscuits of various composition were determined in three-point bending tests. In general, reduction of fat content increased the modulus and the fracture stress of biscuits. The relative magnitude of this effect depended on the fat type. Sucrose syrup slightly enhanced the brittle character of biscuits, compared with crystalline sucrose, indicating that sucrose crystals were not the fracture-inducing defects. Substituting starch for part of the flour had relatively little effect on the mechanical properties. Sugar-free biscuits had a significantly lower modulus and fracture stress. Differential scanning calorimetry showed that, irrespective of composition, starch gelatinisation was slight, presumably due to the limited water content coupled with the low baking temperature. It is concluded that biscuits comprise a glassy matrix; their mechanical properties are mainly determined by air and fat volume fraction as well as the size of inhomogeneities.

The Effect of Protein and Fiber on the Kinetics of Starch Gelatinization and Melting in Waxy Corn Flour

The in situ presence of corn proteins and fibers along with starch in waxy corn flour affect the DSC scan of starch only slightly. The kinetic behaviors of cooking waxy corn flour with limited water contents (25% and 35%, w/w) are very similar to that of cooking waxy cornstarch. There are increases in reaction rate constants for samples with 25% water content when corn flour data are compared to that of corn starch. For samples with 35% water, the rate constants are very close for flour and starch. Cooking of corn flour requires a lower activation energy than cooking of cornstarch.

Characteristic water contents of a fine-grained soil—water system

This paper critically appraises the limitations of the liquid-limit water content of clayey soils determined conventionally either by percussion cup or by the cone penetration method. It is shown that the conventional liquid limit and plastic limit are arbitrary, strength-based water contents and that they cannot represent the plasticity limits, and that the state of the soil— water system at the conventional liquid limit does not correspond to a stress-free reference state. The present investigation identifies three characteristic limiting water contents for a soil— water system which have well-defined, unique mechanisms controlling them, namely the free swell limit, settling limit and shrinkage limit. Simple procedures for the determination of the free swell limit and settling limit of natural soils are presented. The settling limit is shown to be the 'real liquid limit' of any clayey soil. With a number of experimental illustrations, it is clearly shown that the settling limit represents the maximum water-holding capacity of clayey soils and that it corresponds to the stress-free reference state. Cet article fait une évaluation critique des restrictions de la teneur en eau à limite liquide des sols argileux, déterminée de manière convendonnelle par coupe de percussion on par essai de pénétration. II a été démontré que la limite liquide conventionnelle et la limite de plasdcité sont des teneurs en eau arbitraires basées sur la résistance qui ne peuvent représenter les limites de plasdcité et que l'état du système sol-eau à la limite liquide conventionnelle ne correspond pas à un 6tat de référence sans contrainte. Cette étude identifie trois caractéristiques limitant les teneurs en eau pour un système sol-eau qui a des mécanismes uniques et bien définis pour les contr&circler, nommément la limite de gonflement libre, la limite d'affaissement et la limite de retrait. Nous présentons ici des procédures simples pour déterminer la limite de gonflement libre et la limite d'affaissement des sols naturels. Nous montrons que la limite d'affaissement est la 'limite liquide réelle' de tout sol argileux. Avec plusieurs illustrations expérimentales, nous démontrons clairement que la limite d'affaissement représente la capacité maximum de retenue de l'eau des sols argileux et qu'elle correspond à l'état de référence sans contrainte.

Re-examination of compaction characteristics of fine-grained soils

This technical note re-examines the compaction characteristics of three soils, and develops a phenomenological model for their prediction, which will enable compaction data to be handled more confidently. Standard Proctor compaction test data were generated for three soils with liquid limit water contents ranging from 48% to 84%. It was found that by defining a soil in terms of its liquid limit and liquid limit water content, the path of compaction for a specific compactive effort could be predicted via a simple density-water content-liquid limit relationship. The whole compaction path can be confirmed from the series of compaction curves, presented for the practical range of liquid-limit water contents, if just one point is known of the density-water content data and the liquid limit value. It then becomes possible to assess rapidly the water content of the wet soil mix, ready for compaction, by bulk density determination from a single Proctor compaction test. Several series of compaction curves are displayed in charts, and a table shows the comparison between predicted and actual water contents of wet soil mix.

Structural Changes of Cassava Starch Granules after Heating at Intermediate Water Contents

AbstractDSC thermograms of cassava starch granules heated at two intermediate moisture contents of 35 and 45% of the total weight (w.t.) reveal the existence of two endothermic steps in their progressive disorganization. Structural changes have been studied by combining polarized light microscopy and electron microscopy (scanning and transmission electron microscopy). An instability of starch granule behaviour, both at granular and crystalline levels is observed at each treatment temperature. As temperature and moisture content increase, the loss of birefringence was observed in an increasing number of granules, suggesting that there is a competition of granules for water. The loss of birefringence initiates first at the hilum and is associated with the formation of cavities in the central region of the granules, showing that the disorganization first affects the less organized areas of the granule. In limited water content conditions, the radial extension of the central cavity towards the granule surface is not observed. The limited crystalline disorganization which is restricted to the inner part of the granule does not allow either a major swelling of granules or an extensive leaching of macromolecules out of granules. Increasing temperatures progressively induced the loss of granular integrity and the development of an homogeneous matrix. These structural changes are in agreement with the cooperative disorganization model of starch crystallites following which the crystalline disorganization is facilitated by the presence of water or by the plasticization of the amorphous regions connected to these crystallites.

Lower Limit of Soil Water Availability

AbstractEstimating the available soil water reservoir is needed for developing a strategy for optimum management of rainfed crops in marginal dry regions. Previous research on measurement of the lower limit water content of soil water availability (required for calculation of the total soil water reservoir) has shown unexplained discrepancies between field estimates of the water content at which plants are dead or dormant due to soil water deficit and laboratory estimates of the water content at a water potential of − 1.5 kJ kg−1. Whether such discrepancies are due to sample size, handling, or the choice of − 1.5 kJ kg−1 as the lower limit is not clear. This study was designed to determine what the limit is under controlled conditions, and to test the appropriateness of the −1.5 kJ kg−1 value. We used in situ soil psychrometers to measure soil water potential (Ψ) as water was withheld from cotton (Gossypium hirsutum L.) plants in a rain‐sheltered lysimeter monolith and from sorghum [Sorghum bicolor (L.) Moench] in glasshouse pots. The lower limit Ψ was − 2.2 kJ kg−1 in the lysimeter experiment and < − 2.5 kJ kg−1 in the glasshouse. With the lysimeter, the difference between the soil water content corresponding to − 2.2 kJ and − 1.5 kJ kg−1 was <0.01 m3 m−3. Water potential at the greatest measurement depth (2.1 m) decreased rapidly from near 0 to − 1.8 kJ kg−1 over a period of 30 d, while root length density increased from nearly 0 to 2400 m−3. At an advanced stage of soil water deficit, there was limited upward movement of water from depths >2.1 m. No Ψ oscillations, corresponding to so‐called hydraulic lift or nocturnal water transport between soil layers, were found at any depth in the lysimeter (0.5–2.1 m). Our results suggest that for water balance calculations requiring absolute accuracy for the water balance of the soil reservoir, the choice of the − 1.5 kJ kg−1 soil water potential is appropriate and corresponds closely to the field lower limit of soil water availability.

有機溶媒中の酵素反応

In the past decade, in has been established that enzymes exhibit high catalytic activity as a solid state in organic solvents containing little or no water. Because organic solvents are better reaction media than water for most synthetic transformations, such has been applied to a number of organic reactions.This article is intended to provide mechanistic understanding of this phenomenon, which counters conventional wisdom. The key concept here is the high rigidity of protein's conformation under limited water content conditions : the balance of its thermodynamic stability and kinetic rigidity is essential for the enzyme's high catalytic activity and selectivities in organic media. Some applications for organic synthesis are also presented.

Enzymatic production and physicochemical characterization of uncommon wax esters and monoglycerides

AbstractWax esters from fatty alcohols and uncommon fatty acids were synthesized in yields up to 90% when commercially available microbial lipases fromRhizomucor miehei (Lipozyme™) andCandida antarctica (SP 435) were used with limited water content in nonpolar solvents under mild conditions. The corresponding fatty acids were prepared by chemical conversion of naturally occurring resources (agricultural surpluses). Also, when phenylboronic acid was added as solubilizing agent in a nonpolar solvent, the direct enzymatic monoacylation of glycerol with uncommon fatty acids was successful. The measurement of π/A‐isotherms by means of a Langmuir film balance indicated medium film pressures, medium or large molecular areas, and interesting phase behavior. The monolayer of a wax ester at the air/water interface could be directly visualized by Brewster angle microscopy.

Kinetics of the Formations of Gelatinized and Melted Starch at Extrusion Cooking Conditions

AbstractTypical DSC thermograms of starch phase transition in the low moisture content range (15‐40%) showed two thermal transition peaks. This suggests the existence of two different cooking mechanisms. We call them gelatinization and melting. “Gelatinization” describes thermal transition of starch with water and “melting” without water. Kinetics of the formation of gelatinized starch (GEL) and melted starch (MELT) were studied. Conversions caused by gelatinization and melting were separately analyzed by using information from DSC (Differential Scanning Calorimetry) isothermal studies. The rate of formation of gelatinized fraction followed first order kinetics and that of melted fraction zeroth order. The overall reaction rate followed zeroth order because melting is the dominant mechanism of the two under limited water contents of extrusion cooking conditions.

Thermal deamidation of proteins in a restricted water environment

Nonenzymatic deamidation reactions of soy protein, egg lysozyme, milk casein, and wheat gliadin at moisture contents ranging from 0 to 80% at 115 o C for 2 h were studied. The deamidation percentage varied from 3.20 to 18.48% for all four proteins. All proteins had a minimum deamidation rate at the limited water content, approximately 50% for soy protein, 60% for lysozyme, 60% for casein, and 6% for gliadin