Slow Hydration Research Articles

Slow hydrophobic hydration induced polymer ultrafiltration membranes with high water flux

Polymer ultrafiltration membranes with high water flux have long been pursued to improve filtration efficiency and reduce costs of industrial separation processes such as water treatment and food processing. However, increasing water flux is usually accompanied by decreased rejection property in these membranes. In this paper, we show that by using a polymer functionalized with hydrophobically ionizable groups as additive, polymer ultrafiltration membranes with an increasing concentration of the additive from the active layer to the supporting layer are produced in the membrane casting process due to slow hydration of the additive. The hydrated additive becomes hydrophilic after the membrane formation. The resulting membranes exhibit dramatically enhanced water permeability while maintaining excellent separation property. We demonstrate that polyethersulfone/tris(2,4,6-trimethoxyphenyl)polysulfone-methylene quaternary phosphonium chloride (PES/TPQP-Cl) membrane exhibits a water permeability of up to 14.6lm−2h−1kPa−1, which is 35 times that of PES membrane. The membrane also shows excellent anti-biofouling property. The work provides a new methodology for designing high-performance membranes for improving separation efficiency and exploring other novel applications.

Dynamical transition and heterogeneous hydration dynamics in RNA.

Enhanced dynamical fluctuations of RNAs, facilitated by a network of water molecules with strong interactions with RNA, are suspected to be critical in their ability to respond to a variety of cellular signals. Using atomically detailed molecular dynamics simulations at various temperatures of purine (adenine) and preQ1 sensing riboswitch aptamers, which control gene expression by sensing and binding to metabolites, we show that water molecules in the vicinity of RNAs undergo complex dynamics depending on the local structures of the RNAs. The overall lifetimes of hydrogen bonds (HBs) of surface-bound waters are more than at least 1-2 orders of magnitude longer than those of bulk water. Slow hydration dynamics, revealed in the non-Arrhenius behavior of the relaxation time, arises from high activation barriers to break water HBs with a nucleotide and by reduced diffusion of water. The relaxation kinetics at specific locations in the two RNAs show a broad spectrum of time scales reminiscent of glass-like behavior, suggesting that the hydration dynamics is highly heterogeneous. Both RNAs undergo dynamic transition at T = TD ≳ 200 K, as assessed by the mean-square fluctuation of hydrogen atoms ⟨x(2)⟩, which undergoes an abrupt harmonic-to-anharmonic transition at TD. The near-universal value of TD found for these RNAs and previously for tRNA is strongly correlated with changes in hydration dynamics as T is altered. Hierarchical dynamics of waters associated with the RNA surface, revealed in the motions of distinct classes of water with well-separated time scales, reflects the heterogeneous local environment on the molecular surface of RNA. At low temperatures, slow water dynamics predominates over structural transitions. Our study demonstrates that the complex interplay of dynamics between water and the local environment in the RNA structures could be a key determinant of the functional activities of RNA.

Synthesis of Pure Dicalcium Silicate Powder by the Pechini Method and Characterization of Hydrated Cement

Calcium silicate (CS) is a main component of Portland cement and is responsible for the strength development. Recent research has shown that dicalcium silicate cement (CSC) is bioactive and is a potential candidate for bone replacement. Traditionally, dicalcium silicate powder is synthesized by a solid state reaction or a sol-gel method. The solid-state reaction, however, usually needs a higher temperature and a longer calcination time. Furthermore, the dicalcium silicate powder made by the sol-gel method is not pure, and contains a significant quantity of CaO which is harmful to the strength and biological properties of the CSC. The Pechini technique is an alternative, low temperature polymeric precursor route for synthesis of high purity powders. In this study, purer CS powder was synthesized via the Pechini method by calcination at 800°C for 3h. DSC-TGA, XRD, SEM were used for characterization of CS powder and the hydrated cement. The DSC-TGA curves showed that the main exothermic peak was at 479°C and the total mass loss was 79.2%. The XRD patterns of CSC after hydration for 7, 14, and 35 days illustrated that dicalcium silicate hydrate (Ca1.5SiO3.5·xH2O, C-S-H) was formed in the hardened CS paste. The XRD peaks on the diffraction pattern of the C-S-H of the day 35 sample were of greater intensity than those at day 7 and day 14. This demonstrates that the hydration speed was slow and complete hydration could take more than one month. Flake-like crystals were observed on scanning electron micrographs following hardening. The degradation study result showed that there was no mass loss of CSC after the samples were soaked into phosphate buffered saline (PBS) for 40 days. The silicon assay revealed that orthosilicic acid could be released from CSC after the samples were soaked in simulated body fluid (SBF). Silicon is known to be critical to skeletal mineralization. The existence of silicon may stimulate the proliferation of bone and activate cells to produce bone. Investigation of cell attachment confirmed that the MC-3T3 cells attached well to the surfaces of CSC after seeding.

Pockmark formation and evolution in deep water Nigeria: Rapid hydrate growth versus slow hydrate dissolution

AbstractIn previous works, it has been suggested that dissolution of gas hydrate can be responsible for pockmark formation and evolution in deep water Nigeria. It was shown that those pockmarks which are at different stages of maturation are characterized by a common internal architecture associated to gas hydrate dynamics. New results obtained by drilling into gas hydrate‐bearing sediments with the MeBo seafloor drill rig in concert with geotechnical in situ measurements and pore water analyses indicate that pockmark formation and evolution in the study area are mainly controlled by rapid hydrate growth opposed to slow hydrate dissolution. On one hand, positive temperature anomalies, free gas trapped in shallow microfractures near the seafloor and coexistence of free gas and gas hydrate indicate rapid hydrate growth. On the other hand, slow hydrate dissolution is evident by low methane concentrations and almost constant sulfate values 2 m above the Gas Hydrate Occurrence Zone.

Evaluation of the hyperbranched polymer Hybrane H1500 for production of matricial controlled-release particles by hot-melt extrusion

Extrudates of the hyperbranched polymer Hybrane H1500 prepared by hot melt extrusion, with five particle sizes (from <250 μm to 1.5-2.0 mm) and three drug content (10, 20 and 30%) of acetaminophen or caffeine, were evaluated in this study as potential multiparticulate controlled release systems. Hybrane H1500 extrudates (of very low porosity), experienced a very slow hydration, with a limited swelling capacity, and they do not behave as true gels when fully hydrated. Hot melt extrusion provokes the conversion of the acetaminophen into an amorphous state inside the extrudates, whereas for those containing caffeine, some crystals remain for the highest drug proportions (20 and 30%). From both drug extrudates a wide range of dissolution profiles are obtained. Drug release rate depends mostly on extrudate particle size, and in those extrudates containing caffeine, a slight effect of the drug proportion is observed. Dissolution profiles' kinetic analysis suggests that drug release is controlled by the diffusion of the drug through the polymeric hydrated structure, although this mechanism is only clearly and efficiently displayed for the greatest extrudate particles (1.5-2.0 mm).

Physico-chemical characterization of the temperature dependent hydration kinetics of Gleditsia sinensis gum

The physico-chemical properties and hydration kinetics of Gleditsia sinensis gum were investigated to evaluate its temperature dependence. The increase of temperature resulted in improved solubility of G. sinensis gum, and the dissolved galactomannan showed decreased degree of galactose substitution (DSGal) and increased molecular weight (p<0.05, ANOVA). The solubility of G. sinensis galactomannan at 25, 45, 60 and 80°C was 73.4, 83.8, 98.1, and 99.4%, respectively. Weibull and Logarithmic models were well fitted (R2>0.96), and the hydration index t0.8 at different temperatures varied in the range of 51–302min. It was found that galactomannan with low DSGal and high molecular weight exhibited slow hydration rate and poor solubility.

Hydrate Formation/Dissociation in (Natural Gas + Water + Diesel Oil) Emulsion Systems

Hydrate formation/dissociation of natural gas in (diesel oil + water) emulsion systems containing 3 wt% anti-agglomerant were performed for five water cuts: 5, 10, 15, 20, and 25 vol%. The natural gas solubilities in the emulsion systems were also examined. The experimental results showed that the solubility of natural gas in emulsion systems increases almost linearly with the increase of pressure, and decreases with the increase of water cut. There exists an initial slow hydrate formation stage for systems with lower water cut, while rapid hydrate formation takes place and the process of the gas-liquid dissolution equilibrium at higher water cut does not appear in the pressure curve. The gas consumption amount due to hydrate formation at high water cut is significantly higher than that at low water cut. Fractional distillation for natural gas components also exists during the hydrate formation process. The experiments on hydrate dissociation showed that the dissociation rate and the amount of dissociated gas increase with the increase of water cut. The variations of temperature in the process of natural gas hydrate formation and dissociation in emulsion systems were also examined.

Solvent fluctuations in hydrophobic cavity–ligand binding kinetics

Water plays a crucial part in virtually all protein-ligand binding processes in and out of equilibrium. Here, we investigate the role of water in the binding kinetics of a ligand to a prototypical hydrophobic pocket by explicit-water molecular dynamics (MD) simulations and implicit diffusional approaches. The concave pocket in the unbound state exhibits wet/dry hydration oscillations whose magnitude and time scale are significantly amplified by the approaching ligand. In turn, the ligand's stochastic motion intimately couples to the slow hydration fluctuations, leading to a sixfold-enhanced friction in the vicinity of the pocket entrance. The increased friction considerably decelerates association in the otherwise barrierless system, indicating the importance of molecular-scale hydrodynamic effects in cavity-ligand binding arising due to capillary fluctuations. We derive and analyze the diffusivity profile and show that the mean first passage time distribution from the MD simulation can be accurately reproduced by a standard Brownian dynamics simulation if the appropriate position-dependent friction profile is included. However, long-time decays in the water-ligand (random) force autocorrelation demonstrate violation of the Markovian assumption, challenging standard diffusive approaches for rate prediction. Remarkably, the static friction profile derived from the force correlations strongly resembles the profile derived on the Markovian assumption apart from a simple shift in space, which can be rationalized by a time-space retardation in the ligand's downhill dynamics toward the pocket. The observed spatiotemporal hydrodynamic coupling may be of biological importance providing the time needed for conformational receptor-ligand adjustments, typical of the induced-fit paradigm.

Site-Resolved Hydration Dynamics of Staphylococcal Nuclease in Reverse Micelles

Measurements of water dynamics and protein-water interactions are essential to understanding protein folding, structure, function, and dynamics. However, protein-water interactions have historically been difficult to study and have mostly been limited to indirect methods that are unable to measure transient and short-lived interactions. We recently developed a novel method for studying protein-water interactions using NMR spectroscopy by encapsulating proteins of interest in reverse micelles. Appropriate amphiphilic surfactant molecules spontaneously form nanoscale bubbles in the presence of a small volume of water and bulk organic solvent, resulting in reverse micelles with aqueous protein in the interior and organic solvent on the exterior. The removal of bulk water and the effects of nanoconfinement slow protein hydration waters allowing for site-resolved measurement of protein-water interactions and dynamics via the nuclear Overhauser effect. Staphylococcal nuclease (SNase) is an extensively studied 16 kD protein with a large number of mutants that have been well classified using standard biophysical techniques. Here we use a pseudo wild-type hyperstable variant (Δ+PHS) and V66E mutant to study surface protein-water dynamics and overall protein hydration. High resolution NOESY-HSQC and ROESY-HSQCs were collected for SNase encapsulated in reverse micelles. Site-specific ratios of NOE and ROE signal intensity at the water chemical shift describe longevity of interacting waters, and can therefore be mapped to the protein structure to determine areas of slow and fast hydration dynamics. Supported by NSF grant MCB 0842814 and NIH postdoctoral fellowship GM087099 to N.V.N.

Slow dynamics, hydration and heterogeneity in Laponite dispersions

Age dependent hydration, heterogeneity and network rigidity of aqueous Laponite dispersions in their sol, gel and glass phases have been studied systematically in the clay concentration range c = 0.3–3.5 % (w/v) which revealed the following interesting features: (i) both in the sol and gel regime (c < 1.8% (w/v)), the intensity of light scattered I(q,c) scaled with concentration c as, I(q,c) ∼ cα with α = 0.95 at t = 0, and 0.63 after t = 6 months implying that this temporal growth resulted from the formation of a colloidal gel; (ii) in the glass phase (c ≥ 2% (w/v)), scattered intensity from samples remained constant (α = 0), meaning that there was disorder in the system at higher solid contents, and the clay particles were randomly arranged, and this intensity profile did not change with the aging; (iii) the dynamic structure factor data showed low concentration dispersions (gels) having a single mode relaxation time (fast mode) which shifted to longer relaxation time with aging. In the glass phase, in addition to the fast mode that remained invariant of aging, a slow mode which shifted to longer relaxation time with aging was noticed; (iv) rigidity modulus (G′) and yield stress (σ) measurements showed that there are two universal power-law relations governing their behavior as a function of clay concentration; G′, σ ∼ cδ with δ = 2.3 for gels and 2.8 for glass. Both these parameters revealed similar logarithmic time dependence with aging as σ, G′ = βln(tw/tm), where β is a constant and tm is the characteristic time scale for the development of micro structures; (v) Raman spectroscopy data revealed three distinct OH bands characteristic of the structure of water which revealed change in the structured water content with the aging, and the heterogeneity of the samples was established using a Cole–Cole plot. We have proposed a time-dependent phase diagram for the salt free suspensions of Laponite clay using the abovementioned results.

Alterations in seed reserves of Dalbergia nigra ((Vell.) Fr All. ex Benth.) during hydration

Seed imbibitions is the first stage of the germination process and is characterized by the hydration of tissues and cells and the activation and/or induction of the enzymes responsible for mobilizing reserves for respiration and the construction of new cell structures. The objective of this study was to investigate the alterations in reserve substances during slow hydration of Bahia Rosewood (Dalbergia nigra) seeds in water. Seeds from two different lots (Lot I and II) were placed in saturated desiccators (95-99% RH) to hydrate at 15 and 25 °C until water contents of 10, 15, 20 and 25% were reached. At each level of hydration, changes in lipid reserves, soluble carbohydrates, starch and soluble proteins were evaluated. The mobilization of reserves was similarly assessed in both lots, with no differences being observed between the two hydration temperatures. Lipid contents showed little variation during hydration, while the contents of soluble carbohydrates and starch decreased after the 15% water content level. Soluble proteins showed a gradual tendency to decrease between the control (dry seeds) up to 25% water content.

Preparation of MgO- and CaO-Bearing Expansive Agent Used for Cement-Based Materials

Blended expansive agents consisting of MgO and CaO were prepared by calcining the mixtures of dolomite and magnesite. The mineral phases and microstructures of expansive agent were examined by XRD and SEM. The expansion properties of cement pastes containing 5% and 6% of expansive agent as well as the microstructure of hydrated expansive agent in cement paste were investigated. Results indicated that the contents of MgO and CaO in the blended expansive agent could be adjusted by changing the mix proportion of dolomite and magnesite. All the cement pastes containing expansive agent produced rapid expansion. At the same addition dosage, irrespective of curing temperature, expansive agent containing higher content of MgO produced greater expansion in cement pastes, particularly at late age, which probably ascribes to the relatively slow hydration of MgO.

Dynamic Response of a Subsaturated Polymer Electrolyte Fuel Cell in Counterflow Mode

AbstractThis work demonstrates that the operation of a subsaturated polymer electrolyte fuel cell in counterflow mode results in a significantly elongated relaxation time after a load change, if compared to coflow mode. This effect is investigated here by using combined dynamic locally resolved measurements of the current density, the high frequency resistance, and the relative humidity. It is shown that the elongated relaxation time is a consequence of slow membrane hydration in the region of the cell, downstream the anode flow field, where the diffusive flux of water across the membrane occurs from the anode to the cathode. Here, the anode gas stream, which is humidified upstream the anode flow field via back diffusion of water from the cathode to the anode, is the only source of water for both membrane hydration and the internal humidification of the cathode gas stream, which passes the cell in opposite direction.

Reactive belite stabilization mechanisms by boron-bearing dopants

Belite-rich cements hold promise for reduced energy consumption and CO2 emissions, but their use is hindered by the slow hydration rates of ordinary belites. This drawback may be overcome by activation of belite by doping. Here, the doping mechanism of B and Na/B in belites is reported. For B-doping, three solid solutions have been tested: Ca2-x/2□x/2(SiO4)1-x(BO3)x, Ca2(SiO4)1-x(BO3)xOx/2 and Ca2-xBx(SiO4)1-x(BO4)x. The experimental results support the substitution of silicate groups by tetrahedral borate groups with the concomitant substitution of calcium by boron for charge compensation, Ca2-xBx(SiO4)1-x(BO4)x. Otherwise, the coupled Na/B-doping of belite has also been investigated and Ca2-xNax(SiO4)1-x(BO3)x series is confirmed to exist for a large range of x values. Along this series, α'H-C2S is the main phase (for x≥0.10) and is single phase for x=0.25. Finally, a new structural description for borax doping in belite has been developed for α'H-Ca1.85Na0.15(SiO4)0.85(BO3)0.15, which fits better borax activated belite cements in Rietveld mineralogical analysis.

Activation of anhydrate phosphogypsum by K2SO4 and hemihydrate gypsum

Lime pretreated phosphogypsum(PG) was calcined at 500 °C to produce anhydrate gypsum cement. Due to the slow hydration of anhydrate gypsum, additives, K2SO4 and hemihydrate gypsum were selected to accelerate the hydration of anhydrate. The hydration characteristics, the resistance to hydrodynamic water, and the mineralogical studies were investigated. The experimental results suggest that activated by K2SO4 and hemihydrate, anhydrate PG hydrates much more rapidly than that in the presence of only K2SO4 or in the absence of additives. The binder has proper setting time, good strength development, and relatively better resistance to water. The hardened binder has hydrated products of rod or stick like shaped dihydrate gypsum crystals.

Calorimetric study on the influence of calcium sulfate on the hydration of Portland cement–calcium aluminate cement mixtures

The influence of calcium sulfate with different reactivities (anhydrite, α-hemihydrate, and gypsum) on the Portland cement–calcium aluminate cement (PC/CAC) mixtures was presented in the paper. The hydration process and main hydration products (ettringite) of the binders with different content of calcium sulfate was investigated by isothermal conduction calorimetry, setting times, compressive strength, X-ray diffraction (XRD) analysis, and environmental scanning electronic microscope (ESEM) analysis. It is found that the pure PC/CAC mixture without any calcium sulfate addition exhibits very slow hydration kinetics during the first 2 days. By adding calcium sulfate, the setting of the PC/CAC mixture is delayed, but the hydration can be accelerated. The results also show that the reactivity and the amount of the calcium sulfate determine the balance between the hydration products of ettringite and monosulphoaluminate, and also the early hydration kinetics not only in the formation content but in the location of ettringite. In general, when a high content of reactive α-hemihydrate is added, much secondary gypsum forms in voids between cement granules which exert adverse effects on the properties of PC/CAC mixtures. Additionally, ettringite can be formed stably and good binders having good physical properties can be obtained when low reactive anhydrite is added.

THM analysis of a large‐scale heating test incorporating material fabric changes

SUMMARYEngineered barriers are basic elements in the design of repositories for the isolation of high‐level radioactive waste. This paper presents the thermo‐hydro‐mechanical (THM) analysis of a clay barrier subjected to heating and hydration. The study focuses on an ongoing large‐scale heating test, at almost full scale, which is being carried out at the CIEMAT laboratory under well‐controlled boundary conditions. The test is intensely instrumented and it has provided the opportunity to study in detail the evolution of the main THM variables over a long period of time. Comprehensive laboratory tests carried out in the context of the FEBEX and NF‐PRO projects have allowed the identification of the model parameters to describe the THM behaviour of the compacted expansive clay. A conventional THM approach that assumes the swelling clay as a single porosity medium has been initially adopted to analyse the evolution of the test. The model was able to predict correctly the global THM behaviour of the clay barrier in the short term (i.e. for times shorter than three years), but some model limitations were detected concerning the prediction of the long‐term hydration rate. An additional analysis of the test has been carried out using a double structure model to describe the actual behaviour of expansive clays. The double structure model explicitly considers the two dominant pore levels that actually exist in the FEBEX bentonite and it is able to account for the evolution of the material fabric. The simulation of the experiment using this enhanced model provides a more satisfactory reproduction of the long‐term experimental results. It also contributes to a better understanding of the observed test behaviour and it provides a physically based explanation for the very slow hydration of the barrier. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Paulscherrerite from the Number 2 Workings, Mount Painter Inlier, Northern Flinders Ranges, South Australia: "Dehydrated schoepite" is a mineral after all

Paulscherrerite, UO2(OH)2, occurs as an abundant dehydration product of metaschoepite at the Number 2 Workings at Radium Ridge, Northern Flinders Ranges, South Australia. The mineral name honors the contribution of Swiss physicist Paul Scherrer (1890–1969) to mineralogy and nuclear physics. Individual paulscherrerite crystals are tabular, reaching a maximum of 500 nm in length. Paulscherrerite has a canary yellow color and displays no fluorescence under UV light. Chemically, paulscherrerite is a pure uranyl hydroxide/hydrate, containing only traces of other metals (<1 wt% in total). Bulk (mg) samples always contain admixtures of metaschoepite (purest samples have ~80 wt% paulscherrerite). A thermogravimetric analysis corrected for the presence of metaschoepite contamination leads to the empirical formula UO3·1.02H2O, and the simplified structural formula UO2(OH)2. Powder diffraction shows that the crystal structure of paulscherrerite is closely related to that of synthetic orthorhombic α-UO2(OH)2. However, splitting of some X-ray diffraction lines suggests a monoclinic symmetry for type paulscherrerite, with a = 4.288(2), b = 10.270(6), c = 6.885(5) A, β = 90.39(4)°, V = 303.2(2) A3, Z = 4, and possible space groups P 2, P 21, P 2/ m , or P 21/ m . Paulscherrerite-like material was synthesized using various methods, including heating metaschoepite in water at 150 °C and slow hydration of UO3(am) in air; material synthesized using hydrothermal techniques displayed peak splitting indicative of monoclinic symmetry. Paulscherrerite has been reported under the name “dehydrated schoepite” as an early weathering product of uraninite/pitchblende in several deposits, such as Shinkolobwe, Zaire; Nopal I deposit, Mexico; and the granitic pegmatites of New Hampshire, U.S.A.

Microstructural Analysis during the Hydration of Cement-in-Polymer Coatings

Cement-in-polymer (c/p) dispersions allow the full utilisation of the reinforcing abilities of multifilament rovings in concrete. In this work the role of the polymer properties on the performance of the c/p dispersions is investigated and discussed. Two model polymers are chosen and c/p dispersions made with these are investigated regarding the water ingress velocity (NMR), the phase development during cement hydration (XRD), and the microstructure after cement hydration (SEM). Best mechanical performance is achieved with the hydrophobic poly(vinyl acetate) which regulates the water ingress and causes a slow hydration of the cement.

The influence of crystallization inhibition of HPMC and HPMCAS on model substance dissolution and release in swellable matrix tablets

One of the drawbacks with solid solution systems is their thermodynamic instability in solution. Considering the release of these systems from extended-release formulations, in particular swellable matrix tablets, a successful tablet formulation can be regarded as a composition able to maintain the molecular state of the poorly soluble crystalline drug through diffusion in the matrix. This may in turn provide molecular rather than particulate delivery of the substance from the matrix. In this study, the solid state and dissolution behavior of amorphous solid dispersions of a model crystalline substance, butyl paraben in HPMC and HPMCAS, was investigated. In addition, the suitability of HPMCAS as both effective solid solution carrier and as extended-release matrix forming polymer was examined. The release from all systems investigated showed extended-release capacity with a release rate similar to the rate of matrix erosion. However, a detailed study of the factors affecting the release mechanism revealed that upon hydration, the model substance crystallized in the gel layer of the HPMC-based formulation, whereas it remained in amorphous form in the HPMCAS tablets. In the case of HPMCAS formulation, this effect was attributed to (i) the ability of this polymer to keep the model substance in a supersaturated state and (ii) the very slow matrix hydration, resulting in a steep concentration gradient of the drug substance and a short diffusion path through the matrix into the dissolution bulk.