High Bound Water Content Research Articles

Enhancing whipped cream anti-freeze properties: A dual plant system with aquafaba and mung bean protein

The objective of this study was to substitute sodium caseinate (SC) with a dual plant-based alternative to produce a refreshing sour whipped cream at pH 3.0, which could maintain stability when paired with low-pH foods. Aquafaba (AQ) was utilized as a novel foam booster, enhancing the whipped properties of the whipped cream, while pH12-shifting treated mung bean protein (BMBP) functioned as an interfacing stabilizer, improving its stability. Freeze-thaw stability of the aerated emulsion and the protein-protein interactions in the emulsion were characterized by analyzing water distribution, thermodynamics, serum loss, and protein retention rates. The high bound water content and dense bubble distribution of whipped cream prepared by AQ and native mung bean protein (NMBP) delivered superior freeze-thaw stability, shown as reduced serum loss, higher protein retention, and increased hardness. In addition, the internal fat network of the whipped cream made from a 1:1 combination of NMBP and BMBP showed moderate agglomeration with a comparable γmax value as SC-based whipped cream, indicating enhanced resistance to deformation and improved short-term shape retention. In conclusion, the combination of AQ and MBP provided viable options for the replacement of SC in commercial whipped cream.

Hydration, phase assemblage and microstructure of cementitious blends with low-grade limestone

Limestone of the purity mandated by the standards for use in cement manufacture (as raw material or as performance improver) is only a fraction of the mined material. Sometimes, limestone contains impurities like silica, clay, dolomite etc. beyond the levels specified for use as an additive or for cement production. This limestone, commonly known as low-grade limestone, also may have a potential to be used as a supplementary cementitious material. This paper reports a study conducted to understand the hydration behaviour of ordinary Portland cement in combination with low-grade limestone. Low-grade limestone samples with dolomite, silica and clay impurities were collected from various limestone mines in India and used in cementitious blends at various replacement levels after suitable processing. Reaction kinetics was studied using calorimetry and phase assemblage using techniques like X-ray diffraction and thermogravimetry. Mercury intrusion porosimetry was employed to study the microstructure of cementitious blends. Dilution effect of low-grade limestone was studied by measuring compressive strength of cement mortar cubes for various replacement levels. Shortening of induction period, increased peak heat rate and reduced time to peak were observed in the blends of ordinary Portland cement with low-grade limestone. Carboaluminate formation, ettringite stabilisation and higher bound water content were also seen. The studies showed that low-grade limestone also can be used as a partial replacement for ordinary Portland cement without compromising the strength up to 15% replacement. Higher replacement levels, although showing a reduction in strength due to dilution effect, could still be considered for non-structural applications.

High-performance anion exchange membranes achieved by crosslinking two aryl ether-free polymers: poly(bibenzyl N-methyl piperidine) and SEBS

Poly(aryl piperidinium) (PAP), the aryl ether-free polymer backbone, has drawn recent attention as a high-performance anion exchange membrane (AEM) material due to its excellent ion-conduction and alkaline stability. However, the relatively low mechanical (strain) property and poor phase separation of these PAP-based membranes require further improvement. Thus, this study crosslinked the poly(bibenzyl N-methyl piperidine) (PBB), a rigid PAP unit, with poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS), an elastic unit. Crosslinked PBB-SEBS membranes were prepared with different rigid and elastic polymer ratios by tuning the crosslinking degree. The membrane with a crosslinking degree of 40% exhibited a high elongation at break, 70.3%, a high Young's modulus, 486 MPa, and very high ionic conductivity (72.28–146.25 mS cm−1) from the high bound water content and the optimized morphology. Furthermore, it exhibited excellent alkaline (99% conductivity remaining for 720 h, 2 M KOH, 80 °C) and oxidative stability (98% for 120 h, 60 °C). With the highest RH and normalized conductivity in water, the membrane showed peak power density of 555 mW cm−2 in an AEM fuel cell test and a current density of 1042 mA cm−2 at 1.8 V, 178% of the value of the commercially available FAA-3-50, in the AEM water electrolysis test.

Hydrate formation and dissociation characteristics in clayey silt sediment

The geological occurrence of natural gas hydrates in clayey silt sediments has been extensively confirmed. Compared with sandy sediments, clayey silt is characterized by a large specific surface area, high capillary pressure, and high bound water content, which leads to distinct characteristics of hydrate formation and dissociation. The formation and dissociation of methane hydrates in clayey silt sediments with illite or montmorillonite were experimentally investigated. It was determined that an increase in the water content of silt and illite-silt sediments from ~9.47% to ~28.41% caused a decrease in the water-to-hydrate conversion ratio owing to the formation of a hydrate film between water and CH4 gas. However, in montmorillonite-silt sediments, the water-to-hydrate conversion rate increased between 9.47% and 18.94% of water saturation and decreased between 18.94% and 28.41% of water saturation under the combined effects of weakly bound water content and capillary pressure. In the hydrate dissociation experiment, the temperature of sediments with ~9.47% water content decreased more, which was caused by the smaller specific heat capacity of sediments with lower water content. Meanwhile, the temperature drops below the freezing point during the hydrate dissociation process, which is caused by the strong inhibition of hydrate phase equilibrium by montmorillonite. This study demonstrates the effects of clay type and water content on hydrate formation and dissociation, which is helpful for understanding the production behavior of clayey silt hydrate reservoirs.

Selective Accumulation to Tumor Cells with Coacervate Droplets Formed from a Water-Insoluble Acrylate Polymer.

Selective targeting of specific cells without the use of biological ligands has not been achieved. In the present study, we revealed that the coacervate droplets formed from poly(2-methoxyethyl acrylate) (PMEA) and its derivatives selectively accumulated to tumor cells. PMEA derivatives, which are insoluble acrylate polymers, induced coacervation in water to form polymer-dense droplets via hydrophobic interaction. Interestingly, the accumulation of coacervate droplets to tumor cells was involved in the bound water content of PMEA derivatives. Coacervate droplets with a high bound water content accumulated and internalized up to 36.6-fold higher in HeLa cervical tumor cells than in normal human fibroblasts (NHDF). Moreover, the interactions between coacervate droplets and plasma membrane components such as CD44 played a key role in this accumulation process. Therefore, coacervate droplets formed from PMEA derivatives have great clinical potential in tumor cell detection, development of alternative tumor-targeting ligands, and optimization of drug delivery carriers.

Design of a new lyoprotectant increasing freeze-dried Lactobacillus strain survival to long-term storage

BackgroundStabilization of freeze-dried lactic acid bacteria during long-term storage is challenging for the food industry. Water activity of the lyophilizates is clearly related to the water availability and maintaining a low aw during storage allows to increase bacteria viability. The aim of this study was to achieve a low water activity after freeze-drying and subsequently during long-term storage through the design of a lyoprotectant. Indeed, for the same water content as sucrose (commonly used lyoprotectant), water activity is lower for some components such as whey, micellar casein or inulin. We hypothesized that the addition of these components in a lyoprotectant, with a higher bound water content than sucrose would improve lactobacilli strains survival to long-term storage. Therefore, in this study, 5% whey (w/v), 5% micellar casein (w/v) or 5% inulin (w/v) were added to a 5% sucrose solution (w/v) and compared with a lyoprotectant only composed of 5% sucrose (w/v). Protective effect of the four lyoprotectants was assessed measuring Lactiplantibacillus plantarum CNCM I-4459 survival and water activity after freeze-drying and during 9 months storage at 25 °C.ResultsThe addition whey and inulin were not effective in increasing Lactiplantibacillus plantarum CNCM I-4459 survival to long-term-storage (4 log reduction at 9 months storage). However, the addition of micellar casein to sucrose increased drastically the protective effect of the lyoprotectant (3.6 log i.e. 0.4 log reduction at 9 months storage). Comparing to a lyoprotectant containing whey or inulin, a lyoprotectant containing micellar casein resulted in a lower water activity after freeze-drying and its maintenance during storage (0.13 ± 0.05).ConclusionsThe addition of micellar casein to a sucrose solution, contrary to the addition of whey and inulin, resulted in a higher bacterial viability to long-term storage. Indeed, for the same water content as the others lyoprotectants, a significant lower water activity was obtained with micellar casein during storage. Probably due to high bound water content of micellar casein, less water could be available for chemical degradation reactions, responsible for bacterial damages during long-term storage. Therefore, the addition of this component to a sucrose solution could be an effective strategy for dried bacteria stabilization during long-term storage.

Influence of calcined clay/limestone, sulfate and clinker proportions on cement performance

• Calcined clay and limestone promote the hydration of cement at early age. • Clinker and CC/L ratio are relevant factors affecting compressive strength. • CC/L are confirmed to increase bound water content and AFm phase formation. • CC/L influences mechanical strength, bound water content and porosity refinement. Clinker (CK), calcined clay to limestone ratio (CC/L), and sulfate content (SO 3 ) were studied determining their influence on cement performance. A low-grade kaolinite clay characterized before and after calcination was used. Isothermal calorimetry measurements indicate CK influences mainly energy liberation, while CC/L and SO 3 affect kinetics of hydration. Compressive strengths were primarily governed by CK at early age, and its effect is constant throughout hydration; CC/L became relevant as hydration progresses and achieved similar effects as CK beyond 28 d; SO 3 (wt%) has marginal contribution only at early age. All cements, including CC/L, obtained higher compressive strengths than their references (CK + quartz mixes). The latter correspond with higher bound water content, carboaluminate hydrates formation, and a finer porous structure estimated by water absorption. Thus, CK and CC/L are most relevant factors in cement performance, and the improvement is proportional to calcined clay content in the mixture.

Acid stable bi-functional cation exchange membrane based on modified poly(vinylidene fluoride-co-hexafluoropropylene) for electrochemical Bunsen process

Synthesis of 4-(N-isopropylacrylamido)butane-1-sulfonic acid monomer has been achieved by sultone ring opening followed by condensation reaction. Stable and flexible bi-functional cation exchange membranes have been prepared by dehydofluorinated poly(vinylidene fluoride-co-hexafluoropropylene) and 4-(N-isopropylacrylamido)butane-1-sulfonic acid in presence of initiator and vinyl phosphonic acid. Fluorinated carbon chain grafted with bi-functional groups (-SO3H, and –PO3H2) via side chain spacer, are attractive structural features of reported cation exchange membranes. Presence of fluorinated carbon chain grafted with bi-functional charged groups via side chain spacer are responsible for easy accessibility of water. Reported bi-functional PVIP-1.81 cation exchange membrane exhibits 5.84 × 10−2 S cm−1 conductivity and about ~2.5-fold high bound water content, in compare with Nafion 177 membrane due to high molality of charged groups (–SO3H and –PO3H2). Further, PVIP-1.81 cation exchange membrane shows ~100% efficiencies (ηa: 95.8%; and ηc: 96.9%) during electrochemical Bunsen process (water splitting), which rule out side reaction. Further, electrical energy (or equivalent heat energy) (UH2) requirement for producing 1 mol of H2 by electrolysis using PVIP-1.81 membrane (279.46 kJ mol−1-H2) is comparable with that for Nafion117 membrane (280.80 kJ mol−1-H2). These observations confirm the high performance and suitability PVIP-1.81 cation exchange membrane for membrane electrolysis and water splitting (Bunsen process).

Acid resistant sulphonated poly(vinylidene fluoride-co-hexafluoropropylene)/graphene oxide composite cation exchange for water splitting by iodine-sulfur bunsen process for hydrogen production

The acid/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM) is urgently required for water splitting by iodine-sulfur electrochemical Bunsen process (I-S cycle). Under operating environment of I-S cycle, commercially available CEM (perfluorosulfonic acid polymers such as Nafion) exhibits excessive mass transfer via electro-osmosis and its conductivity deteriorates due to membrane dehydration, while aromatic hydrocarbon based polymers showed short lifetimes due to the oxidative degradation. Herein, we achieved partial sulfonation of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) to introduce hydrophilic character in the polymer matrix, and prepared sulphonated PVDF-co-HFP (SPVDF)/sulphonated GO (SGO) composite acid resistant CEMs with different composition for water splitting via I-S process for hydrogen production. These CEMs were extensively characterized for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. About 3-fold high bound water content of suitable assessed SPVDF/SGO40 CEM (bound water content: 3.17%) in compare with Nafion 117 (bound water content: 1.04%) avoids the membrane dehydration and thus any deterioration in membrane conductivity.Iodine−sulfur (I−S) Bunsen process was successfully performed by membrane electrolysis in a two-compartment electrolytic cell (direct contact-mode) using SPVDF/SGO composite CEMs of different compositions. Theoretical and experimental values of acid produced in the anolyte and catholyte, showed good agreement. Further, relatively high current efficiency (close to 100%) for electrochemical Bunsen process using SPVDF/SGO40 CEM confirmed absence of any side reaction, while approximately 300 kJ mol-H2−1 energy was consumed to produce 1 mol of H2. In spite of low conductivity in compare with state-of-art Nafion 117 membrane, SPVDF/SGO40 composite CEM was assessed as suitable candidate for water splitting via I-S (Bunsen) process because of its low-cost nature, high bound water content and excellent stabilities in highly acidic environment attributed to the partial fluorinated segments in the membrane matrix.

Influence of granular fraction and origin of recycled concrete aggregates on their properties

Large quantities of construction and demolition wastes are produced each year. In order to make good use of recycled concrete aggregates (RCA) in concrete, it is very important to study the influence of the granular fraction and the origin of RCA on their properties. In this study, RCA from industrial produced blocks (RCA_Blocks) and slabs (RCA_Slabs) were crushed and then separated into four granular fractions (0/2, 2/6.3, 6.3/14, 14/20 mm). Each granular fraction of RCA was physically characterised. Real RCA from recycling plant were also used for comparison. The results showed that recycled sands offered significantly higher cement paste content (higher bound water content) than coarse recycled aggregates. The fine RCA had therefore a higher water absorption coefficient compared to coarser fractions of RCA. The water absorption of finer fraction of RCA could be extrapolated precisely from the relationship between water absorption and cement paste content (or bound water content) of three coarse fractions of RCA. The values of hardened cement paste content obtained for the RCA_Blocks were lower than those measured on the RCA_Slabs, which was due to a smaller amount of initial cement paste content in blocks. The results showed that RCA_Slabs were more angular than RCA_Blocks.

Petrophysical characterization of shale reservoir based on nuclear magnetic resonance (NMR) experiment: A case study of Lower Cambrian Qiongzhusi Formation in eastern Yunnan Province, South China

In order to characterize the petrophysical properties of shale using NMR technique, eight shale samples from the Lower Cambrian Qiongzhusi Formation in the eastern Yunnan province were measured by porosity and permeability tests, field emission scanning electron microscopy (FE-SEM) and NMR experiment. Pore types were obtained from the shape and distribution of transverse relaxation time (T2) spectrum. Residual porosity and movable porosity could be well estimated based on T2 spectrum area fraction. On the basis of Coates model, we proposed a regional Coates model to calculate the NMR permeability of shale. A method for determining T2cutoff of shale samples was also expounded. Moreover, the specific surface area distributions and pore size distributions could be obtained based on the mathematical equation of T2. Results show that T2 spectrums of shale samples at water-saturated condition can be divided into unimodal and bimodal T2 spectrums. Continuous bimodal T2 spectrums reflect the samples with good connectivity between small pores and large pores, whereas discontinuous bimodal T2 spectrums reflect that the connectivity between small pores and large pores is poor. Shale samples with higher bound water content have a greater T2cutoff. The NMR permeability is close to gas log permeability, which proves the applicability of regional Coates model. In eight shale samples, transition pores account for the largest proportion, followed by mesopores, indicating that transition pores and mesopores are the major sites for the accumulation of shale gas.

Sewage sludge disruption through sonication to improve the co-preparation of coal–sludge slurry fuel: The effects of sonic frequency

The sewage sludge volume has been increasing annually, and if not treated properly, this sludge endangers the environment and human health. Sludge can be considered as a carbon-containing material, and the energy within is utilized easily and economically by blending it with coal to prepare a slurry fuel called coal–sludge slurry (CSS). However, sludge is always disrupted before CSS preparation because of its high bound water content and viscosity. In this study, sonication was performed to disrupt sludge and to enhance co-slurrying with coal. The effects of sonic frequency were highlighted, and the results showed that low-frequency sonication significantly reduces viscosity. Moreover, this process improved CSS slurrying. The characteristic viscosity (the apparent viscosity measured at a shear rate of 100 s−1) of CSS prepared with raw sludge was 1663.6 mPa⋅s; following sludge disruption via sonication (the specific energy was 30 kJ/g dry sludge) at 15, 25, and 35 kHz, the characteristic viscosities of prepared CSSs decreased to 1121.6, 1194.8, and 1234.3 mPa⋅s, respectively. On the basis of the dynamic model of a sonic cavitation bubble, low-frequency sonication intensified cavitation such that the radius and impact velocity of a cavitation bubble increased. This finding was consistent with experimental results.

2-Acrylamido-2-methyl-1-propanesulfonic Acid Grafted Poly(vinylidene fluoride-co-hexafluoropropylene)-Based Acid-/Oxidative-Resistant Cation Exchange for Membrane Electrolysis.

For developing acid-/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM), macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was carried out by controlled chemical grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). To introduce the unsaturation suitable for chemical grafting, dehydrofluorination of commercially available PVDF-co-HFP was achieved under alkaline medium. Sulfonated copolymer (SCP) was prepared by the free radical copolymerization of dehydofluorinated PVDF-co-HFP (DHPVDF-co-HFP) and AMPS in the presence of free radical initiator. Prepared SCP-based CEMs were analyzed for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. High bound water content avoids the membrane dehydration, and most optimal (SCP-1.33) membrane exhibited about ∼2.5-fold high bound water content in comparison with that of Nafion117 membrane. Bunsen reaction of iodine-sulfur (I-S) was successfully performed by direct-contact-mode membrane electrolysis in a two-compartment electrolytic cell using different SCP membranes. High current efficiency (83-99%) confirmed absence of any side reaction and 328.05 kJ mol-H2(-1) energy was required for to produce 1 mol of H2 by electrolytic cell with SCP-1.33 membrane. In spite of low conductivity for reported SCP membrane in comparison with that of Nafion117 membrane, SCP-1.33 membrane was assessed as suitable candidate for electrolysis because of its low-cost nature and excellent stabilities in highly acidic environment may be due to partial fluorinated segments in the membrane structure.

Sulphonated imidized graphene oxide (SIGO) based polymer electrolyte membrane for improved water retention, stability and proton conductivity

Sulphonated imidized graphene oxide (SIGO) (graphene oxide (GO) tethered sulphonated polyimide) has been successfully synthesized by polycondensation reaction using dianhydride and sulphonated diamine. Polymer electrolyte membranes (PEMs) are prepared by using SIGO (different wt%) and sulphonated poly(imide) (SPI). Resultant SPI/SIGO composite PEMs exhibit improved stabilities (thermal, mechanical and oxidative) and good water-retention properties (high bound water content responsible for proton conduction at high temperature by internal self-humidification). Incorporation of covalent bonded SIGO into SPI matrix results hydrophobic−hydrophilic phase separation and facile architecture of proton conducting path. Well optimized sulphonated poly(imide)/sulphonated imidized graphene oxide (15 wt%) (SPI/SIGO-15) composite membrane shows 2.24 meq g−1 ion-exchange capacity (IEC); 11.38 × 10−2 S cm−1 proton conductivity; 5.12% bound water content; and 10.52 × 10−7 cm2 s−1 methanol permeability.Maximum power density for pristine SPI membrane (57.12 mW cm−2) improves to 78.53 mW cm−2 for SPI/SIGO-15 membrane, in single-cell direct methanol fuel cell (DMFC) test at 70 °C using 2 M methanol fuel. Under similar experimental conditions, Nafion 117 membrane exhibits 62.40 mW cm−2 maximum power density. Reported strategy for the preparation of PEMs, offers a useful protocol for grafting of functionalized inorganic materials with in organic polymer chain by imidization.

Preparation, characterization and thermal degradation studies of bi-functional cation-exchange membranes

Cross-linked divinylbenzene (DVB) based bi-functional copolymer (BFC) was synthesized using acrylic acid and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) by free radical copolymerisation reaction. Simple solution casting technique was used to fabricate the bi-functional cation-exchange membranes using polyvinyl alcohol (PVA) as plasticizer. To deliberate the structural and morphological analyses and asses the density of functional groups, state of water, and conductivity of developed membranes, physicochemical characterizations were carried out. Well optimized PVA/BFC-70 membrane showed high bound water content (3.60%) with high membrane conductivity (3.67×10−2Scm−1) and ion-exchange capacity (1.30mequivg−1). The reported CEM, especially PVA/BFC-70, was assessed for the electrochemical applications.

Independent control of water retention and acid–base pairing through double-shelled microcapsules to confer membranes with enhanced proton conduction under low humidity

Proton exchange membranes (PEM) with affordable and controllable proton conductivity under low humidity are crucial to the commercial application of PEM fuel cells. In this study, double-shelled polymer microcapsules bearing a carboxylic acid inner shell and imidazole outer shell (PMC-Ns) are synthesized via distillation–precipitation polymerization and then incorporated into a sulfonated poly(ether ether ketone) matrix to fabricate composite membranes. The inner shell renders the absorbed water of lower chemical potential and higher bound water content, yielding the composite membrane with enhanced water retention properties. The higher water uptake ensures composite membrane facilitated proton transfer via a vehicle mechanism and the lower water loss confers a reduced proton conductivity decline. The outer shell generates sulfonic acid–imidazole pairs within the membranes, which construct low-energy-barrier pathways to facilitate proton transfer via the Grotthuss mechanism. Under identical conditions, PMC-Ns endow much higher proton conductivity to composite membranes than the microcapsules with both carboxylic acid inner shell and outer shell, or both imidazole inner shell and outer shell. Particularly, incorporating 20 wt% PMC-Ns affords the composite membrane a 1.7 times increase in proton conductivity under 100% relative humidity (RH) and a 41.8 times increase in proton conductivity under 20% RH. Moreover, the methanol barrier property of the composite membranes is explored.

Influence of sewage sludge on the rheological properties of petroleum coke–water slurry

ABSTRACTEnvironmental concerns have stimulated proper treatment in utilizing sewage sludge derived from different industries. The main objective of the present study is to prepare high‐quality petroleum coke–sludge slurry (PCSS) with low viscosity and good stability by adding sewage sludge into petroleum coke–water slurry (PCWS), and a systematic investigation of the rheological properties of PCSS and PCWS, along with the sewage sludge, is conducted. The experimental results show that the PCWS is a dilatant fluid and has inferior stability; sewage sludge is a pseudoplastic fluid. As a certain amount of sewage sludge is added into PCWS to obtain PCSS, rheological properties are changed from a shear‐thickening property to a shear‐thinning property. Raw sewage sludge has higher bound water content and larger viscosity. Alkaline chemical additives are selected as sewage sludge modifiers to turn bound water into free‐flowing water and reduce the viscosity. The static stability of PCSS was analyzed by the water separation ratio. Results indicate that sewage sludge has a significant impact on the static stability of PCSS. Water separation ratio decreases and the static stability is improved after addition of the sewage sludge. The higher the sewage sludge amount, the better the static stability of the PCSS. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.

Using hydrophilic polysaccharide to modify supramolecular hydrogel from a low-molecular-mass gelator

Small molecular hydrogels hold important potential applications in bioengineering and biomedicine. However, they suffer usually from weak mechanical and water-retention properties. In this work, hydrophilic dextran polysaccharide was used for the first time to modify the properties of the supramolecular hydrogel derived from a low-molecular-mass gelator, 2, 6-di[ N-(carboxyethyl carbonyl)amino]pyridine (DAP). When the DAP hydrogel was formed in aqueous dextran solution with a rather low viscosity, we found that it could be significantly reinforced with respect to its viscoelastic moduli, complex viscosity and hydrogel strength. Moreover, the modified DAP hydrogel has a higher bound water content. These property changes could be attributed to the formation of intermolecular hydrogen bonds between DAP and dextran. By relating the dynamic rheological data with a scaling model, it was found that native and modified DAP hydrogels had both a fractal aggregate structure and the incorporation of dextran resulted in an increase of the fractal dimension. Scanning electron microscopy revealed that a more complex network structure was formed in the DAP hydrogel with dextran.

Proton exchange membranes modified with sulfonated silica nanoparticles for direct methanol fuel cells

Nanocomposite proton exchange membranes were prepared from sulfonated poly(phthalazinone ether ketone) (sPPEK) and various amounts of sulfonated silica nanoparticles (silica-SO 3H). The use of silica-SO 3H compensates for the decrease in ion exchange capacity of membranes observed when non-sulfonated nano-fillers are utilized. The strong –SO 3H/–SO 3H interaction between sPPEK chains and silica-SO 3H particles leads to ionic cross-linking in the membrane structure, which increases both the thermal stability and methanol resistance of the membranes. The membrane with 7.5 phr of silica-SO 3H (phr = g of silica-SO 3H/100 g of sPPEK in membranes) exhibits low methanol crossover, high bound-water content, and a proton conductivity of 3.6 fold increase to that of the pristine sPPEK membrane.

Metabolism and bound water in overwintering insects

The freezing-tolerant gall fly larva, Eurosta solidaginis, provides an excellent model system for the study of metabolic adaptation and metabolic control for lowtemperature survival during overwintering. Low-temperature acclimation of the larvae results in dramatic alterations in metabolic flux producing a sequential synthesis of two cryoprotectants, glycerol at warmer temperatures followed by sorbitol when larvae are exposed to 5 °C. Regulation of metabolism in the larvae appears to exploit temperature change, temperature effects on enzyme kinetics, and temperature/modulator interactions with enzymes producing the alterations in metabolic flux leading to differential polyol synthesis. For instance, temperature/modulator effects on phosphofructokinase appear to be the major factor halting carbon flow into glycerol synthesis at low temperatures and diverting flux instead into the pathway of sorbitol synthesis. Alterations in the cellular content of bound water and the metabolic pools of free versus bound soluble metabolites may also have important regulatory consequences for low-temperature metabolism. Bound water content of the larvae increases with low-temperature acclimation and is attributable to changes in water binding by both low-molecular-weight (polyols) and highmolecular-weight (proteins, glycogen) subcellular components. A restrictive effect of high bound water content may be one factor causing the strong depression of metabolic activity seen in the larvae as a result of extracellular freezing. In addition, bound water may have a more subtle effect in determining the relative pool sizes of bound versus free metabolites in the cell. 31P-NMR studies of whole larvae show that the content of free phosphorylated intermediates in the cell diminishes with decreasing temperatures despite a measured constancy in the total pool size of these intermediates. An increase in the content of bound metabolites with low temperature may restrict metabolism by limiting the availability of substrates and effectors of enzyme reactions.