Wide Range Of NaCl Concentrations Research Articles

Understanding the NaCl-dependent behavior of hydrogen production of a marine bacterium, Vibrio tritonius.

Biohydrogen is one of the most suitable clean energy sources for sustaining a fossil fuel independent society. The use of both land and ocean bioresources as feedstocks show great potential in maximizing biohydrogen production, but sodium ion is one of the main obstacles in efficient bacterial biohydrogen production. Vibrio tritonius strain AM2 can perform efficient hydrogen production with a molar yield of 1.7 mol H2/mol mannitol, which corresponds to 85% theoretical molar yield of H2 production, under saline conditions. With a view to maximizing the hydrogen production using marine biomass, it is important to accumulate knowledge on the effects of salts on the hydrogen production kinetics. Here, we show the kinetics in batch hydrogen production of V. tritonius strain AM2 to investigate the response to various NaCl concentrations. The modified Han–Levenspiel model reveals that salt inhibition in hydrogen production using V. tritonius starts precisely at the point where 10.2 g/L of NaCl is added, and is critically inhibited at 46 g/L. NaCl concentration greatly affects the substrate consumption which in turn affects both growth and hydrogen production. The NaCl-dependent behavior of fermentative hydrogen production of V. tritonius compared to that of Escherichia coli JCM 1649 reveals the marine-adapted fermentative hydrogen production system in V. tritonius. V. tritonius AM2 is capable of producing hydrogen from seaweed carbohydrate under a wide range of NaCl concentrations (5 to 46 g/L). The optimal salt concentration producing the highest levels of hydrogen, optimal substrate consumption and highest molar hydrogen yield is at 10 g/L NaCl (1.0% (w/v)).

Bio-decolourization of Reactive Blue EFAF using halotolerant Exiguobacterium profundumstrain CMR2 isolated from salt pan

Abstract Two halotolerant bacteria isolated from water samples of saltpan located at Ramanathapuram district, Tamil Nadu and tested their dye decolourization efficiency against four textile dyes. Of the tested strains, strain CMR2 showed maximum decolourization (98%) for Reactive Blue EFAF within 24 h. Further, strain CMR2 was identified as Exiguobacterium profundum using 16 s rDNA sequence analysis. It is noteworthy that the isolated halotolerant bacteria possess the ability to decolorize the reactive blue EFAF dye even in wide range of NaCl concentrations (5–30%) and pH (5–10). Decolourization efficiency was significantly increased upto 85% and 92% when the medium supplemented with starch and peptone as carbon and nitrogen source. Findings from UV–vis, FTIR spectral analysis before and after decolourization confirmed that the dye was decolourized completely via biodegradation. The present study suggest that Exiguobacterium profundum can be used as an effective candidate for the decolourization of waste water containing reactive blue EFAF.

Biodegradation of phenanthrene by a bacterial consortium enriched from Sercina oilfield

Abstract The phenanthrene (PHE) degradation by a halotolerant bacterial consortium enriched from production water of Sercina oilfield in Tunisia was investigated. The consortium PHMM utilized PHE (200 mg/L), as a sole carbon source, in the presence of a wide range of NaCl concentrations, from 1 to 5% (w/v). The maximum growth rate was obtained at 500 mg/L of PHE. A PHE metabolism was assayed by using FTIR, UV and GC–MS analyses. Results revealed that the consortium PHMM metabolized PHE via protochatechuate pathway since intermediates such as naphthalenol and phthalic acid were detected. Phylogenetic analysis showed that the adapted consortium PHMM was composed by two dominant bacterial strains, identified as Pseudomonas sp. (strain PH1) and Staphylococcus sp. (strain PH2). All the results indicated that the microorganisms from the Tunisian oilfield have a promising application in bioremediation of petrochemical contaminated environments and could be potentially useful for the study of PAHs biodegradation.

Bioreduction of hexavalent chromium by Exiguobacterium indicum strain MW1 isolated from marine water of Paradip Port, Odisha, India

ABSTRACTHexavalent chromium-tolerant (1500 mg/L) bacterium MW1 was isolated from harbour water of Paradip Port and evaluated for Cr(VI) reduction potential. The isolate was identified as Exiguobacterium indicum by biochemical and 16S rRNA gene sequence methods. Salt tolerance of the bacterium was evaluated in a wide range of NaCl concentrations (0.5–13%, w/v). The Cr(VI) reduction of the strain was evaluated and optimised with varied Cr(VI) concentrations (100–1000 mg/L), pH (5.0–9.0), temperature (30–40°C) and shaking velocity (100–150 rpm) in two different minimal media (M9 and Acetate). Under optimised conditions, after 192 h of incubation nearly 92%, 50% and 46% reduction in the M9 minimal medium and 91%, 47% and 40% reduction in the acetate minimal medium were observed for 100, 500 and 1000 mg/L of Cr(VI), respectively. The exponential rate equation for Cr(VI) reduction yielded higher rate constant value, that is, 1.27 × 10−2 h−1 (M9) and 1.17 × 10−2 h−1 (Acetate) in case of 100 mg/L and became lower for 500 and 1000 mg/L Cr(VI) concentrations. Further, the association of bacterial cells with reduced product was ascertained by Fourier transform infrared spectrometer, UV–Vis–DRS and field-emission scanning electron microscope–energy-dispersive X-ray analyses. The above study suggests that the higher reducing ability of the marine bacterium E. indicum MW1 will be suitable for Cr(VI) reduction from saline effluents.

Applications of halophilic, thermo-stable protease produced by the extremely halophilic archaeon Natrialba aegyptiaca strain 40T

A halophilic, thermostable protease produced by the extremely halophilic archaeon Natrialba aegyptiaca strain 40T was active over a wide range of NaCl concentrations i.e. 0–32 % (w/v), with maximum activity at 25 % (w/v). Optimum pH and temperature for maximum protease activity were 8 -8.5 and 40-45 oC respectively. The crude protease was successfully applied for dehairing of goat skin and removing of blood stain from cotton cloth.

Thermodynamic modeling of protein retention in mixed-mode chromatography: An extended model for isocratic and dual gradient elution chromatography

An extended model is developed to describe protein retention in mixed-mode chromatography based on thermodynamic principles. Special features are the incorporation of pH dependence of the ionic interaction on a mixed-mode resin and the addition of a water term into the model which enables one to describe the total number of water molecules released at the hydrophobic interfaces upon protein-ligand binding. Examples are presented on how to determine the model parameters using isocratic elution chromatography. Four mixed-mode anion-exchanger prototype resins with different surface chemistries and ligand densities were tested using isocratic elution of two monoclonal antibodies at different pH values (7–10) and encompassed a wide range of NaCl concentrations (0–5M). U-shape mixed-mode retention curves were observed for all four resins. By taking into account of the deprotonation and protonation of the weak cationic functional groups in these mixed-mode anion-exchanger prototype resins, conditions which favor protein-ligand binding via mixed-mode strong cationic ligands as well as conditions which favor protein-ligand binding via both mixed-mode strong cationic ligands and non-hydrophobic weak cationic ligands were identified. The changes in the retention curves with pH, salt, protein, and ligand can be described very well by the extended model using meaningful thermodynamic parameters like Gibbs energy, number of ionic and hydrophobic interactions, total number of released water molecules as well as modulator interaction constant. Furthermore, the fitted model parameters based on isocratic elution data can also be used to predict protein retention in dual salt-pH gradient elution chromatography.

Sodium chloride concentration determines exoelectrogens in anode biofilms occurring from mangrove-grown brackish sediment

Single-chamber microbial fuel cells (MFCs) were inoculated with mangrove-grown brackish sediment (MBS) and continuously supplied with an acetate medium containing different concentrations of NaCl (0–1.8M). Different from MFCs inoculated with paddy-field soil (high power outputs were observed between 0.05 and 0.1M), power outputs from MBS-MFCs were high at NaCl concentrations from 0 to 0.6M. Amplicon-sequence analyses of anode biofilms suggest that different exoelectrogens occurred from MBS depending on NaCl concentrations; Geobacter occurred abundantly below 0.1M, whereas Desulfuromonas was abundant from 0.3M to 0.6M. These results suggest that NaCl concentration is the major determinant of exoelectrogens that occur in anode biofilms from MBS. It is also suggested that MBS is a potent source of microbes for MFCs to be operated in a wide range of NaCl concentrations.

Grafting glycidyl methacrylate to Sepharose gel for fabricating high-capacity protein anion exchangers

To develop ion exchangers of high protein adsorption capacity, we have herein introduced atom transfer radical polymerization (ATRP) method to graft glycidyl methacrylate (GMA) onto Sepharose FF gel. GMA-grafted Sepharose FF resins of four grafting densities and different grafting chain lengths were obtained by adjusting reaction conditions. The epoxy groups on the grafted chains were functionalized by modification with diethylamine (DEA), leading to the fabrication of Sepharose-based anion exchangers of 14 different grafting densities and/or grafting chain lengths. The resins were first characterized for the effects of grafting density, chain length and ionic strength on pore sizes by inverse size exclusion chromatography. Then, the resins were evaluated by adsorption equilibria of bovine serum albumin (BSA) as a function of ionic capacity (IC) (chain length) at individual grafting densities. It was observed that at each grafting density there was a specific IC value (chain length) that offered the maximum equilibrium capacity. Of the resins with maximum values at individual grafting densities, the resin of the second grafting density with an IC value of 330mmol/L (denoted as FF-Br2-pG-D330) showed the highest capacity, 264mg/mL, about two times higher than that of the traditional ungrafted resin Q Sepharose FF (137mg/mL). This resin also showed the most favorable uptake kinetics among the resins of similar IC values but different grafting densities, or of the same grafting density but different IC values. Effects of ionic strength showed that the capacities of FF-Br2-pG-D330 were much higher than Q Sepharose FF at a wide range of NaCl concentrations (0–200mmol/L), and the uptake rates of the two resins were similar in the ionic strength range. Therefore, the dynamic binding capacity values of BSA on FF-Br2-pG-D330 were much higher than Q Sepharose FF as demonstrated at different residence times and ionic strengths. Taken together, the research has proved the success in the fabrication of high-capacity protein anion exchangers by grafting GMA onto Sepharose gel.

Cloning and differential expression analysis of geranylgeranyl diphosphate synthase gene from Dunaliella parva

Dunaliella parva can thrive and adapt to salt stress over a wide range of NaCl concentrations which also is related to carotenoid accumulation in Dunaliella. Dunaliella parva can accumulate carotenoids; however, the underlying mechanism of carotenoid accumulation needs further research. Thus, it is necessary to study biosynthesis and regulation of carotenoids for understanding carotenoid accumulation. In the present study, a gene encoding geranylgeranyl diphosphate synthase (GGPS) from the halophilic green alga D. parva has been cloned and analyzed. It is in the branch of terpene metabolism and named as DpGGPS (D. parva GGPS). The full-length complementary DNA (cDNA) of DpGGPS was 1612 bp, including an open reading frame (ORF) of 1059 bp, 189 bp 5′-untranslated region (5′-UTR) and 364 bp 3′-UTR. The 5′-flanking region was obtained by the genome walking method. Potential regulatory elements, associated with hormones, defense, and stress, were found in the 1310 bp 5′-flanking region. Functional characterization of DpGGPS in E. coli BL21(DE3) demonstrated that DpGGPS encoded a functional GGPS. Analysis of DpGGPS expression revealed a correlation between GGPS expression and the shift of NaCl concentration, which indicated that GGPS could be a salt stress responsive gene. Cloning and expression analysis of GGPS provides a foundation for studying the regulatory mechanism of carotenoid biosynthesis, adaptation mechanism to salt stress, and massive accumulation of carotenoids in D. parva.

Alkaline protease from a new halotolerant alkaliphilic Bacillus agaradhaerens strain ak-r isolated from egyptian soda lakes

Alkaline proteases are hydrolytic enzymes that cleave peptide bonds in proteins and peptides in alkaline conditions, which occupy a pivotal importance with respect to their industrial applications. This study aimed to isolate new alkaline protease producing alkaliphilic bacteria from Egyptian soda lakes and optimize the fermentation process to enhance the enzyme production. The extensive screening process of the samples collected from Egyptian soda lakes resulted in isolation of a potent alkaline protease producing alkaliphilic strain AK-R. The isolate was identified as Bacillus agaradhaerens strain AK-R based on 16S rRNA gene analysis (99%). Wheat bran and gelatin supported maximum alkaline protease production as carbon and nitrogen sources, respectively. Strain AK-R is halo-tolerant thermo-tolerant alkaliphilic bacterium in nature, as it can grow over a wide range of NaCl concentrations (up to 25%) and up to 55 °C, with maximal growth and enzyme production at 2.5-5%, and pH 11 at 35 °C. Among the tested cations, only Mg 2+ and Ca 2+ ions significantly enhanced the enzyme production by about 1.2, and 1.3 fold compared to control, respectively. Alkaline protease secretion was coherent with the growth pattern, reaching maximal yield after about 32 h (mid stationary phase). In conclusion a new halo-tolerant thermo-tolerant alkaliphilic alkaline protease producing Bacillus agaradhaerens strain AK-R was isolated from Egyptian soda lakes. Optimization of the nutritional and cultivation conditions resulted in increase of enzyme yield by 20 fold. Strain AK-R and its extracellular alkaline protease with salt, pH and temperature, tolerance signify their potential application in laundry and pharmaceuticals industries.

Morphological, Chemical Surface, and Diffusive Transport Characterizations of a Nanoporous Alumina Membrane.

Synthesis of a nanoporous alumina membrane (NPAM) by the two-step anodization method and its morphological and chemical surface characterization by analyzing Scanning Electron Microscopy (SEM) micrographs and X-Ray Photoelectron Spectroscopy (XPS) spectra is reported. Influence of electrical and diffusive effects on the NaCl transport across the membrane nanopores is determined from salt diffusion measurements performed with a wide range of NaCl concentrations, which allows the estimation of characteristic electrochemical membrane parameters such as the NaCl diffusion coefficient and the concentration of fixed charges in the membrane, by using an appropriated model and the membrane geometrical parameters (porosity and pore length). These results indicate a reduction of ~70% in the value of the NaCl diffusion coefficient through the membrane pores with respect to solution. The transport number of ions in the membrane pores (Na+ and Cl−, respectively) were determined from concentration potential measurements, and the effect of concentration-polarization at the membrane surfaces was also considered by comparing concentration potential values obtained with stirred solutions (550 rpm) and without stirring. From both kinds of results, a value higher than 0.05 M NaCl for the feed solution seems to be necessary to neglect the contribution of electrical interactions in the diffusive transport.

Cross-modal taste and aroma interactions: Cheese flavour perception and changes in flavour character in multicomponent mixtures

The effect of cross-modal sensory interactions between cheese aroma and cheese taste on both cheese flavour intensity and cheese flavour character were investigated. Cheese aroma consisted of a mixture of ten aroma compounds, whilst cheese taste was constructed with the five basic tastes in water solution. Interactions were investigated using a combination of a high resolution design (HRD) and central composite design (CCD). The HRD was 2 aroma×5 NaCl×5 lactic acid levels. The CCD was constructed based on a 23 factorial design that covered the HRD space. Both HRD and CCD gave a total of 57 samples. A panel of experienced assessors (n=8–10) evaluated cheese flavour intensity relative to reference. In addition, samples were sorted based on similarity of flavour character. Fourteen samples were selected for free choice profiling and analysed using generalised procrustes analysis (GPA). Cheese flavour intensity was non-linear and dependent on both taste level and aroma level. The status of flavour character being cheese-like was dependent on taste levels, where either NaCl or lactic acid at a high or low level altered the flavour character to being atypical of cheese. A cheese-like flavour character was maintained across a wide range of NaCl concentrations, but only across a narrow range of lactic acid concentrations. Aroma level changed the character of cheese flavour. Overall, the balance in concentration of both tastes and aroma levels was important in maintaining cheese flavour character as cheese flavour intensity was modified.

Protein adsorption and chromatography on novel mixed-mode resins fabricated from butyl-modified poly(ethylenimine)-grafted Sepharose

We have previously studied benzoyl-modified poly(ethylenimine) (PEI)-grafted Sepharose FF resins for mixed-mode chromatography (MMC), and found PEI-grafted resin with an ionic capacity (IC) of about 300mmol/L was suitable for fabricating MMC resins to achieve favorable MMC performance. To extend the application of PEI-grafted resins in MMC, we have herein modified a PEI-grafted resin with an initial IC of 315mmol/L (FF-PEI-L315) with hydrophobic butyl groups, and two MMC resins with residual ICs of 280 and 252mmol/L were obtained (denoted as Bu30-PEI315 and Bu60-PEI315). Bovine serum albumin (BSA) and γ-globulin adsorption at pH 8.0 and elution at pH 3.0 were first explored on the two MMC resins. It was found that with increasing butyl density, protein binding capacity increased but the elution percentage decreased, indicating that high butyl density was beneficial in protein adsorption but not favorable in elution. It was considered that the butyl density of Bu60-PEI315 was so high that the electrostatic repulsion at pH 3.0 was insufficient to make the protein dissociate from the resin surface. Then, the eluent was switched to 3-[(3-cholamido-propyl)-dimethylammonio]-1-propanesulfonate (CHAPS) solution, and complete BSA recovery was obtained on Bu60-PEI315. Complete γ-globulin recovery was obtained on Bu60-PEI315 at a lower CHAPS concentration than that for BSA. This suggests the possibility of selective elution of the two proteins by manipulating eluent concentration. The results indicate that CHAPS was a suitable eluent for protein recovery and separation with the MMC resin, particularly for the purification of antibody from feedstock containing serum albumin. Finally, adsorption equilibria and uptake kinetics onto Bu30-PEI315 and Bu60-PEI315 were investigated. At 0mol/L NaCl, BSA binding on the MMC resins was only by electrostatic interaction while γ-globulin showed a bi-modal binding behavior, including electrostatic and hydrophobic interactions. At high NaCl concentrations, both BSA and γ-globulin were bound by hydrophobic interaction. Favorable binding properties for different proteins in a wide range of NaCl concentrations were observed on Bu60-PEI315, indicating its usefulness as an MMC adsorbent.

Efficient Adsorptive Removal of Humic Acid from Water Using Zeolitic Imidazole Framework-8 (ZIF-8)

To develop an efficient adsorbent for humic acid, the present study represents the first attempt to investigate the capability of zeolitic imidazole frameworks to remove humic acid from water. Zeolitic imidazole framework-8 (ZIF-8) is particularly selected as a prototype ZIF to adsorb humic acid owing to its high stability in aqueous solutions. ZIF-8 was synthesized and characterized using scanning electronic microscopy (SEM), powder X-ray diffraction pattern (PXRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analyzer (TGA) and then used to adsorb humic acid under various conditions. The structure of ZIF-8 was found to remain intact after the exposure to humic acid in water. Factors affecting the adsorption were examined, including solid-to-liquid ratio, mixing time, temperature, pH, presence of salt, and surfactants. The adsorption capacity of ZIF-8 was found to be much higher than that of activated carbon, fly ash, zeolites, graphite, etc., showing its promising potential for removal of humic acid. The adsorption mechanism could be attributed to the electrostatic interaction between the positive surface of ZIF-8 and the acidic sites of humic acid, as well as the π–π stacking interaction between imidazole of ZIF-8 and benzene rings of humic acid. The humic acid adsorption to ZIF-8 could be enhanced in the acidic conditions, and the adsorption process remained highly stable in the solutions of a wide range of NaCl concentrations. ZIF-8 can be also regenerated by simple ethanol-washing process and reused for humic acid adsorption. These features enable ZIF-8 to be an efficient and stable adsorbent to remove humic acid from water.

Sorption of Cm(III) and Eu(III) onto clay minerals under saline conditions: Batch adsorption, laser-fluorescence spectroscopy and modeling

The present work reports experimental data for trivalent metal cation (Cm/Eu) sorption onto illite (Illite du Puy) and montmorillonite (Na-SWy-2) in NaCl solutions up to 4.37molal (m) in the absence of carbonate. Batch sorption experiments were carried out for a given ionic strength at fixed metal concentration (mEu=2×10−7m, labeled with 152Eu for γ-counting) and at a constant solid to liquid ratio (S:L=2g/L) for 3<pHm<12 (pHm=−logmH+). The amount of clay sorbed Eu approaches almost 100% (with logKD>5) for pHm>8, irrespective of the NaCl concentration. Variations in Eu uptake are minor at elevated NaCl concentrations. Time-resolved laser fluorescence spectroscopy (TRLFS) studies on Cm sorption covering a wide range of NaCl concentrations reveal nearly identical fluorescence emission spectra after peak deconvolution, i.e. no significant variation of Cm surface speciation with salinity. Beyond the three surface complexes already found in previous studies an additional inner-sphere surface species with a fluorescence peak maximum at higher wavelength (λ∼610nm) could be resolved. This new surface species appears in the high pH range and is assumed to correspond to a clay/curium/silicate complex as already postulated in the literature for kaolinite. The 2 site protolysis non-electrostatic surface complexation and cation exchange sorption model (2SPNE SC/CE) was applied to describe Eu sorption data by involving the Pitzer and SIT (specific ion interaction) formalism in the calculation of the activities of dissolved aqueous species. Good agreement of model and experiment is achieved for sorption data at pHm<6 without the need of adjusting surface complexation constants. For pHm>6 in case of illite and pHm>8 in case of montmorillonite calculated sorption data systematically fall below experimental data with increasing ionic strength. Under those conditions sorption is almost quantitative and deviations must be discussed considering uncertainties of measured Eu concentrations in the range of analytical detection limits.

Effects of redox mediators on azo dye decolorization by Shewanella algae under saline conditions

Azo dye decolorization by Shewanella algae (SAL) in the presence of high concentrations of NaCl and different quinones or humic acids was investigated to reveal the effects of redox mediator under saline conditions. Growth of SAL and the other two marine Shewanella strains coupled to anthraquinone-2,6-disulfonate (AQDS) reduction was observed in a wide range of NaCl concentrations (0-7%). AQDS showed the best enhancing effects, whereas some other quinones demonstrated poorer stimulating or even inhibiting effects on acid red 27 (AR27) decolorization. Different humic acids could also enhance the decolorization. The correlation between specific AQDS-mediated reduction rate and initial AR27 concentration could be described with Michaelis-Menten kinetics (Km=0.2 mM and Vmax=9.3 μmol mg cell(-1) h(-1)). AQDS reduction by SAL was determined to be the rate-limiting step of mediated reduction. Mediated decolorization products of AR27 were determined to be less phytotoxic aromatic amines.

Molecular cloning, expression, purification and characterization of thioredoxin from Antarctic sea-ice bacteria Pseudoalteromonas sp. AN178

Thioredoxin (Trx) is a highly conserved and multi-functional protein that plays a pivotal role in maintaining the redox state of the cell and in protecting the cell against oxidative stress. Trx gene from Antarctic sea-ice bacteria Pseudoalteromonas sp. AN178 was cloned and expressed as soluble protein in Escherichia coli (designated as PsTrx). Trx gene consisted of an open reading frame of 324-bp nucleotides encoding a protein of 108 amino acids with a calculated molecular mass of 11.88kDa. The deduced protein included the conserved Cys-Gly-Pro-Cys active-site sequence. After purification by a single step Ni-NTA affinity chromatography, recombinant PsTrx with a high specific activity of 96.67U/mg was obtained. The purified PsTrx had an optimal temperature and pH of 25°C and 7.0, respectively, and showed about 55% of the residual catalytic activity even at 0-10°C. It had high tolerance to a wide range of NaCl concentrations (0-2M NaCl) and was stable in the presence of H2O2. This research suggested that PsTrx displayed unique catalytic properties.

Isolation and Identification of&lt;i&gt; Halomonas&lt;/i&gt; sp. ZSCW-10: A Moderately Halophilic Bacteria Strain with Cellulase Activity

A moderately halophilic bacteria strain with cellulase (CMCase) activity, ZSCW-10, which can survive under wide range of NaCl concentration (1 %~15 %, w/v) and pH (4.5~9.0), was isolated from the sediment of intertidal zone located in the Xiangshan Island, Zhejiang Province. The strain was identified based on 16S rDNA sequence determination and phylogenetic analysis together with its morphological and physiological characterization. The results indicated that the 16S rDNA homologies were 97% between strain ZSCW-10 and some strains of Halomonas sp.. The phylogenetic tree was constructed with Molecular Evolutionary Genetics Analysis version 5 (MEGA5), showed the closest relationship between strain ZSCW-10 and Halomonas venusta. Based on its physiological and biochemical properties, homology and phylogenetic analysis, strain ZSCW-10 was identified as a subspecies of Halomonas sp.. The optimum culture conditions were: NaCl 6.0%, 32°C, pH 7.5.

Effect of ionic strength and molecular weight on electrical properties and thickness of polyelectrolyte bi-layers

Electric light scattering from aqueous suspensions of positively charged ferric oxide particles is investigated in the presence of poly(sodium styrene sulfonate) and poly(allylamine hydrochloride) of different molecular weights, adsorbed sequentially on the particle surface at different ionic strengths. The adsorption is realized over a wide range of NaCl concentration (10−4 to 10−1M) at pH 4.5 and the suspensions of coated particles are then rinsed to ionic strength of 10−4M. Our measurements indicate that the amplitude of the electro-optical effect increases with increasing concentration of NaCl from 10−4 to 10−2M due to the increased amount of polymers, adsorbing in more coiled conformation and on more highly charged particle surface. However, the electro-optical effect started to decrease at further increase of NaCl concentration, more expressively at higher field intensities and for bi-layers with first layer from polyelectrolyte of lower molecular weight. This is accompanied with a significant increase in the thickness of the deposited bi-layers after their rinsing to low ionic strength. We attribute both effects to partial desorption of polyelectrolyte complexes from the particle surface, which disturb the homogeneity of the bi-layer structure. The latter causes an increase in the amount of mechanically trapped water on the particle surface and the thickness of adsorbed bi-layers increases as well. As a result, an elasto-hydrodynamic effect, which favors perpendicular orientation with respect to the external electric field, becomes possible.

Galvanically Induced Intergranular Corrosion of AA5083-H131 Under Atmospheric Exposure Conditions: Part 1—Experimental Characterization

In a two-part series of papers, the galvanic corrosion behavior of sensitized aluminum alloy (AA)5083-H131 (UNS A95083) when coupled with AISI 4340 (UNS G43400) steel was studied experimentally and computationally, with an emphasis on atmospheric conditions. In Part 1, the electrochemical kinetics of AA5083-H131 and steel in salt solutions of relevance to atmospheric corrosion were determined, including the influence of the degree of sensitization (DoS), potential, and sodium chloride (NaCl) concentration in the context of intergranular corrosion (IGC) propagation. More severe IGC was seen on materials with higher degrees of DoS, with damage depths of 1 mm or more developing in 100 h. The extent of IGC damage over 100 h was proportional to potential for a wide range of NaCl concentrations. These results from full immersion were compared with exposure testing and scanning Kelvin probe (SKP) measurements conducted under atmospheric conditions. It was found that the extent and spatial distribution of IGC damage on the atmospherically exposed material corresponded well to the IGC damage distribution expected from the SKP potential measurements and the damage results from the full immersion experiments. These findings are used as the input data for the computational model to predict the IGC damage distribution presented in the second paper.