The influence of exchangeable cation on thermal behaviour of ground vermiculite

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150°C) and increased the second dehydration effect (150 to 500°C). The dehydroxylation was moved to lower temperatures and was only ΔM(500-1100°C)=3.7±0.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150°C), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [ΔM(150-500°C)=7.6±0.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870°C, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795°C) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870°C) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of the steric hindrance on metallic cation conduction in polymer electrolytes

2,6-Di-t-butylphenol and oligo(ethylene oxide) bound covalently to polyisocyanate were synthesized and characterized. The ionic conductivities of their Li, Na, and K phenolates were studied at various temperatures. The conductivities were in the range of 10^?7?10^?5 S/cm at 30°C. The conductivity of Na and K salts was approximately 10² greater than that of the Li salts. The t-butyl groups serve to dissociate K and Na ions from the phenoxide. The cations, therefore, are more mobile as a result increasing the conductivity. The temperature dependence of ionic conductivity suggests that the migration of ions is controlled by segmental motion of the polymer, shown by linear curves obtained in Vogel–Tammann–Fulchere plots. The polyisocyanate backbone is a rather stiff structure, however, a flexible oligo(ethylene oxide) side chain forms complexes with metal ion. Since the ion transport is associated with the local movement of polymer segments, the rigidity of the polymer backbone does not have much influence on the ion mobility.     

Theoretical study of the atrazine pesticide interaction with pyrophyllite and Ca2+‐montmorillonite clay surfaces

Atrazine, a pesticide belonging to the s‐triazine family, is one of the most employed pesticides. Due to its negative impact on the environment, it has been forbidden within the European Union since 2004 but remains abundant in soils. For these reasons, its behavior in soils and water at the atomic scale is of great interest. In this article, we have investigated, using DFT, the adsorption of atrazine onto two different clay surfaces: a pyrophyllite clay and an Mg‐substituted clay named montmorillonite, with Ca²⁺ compensating cations on its surface. The calculations show that the atrazine molecule is physisorbed on the pyrophyllite surface, evidencing the necessity to use dispersion‐corrected computational methods. The adsorption energies of atrazine on montmorillonite are two to three times larger than on pyrophyllite, depending on the adsorption pattern. The computed adsorption energy is of about −30 kcal mol⁻¹ for the two most stable montmorillonite‐atrazine studied isomers. For these complexes, the large adsorption energy is related to the strong interaction between the chlorine atom of the atrazine molecule and one of the Ca²⁺ compensating cations of the clay surface. The structural modifications induced by the adsorption are localized: for the surface, close to substitutions and particularly below the Ca²⁺ cations; in the molecule, around the chlorine atom when Ca²⁺ interacts strongly with this basic site in a monodentate mode. This study shows the important role of the alkaline earth cations on the adsorption of atrazine on clays, suggesting that the atrazine pesticide retention will be significant in Ca²⁺‐montmorillonite clays. © 2016 Wiley Periodicals, Inc.     

Fourier transform infrared spectroscopy study of the effect of pH on anion and cation adsorption onto poly(acrylo‐amidino diethylenediamine)

The role of hydrogen bonding in the chemistry of transition‐metal complexes remains a topic of intense scientific and technological interest. Poly(acrylo‐amidino diethylenediamine) was synthesized to study the effects of hydrogen bonding on complexes at different pHs. The polymer was synthesized through the coupling of diethylene triamine with polyacrylonitrile fiber in the presence of AlCl₃ · 6H₂O addition. The adsorption capacity of this polymer was 11.4 mequiv/g. The ions used for the adsorption test were CrO, PO, Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺. All experiments were confirmed with Fourier transform infrared. In the study of anion adsorption, at low pHs, only ionic bonds existed, whereas at high pHs, no bonds existed. However, in the middle pH region, both ionic bonds and hydrogen bonds formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion or phosphate ion. When poly(acrylo‐amidino diethylenediamine) and metal ions (Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺) formed complexes, a hydrogen‐bonding effect was not observed with Fourier transform infrared. The quantity of metal ions adsorbed onto poly(acrylo‐amidino diethylenediamine) followed the order Ag⁺ > Cu²⁺ > Fe²⁺ > Ni²⁺. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2010–2018, 2004     

The influence of organic sample solvents on the separation efficiency of basic compounds under strong cation exchange mode

This study investigated the influence of organic sample solvents on separation efficiency of basic compounds under strong cation exchange (SCX) mode. The mixtures of acidic aqueous solution and organic solvent such as acetonitrile, ethanol, methanol and dimethyl sulfoxide (DMSO) were tested as sample solvents. For later-eluting analytes, the increase of sample solvent elution strength was responsible for the decrease of separation efficiency. Thus, sample solvents with weak elution strength could provide high separation efficiencies. For earlier-eluting analytes, the retention of organic sample solvents was the main factor affecting separation efficiency. Weakly retained solvents could provide high separation efficiency. In addition, an optimized approach was proposed to reduce the effect of organic sample solvent, in which low ionic solvent was employed as initial mobile phase in the gradient. At last, the analysis of impurities in hydrophobic drug berberine was performed. The results showed that using acidic aqueous methanol as sample solvents could provide high separation efficiency and good resolution (R > 1.5).     

Microcalorimetric study of the adsorption of PEGylated lysozyme on a strong cation exchange resin

Adsorption of native as well as mono-, di-, and tri-PEGylated lysozyme on Toyopearl Gigacap S-650M in sodium phosphate buffer is studied by isothermal titration calorimetry and by independent adsorption equilibrium measurements at pH 6 and 25°C. The production and separation of PEGylated lysozyme is discussed. Two different PEG sizes are used (5 kDa and 10 kDa) which leads to six different forms of PEGylated lysozyme which were systematically studied. The sodium chloride concentration is varied according to the elution conditions in the production process. The specific enthalpy of adsorption Δh(p)(ads) is determined from the calorimetric and the adsorption equilibrium data. It was found to be exothermal and constant with increasing adsorber loading for native lysozyme. For all PEGylated forms there is an influence of the adsorber loading on Δh(p)(ads) which is found to become more important with increasing PEGylation degree (total molecular weight of conjugated PEG). At low loadings the adsorption of all PEGylated lysozyme forms is exothermal. With increasing loading the adsorption becomes less exothermal and for the species with higher PEGylation degree also endothermal effects are observed at higher loadings. A thermodynamic analysis is carried out by which the enthalpic and entropic contributions to the binding constants are quantified. The findings are discussed on a molecular level. The results provide insight into the adsorption mechanisms of polymer-modified proteins on chromatographic resins.     

The relationship between adsorption energies of methyl on metals and the metallic electronic properties: a first-principles DFT study

A theoretical study of CH3 adsorbed on the (111) surface of some transition and noble metal surfaces M (M = Cu, Ni, Rh, Pt, Pd, Ag, Au) and on the Fe(100) is presented. We find that the hollow site is preferred more than the top one for Fe, Ni, Rh, and Cu, but it is the other way for Pt, Pd, Au, and Ag. In addition, a good linear relationship was observed between the chemisorption energy and d-band center for Group VIII metals or the square of the coupling matrix element for Group IB metals at the hollow site. Interestingly, with a detailed comparison of the adsorption energies at the top and hollow sites, we find that the adsorption energies among each group are very similar on the top site, which supports the theoretical model of Hammer and Norskov that the coupling between the HOMO of adsorbate and sp states of the metal is dominant and almost equal, and that the second coupling to the d-band contributes less but reflects the change of the adsorption energy. It confirms that the coupling to the d band comprises two opposite factors, that is, the d-band center was attractive and the square of the coupling matrix element was repulsive, such that the contributions from the two factors can counteract each other at the top site.     

The reinforcing effect of clay on the mechanical properties of nitric acid–treated fluorosilicone rubber filled PI composites

The mechanical behaviour of fluorosilicone rubber–filled PI composites with and without clay was investigated. The clay filled fluorosilicone rubber composite had the highest interlaminar shear strength value of all the combinations because its higher bond strength may have hindered a large fibre/matrix debonding. The maximum tensile strength was observed for 20 vol% fluorosilicone rubber/PI/5vol%clay composite. The interlaminar shear strength of clay filled fluorosilicone rubber/PI composite was greater than that of fluorosilicone rubber/PI composite, which shows that the adhesion factor of the combination of the PI and fluorosilicone rubber was greater.     

冠丙四肽与ⅠA和ⅡA重金属离子结合作用的初步理论研究

借助于密度泛函理论的B3LYP方法,以冠丙四肽为模型基础,对铷、锶、铯、钡等金属离子与该冠丙四肽的结合形式进行了几何构型优化、能量计算、Mulliken布局数分析等理论研究.结果表明,冠丙四肽的构型在与IA金属离子结合前后略有改变,结合过程中电子由冠肽移向金属离子,碱金属离子铷、铯与冠型环丙四肽的结合作用相差不大,其最...     

The rheological and colloidal properties of bentonite dispersions in the presence of organic compounds III. The effect of alcohols on the coagulation of sodium montmorillonite

The critical coagulation concentration,c _K, of sodium chloride for sodium montmorillonite dispersed in water (solid content 0.025 percent) is 8 mmol/L. It remains virtually constant (7.5–8.5 mmol/L) in water-rich alcohol mixtures (below 50% (v/v) methanol and 40% ethanol and propanol). At higher alcohol contents thec _K decreases to 3.6 mmol/L (70 percent methanol), 1.2 mmol/L (70 percent ethanol), and 0.8 mmol/L (60 percent propanol). In the presence of 10^–4 M sodium diphosphate thec _K in water rises to 195 mmol/L. In contrast to the behavior in the absence of diphosphate, even small amounts of alcohol reduce the critical coagulation concentration. In 70% methanol thec _K is 7.5 mmol/L, in 70 percent ethanol 2.5 mmol/L and in 60% propanol 5 mmol/L. The main mechanism is coagulation by contacts between negatively charged edges and faces.At high alcohol contents montmorillonite-alcohol complexes (interlayer solvates) are formed and the colloidal dispersions become unstable even in the absence of salt. Transition from the state with diffuse ionic layers into the quasi-crystalline structure of the interlayer solvates is also evident from the sediment volume which changes with the alcohol content. Maxima are observed which are indicative of band-type structures as intermediate states between the colloidally dispersed particles with repulsive interaction and the discrete particles of the montmorillonite-alcohol complexes.     

The role of organoclay on the properties of Polymethylsilsesquioxane: A systematic study

In this study, an attempt is made to improve the properties of PMSQ, an organosilicone polymer which possesses distinguished properties, through an easy and facile route by the inclusion of organically modified montmorillonite clay. PMSQ-clay composites were prepared by solution blending of the components initially and then heat curing under load. The effect of clay content, varied at 5–40 wt.%, on mechanical, thermal and dynamic mechanical properties was evaluated and the optimum was obtained for 20%. Morphology investigation as well as microstructure analysis revealed intercalated to exfoliated morphology of PMSQ-clay composite. An appreciable improvement in mechanical properties of PMSQ, compressive strength and impact strength in particular, was achieved by clay inclusion up to 20%. The properties declined at ≥ 30% clay loading. The composites showed increased thermal stability compared to unmodified PMSQ up to 400 °C. Also, increase in clay content accelerated conversion to ceramic SiOC. PMSQ-clay composites exhibited good visco-elastic characteristics with higher T_g probably due to enhanced polymer-clay interactions. Thus, a simple and viable method to enhance the mechanical and thermal characteristics of PMSQ by way of preparing its composite with the reinforcing filler organoclay is demonstrated here.     

The effect of metallic cations on the electrophoretic properties of a pretreatedHevea latex

High-ammonia latex concentrate prepared from doubly-centrifuged fieldHevea latex was exhaustively dialysed to remove any residual water-soluble non-rubber constituents. The electrophoretic mobilities of the dialysed latex in the presence of various metallic cations were investigated as a function of electrolyte concentration. The mobility decreased with increasing concentration of the cations Na⁺, Ba²⁺, Mg²⁺ and Ca²⁺ in a manner consistent with the effect of simple electrolyte on compression of the electric double layer. Anomalous behaviour was noted for the divalent ion copper, in that it reversed the charge of the latex particles at a concentration even lower than that of uranyl ions. Multivalent cations (lanthanum, cerium and thorium) had a profound influence on the latex particles where very low charge reversal concentrations were observed. It is believed that strong adsorption of hydrolysed species from the metallic ions was responsible for reversing the charge of the originally negative latex particles. These experiments indicated that the efficiency with which the cations reversed the charge of the latex particle surface was in the order: lanthanum > cerium > copper > thorium > uranyl > calcium > magnesium > barium > sodium. The number of cation binding sites on the latex particle surface and the chemical free energies of cation adsorption were calculated. It was found that the interaction of the latex particle with the hydrolysable metallic cations was much more stronger than that with the simple divalent cations and that this intercation was comparable to that of biological surfaces.     

The effect of cation size on ion pairing of methyl orange dye with tetraalkylammonium and benzyltrialkylammonium ions in aqueous solution

Formation constants have been measured by a solvent distribution method for the ion pairing of an arene sulfonate, methyl orange dye, with two series of quaternary ammonium ions: R₄N⁺(R=Et,n-Pr,n-Bu, andn-Pent) and C₆H₅CH₂R₃N⁺ (R=Me, Et,n-Pr,n-Bu,n-Pent, andn-Hex). Ion pairing increases dramatically as the length of the R group increases beyond butyl. Using a hard-sphere model for contact ion pairs, it is estimated that coulombic attraction contributes about –kT to the binding free energy and decreases slightly with increasing size of R₄N⁺. Other factors related to solvation effects, of which cosphere overlap predominates, contribute from –2kT to –7kT of binding energy. Plots of logK for association as a function of cation size show an inflection with decreasing slope between R=propyl and R=butyl. Possible causes for the inflection are considered.     

The effect of thiolation on the mechanical and protein adsorption properties of polyurethanes

Segmented polyurethanes are important polymers for a number of industrial and technological applications. The purpose of this work was to synthesize polybutadiene-based polyurethanes and subsequently graft carboxylate and sulfonate side chains via thiol-ene reaction. Spectroscopic investigations showed that grafting yielded good conversion for the vinyl unsaturation of the polybutadiene soft segment. DSC and tensile testing revealed that grafted polyurethanes had a better segmental compatibility and superior mechanical properties than the control polyurethane without grafting. The carboxylic side chains of the soft segment were responsible for the observed improved mechanical properties. Initial protein adsorption tests on these polymers were found to be higher than the control surface. The polyurethanes of the current study could be used for biomedical applications where protein attachment to the surface is needed for specific cell adhesion and tissue repair.     

The addition of clay on the mechanical properties of surface‐treated CF‐filled PA66 composites

Polyamide 66 (PA66) composites filled with clay and carbon fiber (CF) were prepared by twin‐screw extruder in order to study the influence of nanoparticle reinforcing effect on the mechanical behavior of the PA66 composites (CF/PA66). The mechanical property tests of the composites with and without clay were performed, and the fracture surface morphology was analyzed. The results show that the fracture surface area of the clay‐filled CF/PA66 composite was far smoother than that of the CF/PA66 composite, and there formed a tense interface on the CF surface after the addition of clay. The tensile and flexural strength of CF/PA66 composites with clay was improved. The impact strength decreased because of the high interfacial adhesion. In conclusion, the addition of clay favored the improvement of the higher interface strength and so had good effect on improving the tensile and flexural properties of the composites. Copyright © 2017 John Wiley & Sons, Ltd.     

Aggregative structure of the 1‐octadecyl‐3‐methylimidazolium cation in the interlayer of montmorillonite and its effect on polypropylene melt intercalation

A series of organomontmorillonites were synthesized from pristine sodium montmorillonite via ion exchange in toluene with 1‐octadecyl‐3‐methylimidazolium chloride, a kind of ionic liquid with high thermal stability, as a modifier. The amount and aggregative state of the 1‐octadecyl‐3‐methylimidazolium cation ([C18mim]⁺) adsorbed in the interlayer of organomontmorillonite (MMT) were investigated with thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, X‐ray diffraction (XRD), and differential scanning calorimetry. XRD patterns showed that [C18mim]⁺ was successfully intercalated into the interlayer of MMT, and the interlayer distances of the clays increased dramatically. On the basis of the TGA results, three types of arrangement models of [C18mim]⁺ could be seen, and they were related to the loading level of [C18mim]⁺ in the gallery of MMT. The effects of the aggregative structure of [C18mim]⁺ in the interlayer of MMT on polypropylene melt intercalation was also examined. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1252–1259, 2007     

The effect of high pressure on the ion pair equilibrium constant of alkali metal fluorides: A spectrophotometric study

Bromophenol blue indicator was used in UV-visible spectrophotometric measurements to study ion association constants of alkali metal fluorides. The equilibrium constants for the ion pair formation of the alkali metal fluorides were determined as a function of ionic strength at one atmosphere pressure and 25°C. The effect of pressure on these association constants was measured at a constant total ionic strength of 1.0 mol-kg^–1 over a pressure range of 1 to 2000 atmospheres at 25°C. The pressure dependences of the stoichiometric association constants of the alkali metal fluorides are given by: lnK _LiF ^* =0.77–2.47×10^–4P–2.12×10^–8P²; lnK _NaF ^* =0.53–1.08×10^–4P–1.66×10^–8P²; lnK _KF ^* =0.24–4.41×10^–5P–7.15×10^–8P²; lnK _RbF ^* =–0.17–8.65×10^–5P–4.51×10^–8P²; and lnK _CsF ^* = –0.37–1.14×10^–4P–6.82×10^–8P², where P is the pressure in atmospheres. The stoichiometric molar volume and compressibility changes for ion pair formation of the alkali metal fluorides were evaluated from the pressure dependence of K _MF ^* data. The thermodynamic association constants were also calculated making use of activity coefficient data from the Pitzer equations. The partial molal volume and compressibility changes for ion pair formation of each alkali metal fluoride are reported.     

Mechanistic aspects of the Wolff-Kishner reaction. V. The cation effect on the reaction of benzophenone hydrazone in butyl carbitol and decyl alcohol

The rate of the Wolff-Kishner reaction of benzophenone hydrazone in butyl carbitol increases as the cation of the alkoxide base is varied in the order K>Na>Li>Mg. The replacement of butyl carbitol by 1-decanol also accelerates the reaction, and an additional increase is caused by the presence of crown ether. On the basis of changes in the activation parameters, it is concluded that the reactivity of the hydrazone anion increases as the contact ion pair becomes more fully solvated and dissociated.     

The effect of structural parameters of biporous packing with an impermeable core on the gas separation efficiency

The effect of the structural parameters of granules of biporous sorbent with an adsorbing surface layer and inert core on the gas separation efficiency has been studied. The adsorbent has some advantages over sorbents with the bulk volume accessible for an adsorbate. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1193–1195, June, 1999.     

Metal-stabilized carbanions : III. The effect of coordination with π-tricarbonylchromium on the paratropic properties of biphenylene. An NMR study

The ¹H- and ¹³C-NMR spectra of biphenylene and its mono- and bis-tricarbonylchromium complexes have been recorded and analyzed. The comparison of the data for the complexes with those for the free ligand suggests that a substantial reduction of the paratropic character of the molecule occurs upon complexation. In the bis-complexed biphenylene, the two electronic sextets behave as separate non-interacting systems.