Rheological behavior of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound in the presence of different electrolytes

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) in the presence of different electrolytes (NaCl, CaCl₂ and AlCl₃) were investigated. It is found that the network-like structure of pure CS solution is formed by the interaction between CS molecules. Both the equilibrium viscosities and the elastic response of CS solution decrease with the addition of NaCl, CaCl₂ and AlCl₃. Small amplitude sinusoidal oscillation tests show that a three-dimensional network of the HTlc/CS suspension can be formed through the bridge effect between CS molecules and HTlc particles due to the hydrogen bonding between the ether groups or hydroxyl groups of CS and the hydroxyl groups of HTlc. Both the equilibrium viscosity and dynamic property of the HTlc/CS suspensions indicate that the network-like structural strength of the suspensions increases firstly and then decreases with increasing HTlc content. The equilibrium viscosity and the elastic response of the HTlc/CS suspensions decrease gradually with the addition of NaCl or CaCl₂, but decrease firstly then increase and then decrease with increasing AlCl₃ concentration, i.e., the structural strength of the HTlc/CS suspensions can be strengthened by the addition of appropriate amount of AlCl₃ content.     

Effects of Mg: Al molar ratio on the rheology of aqueous suspensions containing cationic starch and Mg/Al-hydrotalcite-like compounds

Hydrotalcite-like compounds (HTlcs) Mg₂Al-HTlc, Mg₃Al-HTlc, and Mg₄Al-HTlc were synthesized by co-precipitation method. The effects of the Mg: Al molar ratio in the Mg/Al-HTlc samples on the rheological properties of the Mg/Al-HTlc–cationic starch (CS) suspensions were investigated. The Mg: Al molar ratio in the Mg _n /Al-HTlc samples affects the structural strength and the thixotropic type of the Mg _n /Al-HTlc–CS suspensions.     

Flocculation of aqueous silica suspensions using cationic polyelectrolytes

Flocculation of model silica suspensions by cationic polyelectrolytes was studied using optical and microelectrophoretic techniques. Polymer charge density effects were determined by varying the degree of quaternization or by changing pH, depending on the nature of the amine group present.Charge neutralization appears to be the principal flocculation mechanism, although polymer bridging may play a role once the particle surface charge is significantly reduced. Silica retains a net negative ζ-potential (−25 ± 5 mV) under optimal flocculation conditions. This finding is discussed semi-quantitatively in terms of an “electrostatic patch” adsorption model for flocculation.     

Dielectric properties of aqueous zwitterionic liposome suspensions

The dielectric spectra of aqueous suspensions of unilamellar liposomial vesicles built up by zwitterionic phospholipids (dipalmitoylphosphatidyl-choline, DPPC) were measured over the frequency range extending from 1 kHz to 10 MHz, where the interfacial polarization effects, due to the highly heterogeneous properties of the system, prevail. The dielectric parameters, i.e., the permittivity epsilon'(omega) and the electrical conductivity sigma(omega), have been analyzed in terms of dielectric models based on the effective medium approximation theory, considering the contribution associated with the bulk ion diffusion on both sides of the aqueous interfaces. The zwitterionic character of the lipidic bilayer has been modeled by introducing an "apparent" surface charge density at both the inner and outer aqueous interface, which causes a tangential ion diffusion similar to the one occurring in charged colloidal particle suspensions. A good agreement with the experimental results has been found for all the liposomes investigated, with size ranging from 100 to 1000 nm in diameter, and the most relevant parameters have briefly discussed in the light of the effective medium approximation theory.     

Synthesis and physicochemical properties of low-substituted cationic ethers of starch

The kinetics of the formation of cationic starch ethers under the action of 3-chloro-2-hydroxypropyltrimethylammonium chloride is studied in relation to the reactant molar ratio, temperature, and concentration of the starch suspension. Comparative data on how the content of the introduced catoinic groups depends on the origin of native starch are presented. The efficiency of starch cationization and the physicochemical properties of the synthesized samples are examined by chemical analysis, scanning electron microscopy, X-ray diffraction analysis, and thermal gravimetric analysis.     

双烃链正,负离子表面活性剂复合物水溶液的表面化学性质研究

本文研究了具有双烃链的正、负离子表面活性剂混合水溶液的表面和液相性质、。负离子表面活性剂是琥珀酸二己酯磺酸钠[简写为(C6)2SNa],正离子表面活性剂是氯化二正辛基羟乙基甲基铵[(C8)2NCl]和氯化辛基羟乙基二甲基铵[C8NCl]。为了增加复合物的溶解度,在铵基上引入了羟乙基。测定了表面张力-浓度关系,用GIBBS公式计算表面吸附量和吸附分子面积。结果表明,由于正、负表面活性离子之间的强烈相互作用,所研究的两种混合物体系的表面活性远高于单独的表面活性剂。在等摩尔混合和离子强度0.1mol/kg情况下,(C6)2SNa-(C8)2NCl体系的吸附层组成是对称的(摩尔比为1:1),且在临界胶团浓度(cmc)以上析出新相,表明此cmc实质上是复合物的溶解度;而(C6)2SNa-C8NCl体系的吸附层为不对称组成(摩尔比非1:1),在cmc以上可能形成相当大的胶团,两种体系混合溶液的起泡性有极大差异。     

Salt-induced aggregation in cationic liposome aqueous suspensions resulting in multi-step self-assembling complexes

The interaction of uni-univalent salt with cationic liposomes in aqueous suspension has been investigated by means of dynamic light scattering measurements and the hydrodynamic radius of the resulting aggregates has been evaluated for different ionic strengths. We observe the simultaneous presence of two different steady-state structures, in the 100–500 nm and 5 μm range, respectively, whose relative concentrations depend on the salt content. This behavior differs from that observed in usual charge stabilized colloidal suspensions and that giving rise to lipoplex formation in presence of polynucleotides. This peculiar behavior is briefly discussed in the light of Derjaguin–Landau–Verwey–Overbeek (DLVO) colloidal stability theory.     

Aggregation and sedimentation stability of microcrystalline cellulose suspensions in aqueous aluminum nitrate solutions

The aggregation and sedimentation stability of dilute suspensions of microcrystalline cellulose in aqueous solutions of Al(NO₃)₃(2 × 10⁻⁵–2 × 10⁻³ mol/l) is studied by the photometric method at pH 2–11. It is found that, in the absence of Al(NO₃)₃, microcrystalline cellulose suspensions are stable with respect to aggregation throughout the pH range in question. The addition of Al(NO₃)₃ induces the coagulation and accelerates the sedimentation of microcrystalline cellulose aggregates. At all concentrations of Al(NO₃)₃, the maximum loss in stability is observed at pH 7–9. Original Russian Text ? P.M. Mosur, A.V. Lorentsson, Yu.M. Chernoberezhskii, 2009, published in Kolloidnyi Zhurnal, 2009, Vol. 71, No. 4, pp. 566–568.     

Lyocell blend fibers with cationic starch: potential and properties

The regeneration of cellulose from solution state offers opportunities for blending with a secondary polymer. Cellulose/cationic starch blends were spun into fibers from -methylmorpholine- oxide solution, and the fibers were characterized by moisture absorption, dye absorption, and enzymatic hydrolysis. Cellulose/starch-blend fibers with up to 30% starch content were found to retain up to three times as much water, take up to five times as much dye, and be degradable much faster by cellulase hydrolysis compared with control lyocell fiber. ID addition to starch content, the fiber's performance depended on the degree of substitution of the starch by cationic substituents.     

pH dependent stability of aqueous suspensions of graphene with adsorbed weakly ionisable cationic polyelectrolyte

Stable graphene suspensions were prepared through ultrasonic exfoliation followed by surface modification with the cationic polyelectrolyte poly(ethyleneimine) (PEI). The stability of the suspensions was found to be dependent upon the pH of the solution and the molecular weight of the PEI adsorbed. For the graphene sheets with adsorbed PEI with a molecular weigh of 600 Da, the particles were stabilised through an increased electrostatic repulsion at low pH inferred from in an increase in the measured zeta potential of the particles. However, the graphene with higher molecular weight PEI (70 kDa) was stable over a comparatively larger pH range through a combination of electrostatic repulsion at low pH and steric repulsion at elevated pH. Thus, solution conditions allowing the control of the colloidal sized graphene particles can be easily tuned through judicious management of solution conditions as well as polymer layer properties.     

Synthesis and characterization of a strong-fluorescent Eu-containing hydrotalcite-like compound

A novel strong-fluorescent Eu-containing hydrotalcite-like compound (Eu-HTlc) was synthesized using the coprecipitation method, in which aluminum(III) was partially substituted by Europium (III) in the hydrotalcite-like layers, and thenoyltrifluoroacetone, 1,10-phenanthroline were dispersed into the anions in the interlayer region. The sample was characterized by XRD, XPS, FT-IR, ICP, TG-DSC, TEM and fluorescence spectra, and its composition and structure were determined. The results indicated that the sample exhibited a characteristic red light (614 nm). The fluorescent lifetime and fluorescence quantum yield of Eu-HTlc were measured to be respectively 893 μs and 66.44%, higher than those of Eu(III)-thenoyltrifluoroacetone-1,10-phenanthroline complex [Eu(TTA)₃phen]. The result of TG-DSC measurement showed the enhanced thermal stability of Eu-HTlc compared with that of MgAl-LDHs and Eu(TTA)₃phen. With excellent photoluminescent property and thermal stability, low contents of rare earth ions and ligands, the Eu-HTlc may become one of the novel fluorescent materials with potential applications.     

Preparation and properties of superabsorbent containing starch and sodium humate

Starch and sodium humate were utilized as raw material for synthesizing starch‐g‐poly(acrylic acid)/sodium humate (St‐g‐PAA/SH) superabsorbent by graft copolymerization reaction of starch (St) and acrylic acid (AA) in the presence of sodium humate (SH) in aqueous solution. The effect of weight ratio of AA to St, initial monomer concentration, neutralization degree of AA, amount of crosslinker, initiator and SH on water absorbency of the superabsorbent were studied. The swelling rate and swelling behavior in NaCl solution as well as reswelling ability of the superabsorbent were systematically investigated. The results showed that the superabsorbent synthesized under optimal conditions with SH content of 7.7 wt% and St content of 11.5 wt% exhibits water absorbency of 1100 g/g in distilled water and 86 g/g in 0.9 wt% NaCl solution, respectively. Introducing SH into the St‐g‐PAA polymeric network can improved the swelling rate and reswelling capability of the superabsorbent. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and characterization of Mg-Al hydrotalcite-like compounds containing cerium

Hydrotalcite-like compounds (HTlcs) containing Mg(2+), Al(3+), and Ce(3+) in the hydroxide layer and with carbonate as charge-balancing anion have been prepared by a co-precipitation (at constant pH) method. The Al/Ce ratio in the final product depends on the concentration in the initial solution. The crystallinity of the layered materials decreases with the increase in cerium content, probably, due to the distortions introduced by the large difference in the ionic radii of the cations. All the synthesized materials were characterized by XRD, FT-IR spectroscopy and TG/DTA. The textural properties were determined from low-temperature nitrogen adsorption-desorption measurements.     

铝/镁混合金属氢氧化物正电胶体粒子体系的触变性

采用恒定低剪切速率方法和动态实验方法研究了铝/镁混合金属氢氧化物(MMH)悬浮体的流变性,着重考察了剪切历史和恢复时间等因素对悬浮体触变性的影响,发现MMH粒子深度的增加使得悬浮体从粘性流体变为“类固体”;恒定低剪切速率方法和动态实验方法研究悬浮体的结构恢复过程给出了不同的结果,唯象地解释了MMH悬浮体触变性产生的原因,认为触变性结构是由于粒子间的静电排斥作用而形成的,与粘土悬浮体相比,两者的流变性具有诸多相似之处,只是所带电荷符号相反。     

Determination of lead in paints by electro-oxidation in cationic surfactant—aqueous sodium hydroxide suspensions

It was shown that anodic voltammetry can be used to determine lead in paint samples by solubilizing the sample in an aqueous solution using a cationic surfactant (Hyamine 2389, prdominantly methyldodecylbenzyltrimethylammonium chloride). In addition to solubilizing the solid paint particles, the cationic surfactant increased the oxidation potential of water to the point where one could observe, in concentrated sodium hydroxide solutions, an anodic peak for the oxidation of lead monoxide to lead dioxide. If the surfactant was below the critical micelle concentration, the height of the peak was linearly proportional to the concentration of lead oxide in the paint. The technique was experimentally verified by comparing the concentration of lead in a commercial paint sample, as determined by x-ray fluorescence, with the concentration determined voltammetrically.     

Viscoelastic properties of cationic starch adsorbed on quartz studied by QCM-D

The adsorption and viscoelastic properties of layers of a cationic polyelectrolyte (cationic starch, CS, with 2-hydroxy-3-trimethylammoniumchloride as the substituent) adsorbed from aqueous solutions (pH 7.5, added NaCl 0, 1, 100, and 500 mM) on silica were studied with a quartz crystal microbalance with dissipation (QCM-D). Three different starches were investigated (weight-average molecular weights M(w) approximately 8.7 x 10(5) and 4.5 x 10(5) with degree of substitution DS = 0.75 and M(w) approximately 8.8 x 10(5) with DS = 0.2). At low ionic strength, the adsorbed layers are thin and rigid and the amount adsorbed can be calculated using the Sauerbrey equation. When the ionic strength is increased, significant changes take place in the amount of adsorbed CS and the viscoelasticity of the adsorbed layer. These changes were analyzed assuming that the layer can be described as a Voigt element on a rigid surface in contact with purely viscous solvent. It was found that CS with low charge density forms a thicker and more mobile layer with higher viscosity and elasticity than CS with high charge density. The polymers adsorbed on the silica even when the ionic strength was so high that electrostatic interactions were effectively screened. At this high ionic strength, it was possible to study the effect of molecular weight and molecular weight distribution of the CS on the properties of the adsorbed film. Increasing the molecular weight of CS resulted in a larger hydrodynamic thickness. CS with a narrow molecular weight distribution formed a more compact and rigid layer than broadly distributed CS, presumably due to the better packing of the molecules.     

Effect of surface charge of carbonate-containing aluminum hydroxide on particle interactions in aqueous suspensions

The area under the curve (AUC) of the modified Lorentzian power spectrum as determined by fiber optic Doppler anemometry (FODA) is directly related to the number of freely diffusing particles in suspension. The initiation of particle interactions is characterized by deviation from a linear volume fraction-AUC relationship. The AUC approaches zero when an extensive particle network forms which dampens the random motion of particles. The rheological behavior supports this conclusion as a yield value was first noted when the AUC approached 0. The ability of AUC to monitor particle interactions was confirmed by a decrease in AUC when a latex dispersion was flocculated by NaCl, CaCl₂, or AlCl₃. Both the volume fraction at which particle interactions were initiated, φ_d, and the volume fraction at which particle random motion was dampened, φ_c, decreased when the pH of an aluminum hydroxide suspension was adjusted closer to the point of zero charge. The AUC was useful in studying the disaggregation of an aluminum hydroxide suspension by shear. Shear was found to also produce aggregation under specific conditions of surface charge and volume fraction. The reversibility of shear-induced changes in particle interactions was studied and the conditions of surface charge and volume fraction which control the reversibility of the particle structures were defined.     

Structural and thermal properties of Co-Cu-Fe hydrotalcite-like compounds

The structural properties and thermal decomposition processes of Co-Cu-Fe ternary hydrotalcites (HT) have been studied through X-ray diffraction, thermogravimetric measurements, Fourier-transform infrared and Mössbauer spectroscopies. Due to the strong Jahn-Teller effect, the Cu-Fe layered system is stabilized only in the presence of Co²⁺. At low Co²⁺ contents, additional phases are segregated in the solids. X-ray patterns show the presence of Cu(OH)₂ and CuO. The decomposition process was investigated by in situ X-ray, in situ Mössbauer and FTIR experiments. By increasing the temperature from 25 °C up to 180 °C we observed that the structural disorder increases. This effect has been likely attributed to the Co²⁺→Co³⁺ oxidation since thermal decomposition was carried out under static air atmosphere. Part of the Co³⁺ cations could migrate to the interlayer region, thus forming a metastable compound that still has a layered structure. Collapse of the layered structure was observed at about 200 °C. By further increasing the temperature the system becomes more crystalline and the formation of Co₃O₄ is observed in the X-ray patterns. In Cu-rich HT, some of the carbonate anions are released at temperatures higher than 550 °C and this phenomenon is attributed to the formation of a carbonate-rich phase. The specific surface area data present its highest values in the temperature range where the collapse of the layered structure takes place.     

Rheological properties of concentrated aqueous solutions of anionic and cationic polyelectrolyte mixtures

The rheological properties of aqueous solutions of poly(acrylic acid), poly(diallyldimethyldiammonium chloride), and their mixtures at 25°C have been studied. The concentrated solutions of the mixtures contain 18 wt % of both polymers taken at different ratios. The ratio of cationogenic and anionogenic groups φ varied from 0 to 0.4 is taken as a criterion for selection of mixture composition. An increase in φ, reflecting a more intense formation of polyelectrolyte complexes in solution, is accompanied by a significant rise in the low-frequency loss modulus and, especially, in the storage modulus, as well as by an increase in viscosity over the entire studied range of shear rates. This behavior may be explained by the presence of an additional spatial structure with junctions formed by interacting complementary charged groups. In the general case, the formation of poly(acrylic acid)-poly(diallyldimethyldiammonium chloride) polyelectrolyte complexes is said to take place in solution. The excess of rheological characteristics of mixture solutions over the corresponding characteristics of poly(acrylic acid) solutions is found to be the power function of parameter φ. The additional spatial network derived from polyelectrolyte complexes and occurring in solution is destroyed at lower shear stresses than is the network of intermolecular entanglements. At high shear stresses, orientational effects may cause phase separation of the systems owing to a change in the hydrophilic-hydrophobic balance between complexes of poly(acrylic acid) with poly(diallyldimethyldiammonium chloride) and water.     

Rheological properties of aqueous Pluronic-alginate systems containing liposomes

Rheological and erosion studies regarding a liposome-containing polymeric blend that is propaedeutic to its use in paving techniques in tubular organs, such as blood vessels, are reported. Attention is focused on an aqueous polymeric blend composed of Pluronic (PF127) and alginate (Protanal LF 10/60) because both polymers, when dissolved in water at a sufficiently high concentration, are subjected to different structural mechanisms, which are driven by temperature increase and addition of bivalent cations, respectively, and both result in marked viscoelastic and plastic properties. After proving the compatibility between PF127 and alginate, we show that the structural transition temperature of the blend, T(ST), can be properly modulated. In particular, we found that T(ST) for an aqueous solution of pure Pluronic 20% w/w is about 21 degrees C and that even slight reductions in polymer concentration result in considerable T(ST) decrease. The addition of salts or alginate (provided as Na-alginate) provokes a substantial decrease of T(ST) and thus the alginate concentration in the blend should not exceed 1% w/w. In addition, liposomes slow down the structural transition but do not substantially affect the rheological properties of the system in the final state at higher temperatures, thus showing that they can be added to the polymeric blend without significant effects. Finally, erosion tests show that after contact with a source of bivalent cations, the polymeric blend containing PF127 and alginate shows an erosion resistance neatly improved with respect to the simple structured Pluronic system having the same polymer concentration. As a whole, all these results constitute the basis for future potential applications of the considered polymeric blend in tubular organs such as blood vessels.