超声功率对石灰乳活性影响研究

为获得高活性度的石灰乳,在石灰乳化过程引入超声作用,分别采用沉降实验、粒度分析和表观形态观察、中和反应活性实验对超声作用后石灰乳的性质进行了分析,比较机械搅拌和不同超声功率作用下石灰乳的分散稳定性、中和反应活性及粒度分布情况,以考察超声作用对石灰乳化过程和石灰乳性质的影响。结果表明:与机械搅拌相比,在一定功率范围内,超声作用可降低石灰乳的沉降速率,提高其分散稳定性;减小石灰乳体系中未溶解Ca(OH)2乳颗粒的粒径,并缩小其粒径的分布范围,抑制石灰乳结块的产生;超声作用还增加了Ca(OH)2颗粒的比表面积和溶解速度,进而提高石灰乳的中和反应活性。     

Concentration effects on irreversible colloid cluster aggregation and gelation of silica dispersions

Effects of particle concentration on the irreversible aggregation of colloidal silica are studied using in situ destabilization via the ionic strength increase derived from the enzymatic hydrolysis of urea by urease. Aggregation is monitored by time-resolved optical density and dynamic light scattering measurements. It terminates at a gel boundary, signaled by a prominent increase of the optical density and incipient non-ergodicity. Raman scattering is used to demonstrate that the enzymatic reaction continues, well beyond gelation for the compositions studied here, until the urea is consumed. Calibration of the ionic conductivity permits for constructing stability diagrams in terms of particle and salt concentration. As with reversible gelation, the process exhibits a collective character in that lower ionic strengths are required for gelation of concentrated dispersions and vice versa. However, light scattering demonstrates that the gel boundary is preceded here by a line marking the transition from reversible to irreversible cluster formation, with the two transition boundaries tracking each other. Comparisons are made with dispersions destabilized by direct addition of salt solutions, which gel under very different conditions.     

Migration and precipitation of soluble species during drying of colloidal films

The evaporation-induced convection resulted in a transport of dissolved species, a water-soluble polymer (carboxymethylcellulose) and dissolved CaCO(3), to the drying front of silica and CaCO(3) dispersions where the material eventually precipitates. Scanning electron microscopy and chemical analysis showed that the concentration of carboxymethylcellulose, CMC, is highest in the centre of the dried silica film and decreases towards the perifery. The colloidal films of the monodisperse silica particles displayed a high degree of structural order even at high concentrations of the non-adsorbed polymer CMC, which suggests that any depletion induced interparticle attraction is insufficient to affect the assembly of the colloidal crystal. The CaCO(3) particles are slightly soluble and we found that rod-like crystals reprecipitated in the centre of the particle films on top of the polyacrylate-coated particles. Addition of CMC disturbs the formation of distinct crystal shapes which was attributed to a complexation of Ca(2+) in solution.     

Preparation of Colloidal Transition Metals in Polymers by Reduction with Alcohols or Ethers

Colloidal dispersions of rhodium, palladium, osmium, iridium, and platinum are prepared by refluxing the methanol-water solutions of rhodium(III) chloride, palladium(II) chloride, osmium(VIII) oxide, sodium chloroiridate, and chloroplatinic acid, respectively, in the presence of poly(vinyl alcohol) as a protective colloid. The preparations of colloidal dispersions of rhodium are successful in the presence of vinyl polymer with polar group such as poly(vinyl alcohol), polyvinylpyrrolidone, or poly(methyl vinyl ether). Polyethyleneimine, gelatin, polyethylene glycol), and dextran are ineffective as the protective colloid. Water-soluble primary alcohols such as methanol and ethanol, water-soluble secondary alcohols such as 2-propanol, and water-soluble diethers such as 1,4-dioxane are available as reductants for preparation of the colloidal dispersion of rhodium. The average diameters of metal particles in the colloidal dispersions of palladium, rhodium, platinum, iridium, and osmium in poly(vinyl alcohol) are determined by electron microscopy to be 53, 40, 27, 14, and < 10 Å, respectively. The particle size distribution in each colloidal dispersion is sharp within 50 Å wide. The particles in the colloidal dispersions of both iridium and osmium are highly dispersed with no aggregation, while in the colloidal dispersions of rhodium, palladium, and platinum, there exist aggregates of 5-15, 5-30, and 100-200 particles, respectively. Colloidal dispersions of rhodium, palladium, osmium, and platinum are effective as catalysts for hydrogenation of cyclohexene at 30.0°C under atmospheric hydrogen pressure.     

Stability of Aqueous Dispersions of the Hydrated Titanium Dioxide Prepared by Titanium Tetrachloride Hydrolysis

The aggregation stability of aqueous dispersions of the hydrated anatase and rutile samples in the neutral and alkaline pH regions is related to the electrostatic stabilization factor and is described in terms of the classical DLVO theory. The abnormally high stability of the dispersions with respect to 1 : 1 and 1 : 2 coagulating electrolytes, which is exhibited in the acidic pH region, is explained by the existence of well-developed gel layers at the particle surfaces. The specific role in the formation of such layers is played by the sulfate ions.     

Effects of polymer wrapping and covalent functionalization on the stability of MWCNT in aqueous dispersions

The colloidal behavior of aqueous dispersions of functionalized multiwall carbon nanotubes (F-CNTS) formed via carboxylation and polymer wrapping with polyvinyl pyrrolidone (PVP) is presented. The presence of polymer on the nanotube surface provided steric stabilization, and the aggregation behavior of the colloidal system was quite different from its covalently functionalized analog. Based on hydrophobicity index, particle size distribution, zeta potential as well as the aggregation kinetics studied using time-resolved dynamic light scattering, the PVP wrapped CNT was somewhat less prone to agglomeration. However, its long-term stability was lower, and this was attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface.     

Redispergation of TiO2 particles in aqueous solutions

The colloidal stability of TiO2 dispersions in aqueous solutions was studied. Aqueous solutions of ATLAS G-3300 (1.57 x 10(-3) mol/l), TRITON X-100 (5 x 10(-5) mol/l), and PMAA (4 x 10(-6) and 5.81 x 10(-3) mol/l) have been used as medium for redispergation of TiO2 particles. Stability of dispersions was investigated at different pH values by two different methods. By using analytical centrifuge the sedimentation velocity of TiO2 particles was directly measured and by means of light scattering the particle size of dispersed particles has been monitored. Combination of these two methods allowed determination of the aggregation degree of TiO2 particles as well as structure of the aggregates formed in aqueous phase. It has been found that redispergation process does not provide complete separation of virgin TiO2 particles. Even in the case of stable dispersions some aggregates were found, which consisted of 2-4 virgin TiO2 particles. With increasing colloidal stability of dispersions aggregates appear to be spherically shaped. In the system where TRITON X-100 was used, formation of secondary aggregates by fusion of primary ones was observed.     

The effect of block copolymer EPE1100 on the colloidal stability of Mg-Al LDH dispersions

The adsorption isotherm of block copolymer EPE1100 (polyethylene oxide-polypropylene oxide-polyethylene oxide) on the surfaces of Mg-Al LDH particles was determined through a solution depletion method combined with TOC measurement. X-ray diffraction patterns showed that the adsorption of EPE1100 molecules only occurred on the outer surfaces of LDH particles and they did not intercalate into the galleries between the layers. The adsorption of EPE1100 molecules changed the morphology of the particles. The effect of EPE1100 on the colloidal stability of LDH dispersion was investigated from three aspects: after the freezing-melting cycle, after the shearing rotations, and after the addition of electrolyte. The results indicated that the effect of EPE1100 on the colloidal stability of LDH dispersions was strongly related to the state of copolymer adsorption on LDH particle surfaces. It was inferred that the hydrated repulsive force and steric-repulsive force played important roles in determining the stability of the dispersions.     

Analysis of Roman wall paintings found in Verona

The present paper deals with the analysis of roman wall paintings fragments recovered from twelve buildings of Verona, Italy. The analytical techniques used were Optical Microscopy, Scanning Electron Microscopy (SEM) equipped with an EDS microanalysis detector, Xray powder diffraction (XRD) Fourier Transform infrared spectroscopy (FTIR) and Raman Spectroscopy. The wall preparation generally consisted of three layer: the pictorial layer, an intonachino layer of hydrated lime and a plaster one made of slaked lime and sand. The pigments found in the studied domus are different reflecting the taste and culture of Xa Regio of Italy but also the economical possibilities of the dominus and the building period.     

Specific cation adsorption on protein-covered particles and its influence on colloidal stability

Protein coated particles present an anomalous colloidal stability at high ionic strength when the classical theory (DLVO) predicts aggregation. This observed deviation from DLVO behaviour appears for electrolyte concentrations above some critical bulk value. As we have suggested in previous publications the existence of an additional short-range repulsive 'hydration force' due to specific hydrated cation adsorption could explain this anomalous stability. The overlap of the hydration layers when two particles approach should provoke this repulsive force. New evidence of this mechanism has been observed when electrophoretic mobilities of protein-carrying latex particles were measured at various concentrations of sodium and calcium chloride. In the latter case a sign reversal of zeta-potential was found, probably due to the specific adsorption of Ca(2+) ions on protein molecules. The adsorption increases with the medium pH. These results have been analyzed following the treatment proposed by Ohshima and co-workers for large charged colloidal particles coated with a layer of protein. This study shows an increase in the positive fixed-charge density on the protein caused by the adsorption of cations.     

On the origin of colloidal particles in the dispersion polymerization of aniline

When aniline is oxidized in an aqueous medium in the presence of a steric stabilizer, colloidal polyaniline (PANI) dispersions are obtained. The generally accepted model of the stabilization assumes that the macromolecules of the water-soluble steric stabilizer are adsorbed at the polymer, precipitating during the dispersion polymerization, and provide steric protection against further aggregation. An alternative mechanism of conducting-polymer particle formation is proposed in the present study. We suggest that the steric stabilizer provides a site for adsorption of oligoaniline initiation centers; subsequent polymerization from anchored centers yields particle nuclei that grow to produce colloidal PANI particles. This hypothesis is based on the observation that the colloidal particles are obtained only in the case where the steric stabilizer is introduced in the early stages of polymerization when aniline oligomers are present in the reaction mixture. If the stabilizer had been added during the growth of PANI chains, colloidal dispersions would not have been produced. The process of particle growth is completely analogous to the formation of conducting PANI films on the surface of microparticles and various materials. There, the polymerization of aniline at the surfaces is preferred to the same process proceeding in the bulk of the reaction mixture. While the films grow at the interfaces with the reaction mixture, the dispersion particles similarly emanate from the stabilizer chains. The particle size, the formation of nonspherical morphologies, the importance of the chemical nature of the stabilizer chains, and the general relation between the conducting-polymer film and particle growth are discussed in the light of the proposed model.     

Calcium-based hydrated minerals: Promising halogen-free flame retardant and fire resistant additives for polyethylene and ethylene vinyl acetate copolymers

In this study, we evaluated the potential flame retardant effect of calcium-based hydrated minerals, such as hydrated lime, partially and completely hydrated dolomitic limes in polyethylene (MDPE) and ethylene vinyl acetate copolymers (EVA) and compared to that obtained with magnesium di-hydroxide (MDH). The most significant flame retardant effects, observed using the mass loss calorimeter test, indicated that Ca-based MDPE composites showed similar peak Heat Release Rate (pHRR) level to that obtained with MDH composite while the pHRR was lower for Ca-based fillers in EVA compositions. X-ray Diffraction (XRD) data, combined with thermal analysis results, indicated that the calcium di-hydroxide plays a role in the formation of an intumescent cohesive residue during the combustion. Indeed, Ca(OH)₂ reacts with CO₂ formed during the thermal degradation of the polymer to generate CaCO₃ (calcium carbonate) that contributes to the enhancement of the mechanical resistance of the residue.     

Heteroflocculation of binary latex dispersions of similar chemistry but varying size

The stability of dilute bimodal (diameter:100 and 200 nm) model latex dispersions is studied as a function of electrolyte concentration and particle number fraction by measuring perikinetic aggregation with dynamic light scattering. A formally correct expression for the effective, doublet stability ratio of a bimodal system is derived that accounts for the difference in the particle size and hence, extends the derivation by Hogg and co-workers [Trans. Faraday Soc. 62 (1966) 1638]. Including the particle size ratio predicts slightly lower stability ratios for polydisperse but chemically similar systems. Stability ratios for binary mixtures of model colloidal latices are extracted from aggregation measurements in the fractal aggregation regime and are compared to predictions based on DLVO calculations of the potential. The results suggest that the composition of the aggregates is dependent on the relative stability of the two components (and consequently, on electrolyte concentration) and is richer in the least stable component.     

Rhombohedral-scalenohedral calcite transition produced by adjusting the solution electrical conductivity in the system Ca(OH)2-CO2-H2O

This work is aimed to investigate the effects of the adjustment of the electrical conductivity (kappa25) during the semicontinuous carbonation of Ca(OH)2 suspension (slaked lime) on the morphology of the precipitated calcite (CaCO3) particles. The experiments were carried out at 30, 45, and 60 degrees C. A gradual morphological change from rhombohedral to scalenohedral shapes was produced with an increase of kappa25 from 1 to 7 mS/cm at each temperature. The explanation of this morphological change is given in terms of the increase of both the supersaturation and the ratio between concentrations of charged species containing calcium and carbonate ([Ca]ch/[CO3]ch) in the aqueous phase as the kappa25 set-point increases, prior to the precipitation process. In addition to the rise of the supersaturation this change most probably takes place because the increase of the [Ca]ch/[CO3]ch ratio affects the growth rate of the rhombohedral {104} and scalenohedral {21-1} faces in a different manner: (i) favoring the equality between the surface coverage of Ca2+ and CO3(2-) on the stoichiometric {104} face, thus enhancing the formation of CaCO3(0) growth units and then its growth rate and (ii) inhibiting the growth of the {21-1} face by adsorption of the excess calcium species.     

Formation and Catalytic Functionality of Synthetic Polymer-Noble Metal Colloid

Colloidal dispersions of noble metals in synthetic polymers are prepared by reduction with alcohol. Reflux of a solution of rhodium(III) chloride and poly(vinyl alcohol) (PVA) in a methanol-water mixed solvent under argon or air for 4 hr gives a homogeneous solution of colloidal dispersion of rhodium (Rh-PVA-MeOH/H₂O). The particle size of metallic rhodium is distributed n a narrow range of 30-70 Å, and the average diameter is 40 A. The formation of colloidal rhodium proceeds through three steps: coordination of poly(vinyl alcohol) to rhodium(III) ion, reduction with methanol to form small particles (8 Å in diameter), and growth of the small particle to large particle (40 Å in diameter). Polyvinylpyrrolidone (PVP) and poly(methyl vinyl ether) (PMVE) can be used in place of poly(vinyl alcohol) and result in colloidal dispersions, respectively, similar to Rh-PVA-MeOH/H₂O. Colloidal dispersions in nonaqueous solvent can be prepared by using ethanol instead of methanol-water (Rh-PVP-EtOH) and by using methanol instead of methanol-water, with addition of small amount of methanol solution of sodium hydroxide (Rh-PVP-MeOH/NaOH). The average diameters of rhodium particles in Rh-PVP-EtOH and Rh-PVP-MeOH/NaOH are 22 and 9 Å, respectively. The colloidal dispersions of palladium, silver, osmium, iridium, platinum, and gold in aqueous or nonaqueous solvent are prepared by using polyvinylpyrrolidone. The colloidal dispersions are very stable even under air for 20 days. Those of rhodium, palladium, and platinum are effective catalysts for hydrogenation of olefins at 30°C under an atmospheric hydrogen pressure. The colloidal dispersion of palladium catalyzes highly selective hydrogenation of diene and dienoate to monoene and monoenoate, respectively.     

Next‐Generation Polymer Shells for Inorganic Nanoparticles are Highly Compact,Ultra‐Dense,and Long‐Lasting Cyclic Brushes

Cyclic poly‐2‐ethyl‐2‐oxazoline (PEOXA) ligands for superparamagnetic Fe₃O₄ nanoparticles (NPs) generate ultra‐dense and highly compact shells, providing enhanced colloidal stability and bio‐inertness in physiological media. When linear brush shells fail in providing colloidal stabilization to NPs, the cyclic ones assure long lasting dispersions. While the thermally induced dehydration of linear PEOXA shells cause irreversible aggregation of the NPs, the collapse and subsequent rehydration of similarly grafted cyclic brushes allow the full recovery of individually dispersed NPs. Although linear ligands are densely grafted onto Fe₃O₄ cores, a small plasma protein such as bovine serum albumin (BSA) still physisorbs within their shells. In contrast, the impenetrable entropic shield provided by cyclic brushes efficiently prevents nonspecific interaction with proteins.     

Next‐Generation Polymer Shells for Inorganic Nanoparticles are Highly Compact,Ultra‐Dense,and Long‐Lasting Cyclic Brushes

Cyclic poly‐2‐ethyl‐2‐oxazoline (PEOXA) ligands for superparamagnetic Fe₃O₄ nanoparticles (NPs) generate ultra‐dense and highly compact shells, providing enhanced colloidal stability and bio‐inertness in physiological media. When linear brush shells fail in providing colloidal stabilization to NPs, the cyclic ones assure long lasting dispersions. While the thermally induced dehydration of linear PEOXA shells cause irreversible aggregation of the NPs, the collapse and subsequent rehydration of similarly grafted cyclic brushes allow the full recovery of individually dispersed NPs. Although linear ligands are densely grafted onto Fe₃O₄ cores, a small plasma protein such as bovine serum albumin (BSA) still physisorbs within their shells. In contrast, the impenetrable entropic shield provided by cyclic brushes efficiently prevents nonspecific interaction with proteins.     

Preparation and characterization of calcium phosphate–albumin colloidal particles by high ultrasonic irradiation

Using high intensity ultrasonic irradiation, we prepared calcium phosphate–albumin colloidal particles from aqueous solutions of Ca(H₂PO₄)₂ and Ca(OH)₂ in the presence of bovine serum albumin (BSA). The effect of concentration of BSA (2–5 g/L) properties of the colloidal particles was studied at constant temperature. The effect of a resting period on the size distribution of the colloidal particles was also investigated. Morphology, phase composition, average diameter, size distribution and zeta potential were obtained by transmission electron microscopy, X-ray diffraction, particle size determination by PCS and electrokinetic measurements.     

Effect of dispersion pH on the formation and stability of Pickering emulsions stabilized by layered double hydroxides particles

Using positively charged plate-like layered double hydroxides (LDHs) particles as emulsifier, liquid paraffin-in-water emulsions stabilized solely by such particles are successfully prepared. The effects of the pH of LDHs aqueous dispersions on the formation and stability of the emulsions are investigated here. The properties of the LDHs dispersions at different pHs are described, including particle zeta potential, particle aggregation, particle contact angle, flow behavior of the dispersions and particle adsorption at a planar oil/water interface. The zeta potential decreases with increasing pH, leading to the aggregation of LDHs particles into large flocs. The structural strength of LDHs dispersions is enhanced by increasing pH and particle concentration. The three-phase contact angle of LDHs also increases with increasing pH, but the variation is very small. Visual observation and SEM images of the interfacial particle layers show that the adsorption behavior of LDHs particles at the planar oil/water interface is controlled by dispersion pH. We consider that the particle-particle (at the interface) and particle-interface electrostatic interactions are well controlled by adjusting the dispersion pH, leading to pH-tailored colloid adsorption. The formation of an adsorbed particle layer around the oil drops is crucial for the formation and stability of the emulsions. Emulsion stability improves with increasing pH and particle concentration because more particles are available to be adsorbed at the oil/water interface. The structural strength of LDHs dispersions and the gel-like structure of emulsions also influence the stability of the emulsions, but they are not necessary for the formation of emulsions. The emulsions cannot be demulsified by adjusting emulsion pH due to the irreversible adsorption of LDHs particles at the oil/water interface. TEM images of the emulsion drops show that a thick particle layer forms around the oil drops, confirming that Pickering emulsions are stabilized by the adsorbed particle layers. The thick adsorbed particle layer may be composed of a stable inner particle layer which is in direct contact with the oil phase and a relatively unstable outer particle layer surrounding the inner layer.     

Colloidal dispersions of tannins in water-ethanol solutions

The molecular interactions of grape-seed tannins dissolved in water-ethanol solutions have been studied through small angle neutron scattering, light scattering, and physical separation techniques. Through selective precipitation in different solvent mixtures, three populations of tannin macromolecules have been identified: T1 (2% of the total tannin), which forms colloidal particles when the ethanol content of the solvent is brought below phiA = 0.6; T2a (33% of the tannin), which phase-separates below phiA = 0.08 in ionic conditions that are typical of wine; and T2b (65% of the tannin), which remains in solution regardless of ethanol content. Each population remains molecularly dissolved (i.e., it does not form any association structures such as stacks or micelles) until the threshold where dense colloidal particles are formed through nucleation and growth. The colloidal dispersions are metastable, due to the adsorption of organic acids on the particle surfaces; increasing ionic strength and reducing ethanol content cause the loss of this metastability and the aggregation of the particles.