Fe3+离子对硅酸体系聚合行为的影响

向不含金属离子的硅酸体系中加入Fe3+离子,研究了体系胶凝时间、溶胶粒径、凝胶比表面积、官能团及热稳定性的变化. 结果表明,加入Fe3+降低了体系pH值;初始pH≤2时,Fe3+起促凝作用,初始pH≥3时,Fe3+起缓凝作用. 初始pH=2时,放置24 h溶胶粒径随Fe3+浓度增加而增大,凝胶比表面积逐渐增大,Fe3+浓度为0.03 mol/L时粒径为444 nm,比表面积为1500 m2/g;初始pH=3时,放置24 h溶胶粒径随Fe3+浓度增加呈先增大后减小的趋势,最大粒径达379 nm,而凝胶比表面积逐渐减小,Fe3+浓度为0.03 mol/L时为81 m2/g. Fe3+引起聚硅酸网络结构变形,导致凝胶部分吸收峰强度减弱和移位及凝胶结合水减少和晶化转变峰变弱.     

Stability of kaolinite dispersions in the presence of sodium and aluminum ions

The stability of colloidal kaolinite dispersions in the presence of NaCl and AlCl₃ was studied by measuring turbidity, electrophoretic mobility and adsorption. The kaolinite particles coagulated at pH 2.5–3.5 and were dispersed at pH >4.5. These results well obeyed the classic DLVO theory if the mean zeta potential of the kaolinite particles in aqueous solutions was taken into account in the computation of potential energy of electrical double layer repulsion, which suggests that the kaolinite particles might coagulate in the same way as normal colloidal particles. The kaolinite particles in aqueous aluminum salt solution only coagulated at a medium AlCl₃ concentration, and formed a stable dispersion at a high salt concentration. This is caused by Stern-layer adsorption of hydrolyzed aluminum species, probably adsorbed on the kaolinite surfaces through hydrogen bonds between the hydroxyl groups of the aluminum species and the oxygen atoms on the kaolinite surfaces.     

The reaction of kaolin with fluorides: I. Effect of neutral and acid sodium fluoride solutions

The reaction between kaolinite and neutral and acid sodium fluoride solutions was investigated at different temperatures and over the acid pH range. The stoicheiometric replacement of hydroxyls in the kaolinite crystal lattice by fluoride ions, as reported by earlier workers, was not confirmed. The release of hydroxyl ions into solution was due predominantly to the disruption of the kaolinite crystal lattice. In the presence of sodium ions and at pH < 7, sodium fluoro-silicate and cryolite were found as solid phases. At pH > 7, only cryolite was found as a solid phase. Small, spherical, particles were observed in all cases. These particles were believed to be amorphous silica, formed as an intermediate phase in the disruption process.     

Synthesis and colloidal stability of poly(N‐isopropylacrylamide) microgels with different ionic groups on their surfaces

Temperature‐sensitive poly(N‐isopropylacry‐lamide) (PNIPAM) microgels with sulfate, amidino, or carboxylic groups on their surfaces, were synthesized by precipitation polymerization based on ammonium persulfate (APS), 2,2′‐azobis(amidinopropane) dihydrochloride (V50), or 4,4′‐azobis(4‐cyanovaleric acid) (ACVA) as initiator, respectively. Their particle sizes and swelling ratios depended on the reaction pH due to the pH dependence of the ionization degree of the decomposed fragments originating from the initiators and their hydrophilicity–hydrophobicity. The more hydrophobic initiators partitioned into the interior of the PNIPAM microgels under certain pH conditions initiated the crosslinking reaction between the PNIPAM chains, leading to higher crosslinking density of the microgels resulting in their smaller swelling ratio. pH dependence of surface charge density of the microgels with amidino groups or carboxylic acid groups on their surfaces was evidenced by the variation of their ζ‐potentials as a function of pH. Correspondingly, due to their pH dependence of electrostatic repulsive effect, the colloidal stability of the microgels with amidine groups or carboxylic acid groups on their surfaces was dependent on the pH value of dispersion medium. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3893–3898, 2007     

胶体五氧化二锑的制备及性质

以H3PO4 作为稳定剂,经双氧水氧化法制备胶体Sb2O5,对影响胶粒大小与分布的因素以及胶粒的荷电性、物相组成、光吸收特性、热稳定性进行了研究。结果表明,在 95℃、n(H3PO4 ) /n(Sb) =0 1~0 3、n(H2O2 ) /n(Sb2O3 ) >2 0条件下,制备出胶粒粒径 30nm左右的高度分散的胶体Sb2O5,胶粒表面带负电,等电点从pH=1 .85向更酸性范围移动,在 2相似文献   

Composite polymeric particles with ZnS shells

We report on a preparation of hybrid particles with polymeric cores and ZnS shells. Two types of monodisperse sterically stabilized polystyrene particles with hydroxyl-terminated PEG chains (PS/PEGMA) or β-diketone groups (PS/AAEM) on the surface have been prepared and characterized. Formation of ZnS layer on the surface of submicron particles has been studied by SEM and EDX. Deposition of ZnS on the surface of PS/PEGMA particles is not uniform and leads to formation of ‘raspberry’ morphology with rough surface. It has been found that presence of β-diketone groups on the particle surface leads to formation of well-defined ZnS layers. It has been assumed that such effect is due to the complexation of Zn cations by β-diketone groups leading to nucleation and growth of ZnS crystals on the polymer particle surface. Polymeric particles were completely covered with ZnS if the loaded amount of inorganic material was higher then 40 wt%. The thickness of ZnS layer on the particle surface can be easily varied by changing the ZnS load (in present study maximal thickness of the ZnS shell was 70 nm). It has been found that increase of the ultrasound power leads to considerable increase of the ZnS deposition on the particle surface without strong changes of the particle morphology. Hybrid particles have been investigated with XRD technique and their optical properties were studied by UV-spectroscopy. The colloidal stability of obtained particles was studied by separation analyser. Sedimentation experiments indicate that colloidal stability of obtained composite particles depends strongly on loaded ZnS amount and pH value of the aqueous medium. It has been found that highest sedimentation velocities (or maximum of instability) were determined by ZnS loads, which provide complete coverage of the particle surface. Increase of the ZnS layer thickness led to better stability of hybrid particles in aqueous medium.     

Effect of the type of polymer functional groups on the structure of its film formed on the alumina surface – Suspension stability

The effects of polymer functional group and solution pH on stability of colloidal Al₂O₃ water suspension were studied. Both the nonionic polymers: polyethylene glycol (PEG), polyethylene oxide (PEO) and the ionic ones: polyacrylic acid (PAA), polyacrylamide (PAM), polyvinyl alcohol (PVA) were used in the experiments. The following methods were applied: turbidimetry (stability measurements), spectrophotometry (determination of polymer adsorption), viscosimetry (thickness of polymer adsorption layer), potentiometric titration (solid surface charge density) and microelectrophoresis (potential zeta). It was shown that anionic polyacrylic acid is both the most effective stabilizer (at pH 9) and flocculant (at pH 3) of the alumina suspension. Its carboxyl groups have the greatest affinity for the surface active sites (the largest adsorption) of all functional groups present in the other examined polymers. The latter, i.e. hydroxyl (PEG, PEO, and PVA) and acetate (PVA) show a much lower affinity for the Al₂O₃ surface (negligible adsorption) and minimally affect the stability of the alumina-solution system.     

Characterisation and processing of aqueous LaNi0.6Fe0.4O3 Suspensions into Porous Electrode Layers for Alkaline Water Electrolysis

The colloidal properties and processing of aqueous LaNi_0.6.Fe_0.4O₃ suspensions into electrode layers with hierarchical pore sizes has been investigated by light scattering, electron microscopy and rheology. We found that the colloidal stability of the oxide particles and the resulting microstructure of the electrode layers were similar when dispersing the particles at their intrinsic pH, or when adding polyvinylpyrrolidone. The addition of the ammonium salt of poly(methaacrylic acid) resulted in a poor colloidal stability and the concentrated suspensions became viscoelastic during processing. Addition of rice starch resulted in an increase of the porosity but the cast electrode layers cracked and delaminated.     

Dispersion of Boron Nitride Powders in Aqueous Suspensions with Cellulose

The dispersion of nitride and carbide ceramic particles in water is difficult, due to the absence of hydroxyl groups on their surface. Boron nitride (BN) is not an exception and despite its numerous applications, no effective dispersant has been identified so far. We demonstrate here the dispersion properties of two cellulose derivatives for hexagonal BN powders, hydroxyl ethyl cellulose and methyl cellulose. The effect of particle size and cellulose concentration was investigated. The adsorption of cellulose onto the surface of the BN particles was confirmed by isotherm adsorption. Zeta potential measurements show a charge screening effect of the cellulose The suspensions obtained were highly loaded and stable versus pH, and thus could lead to homogeneous codispersion of BN particles and sintering additives.     

Rheological properties of ethylcellulose latex

Because of their large specific surface area, aqueous‐based pseudolatex systems of ethylcellulose can absorb large amounts of drugs. In addition, the stability of polymeric particles in biological fluids delays the release of the drug as in controlled drug delivery systems. The aim of the present study was to characterize the rheological properties of latex particles as a measure of their colloidal stability. Here, we report the effect of three variables: pH, electrolyte concentration, and temperature. The rheograms clearly show that the polymer suspensions displayed Bingham plastic behavior. Internal structuring of the latex was greatest at acid and natural pH values, particularly at the highest ionic strength. In acid solutions, only temperature appeared to play a fundamental role; both the shear stress corresponding to the onset of nonlinear viscoelasticity and the elastic modulus at all frequencies were higher at 37°C than those at room temperature. This is assumed to be a consequence of deformation of the polymer particles upon heating. The effect of ionic strength was noticeable only at the natural pH (pH ? 6.5). At high concentrations of sodium chloride, the particles aggregated because of the decrease in double layer repulsion, and as a result, the latex became structured and its elastic modulus subsequently increased. Interestingly, when the temperature was increased further, this structure presumably broke, down, at least partially, and the storage modulus was reduced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 847–851, 2006     

The Ultrafiltration of Very Dilute Colloidal Gold Suspensions

The ultrafiltration behaviour of very dilute colloidal suspensions has been investigated in terms of transmembrane pressure and pH in a batch cell with and without stirring using PM30 and SKIP membranes.For small (10 nm) colloidal gold particles the unstirred flux was higher than the stirred. An increase in concentration polarization due to the lack of stirring shields the electrostatic repulsion between particles, resulting in aggregation of particles that are retained at the membrane surface. This loosely packed layer can be responsible for the higher flux in the unstirred condition. For large (50 nm) gold particles, greater flux was achieved in stirred condition due to the decrease in concentration polarization.While the SKIP membranes showed a complete retention for larger colloidal gold particles, for smaller particles the retention was complete after around 1 minute. The PM30 membrane completely retained colloidal gold particles of both sizes.Lower flux with higher flux decline was obtained for the smaller colloidal gold particles compared to the larger ones. The cross section micrographs show that the larger sol forms a less densely packed deposit layer on the membrane surface. Changing the pH of the colloidal gold suspension resulted in a substantial change to the flux and retention. However the level of local ionic concentration at the membrane surface appears to be of utmost importance as it affects the degree of colloidal aggregation and packing of the deposit layer, thus influencing flux and retention.Analysis of the filtration data coupled with electron microscopy showed that cake filtration was the dominant mechanism during the course of ultrafiltration as well as microfiltration of very dilute colloidal gold suspensions.     

Deposition of magnetite particles from flowing suspensions under flow‐boiling and single‐phase forced‐convective heat transfer

The deposition rate of colloidal magnetite particles was measured under both single‐phase forced‐convective and flow‐boiling conditions. All measurements were made at alkaline pH where both the heat transfer surface and the surface of the magnetite particles appear to be negatively charged. For single‐phase forced convection, the deposition rate constant is lower than the mass transfer coefficient for colloidal particles, and the difference is attributed to the force of repulsion between the negatively charged surfaces of the particle and substrate. The deposition rate measured under flow‐boiling conditions is lower than that reported for the deposition of colloidal particles at neutral pH. The difference is, again, attributed to the force of repulsion between the particle and substrate. Particle removal rates were significantly lower than deposition rates; analysis using the theory of turbulent bursts suggests a removal efficiency of only 10^?9% for each turbulent burst. The low removal efficiency is consistent with the particle diameter being significantly smaller than the thickness of the laminar sublayer in these tests.     

Electrophoretic mobility of magnetite particles in high temperature water

Magnetite (Fe₃O₄) is one of the most common oxides forming deposits and particulate phases in industrial high temperature water circuits. Its colloidal characteristics play a principal role in the mechanism of deposit formation and can be used as controlling factors to prevent or minimize deposit formation and damage of industrial pipelines due to under-deposit corrosion. In this study, a high temperature particle electrophoresis technique was employed to measure the zeta potential at the magnetite/water interface—the parameter that controls colloidal stability of particles, their aggregation, and deposition. The measurements were made at temperatures up to 200 °C over a wide range of pH. The isoelectric points of magnetite, at which the deposition of particles is increased, were determined at pH 6.35, 6.00, 5.25, and 5.05 for temperatures 25, 100, 150, and 200 °C, respectively. The observed temperature dependence of zeta potential and the isoelectric pH point of magnetite can help to explain the extent of interactions between the colloidal particles and the steel wall surfaces under hydrothermal conditions, and indicate methods for controlling and mitigating oxide deposition in high temperature water cycles.     

Surface characterization of hydrophilic functional polymer latex particles

Surface characteristics of styrene/acrylamide/acrylic acid copolymer and styrene/2-hydroxyethyl methacrylate/acrylic acid copolymer latexes prepared without emulsifier using potassium persulfate as initiator and their colloidal stabilities were investigated. The negative ζ-potentials decreased with increasing the amount of acrylamide and 2-hydroxyethyl methacrylate copolymerized. In spite of the increase in surface charge density, the negative ζ-potentials decreased through the maximum with increasing pH. The colloidal stabilities for NaCl concentration were remarkably enhanced with increasing both pH and the amount of acrylamide and 2-hydroxyethylmethacrylate. These results suggest that the contration and expansion of water-soluble polymer layer surrounding the particles play an important role in the surface properties.     

Evaluation of silicon-based strengthening agents on porous limestones

Deteriorated porous bioclastic limestones from the archaeological area of Aptera, Crete, Greece, were treated with silicon-based strengthening products, tetraethoxysilanes, elastified silicic acid ethyl esters, an aqueous colloidal dispersion of silica particles, as well as an oligomeric siloxane water repellent. Changes in color, water vapor permeability, water absorption by capillary suction, porosity and pore size distribution were evaluated after treatment. Energy dispersive X-ray fluorescence and Fourier transform infrared spectroscopy indicate the penetration depth of the applied products. The effectiveness of strengthening was also evaluated by measuring the tensile strength. The pore size distribution was insignificantly modified decreasing only the ratio of coarse pores. The applied products penetrated up to a depth of 30 mm. All the studied products create linkages across the interface between calcite and the alkoxysilanes-derived gels, due to the hydroxyl groups of the quartz included in the limestones. Better reinforcing results were obtained by applying the elastified silicic acid ethyl ester. The elastified silicic acid ethyl ester confers chromatic stability on the stone, shows insignificant modification of the water vapor permeability and reduces the absorbed quantity of water.     

FITC and Ru(phen)32+ co-doped silica particles as visualized ratiometric pH indicator

The performance of fluorescein isothiocyanate (FITC) and tris(1, 10-phenanathroline) ruthenium ion (Ru(phen)32+) co-doped silica particles as pH indicator was evaluated. The emission intensity ratios of the pH sensitive dye (FITC) and the reference dye (Ru(phen)32+) in the particles were dependent on pH of the environment. The changes in emission intensity ratios of the two dyes under different pH could be measured under single excitation wavelength and readily visualized by naked eye under a 365-nm UV lamp. In particular, such FITC and Ru(phen)32+ co-doped silica particles were identified to show high sensitivity to pH around the pKa of FITC (6.4), making them be potential useful as visualized pH indicator for detection of intracellular pH micro-circumstance.     

Preparation of transparent polystyrene nano-latexes by an UV-induced routine emulsion polymerization

Transparent polystyrene (PS) latexes were prepared by photo-polymerization of a routine styrene (St) emulsion with a surfactant concentration of 0.4 wt% and a monomer concentration of 10 wt%, by using UV light as well as a hydrophilic photo-initiator. The entire polymerization could be performed within 1-2 h and display a conversion higher than 90%. The particle sizes could be tuned in the range of 20-40 nm. The formation mechanism for these of nano-sized latex particles was attributed to an in situ formation of PS chains with terminal hydroxyl groups. The presence of the hydroxyl-functionalized polymer chains seemed to promote a colloidal stability of the small latex particles and prevent coagulation even at low surfactant concentrations.     

改性活性炭强化催化臭氧氧化降解草酸

对工业活性炭进行酸预处理、硝基化和氨基化表面改性,并在半连续反应器中研究其催化臭氧氧化降解草酸的活性. 结果表明,酸预处理的活性炭比表面积、等电点pH值(pHpzc)和碱性官能团含量提高了5%~10%,但催化降解草酸效率降低15.6%,氨基化活性炭的pHpzc和碱性官能团含量分别由2.6和234.8 mmol/g升至7.0和764.5 mmol/g,而硝基化活性炭的pHpzc和表面碱性官能团含量均降低. 在中性和酸性溶液中,两种改性活性炭降解草酸的活性均高于预处理活性炭. 在pH=7的溶液中,氨基化活性炭在45 min内催化降解草酸降解率为42.4%. 加入叔丁醇会抑制活性炭催化降解草酸,活性炭催化臭氧氧化草酸主要是羟基自由基起作用.     

Surface properties of polymethylenediamine-fixed styrene/acrylic acid copolymer latex

Surface charge density, ζ-potential, and dispersion stability of polymethylenediamine (PMD)-fixed styrene/acrylic acid copolymer [P(St/AA)] latex were investigated. PMD-fixed P(St/AA) latices are amphoteric and have isoelectric points at pH 4–7. Though the flocculations were observed at neutral pH, the pHs where the flocculation rates were maximum are slightly higher than were the isoelectric points. This result suggests the influence of the expansion of PMD-fixed polymer layer surrounding the particles on the flocculation. The fixation of PMD to the surface of P(St/AA) latex lowers the dispersion stability for high electrolyte concentration.     

Effect of pH on the retention of inorganic fillers

The effect of pH on the retention of various inorganic fillers has been studied. It is found that the isoelectric point of the filler has no effect on its retention characteristics with our particular sulphate bleached pulp. This is due to the fact that the surface of the filler is modified by either the adsorption of or the flocculation with the fines and colloidal material originating from the fibre surface. This surface modification produces a shift of the apparent isoelectric point of the fillers and in many cases gives rise to heteroflocculation of the fibres and filler particles only when the pH is at more acid values than 4.0.