Some anomalous effects of sodium ions on the electrophoretic mobility and heteroaggregation of microgel particles

Experiments on the kinetics of heteroaggregation between oppositely charged particles, using both dynamic light scattering and turbidity methods, are reported. The negatively charged particles were cross-linked poly( [Formula: see text] -isopropylacrylamide) [PNIPAM] microgel particles, prepared using a carboxylic-acid-based initiator; these particles are swollen at room temperature. The positive particles were poly(4-vinylpyridine) [P4VP] particles, prepared using an amidinium-based initiator; such particles do not respond to temperature changes but do swell below pH approximately 4, where the pyridine moieties become protonated. As expected, the rate of heteroaggregation was shown to be largely independent of added salt concentration (up to approximately 20 mM), for a variety of alkali metal chlorides (MCl, where M = Li, Na, K, or Rb). However, an unexpected, significant decrease in the aggregation rate was observed at certain specific sodium chloride concentrations (typically at approximately 1 and also approximately 4 mM). Similar effects were not seen with the other alkali metal chloride salts. This strange effect was eventually attributed to the fact that the net charge on the positively charged P4VP particles had been reduced by the adsorption of (anionic) silicate species leached from the glassware container. Sodium silicates are known to be significantly more soluble than those of the other alkali metal ions, particularly at high pH. Moreover, P4VP particles dispersed in water, ostensibly at neutral pH, do buffer the aqueous medium to pH values around 9 or higher. This mechanism was confirmed by determining the electrophoretic mobility of the P4VP particles as a function of pH in the presence of the various alkali metal chloride salts. The mobility remained positive in 1 mM salt solutions over the pH range 3 to 11 for all the salts, except for sodium chloride; in that case the mobility reversed sign at alkaline pH values. A similar effect was observed for a cationic polystyrene latex sample, prepared with the same amidinium-based initiator. These experiments demonstrate the importance of soluble silicates, leached from glass storage vessels, particularly in the presence of sodium ions. Needless to say, the "anomalous" effects disappeared when plastic storage vessels were used in place of the glass ones.     

Highly regenerable ionic liquid microgels as inherently metal‐free green catalyst for H2 generation

Polymeric ionic liquid (PIL) microgel of poly([2‐(methacryloyloxy)ethyl]trimethylammonium chloride) (p(MTMA)) was synthesized by using an inverse suspension polymerization technique. The anion‐exchanged PIL microgels via chloride replacement from p(MTMA) were prepared as p(MTMA)‐potassium thiocyanate (p(MTMA)‐KSCN), p(MTMA)‐sodium tetrafluoroborate (p(MTMA)‐NaBF₄), and p(MTMA)‐sodium dicyanamide (p(MTMA)‐NaN(CN)₂) microgels by treatment with corresponding salts of potassium thiocyanate (KSCN), sodium tetrafluoroborate NaBF₄, and sodium dicyanamide NaN(CN)₂ in aqueous media. The prepared microgels were found to be efficient metal‐free catalysts, and their catalytic activity in H₂ production from the methanolysis of NaBH₄ was investigated. Moreover, various parameters affecting H₂ production such as the effect of microgel size, the concentration of NaBH₄, the effect of the anion in the microgel, the reusability of the microgel, and temperature were investigated. The Ea value calculated for the methanolysis reaction of NaBH₄ catalyzed by p(MTMA) microgels was found as 24.1 ± 0.7 kJ mol⁻¹ ranging from −15 to 45°C, and this Ea value is lower than some Ea values for the same reaction. Interestingly, 10‐time successive use of p(MTMA) microgel as catalyst in NaBH4 methanolysis reduced its catalytic activity to 49%, whereas the anion‐exchanged forms of p(MTMA) microgel, p(MTMA)‐KSCN, p(MTMA)‐NaBF₄, and p(MTMA)‐NaN(CN)₂ only reduced their catalytic activity to 89, 86, and 79%, respectively, after 10 consecutive uses. Therefore, these anion‐exchanged microgel catalysts are highly efficient in comparison with virgin p(MTMA) microgels for regenerable H₂ generation from the methanolysis of NaBH₄.     

Studies on extraction of beryllium from thiocyanate solutions by quaternary ammonium halides

A 0.4M tricaprylmethylammonium chloride solution in n-hexane was used for the quantitative extraction of beryllium from hydrochloric acid (pH 3) and 5M potassium thiocyanate. Beryllium was stripped from the organic phase with 1M sodium hydroxide, then determined volumetrically with bismuthyl perchlorate and bromocresol green indicator. Beryllium was extracted in presence of a large number of elements which are usually associated with it in beryl and in fission products of nuclear fuel.     

Functionalization of poly(<Emphasis Type="Italic">N</Emphasis>-ethylmethacrylamide) thermosensitive particles by phenylboronic acid

The synthesis of poly(N-ethylmethacrylamide) (NEMAM) thermosensitive particles functionalized with phenylboronic acid (PhBA) groups has been performed by emulsion/precipitation polymerization of NEMAM in water at 90 °C, using ethylene glycol dimethacrylate (EGDMA) as an hydrophobic crosslinker, phenylboronic acid methacrylamide (PhBAMA) as a functional monomer, and potassium persulfate (KPS) as an initiator. The influences of the PhBAMA concentration and mode of monomer addition (batch or shot-growth processes) have been examined both on the polymerization kinetics and on the physicochemical and colloidal properties of the final particles. Results have been discussed according to the ionogenic and hydrophobic nature of the functional monomer. We have directly and clearly provided evidence that PBA was successfully incorporated at the particle surface by using ESCA analysis, especially when using a shot-growth process, a result that was indirectly confirmed by investigating the electrophoretic mobility behavior of the various latexes as a function of pH.     

Isoselective Ring‐Opening Polymerization of rac‐Lactide Catalyzed by Sodium/potassium Tetradentate Aminobisphenolate Ion‐paired Complexes

Two sodium/potassium tetradentate aminobisphenolate ion‐paired complexes were synthesized and structurally characterized. These ion‐paired complexes are efficient catalysts for the ring‐opening polymerization of rac‐lactide (rac‐LA) in the presence of 5 equivalents BnOH as an initiator and the side reaction of epimerization can be suppressed well at low temperatures. The polymerizations are controllable, affording polylactides with desirable molecular weights and narrow molecular weight distributions; the highest molecular weight can reach 50.1 kg mol^?1 in this system, and a best isoselectivity of P_m=0.82 was achieved. Such polymerizations have rarely been reported for isoselective sodium/potassium complexes without crown ether as an auxiliary ligand. The solid structures suggest that BnOH can be activated by an interaction with the anion of sodium/potassium complex via a hydrogen bond and that the monomer is activated by coordination to sodium/potassium ion.     

Emulsion polymerization of styrene. I. Review of experimental data and digital simulation

Isothermal emulsion polymerization at 60°C of styrene in a batch reactor were studied by using sodium lauryl sulfate as surfactant and potassium persulfate as initiator source. The concentrations of surfactant and initiator were varied during the runs. The polymerization evolution was followed as samples were taken at regular intervals. These emulsion samples were analyzed for monomer conversion, rate of polymerization, as well as for the size and the size distribution of the particles. The molecular weight and molecular weight distribution were obtained by gel permeation chromatography. Our study showed that fresh nucleation takes place even at high conversion, causing a continuous shifting toward broadening of particle size distribution. Contrary to the theory of Smith and Ewart, which assumes a constant number of particles during interval II of the polymerization reaction, our digital simulation of the reaction presents better experimental results with a variable number of particles, and indicates that the Hui–Hamielec model for termination constant k_t as function of conversion is not applicable under our working conditions.     

“Reviews in Macromolecular Chemistry”

Abstract

In the homopolymerization and copolymerization of vinyl acetate with dibutyl maleate in the presence of the sodium salt of sulfosuccinic acid semiester with nonylphenol ethoxylated with 25 mol ethylene oxide, the initiator, potassium persulfate (KPS), has a higher decomposition rate than in water even after consumption of monomer. The value of the initiator productivity, P, defined as the ratio of the formed polymer over the decomposed KPS, decreases as the batch stage of the semicontinuous process proceeds. The initiator reacts either with free surfactant molecules or with those grafted on poly(vinyl acetate) chains. During the stage of continuous addition of monomers and KPS, a smaller initiator concentration no longer provides proportionality between the added and decomposed amounts of initiator. The increased monomer concentration at the beginning of continuous addition causes the rate of KPS splitting to decrease as most of the surfactant is bound to the surface monomer/polymer particles.     

Emulsifier-free emulsion copolymerization of styrene and acrylamide using an amphoteric initiator

Emulsifier-free emulsion copolymerization of styrene (St) and acrylamide (AAm) has been investigated in the presence of an amphoteric water-soluble initiator, 2,2′-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine]hydrate (VA057). The kinetics of polymerization and the colloidal properties of the resulting latices were studied and compared with the cases using ionic initiators. When adopting the amphoteric initiator at pHs lower than 10, stable amphoteric poly (St/AAm) latices, evidenced by the electrophoretic mobility, were prepared directly. Meanwhile, almost the same conversion versus time curves appeared and there were no apparent differences in the final particle sizes for those polymerizations, whereas in the polymerization at pH 10, a much lower rate of copolymerization and a larger size of particles were observed. The surface charge density and the growth rate of latex particles produced with VA057 at pH<10 were comparable to those of the particles with a cationic initiator, 2,2′-azobis(2-amidinopropane)dihydrochloride, but were apparently lower than those with an anionic initiator, potassium persulfate, when the polymerizations were carried out under corresponding conditions. The number of initiator fragments incorporated onto the particle surfaces was independent of polymerization pH, except for pH 10. The abnormal performance of VA057 at pH 10 was attributed to its degradation due to hydrolysis. Received: 14 December 1999 Accepted: 22 February 2000     

Hydrogen ion-selective poly(vinyl chloride) membrane electrode based on a calix[4]arene.

A hydrogen ion-selective poly(vinyl chloride) membrane electrode was constructed using 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetracyanomethoxycalix[4]arene as a neutral carrier. The electrode showed an apparent Nernstian response in the 2-11.5 pH range with a slope of 54.0 +/- 0.2 mV/pH at 20 +/- degrees C. This electrode showed a rapid response of the emf to changes in the pH, high ion selectivity with respect to lithium, sodium and potassium, and characteristics similar to those reported for the conventional pH glass membrane electrode. It can be used as a potentiometric indicator electrode in hydrofluoric acid solutions. The effects of iodide, thiocyanate, perchlorate and bromide on the characteristics of the electrode were also considered.     

Pickering emulsion polymerization of graphene oxide-stabilized styrene

Polystyrene (PS) particles were prepared via Pickering emulsion polymerization using graphene oxide (GO) as the stabilizer. The results show that pH is an important factor in the stability of Pickering emulsions. The effects of two different phase initiators, the water phase initiator potassium persulfate and the oil phase initiator azobisisobutyronitrile, on the morphology of PS particles in Pickering emulsion polymerization had been investigated in detail. Wrinkled particles were prepared using the water phase initiator, and spherical particles were prepared using the oil phase initiator. In addition, hexadecane was used as the auxiliary stabilizer in the polymerization, which narrowed the diameter distribution of the PS spheres, and the hollow PS spheres were fabricated. The size of the GO particles also influenced the final morphology of the particles. Nano-sized polymer particles were grafted onto the surface of micro-sized GO. Small GO particles were suitable for Pickering emulsion polymerization to prepare the composite particles. The thermogravimetric analysis of the prepared particles confirmed that they were PS/GO composite particles, which could have a wide range of potential applications, such as in catalysts, sensors, environmental remediation, and energy storage.     

Adsorption of Bovine Serum Albumin onto Polystyrene Latex Particles Bearing Saccharidic Moieties

The adsorption of bovine serum albumin (BSA) onto polystyrene latexes bearing various amounts of sugar moieties has been investigated as a function of pH and ionic strength and the results were compared to those for bare polystyrene latexes having negative surface charges. The functionalized latexes were produced by seeded copolymerization of (0.3 μm) liposaccharidic monomer onto polystyrene particles obtained by soap-free emulsion polymerization of styrene using potassium persulfate as initiator. At first, the electrophoretic mobility behavior of the various latexes was examined as a function of pH: a significant decrease was observed in the case of saccharide-containing latex particles compared to the bare particles. The adsorption of BSA onto these latexes exhibited a reduced amount of adsorbed BSA for those latex particles bearing saccharide groups. This adsorbed amount depends on the yield of saccharidic monomer incorporated onto the surfaces of the latex particles.     

Dipolar anions are not preferentially attracted to the oil/water interface

Homogenization of hexadecane in water at pH 9 gives the same surface charge density in the presence of 0.2 mM thiocyanate or acetate anions as in the presence of chloride, indicating that these dipolar anions are not preferentially adsorbed at the oil/water interface. The decrease in the zeta potential of the emulsion droplets as the sodium salts of iodate, thiocyanate, or acetate are added from 0.1 to 10 mM is the same as that when sodium chloride is added, leading to the same conclusion. Increasing the sodium hydroxide concentration from pH 9 to 11.5 has a different effect on the zeta potential, consistent with the specific adsorption of hydroxide ion at the oil/water interface.     

Imaging fiber microarray fluorescent ion sensors based on bulk optode microspheres

Optical imaging fibers with micrometer-sized wells were used as a sensing platform for the development of microarray optical ion sensors based on selective bulk extraction principles established earlier for optodes. Uniform 10 μm sized microspheres based on plasticized poly(vinyl chloride) containing various combinations of ionophores, fluoroionophores and lipophilic ion-exchangers were prepared for the detection of sodium, potassium, calcium and chloride, and deposited onto the wells of etched fiber bundles. Specifically, sodium sensing particles were based on tert-butylcalix[4]arene tetraacetic acid tetraethylester, potassium particles on 2-dodecyl-2-methyl-1,3-propanediyl bis[N-[5′-nitro(benzo-15-crown-5)-4′-yl]carbamate] (BME-44), calcium particles on an acrylic derivative of ETH 129 (AU-1) covalently attached to a methacrylic polymer, and chloride particles based on the anticrown ionophore [9]mercuracarborand-3 (MC-3). The fluorescence emission characteristics of individual microspheres were observed from the backside of the fibers and were found to selectively and rapidly change as a function of the sample composition. The optical characteristics of the particles were found to be comparable to that of corresponding thin optode films and particles deposited onto microscope glass slides. The measuring ranges (logarithmic molar concentrations) at pH 7.0 were found as −3 to 0 for sodium, −3.5 to −0.5 for potassium, −7 to −2 for calcium, and −5 to 0.5 for chloride. Selectivities were determined over other common electrolytes and found to be sufficient for physiological applications. The simultaneous deposition of sodium and chloride sensing particles was successfully performed, demonstrating that such microarray sensors are capable of simultaneously sensing multiple analytes. This technology is compatible with other microsphere-based fluorescent sensing principles, forming a promising total analysis platform for a variety of applications.     

Synthesis of highly monodisperse particles composed of a magnetic core and fluorescent shell

Highly monodisperse particles composed of a magnetic silica core and fluorescent polymer shell were synthesized with a combined technique of heterocoagulation and soap-free emulsion polymerization. Prior to heterocoagulation, monodisperse, submicrometer-sized silica particles were prepared with the Stober method, and magnetic nanoparticles were prepared with a modified Massart method in which a cationic silane coupling agent of N-trimethoxysilylpropyl- N, N, N-trimethylammonium chloride was added just after coprecipitation of Fe (2+) and Fe (3+). The silica particles with negative surface potential were heterocoagulated with the magnetic nanoparticles with positive surface potential. The magnetic silica particles obtained with the heterocoagulation were treated with sodium silicate to modify their surfaces with silica. In the formation of a fluorescent polymer shell onto the silica-coated magnetic silica cores, an amphoteric initiator of 2,2'-azobis[ N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was used to control the colloidal stability of the magnetic cores during the polymer coating. The polymerization of St in the presence of a hydrophobic fluorophore of pyrene could coat the cores with fluorescent polymer shells, resulting in monodisperse particles with a magnetic silica core and fluorescent polymer shell. Measurements of zeta potential for the composite particles in different pH values indicated that the composite particles had an amphoteric property originating from VA-057 initiator.     

测定溶解度组装阴离子手性离子液体的研究

本文利用无机盐和有机盐在有机溶剂中的溶解度的差异,设计组装手性羧酸阴离子离子液体.测定氯化钠、氯化钾、溴化钠和溴化钾和手性有机羧酸盐((R)-2-羟基-4-苯丁酸钠或钾)在甲醇、乙醇或丙酮中的溶解度,一定温度下计算溶解度比值,理论推测该条件下阴离子交换比例.研究发现,当无机盐与有机盐的溶解度比值小于0.05时,阴离子交...     

The role of initiation in the synthesis of silica/poly(methyl methacrylate) nanocomposite latex particles through emulsion polymerization

Silica/poly(methyl methacrylate) nanocomposite latex particles have been synthesized by emulsion polymerization of methyl methacrylate using a nonionic surfactant: nonylphenol poly(oxyethylene) and three different initiators, namely: 2,2′-azobis(2-amidinopropane) dihydrochloride (AIBA), potassium persulfate (KPS) and azobis(isobutyronitrile) (AIBN), being cationic, anionic and nonionic, respectively. A silica sol with an average diameter of 68 nm was used as the seed. The polymerization reaction was conducted under alkaline conditions in order to evaluate the role of the surface charge of the hydrophilic silica on the coating reaction. AIBA was found to be adsorbed on the silica surface owing to electrostatic interactions of the amidine function of the cationic initiator with the silanolate groups of the oxide surface, while the anionic and the nonionic initiators did not adsorb on silica under the same conditions. Nonetheless, whatever the nature of the initiator, polymerization took place on the silica particles as evidenced by transmission electron microscopy. The extent of interaction between the inorganic surface and the polymer particles was quantified by means of ultracentrifugation and a material balance. As much as 65% by weight of the total polymer formed was found to be present at the silica surface using AIBA, while only 40% for KPS and 25% for AIBN was found to cover the silica particles under alkaline conditions. We demonstrate that by using a cationic initiator and by controlling the pH of the suspension it is possible to significantly decrease the amount of free polymer. Coating of the silica particles took place through a kind of in situ heterocoagulation mechanism. Received: 8 December 2000 Accepted: 22 February 2001     

Polypyrrole-coated natural rubber latex by admicellar polymerization

Admicellar polymerization has been used for the preparation of an electrically conductive polypyrrole coating on latex particles. An anionic surfactant, sodium dodecyl sulfate (SDS), was adsorbed onto natural rubber (NR) latex particles to form the surfactant bilayers after adjusting the pH below the point of zero charge of the latex surface. Adsorption of SDS and pyrrole adsolubilization were determined as a function of pyrrole and sodium chloride concentrations. Pyrrole caused a decrease in SDS adsorption at equilibrium. Sodium chloride increased the surfactant adsorption and the pyrrole adsolubilization. Thermogravimetric results showed the presence of polypyrrole. The conductivity of the polypyrrole-coated NR latex film prepared by admicellar polymerization without salt was the lowest; however, with salt addition, the conductivity of the film improved significantly. The oxidative polymerization technique resulted in a relatively higher conductivity than oxidative admicellar polymerization.     

Uniform encapsulation of fine inorganic powder with soapless emulsion polymerization

The encapsulation of inorganic powder of submicron sizes was attempted with soapless emulsion polymerization of methyl methacrylate in water in the presence of the powder. The powders used were barium sulfate and calcium carbonate. The polymerizations were initiated by potassium persulfate and by sodium bisulfite-oxygen redox reaction. The encapsulation state of the powder with the polymer formed varied considerably with the initiators used. With potassium persulfate initiator the powder surface was partially or totally covered by polymer particles, while with redox initiator under air atmosphere the powder surface was well encapsulated with a film-like polymer layer. From the differences in the encapsulation states, an encapsulation mechanism is suggested for each initiator system. Based upon this mechanism, a new encapsulation process capable of covering uniformly fine powders with a film polymer is proposed. An important factor in the new process is the addition of an extremely small quantity of a surfactant into the reaction system prior to the polymerization.     

Sodium meta-vanadate as volumetric reagent : Iodine monochloride method

Sodium meta-vanadate has been used as an oxidising agent in hydrochloric acid medium for the volumetric estimations of potassium iodide, sodium arsenite, mercurous chloride, potassium thiocyanate, sodium sulphite, sodium bisulphite, sodium thiosulphate, ferrous sulphate and hydrazine sulphate, using iodine monochloride as a catalyst and preoxidiser. Chloroform is used as an indicator. It is coloured pink due to the liberation, of iodine during the titration and becomes light pale yellow at the end-point due to the formation of iodine monochloride.     

Indirect spectrophotometric determination of chloride by solvent extraction as tris(1,10-phenanthroline)iron(II) thiocyanate

An indirect spectrophotometric method for the determination of small amounts of chloride in fresh waters is described. Chloride ions react with mercury(II) thiocyanate to liberate thiocyanate ions, which can be selectively extracted into nitrobenzene with tris(1,10-phenanthroline)iron(II) chelate cations. The red color (516 nm) of the organic phase measured against a reagent blank is proportional to the initial concentration of chloride ions in the aqueous phase. At least an equimolar amount of tris(1,10-phenanthroline)iron(II) chelate and a 3-fold amount of mercury(II) thiocyanate are needed; the optimal pH range is 1.5–3.5. Beer's law is obeyed over the concentration range of 0.8–5.6 10^-5 M of chloride. The color stability and the apparent sensitivity are better than those of the mercury(II) thiocyanate-iron(III) method. Large amounts of sulphate, phosphate, fluoride, carbonate, acetate, potassium, sodium, and ammonium ions had negligible or no effect ; bromide, iodide, cyanide, sulphide, and thiocyanate interfere.