The effect of pretreatment of calcite dispersions with anionic sodium polyacrylate on their flocculation behavior induced by cationic starch

The flocculation performance of cationic starches on calcite pretreated with anionic sodium polyacrylate (NaPA) was investigated by measuring the mean particle size and the dynamic mobility of the calcite dispersions. Cationic starches of different molecular weight and degree of substitution were used. By varying the amount of anionic sodium polyacrylate, which has a strong affinity to the calcium carbonate surface, one is able to anionically modify the particles and reverse the charge character of the originally cationic calcium carbonate. By such modification of the charge character of the calcium carbonate dispersion, it is possible to approach the mechanisms of flocculation caused by cationic macromolecules like starch. The importance of different mechanisms of flocculation, such as bridging, charge neutralization, and flocculation induced by polyelectrolyte complexes (PEC), was further investigated in this work. It was found that when the NaPA is completely absorbed at the calcite surfaces the mechanism of the flocculation induced by the starch is mainly bridging flocculation. Excess NaPA in the calcium carbonate dispersion will result in polyelectrolyte complexes formed between the non-absorbed NaPA and the oppositely charged starch polymers. These complexes will in most cases strongly enhance the flocculation due to mainly charge neutralization. Depending on the ratio of non-absorbed NaPA and the starch in the aqueous phase, the calcite dispersion is either re-stabilized or more strongly flocculated due to the formed polyelectrolyte complexes. Both the mobility and the particle size measurements support the mechanisms described. It was further demonstrated that the molecular weight and degree of substitution of the starches might be adjusted to control the flocculation behavior.     

One-pot fabrication of noble-metal nanoparticles that are encapsulated in hollow silica nanospheres: dual roles of poly(acrylic acid)

An efficient and facile one-pot method was developed to fabricate noble-metal nanoparticles (NMNs; Au, Pt, PdO and Ag) that were encapsulated within hollow silica nanospheres (HSNs; NMNs@HSNs) with a size of about 100?nm. NMNs@HSNs were afforded in very high yields between 85-95?%. Poly(acrylic acid) (PAA) polyelectrolyte played a dual role in the fabrication process, both as a core template of the HSNs and as a captor of the NMNs through coordination interactions between the COO(-) groups on the ammonium polyacrylate (APA) polyanionic chains and the empty orbital of the Au atom. The amount of Au loading in Au@HSNs was easily regulated by varying the volume of the HAuCl(4) solution added. In addition, these rattle-type particles were successfully applied in the catalytic reduction of 2-nitroaniline (2-NA) as a model reaction, thus indicating that the micropores in the silica shell could achieve the transport of small species--with a size smaller than that of the micropores--into the cavity. Thus, these fabricated NMNs@HSNs have promising applications in catalysis.     

Adsorption of Polyelectrolyte-Nanoparticle Systems on Silica: Influence on Interaction Forces

In this work, we have studied the interfacial properties of cationic polyelectrolyte (PE) and silica nanoparticle (NP) systems at macroscopic silica surfaces by means of ellipsometry. The influence of adsorbed layers on the interactions between silica surfaces was also investigated using the bimorph surface force apparatus. Added nanoparticles were observed to strongly swell the interfacial polyelectrolyte layers, an effect partly related to neutralization of charged polyelectrolyte groups. The effect was more pronounced for low charged than for highly charged polyelectrolytes. Overall, the presence of nanoparticles seemed to increase the repulsive interaction measured between silica surfaces. The force measured on approach was long range and quite strongly repulsive. On separation, an attractive bridging interaction was measured for polyelectrolyte-covered surfaces. For the low charged polyelectrolyte used in the study, the force turned repulsive on addition of nanoparticles. For the highly charged polyelectrolyte used, a change from a very strong attraction (involving a jump of the surfaces out of contact) to a very long-range elastic attractive force was observed on adding nanoparticles. The long-range elastic force indicates that polymer chains and nanoparticles form a transient network in the gap between the surfaces. The observed difference in the outward force curves may explain why the addition of nanoparticles appears to improve, e.g., shear-resistance and reflocculation characteristics of polymeric flocculants. Copyright 2000 Academic Press.     

One‐Pot Fabrication of Noble‐Metal Nanoparticles That Are Encapsulated in Hollow Silica Nanospheres: Dual Roles of Poly(acrylic acid)

An efficient and facile one‐pot method was developed to fabricate noble‐metal nanoparticles (NMNs; Au, Pt, PdO and Ag) that were encapsulated within hollow silica nanospheres (HSNs; NMNs@HSNs) with a size of about 100 nm. NMNs@HSNs were afforded in very high yields between 85–95 %. Poly(acrylic acid) (PAA) polyelectrolyte played a dual role in the fabrication process, both as a core template of the HSNs and as a captor of the NMNs through coordination interactions between the COO^? groups on the ammonium polyacrylate (APA) polyanionic chains and the empty orbital of the Au atom. The amount of Au loading in Au@HSNs was easily regulated by varying the volume of the HAuCl₄ solution added. In addition, these rattle‐type particles were successfully applied in the catalytic reduction of 2‐nitroaniline (2‐NA) as a model reaction, thus indicating that the micropores in the silica shell could achieve the transport of small species—with a size smaller than that of the micropores—into the cavity. Thus, these fabricated NMNs@HSNs have promising applications in catalysis.     

Fabrication of teardrop-shaped silica particles in polyelectrolyte diluted solution through in situ sol–gel process

A new strategy to fabricate teardrop-shaped silica particles is presented. Monodispersed teardrop-like silica particles were obtained through basic catalyzed sol–gel process of tetraethoxysilane by employed sodium polyacrylate as soft template. Increasing the salt concentration of solution, the morphology of silica particles can transform from teardrop-like to hollow structures, and finally formed solid particles. The morphologies of silica particles are characterized by TEM and SEM. Our finding can be scaled up for large-scale synthesis of unusual structures of inorganic or composite materials in a predictable manner. This study is expected to provide further understanding of the role of polyelectrolyte in the synthesis of inorganic materials towards design of unusual architectures and functional materials.     

Experimental analysis of negative salt rejection in nanofiltration membranes

The rejections of mixtures of polyelectrolyte (sodium polyacrylate) and a monovalent salt (NaCl) were measured as a function of flux for two nanofiltration (NF) membranes. These rejections were corrected for concentration polarization of both salt and polyelectrolyte. The feed concentration ratio of polyelectrolyte to salt ranged from 2 to 20. The extent of reduction in monovalent salt rejection in the presence of polyelectrolyte could be predicted based on the Donnan effect after evaluating the unbound fraction of polyelectrolyte counterion, φ_P, in independent dialysis experiments. In the dialysis experiments it was found that β was 0.32. From this the value of the Donnan partition coefficient, β was evaluated allowing for the effect of concentration polarization of both polyelectrolyte and salt. The concentration polarization of polyelectrolyte resulted in β changing as a function of flux.     

聚电解质溶液浓度区域的划分

按照De Gennes提出的标度概念,柔性高分子溶液可以划分为稀溶液,亚浓溶液和浓溶液3个区域,它们之间分别以接触浓度C^**和交叠浓度C^**为分界线．钱人元等根据聚苯乙烯溶液激基荧光强度浓度依赖性的实验结果,提出稀溶液区还应细分为极稀溶液和稀溶液两个区域,它的分     

Particulate hematite diffusion in sodium polyacrylate solutions. The effect of ionic strength

The diffusion coefficients of hematite particles in polyelectrolyte solution have been investigated using dynamic light scattering. Two apparent diffusion coefficients, a fast and a slow diffusional mode, are observed for the hematite particles in high-molecular-weight sodium polyacrylate solution at pH 10.5. The slow diffusion coefficient (Dslow) shows a decrease with increase in polyelectrolyte concentration. The fast diffusion coefficient (Dfast) shows an increase to a maximum with increasing polyelectrolyte concentration and then a rapid decrease as the polyelectrolyte concentration increases further. With an increase in ionic strength from 10(-4) to 0.1 M NaNO3, the maximum value of Dfast increased in magnitude, while the polyacrylate concentration at which the maximum occurs is seen to increase. The dependence of Dfast on the measurement angle indicates that it is coupled to the fluctuations of the chains. The observed behavior is attributed to the hematite probe particle sensing both macroscopic (viscous) and elastic fluctuations associated with the polyelectrolyte motion.     

Adsorption of poly(vinyl formamide-co-vinyl amine) onto silica particle surfaces and stability of the formed hybrid materials

In order to produce silica/polyelectrolyte hybrid materials the adsorption of the polyelectrolyte poly(vinyl formamide-co-vinyl amine), P(VFA-co-VAm) was investigated. The adsorption of the P(VFA-co-VAm) from an aqueous solution onto silica surface is strongly influenced by the pH value and ionic strength of the aqueous solution, as well as the concentration of polyelectrolyte. The adsorption of the positively charged P(VFA-co-VAm) molecules on the negatively charged silica particles offers a way to control the surface charge properties of the formed hybrid material. Changes in surface charges during the polyelectrolyte adsorption were studied by potentiometric titration and electrokinetic measurements. X-ray photoelectron spectroscopy (XPS) was employed to obtain information about the amount of the adsorbed polyelectrolyte and its chemical structure. The stability of the adsorbed P(VFA-co-VAm) was investigated by extraction experiments and streaming potential measurements. It was shown, that polyelectrolyte layer is instable in an acidic environment. At a low pH value a high number of amino groups are protonated that increases the solubility of the polyelectrolyte chains. The solvatation process is able to overcompensate the attractive electrostatic forces fixing the polyelectrolyte molecules on the substrate material surface. Hence, the polyelectrolyte layer partially undergoes dissolving process.     

Morphosynthesis of strontianite nanowires using polyacrylate templates tethered onto self-assembled monolayers

Strontianite nanowires have been synthesized on self-assembled monolayers (SAM) in the presence of polyacrylate templates. The morphology of this product exhibits characteristic differences from that of products obtained in the absence of polyacrylate. It is demonstrated that the template-induced crystallization process involves the interaction between the SAM surface, polyacrylate (a dissolved polyelectrolyte), and the cations/anions in solution. By the combination of these components, hierarchically ordered mineral hybrid structures are formed.     

Colloidal micro- and nano-particles as templates for polyelectrolyte multilayer capsules

Colloidal particles play an important role in various areas of material and pharmaceutical sciences, biotechnology, and biomedicine. In this overview we describe micro- and nano-particles used for the preparation of polyelectrolyte multilayer capsules and as drug delivery vehicles. An essential feature of polyelectrolyte multilayer capsule preparations is the ability to adsorb polymeric layers onto colloidal particles or templates followed by dissolution of these templates. The choice of the template is determined by various physico-chemical conditions: solvent needed for dissolution, porosity, aggregation tendency, as well as release of materials from capsules. Historically, the first templates were based on melamine formaldehyde, later evolving towards more elaborate materials such as silica and calcium carbonate. Their advantages and disadvantages are discussed here in comparison to non-particulate templates such as red blood cells. Further steps in this area include development of anisotropic particles, which themselves can serve as delivery carriers. We provide insights into application of particles as drug delivery carriers in comparison to microcapsules templated on them.     

Hard versus soft particle electrokinetics of silica colloids

To verify the existence of a gel layer at the surface of silica, dependences of the electrophoretic mobility of fresh and aged colloidal silica particles on the KCl concentration are measured. These dependences, corrected for the relaxation/polarization effect, are fitted by analytical expressions based on the model of hard, soft, and brush surfaces. A bad fit is obtained for both silicas when its surface is considered ideal (hard). Much better fits are achieved with the invariable soft layer model for the fresh silica but especially for the aged silica whose surface is less charged probably as a result of an extension and/or loosening of the layer. A perfect fit is found for aged silica when applying a trivial model of the soft polyelectrolyte layer combined with the scaling model of polyelectrolyte brushes.     

Polyacrylate/silica nanocomposite materials prepared by sol-gel process

Polyacrylate/silica nanocomposite was prepared by sol-gel process via in situ emulsion polymerization. The influence of the synthetic conditions, such as the ratio of different monomers and the contents of tetraethoxysilane (TEOS), γ-methacryloxypropyltrimethoxysilane (Z-6030), diethanolamine (DAM) and ammonium persulfate (APS) on the physical mechanical properties of polyacrylate/silica nanocomposite was investigated in details. Dynamics Laser Scattering (DLS) indicated that the average diameter of the polyacrylate/silica latex particles (177 nm) was bigger than that of the pure polyacrylate latex particles (105.3 nm), but the ζ potential of polyacrylate/silica was decreased respectively in contrast to that of the polyacrylate. Differential Scanning Calorimeters (DSC) analysis confirmed that the glass transition temperature of polyacrylate/nano-SiO₂ (T_g = −24 °C) was higher than that of polyacrylate (T_g = −36 °C). UV analysis showed that the UV absorbency of polyacrylate/silica was improved evidently in contrast to that of polyacrylate.     

Adsorption of polyelectrolyte-nanoparticle systems on silica: influence of ionic strength

In this work the effect of ionic strength on the adsorption behavior of cationic polyelectrolyte (acrylamide-acrylamidopropyltrimethylammonium chloride) and negatively charged silica particles has been studied by means of ellipsometry. The adsorption of the polyelectrolyte was observed to increase with increasing salt concentration, a behavior typical for polyelectrolytes with a screening-reduced solvency and a nonelectrostatic affinity for the surface. A similar dependence on the ionic strength was observed when studying the electrolyte effect on the nanoparticle adsorption to the preadsorbed polyelectrolyte film, suggesting that the polyelectrolyte surface conformations largely govern the binding capacity of the particles to the surface.     

Matrix polyelectrolyte microcapsules: new system for macromolecule encapsulation

A new approach to fabricate polyelectrolyte microcapsules is based on exploiting porous inorganic microparticles of calcium carbonate. Porous CaCO3 microparticles (4.5-5.0 microns) were synthesized and characterized by scanning electron microscopy and the Brunauer-Emmett-Teller method of nitrogen adsorption/desorption to get a surface area of 8.8 m2/g and an average pore size of 35 nm. These particles were used as templates for polyelectrolyte layer-by-layer assembly of two oppositely charged polyelectrolytes, poly(styrene sulfonate) and poly(allylamine hydrochloride). Calcium carbonate core dissolution resulted in formation ofpolyelectrolyte microcapsules with an internal matrix consisting of a polyelectrolyte complex. Microcapsules with an internal matrix were analyzed by confocal Raman spectroscopy, scanning electron microscopy, force microscopy, and confocal laser-scanning fluorescence microscopy. The structure was found to be dependent on a number of polyelectrolyte adsorption treatments. Capsules have a very high loading capacity for macromolecules, which can be incorporated into the capsules by capturing them from the surrounding medium into the capsules. In this paper, we investigated the loading by dextran and bovine serum albumin as macromolecules. The amount of entrapped macromolecules was determined by two independent methods and found to be up to 15 pg per microcapsule.     

Electric field sensitivity of conducting hydrogels with interpenetrating polymer network structure

In this article, we reported the synthesis, structure and electric field sensitivity of polyacrylate/polyaniline (PAA/PANI) and poly(2-acrylamido-2-methyl propylsulfonic acid-acrylic acid)/polyaniline [P(AMPS-AA)/PANI] conducting hydrogels with an interpenetrating polymer network (IPN) structure. Scanning electron microscope showed that the conducting hydrogels presented porous structures consisting of PANI nanofibers. The results of Fourier-transform infrared and X-ray diffraction revealed that the PANI was in its conductive emeraldine state and partial crystallization. The unique morphology and molecular structure of the conducting hydrogels were expected to show unusual electric field responses. The conducting hydrogels were subjected to an electric field in NaCl solution for bending behaviors. It was demonstrated that the electric field response was improved by increasing aniline dosage, applied voltage and concentration of aqueous NaCl solution. The bending mechanism was attributed to polyelectrolyte hydrogel matrix and emeraldine PANI nanofibers.     

STABILITY MEASUREMENT AND DISPERSION PROCESS OF CaC03 SUSPENSIONS IN SODIUM POLYACRYLATE AQUEOUS SOLUTIONS

To use an automatic sedimentometer for suspension stability measurement, we compared the results given by this technique to other, more conventional, measurements of suspension properties: sediment volume, sedimentation rate, viscosity. The study was conducted with aqueous dispersions of synthetic calcium carbonate in the presence of sodium polyacrylate as a dispersing agent. Besides a very good correlation between all techniques, the combination of measurements gives an analysis of the polymer action process. There is first a step where bulky floes are disintegrated into dense aggregates, then the breaking up of aggregates into fine particles. The limit between both steps is sharply defined at a polymer concentration 830 mg/1.     

The effect of polymer adsorption on the wetting properties of partially hydrophobized magnetite

Upon reverse flotation of iron ore, the surface of the iron ore concentrate may become partially hydrophobized due to adsorption of flotation collector, which is facilitated by the calcium ions present in the process water. Hydrophobic areas on the concentrate surface may introduce problems in subsequent pelletization of the concentrate. A possible way to restore the wettability of the surface could be by modifying the surface with a hydrophilic polymer. The effect of hydrophilic polymers of different types, viz. cationic, anionic, and non-ionic, on the wettability of the magnetite surface after adsorption of a surfactant was investigated. Although all the polymers could adsorb on magnetite at pH 8.5, the contact angle measurements revealed that only anionic ammonium polyacrylate could decrease the contact angle of synthetic magnetite after surfactant adsorption to a level close to that of as-synthesized magnetite. Such effect was probably achieved due to shielding of the hydrophobic surfactant chains from the aqueous phase by hydrophilic polyacrylate molecules. The fact that polyacrylate adsorption on magnetite occurred via calcium ions makes polyacrylate suitable for application in calcium-rich process water. The results presented in this work illustrate that ammonium polyacrylate could be successfully used to improve the wettability of magnetite after adsorption of surfactants.     

Neutral hydrophilic coatings for capillary electrophoresis prepared by controlled radical polymerization

In the present study, porous silica particles as well as impervious fused-silica wafers and capillary tubes were modified with hydrophilic polymers (hydroxylated polyacrylamides and polyacrylates), using a surface-confined grafting procedure based on atom transfer radical polymerization (ATRP) which was also surface-initiated from α-bromoisobutyryl groups. Initiator immobilization was achieved by hydrosilylation of allyl alcohol on hydride silica followed by esterification of the resulting propanol-bonded surface with α-bromoisobutyryl bromide. Elemental analysis, IR and NMR spectroscopies on silica micro-particles, atomic force microscopy, ellipsometry and profilometry on fused-silica wafers, as well as CE on fused-silica tubes were used to characterize the chemically modified silica substrate at different stages. We studied the effect of monomer concentration as well as cross-linker on the ability of the polymer film to reduce electroosmosis and to prevent protein adsorption (i. e., its non-fouling capabilities) and found that the former was rather insensitive to both parameters. Surface deactivation towards adsorption was somewhat more susceptible to monomer concentration and appeared also to be favored by a low concentration of the cross-linker. The results show that hydrophilic polyacrylamide and polyacrylate coatings of controlled thickness can be prepared by ATRP under very mild polymerization conditions (aqueous solvent, room temperature and short reaction times) and that the coated capillary tubes exhibit high efficiencies for protein separations (0.3–0.6 million theoretical plates per meter) as well as long-term hydrolytic stability under the inherently harsh conditions of capillary isoelectric focusing. Additionally, there was no adsorption of lysozyme on the coated surface as indicated by a complete recovery of the basic enzyme. Furthermore, since polymerization is confined to the inner capillary surface, simple precautions (e.g., solution filtration) during the surface modification process are sufficient to prevent capillary clogging.     

Layered polyelectrolyte-silica coating for nanocapsules

This paper demonstrates the ability to grow silica directly on a deposited surface of polyelectrolyte. Using this strategy, we describe the deposition of layered polyelectrolyte-silica coating on negatively charged surfaces of polystyrene particles and latex nanocapsules, which could not be coated directly with silica alone. By etching away the underlying polystyrene bead, we were able to form polyelectrolyte-silica capsules that were mechanically robust. Using scanning and transmission electron microscopy, we imaged and studied the coating after the deposition of each layer of polyelectrolyte and silica. We then applied this new coating to latex nanocapsules that were loaded with fluorescein molecules. We found that the coating procedure did not cause the loaded molecules to leak out from the capsules, and we determined that the variation in the number of loaded molecules among capsules arose from differences in the volume of the nanocavities and was not caused by the loading and coating of the capsules. This layered architecture permits the thickness of the coating to be controlled in principle over a wide dynamic range, but more importantly, this coating could act as an effective seal to prevent undesired leakage from nanocapsules and thus increase the long-term storability of loaded capsules. Over a 30-day period, we determined that leakage from uncoated capsules was significant but negligible for ones that were coated with two layers of polyelectrolyte-silica. Using single-pulse UV photolysis of individual nanocapsules, we demonstrate that the molecules contained within coated capsules could be released effectively and on demand with a single laser pulse.