PAA Concentration Research Articles

Continuous, size and shape-control synthesis of hollow silica nanoparticles enabled by a microreactor-assisted rapid mixing process

Hollow silica nanoparticles (HSNPs) were synthesized using a microreactor-assisted system with a hydrodynamic focusing micromixer. Due to the fast mixing of each precursor in the system, the poly(acrylic acid) (PAA) thermodynamic-locked (TML) conformations were protected from their random aggregations by the immediately initiated growth of silica shells. When altering the mixing time through varying flow rates and flow rate ratios, the different degrees of the aggregation of PAA TML conformations were observed. The globular and necklace-like TML conformations were successfully captured by modifying the PAA concentration at the optimized mixing condition. Uniform HSNPs with an average diameter ∼30 nm were produced from this system. COMSOL numerical models was established to investigate the flow and concentration profiles, and their effects on the formation of PAA templates. Finally, the quality and utility of these uniform HSNPs were demonstrated by the fabrication of antireflective thin films on monocrystalline photovoltaic cells which showed a 3.8% increase in power conversion efficiency.

Radiation-induced synthesis of poly(acrylic acid) nanogels

Nanogel is a two-component system of a diameter in the range of tens of nanometers, consisting of an intramolecularly crosslinked polymer chain and solvent, typically water, filling the space between segments of the macromolecule. Microgels are bigger than nanogels and their size range is between 100nm to 100µm. One of the methods used for synthesizing nanogels is linking the segments of a single macromolecule with the use of ionizing radiation, by intramolecular recombination of radiation-generated polymer radicals. The main advantage of this technique is absence of monomers, catalysts, surfactants or crosslinking agents. This method is an interesting alternative way of synthesizing polymeric carriers for biomedical applications.The aim of the study was radiation synthesis and characterization of poly(acrylic acid) – PAA – nanogels and microgels. The physico-chemical properties were described by determination of weight-average molecular weight and dimensions (radius of gyration, hydrodynamic radius) of the nanogels and microgels. Influence of polymer concentration and dose on these parameters was analyzed. Adjusting the PAA concentration and absorbed dose, one can control the molecular weight and dimensions of nanogels. The solutions of PAA were irradiated with two sources of ionizing radiation: γ-source and electron accelerator. The former method yields mainly microgels due to prevailing intermolecular crosslinking, while the latter promotes intramolecular recombination of PAA-derived radicals and in consequence formation of nanogels. In the future radiation-synthesized PAA nanogels, after functionalization, will be tested as carriers for delivering radionuclides to the tumor cells.

Self-Assembly and Shape Control of Hybrid Nanocarriers Based on Calcium Carbonate and Carbon Nanodots

We describe a platform for the synthesis of functional hybrid nanoparticles in the submicrometer range with tailorable anisotropic morphology. Fluorescent carbon dots (CDs) and poly(acrylic acid) (PAA) are used to modify the crystallization and assembly of calcium carbonate (CaCO3). Carboxylic groups on CDs sequester calcium ions and serve as templates for CaCO3 precipitation when carbonate is added. This creates primary CaCO3 nanoparticles, 7 nm in diameter, which self-assemble into spheres or rods depending on the PAA concentration. At increasing polymer concentration, oriented assembly becomes more prevalent yielding rod-like particles. The hybrid particles show colloidal stability in cell medium and absence of cytotoxicity as well as a loading efficiency of around 30% for Rhodamine B with pH-controlled release. Given the morphological control, simplicity of synthesis, and efficient loading capabilities the CD-CaCO3 system could serve as a novel platform for advanced drug carrier systems.

Salicylic acid-based pH-sensitive hydrogels as potential oral insulin delivery systems

Salicylic acid (SA)-based physically crosslinked pH-sensitive hydrogels were developed for oral insulin delivery using various ratios of salicylate-based poly(anhydride-ester) and poly(acrylic acid) (PAA). Pore size, swelling behavior, insulin loading, insulin and SA release rates of the gels were varied by changing PAA concentration. About 50% of insulin was incorporated within all of the hydrogels, with about 4–8% of insulin released in acidic conditions (pH 1.2) over 2 h. In pH simulating the intestine (pH 6.8), 90% of the insulin and 70% of SA were released within 24 h from the hydrogel system. These results suggest that hydrogels enable pH-dependent protein delivery and can be used for oral insulin and SA delivery to benefit diabetes patients.

The influence of poly(acrylic acid) on micellization and gelation characteristics of aqueous Pluronic F127 copolymer system

The influence of anionic homopolymer poly(acrylic acid) (PAA) of low (1800 g/mol) and high (450,000 g/mol) molecular weights on the micellization and gelation characteristics of aqueous Pluronic F127 (EO97PO69EO97) triblock copolymer (with EO = ethylene oxide and PO = propylene oxide) was studied using differential scanning calorimetry, dynamic light scattering, spectrophotometry, tube inversion technique, and rheometry. It is found that the addition of PAA decreases the critical micellization temperature (CMT) of F127 due to their association via hydrogen bonding. This association becomes stronger at temperatures ≥CMT, arising from the increased affinity between the PO units and PAA. F127-PAA complexation results in lesser PO dehydration and smaller micellization enthalpy (∆H). With increasing PAA concentration, this effect becomes stronger and more F127 bound on PAA is present in the sample, eventually leading to vanishing ΔH. In the presence of PAA, gel region of F127 decreases with increasing PAA concentration due to the order disrupting effect of PAA on the arrangement of packed micelles. Both the micellization and gelation processes of F127 in the presence of PAA are thermoreversible. The PAA effects on both processes become considerably weak at high pH.

Development of Biomimetic Scaffolds with Both Intrafibrillar and Extrafibrillar Mineralization.

Bone is an organic-inorganic hierarchical biocomposite. Its basic building block is mineralized collagen fibers with both intrafibrillar and extrafibrillar mineralization, which is believed to be regulated by noncollagenous proteins (NCPs) with polyanionic domains. In this study, collagen fibrils with both intrafibrillar and extrafibrillar mineralization were successfully prepared and the mechanism of biomineralization was proposed. Building on this success, a unique biomimetic lamellar scaffold composed of collagen fibrils with both intrafibrillar and extrafibrillar mineralization was fabricated using a combination of self-compression and unidirectional freeze-drying approach. To achieve intrafibrillar mineralization, we used poly(acrylic acid) (PAA) to sequester calcium and phosphate ions to form fluidic PAA-amorphous calcium phosphate (PAA-ACP) nanoprecursors. At the presence of sodium tripolyphosphate (TPP), PAA-ACP nanoprecursors were modulated to orderly deposit within the gap zone of collagen fibrils. The effect of PAA concentration on the intrafibrillar and extrafibrillar mineralization of reconstituted collagen fibrils was investigated. It was found that with the decrease in PAA concentration, the inhibitory effect of PAA on mineralization and the stability of ACP nanoprecursors decreased. As a result, more minerals were deposited both within and on the surface of the collagen fibrils. Moreover, with the ability to reproduce biomineralization of collagen fibrils, it allowed us to fabricate biomimetic hierarchical collagen/hydroxyapatite scaffolds composed of both intrafibrillar and extrafibrillar minerals using a bottom-up approach. This technique renders a promising biomimetic scaffold, which will be suitable for bone repair and regeneration.

Flower like micellar assemblies in poly(styrene)-block-poly(4-vinyl pyridine)/poly(acrylic acid) complexes

The formation of rare flower like micelles in poly(styrene)-block-poly(4-vinyl pyridine)/poly(acrylic acid) (PS-b-P4VP/PAA) diblock copolymer/homopolymer complexes is reported. The self-assembly as well as the morphological changes in the complexes were induced by the addition of a high molecular weight PAA/ethanol solution into the PS-b-P4VP solution in dimethyl formamide followed by dialyses. The composition-dependent micelles were varying in size and shape with increase in PAA concentration in solution. The complex aggregates in solution were characterized by dynamic light scattering (DLS) whereas morphologies in the solid complexes were observed using transmission electron microscopy (TEM). Flower like micelles are formed in complexes at 20wt% PAA concentration followed by ‘spikey’ micellar assemblies at 40wt% PAA. The size of the micelles was found to be increased upon the addition of PAA into the block copolymer solution. Infrared studies revealed the intermolecular hydrogen bonding interactions between the complementary binding sites on PAA and the P4VP block of the block copolymer. Finally, a model was proposed to explain the self-assembly and morphological transitions in these complexes based on the experimental results obtained.

Removal of heavy metals from aqueous solution by polyacrylic acid enhanced ultrafiltration

One of the recently developed water treatment processes is the polyelectrolyte-enhanced ultrafiltration (PEUF). This technique combines a membrane filtration process (ultratfiltration) and a cation–polyectrolyte complexation technique. PEUF is shown to be an efficient technology for the removal of heavy metals from liquid effluents even at low concentrations. In this proposal, the removal of three heavy metals (cadmium, copper and zinc) from aqueous solutions by PEUF process was investigated. The poly(acrylic acid) (PAA) with an average molecular weight 100 kDa was used as complexing agent. The ultrafiltration experiments were performed using a tangential cell system equipped with a polyethersulphone membrane having a 10.000 molecular weight cut-off (MWCO). To improve the retention of the heavy metal ions, the effect of some operating parameters and solution characteristics were studied. For different PAA concentrations, this study showed that all permeate fluxes increased linearly by increasing transmembrane pressure. For the three studied metals, the best retentions were observed at 2 × 10–3 mol L–1 PAA concentration, 3 bar transmembrane pressure and pH above 5. The removal of cadmium, copper and zinc exceeded, respectively, 80, 93 and 70%.

Retention of samarium ions from aqueous solutions by poly(acrylic acid)-enhanced ultrafiltration

Rare earth elements (REE) are widely used in variety of commercial applications, which results in public exposure to them, and it is a matter of concern. Recent studies have demonstrated that the toxicity of (REE) as a group is similar to the toxicity of heavy metals. Many methods were used to remove lanthanides from wastewaters generated from their commercial use. Samarium, a REE, which may be removed from the aqueous solution by polyelectrolyte-enhanced ultrafiltration process, was investigated using poly(acrylic acid) (PAA) with average molecular weight 100,000 Da. The ultrafiltration studies were carried out using a tangential cell system. Polyethersulfone membrane with molecular weight cutoff of 5,000 Da and an effective filtration area of 50 cm2 were used (PES-5). Several parameters, such as transmembrane pressure, PAA concentrations, and pH, have been optimized to improve the retention of the Sm(III) ions. Results shows that the permeate flux increases linearly with increasing transmembrane pressure. It can be seen that with the increase in the concentration of PAA, the Sm(III) ions retention also increases until reaching 80%. A better retention was observed at 2 × 10−4 mol L−1 PAA concentration and 3 bar transmembrane pressure. The pH effect study on samarium ions revealed a maximum retention around 70% for pH 5.

Freshwater dispersion stability of PAA-stabilised cerium oxide nanoparticles and toxicity towards Pseudokirchneriella subcapitata

An aqueous dispersion of poly (acrylic acid)-stabilised cerium oxide (CeO2) nanoparticles (PAA-CeO2) was evaluated for its stability in a range of freshwater ecotoxicity media (MHRW, TG 201 and M7), with and without natural organic matter (NOM). In a 15day dispersion stability study, PAA-CeO2 did not undergo significant aggregation in any media type. Zeta potential varied between media types and was influenced by PAA-CeO2 concentration, but remained constant over 15days. NOM had no influence on PAA-CeO2 aggregation or zeta potential. The ecotoxicity of the PAA-CeO2 dispersion was investigated in 72h algal growth inhibition tests using the freshwater microalgae Pseudokirchneriella subcapitata. PAA-CeO2 EC50 values for growth inhibition (GI; 0.024mg/L) were 2–3 orders of magnitude lower than pristine CeO2 EC50 values reported in the literature. The concentration of dissolved cerium (Ce3+/Ce4+) in PAA-CeO2 exposure suspensions was very low, ranging between 0.5 and 5.6μg/L. Free PAA concentration in the exposure solutions (0.0096–0.0384mg/L) was significantly lower than the EC10 growth inhibition (47.7mg/L) value of pure PAA, indicating that free PAA did not contribute to the observed toxicity. Elemental analysis indicated that up to 38% of the total Cerium becomes directly associated with the algal cells during the 72h exposure. TOF-SIMS analysis of algal cell wall compounds indicated three different modes of action, including a significant oxidative stress response to PAA-CeO2 exposure. In contrast to pristine CeO2 nanoparticles, which rapidly aggregate in standard ecotoxicity media, PAA-stabilised CeO2 nanoparticles remain dispersed and available to water column species. Interaction of PAA with cell wall components, which could be responsible for the observed biomarker alterations, could not be excluded. This study indicates that the increased dispersion stability of PAA-CeO2 leads to an increase in toxicity compared to pristine non-stabilised forms.

Poly(Acrylic Acid)–Poly(Ethylene Glycol) Nanoparticles Designed for Ophthalmic Drug Delivery

Poly(acrylic acid) (PAA) and poly(ethylene glycol) (PEG), four-arm, amine-terminated particles with nanometer size and spherical shape were obtained by the polymers cross-linking, via activation with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride, in a w/o emulsion. The morphology and surface charge of the final particles are strongly dependent on the molar ratio of PAA-PEG and the PAA concentration. The physicochemical characteristics correlated with the drug-loading capacity, in vitro and ex vivo release kinetics of pilocarpine hydrochloride and biocompatibility results indicate that these nanoparticles exhibit the prerequisite behavior for use as carriers of ophthalmic drugs.

Polyacrylate-Assisted Size Control of Silver Nanoparticles and Their Catalytic Activity

In this work, a simple one-step method of silver nanoparticle (NPs) preparation with controlled size is introduced. Silver NPs were prepared by reduction of [Ag(NH3)2]+ complex cation by d-maltose in the presence of low concentrations (1 × 10–10 mol/L to 1 × 10–7 mol/L) of high-molecular-weight poly(acrylic acid) (PAA). This modification of the reduction reaction results in managing of the prepared silver nanoparticles’ size in the range from 28 nm (the reaction system without PAA) to 77 nm (system with the highest used PAA concentration). The presence of poly(acrylic acid) influences both nucleation process and also the subsequent stage of nanoparticle growth. The rate of nuclei formation by homogeneous nucleation is affected by PAA due to the formation of the strong complex with silver ions which results in a prolongation of the initiation phase of the reduction process proportionally to PAA concentration. The formation of the adsorption layer of PAA on the surface of the emerging silver nuclei prevents...

Calcium sulfate dihydrate (gypsum) scale inhibition by PAA, PAPEMP, and PAA/PAPEMP blend

The effects of poly(acrylic acid), PAA, polyamino polyether methylene phosphonic acid, PAPEMP, and PAA / PAPEMP blend on calcium sulfate dihydrate (gypsum) are reported in this paper. It has been found that gypsum inhibition by PAA increases with increasing PAA concentration. Among the various phoshonates (i.e., aminotris(methylene phosphonic acid), AMP; hydroxyphosphono acetic acid, HPA; hydroxyethylidene 1,1-diphosphonic acid, HEDP; 2-phosphonobutane 1,2,4-tricarboxylic acid, PBTC; and polyether polyamino phosphonic acid, PAPEP) evaluated, PAPEMP shows the best inhibition for gypsum precipitation. It has also been observed that presence of PAPEMP exhibits synergistic effect on the performance of PAA. Results on calcium ion compatibility of various phosphonates show that PAPEMP compared to other phosphonates tested show higher tolerance to calcium ions.

Depletion Flocculation Induced by Synergistic Effects of Nanoparticles and Polymers

The depletion flocculation of stable suspensions of charged microparticles (1.2 μm diameter polystyrene) by mixtures of silica nanoparticles (7 nm) and poly(acrylic) acid (PAA, Mn = 24 500) was studied. The experiments revealed a very clear critical flocculation concentration of PAA that was lowered by the addition of the silica nanoparticles. Equilibrium pair potentials between the particles, calculated from force profiles measured between a silica particle and plate using colloid probe atomic force microscopy, showed clear a synergistic effect in that the magnitude of the depletion and structural forces produced in the mixed PAA/nanoparticle system was significantly greater than the sum of the forces in systems containing only PAA or only nanoparticles. This effect arises from adsorption of the PAA onto the nanoparticles, creating much larger charged complexes. Comparing the calculated pair potentials to the observed flocculation results revealed that flocculation occurred once the magnitude of the secondary energy well formed by the attractive depletion force exceeded 5 kT.

Copper and Zinc removal from aqueous solutions by polyacrylic acid assisted-ultrafiltration

Copper and Zinc removal from aqueous solution by polyelectrolyte enhanced ultrafiltration (PEUF) process was investigated using poly(acrylic acid) (PAA) with average molecular weight 100kDa. The ultrafiltration studies were carried out using a tangential cell system, equipped with 10,000 MWCO regenerated cellulose. Several parameters have been studied such as: transmembrane pressure, PAA concentration, pH and ionic strength to improve the retention of the metal ions. The removal of Zn2+ and Cu2+ is respectively more than 70% and 93%. A better retention was observed at 2·10−3molL−1 PAA concentration and 3bar transmembrane pressure. The pH effect on the Zinc and Copper recovery revealed a maximum retention around 75% and 97%, respectively, for pH=5. The study of the ionic strength effect has shown a retention decrease with the salt concentration increase. Selectivity was studied using a solution containing the two metal ions. Zinc retention decreases compared to single metal solutions, and this is more significant in the case of Copper ions.

Bio- and bioelectro-catalytic properties of polyaniline/poly(acrylic acid) composite films bearing covalently-immobilized acid phosphatase

Conducting films composed of polyaniline (PANI) and poly(acrylic acid) (PAA) were prepared by electrochemical polymerization of aniline in the presence of various concentrations of PAA. The content of PAA moiety on the surface of the composite films (PANI/PAA films) was estimated by determination of carboxyl groups and found to be controlled by the concentration of PAA in polymerization solution. Acid phosphatase (ACP) was immobilized covalently on the PANI/PAA films by the condensation reaction with the carboxyl groups on the films. It was confirmed that the enzyme activity of the ACP-immobilized PANI/PAA film increased with increasing content of PAA moiety on the surface of the film, accompanying an increase in the amount of the immobilized ACP. The activity of the covalently immobilized ACP was significantly higher than that of the ACP adsorbed on the PANI/PAA film. By use of the ACP-immobilized PANI/PAA film as an enzyme electrode, bioelectrocatalytic oxidation of L-ascorbic acid 2-phosphate (ASA2P) was examined. The enzyme electrode gave the current due to the oxidation of ASA2P in proportion to the content of PAA moiety on the surface of the PANI/PAA film used, which was relevant to the activity of the covalently immobilized ACP.

Preparation of amorphous calcium carbonate nanoparticles from impure dolomitic marble with the aid of poly(acrylic acid) as a stabilizer

Nanomaterials of Precipitated Calcium Carbonate (PCC) such as Amorphous Calcium Carbonate (ACC) nanoparticles are highly demanded industrial products. These products are prepared in industrial scale, using pure CaCO3 natural resources such as pure carbonate rocks, cockle shells, corals, and pearls. Such natural resources could be consumed rapidly due to their excessive use in PCC industries. Therefore, the development of novel procedures to prepare nanoparticles of PCC using impure minerals is desirable. Herein, we report a simple, novel and economical method to synthesize poly(acrylic acid) (PAA) stabilized ACC nanoparticles using extensively distributed impure dolomitic marbles in place of natural pure CaCO3 raw materials. The yields of final ACC products are enhanced using a bubbling column which can produce small bubbles to improve bubbling efficiency. The average particle sizes of final calcium carbonate products are in the range 21–53nm. The best conditions to produce ACC, among the conditions used in the proposed method, are temperature of 40°C, pH of 4.5 and PAA concentration of 10−2M. One or more crystalline phase(s) of PCC is associated with ACC in each product and its nature depends on the conditions used in the synthesis of these products. The unstable vaterite form of PCC is formed when the PAA concentration is less than 0.5M and at lower temperatures such as room temperature. The stability of the vaterite phase decreases when the temperature and the PAA concentration are increased. The synthesized ACC nanoparticles are in required purity and quality to be suitable for industrial applications.

Understanding the molecular basics behind catalyst shaping: Preparation of suspensions of vanadium–aluminum mixed (hydr)oxides

Shaping is often disregarded in catalysis science. Aiming to fill the gap between catalysis in academy and industry, the objective of this work was to systematically study the shaping of vanadium aluminum (hydr)oxides (VAlO) via wet methods. These materials are formulations active in propane ODH and ammoxidation. The physical and chemical stability of suspended VAlO powders was evaluated along with the development of a method to prepare rheologically homogeneous concentrated suspensions of VAlO. Their physical stability was assessed by following changes in relevant properties; namely, their particle size distribution, density, surface area and porosity, and isoelectric point (IEP), by considering the sedimentation of VAlO in aqueous medium, and by evaluating preparation parameters such as: effect and concentration of dispersant, powder content, and sonication time on the rheology of the suspensions. Results showed that due to their physical properties, the preparation of concentrated VAlO suspensions is impracticable without the use of a dispersant, herein poly(acrylic acid) (PAA), that counteracts particle settling. The chemical stability of suspended VAlO powders was determined by preparing diluted suspensions at different pHs and then analyzing the phenomena behind the dissolution of vanadium and aluminum and its correlation with the surface chemistry of the recovered powders. On the basis of the above analysis, appropriate conditions for having physically and chemically stable concentrated VAlO suspensions were established: particularly, pH near the IEP for minimum metal dissolution, VAlO concentration ≤50wt.%, PAA concentration 0.2–0.5wt.%, and sonication time of 1min. Slip casted cylinders of VAlO were obtained using these conditions.

Treating Bloodmeal with Peracetic Acid to Produce a Bioplastic Feedstock

Peracetic acid is used to remove the color and odor from bloodmeal to produce a new bioplastic feedstock. The effects on bloodmeal molecular mass, crystallinity, thermal stability, solubility, product color and smell is investigated. 3 wt% PAA is the lowest concentration to sufficiently remove the odor from bloodmeal. Protein molecular mass is unaffected by PAA concentration. The crystallinity decreases from 35 to 31–27% when treated with 1–5 wt% PAA. Treating bloodmeal with 1–5 wt% PAA also reduces the protein's thermal stability, glass transition temperature (from 225 down to 50 °C) and increases its solubility in PBS, SDS, and sodium sulfite.

Dispersion and Rheology of Aqueous Zirconium Diboride Nanosuspensions

The dispersion and rheology of aqueous ZrB2 nanosuspensions were investigated by zeta potential measurements, particle size measurements, sedimentation tests, and rheology measurements, with poly (acrylic acid) (PAA) as dispersant. Results showed that the dispersion and rheology of nanosized ZrB2 suspensions in aqueous media were dependent on pH value, PAA concentration, solid loading, and ball milling time. Concentrated (up to 30 vol% solid loading) and well‐stabilized aqueous ZrB2 nanosuspension with low viscosity (0.485 Pa s at 60/s) was prepared at pH 10, with 1.0 wt% PAA.