Weight Polyacrylic Acid Research Articles

Bifunctional low molecular weight polyacrylic acid as aqueous binder and coating agent enables high performance LiMn2O4 cathode for lithium-ion batteries

LiMn2O4 is considered to be a promising cathode material for lithium-ion batteries due to its decent energy density, low price and environmental benignity. However, the problems of Mn dissolution, migration and deposition during the cycle, seriously affect its lifespan, especially at high temperature. In this study, we developed a strategy by which we killed two birds with one stone. A low molecular weight polyacrylic acid (PAA) mixed with sodium carboxymethyl cellulose (CMC) is applied as binder and coating agent for cathode particles at the same time. The conventional and environmental unfriendly polyvinylidene difluoride (PVDF)-N-methylpyrrolidone (NMP) system is replaced by the cheap and green aqueous binder with improved adhesive effect. Furthermore, the binder-based surface coating layer not only alleviates the side reaction between the electrolyte and the cathode particles, but also chelates the dissolved Mn2+ by the large amount of carboxyl groups in PAA molecules and so prevents the following migration and deposition of Mn2+. In the button half-cell with low molecular weight PAA based binder, the capacity retention reaches 94.1 % after 1000 cycles at room temperature and 92.0 % after 200 cycles at 60 degrees centigrade. Meanwhile, 18650-type cylindrical cells were prepared with this binder, which shows a great high temperature storage performance. After the cell was held at 60 degrees centigrade for 25 days at full charged state, the internal resistance increased by only 1.25mΩ, the voltage decreased by only 0.1 V, the residual capacity retention and recovery capacity retention reaches 85.6 % and 92.2 %. This work shows the great potential of the aqueous binder in dealing with the problem of Mn dissolution during the cycling of manganese-based cathode materials for lithium-ion batteries.

Mussel-inspired Self-assembly into Polymer Coatings of Different Molecular Weight Electrolytes for Enhanced Self-healing and Corrosion Properties.

Self-healing coatings offer tremendous application prospects in the field of preventing metal corrosion because of their superior functionality. The coordination of barrier performance and self-healing ability, however, continues to be difficult. Herein, a polymer coating based on polyethyleneimine (PEI) and polyacrylic acid (PAA) with self-repairing and barrier ability was designed. Introducing the catechol group into the anti-corrosion coating increases the adhesion and self-healing efficiency of the coating, providing a guarantee for the long-term stable bonding between the anti-corrosion coating and the metal substrate. Small molecular weight PAA polymers are added to polymer coatings to increase their self-healing capabilities and corrosion resistance. Because layer-by-layer assembly creates reversible hydrogen bonds and electrostatic bonds that help the coating repair itself when it is damaged, and because the traction of small molecular weight polyacrylic acid speeds up this process. When polyacrylic acid (PAA) with a molecular weight of 2000 was present in the coating at a concentration of 1.5 mg/mL, the coating's self-healing capability and corrosion resistance were at their peak. The PEI-C/PAA45W -PAA2000 coating completed the self-healing within 10 min, and the corrosion resistance efficiency (Pe ) was as high as 90.1 %. The polarization resistance (Rp ) was maintained at 7.67×104 Ω cm2 after immersion for more than 240 h. It was better than other samples in this work. The polymer provides a new idea for the prevention of metal corrosion.

Upregulation of mitochondrial dynamics is responsible for osteogenic differentiation of mesenchymal stem cells cultured on self-mineralized collagen membranes

Collagen membranes crosslinked with high molecular weight polyacrylic acid (HPAA) are capable of self-mineralization via in situ intrafibrillar mineralization. These HPAA-crosslinked collagen membranes (HCM) have been shown to promote osteogenic differentiation of mesenchymal stem cells (MSCs) and enhance bone regeneration in vivo. Nevertheless, the biological triggers involved in those processes and the associated mechanisms are not known. Here, we identified the contribution of mitochondrial dynamics in HCM-mediated osteogenic differentiation of MSCs. Mitochondriogenesis markers were significantly upregulated when MSCs were cultured on HCM, committing the MSCs to osteogenic differentiation. The mitochondria fused to form an interconnected mitochondrial network in response to the high energy requirements. Mitochondrial fission in MSCs was also triggered by HCM; fission slightly declined at 14 days to restore the equilibrium in mitochondrial dynamics. Mitophagy, another event that regulates mitochondrial dynamics, occurred actively to remove dysfunctioned mitochondria and isolate damaged mitochondria from the rest of network. The mitophagy level of MSCs was significantly elevated in the presence of HCM. Taken together, the present findings indicate that upregulation of mitochondrial dynamics via mitochondriogenesis, fusion, fission and mitophagy is responsible for HCM-mediated osteogenic differentiation of MSCs. Statement of significanceHigh molecular weight polyacrylic acid (HPAA)-crosslinked collagen membrane (HCM) was found to promote in-situ bone regeneration because of it can stimulate osteogenic differentiation of mesenchymal stem cells (MSCs). Nevertheless, the biological triggers involved in those processes and associated mechanisms are not known. This study identifies that activation of mitochondrial dynamics is centrally involved in HCM-mediated osteogenic differentiation of MSCs. The HCM accelerates mitochondriogenesis and regulates homeostasis of the mitochondrial network in response to the increased energy demand for osteogenic differentiation. Concomitantly, mitophagy actively occurs to remove dysfunctioned mitochondria from the rest of the mitochondrial network. Identification of the involvement of mitophagy in HCM-mediated osteogenic differentiation of MSCs opens new vistas in the application of biomimetic mineralization in bone tissue regeneration.

ZnAl hydrotalcites modified with nanocomposites nZVI–PAA for environmental remediation

Diffraction patterns of polyacrylic acid (PAA) encapsulated-(Fe)-modified ZnAl hydrotalcite (ZnAlH) showed the integration of Fe in the H lattice, resulting in a hybrid nanocomposite (Fe-PAA-ZnAlH), which was mainly verified with the characteristic shift in the 59–63° (2θ) region of the ZnAlH (110) reflection plane. The rise in the unit cell parameters (c and a ) as the Fe % incremented, denoted incorporation of Fe in the ZnAlH red. Nonetheless, changes in the immobilizer molecular weight (PAA MW) from 1250 kDa to 5.1 kDa did not cause a difference in the distance between layers (c parameter) but in the cation-cation separation ( a parameter), which meant that the nanoparticle was not located between layers, but in the lattice. The resulting band gap energies of the calcined hybrid nanocomposites were among 1.07–1.21 eV, which is an additional support of Fe +3 integration, suggesting insertion of Fe +3 3d orbitals between the valence and the conduction band of ZnO. Furthermore, nZVI were prepared through a pre-agglomeration reduction method, where COOH-groups were bound to metal cations. Initially, aqueous Fe +2 was bound to PAA [Fe +2 -PAA], then reduced to obtain enclosed hybrid (nZVI-PAA). Less stability and more aggregation were observed with the lower molecular weight PAA. Additionally, PAA dissociation caused by pH changes affected the clustering of the nZVI particles. At higher MW, the hydrodynamic diameter and size distribution become smaller and tighter, respectively, allowing a more monodispersed population with sphere shape and organized in core–shell beads chains.

Matrix stiffening by self-mineralizable guided bone regeneration

Collagen membranes produced in vitro with different degrees of intrafibrillar mineralization are potentially useful for guided bone regeneration (GBR). However, highly-mineralized collagen membranes are brittle and difficult for clinical manipulation. The present study aimed at developing an intrafibrillar self-mineralization strategy for GBR membrane by covalently conjugating high-molecular weight polyacrylic acid (HPAA) on Bio-Gide® membranes (BG). The properties of the self-mineralizable membranes (HBG) and their potential to induce bone regeneration were investigated. The HBG underwent the progressive intrafibrillar mineralization as well as the increase in stiffness after immersed in supersaturated calcium phosphate solution, osteogenic medium, or after being implanted into a murine calvarial bone defect. The HBG promoted in-situ bone regeneration via stimulating osteogenic differentiation of mesenchymal stromal cells (MSCs). Hippo signaling was inhibited when MSCs were cultured on the self-mineralized HBG, and in HBG-promoted MSC osteogenesis during in-situ bone regeneration. This resulted in translocation of the transcription co-activators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) into the nucleus to induce transcription of genes promoting osteogenic differentiation of MSCs. Taken together, these findings indicated that HBG possessed the ability to self-mineralize in situ via intrafibrillar mineralization. The increase in stiffness of the extracellular matrix expedited in-situ bone regeneration by inactivating the Hippo-YAP/TAZ signaling cascade. Statement of significanceGuided bone regeneration (GBR) membranes made of naturally derived collagen have been widely used in the bone defect restoration. However, application of collagen GBR membranes run into the bottleneck with the challenges like insufficient stress strength, relatively poor dimensional stability and unsatisfactory osteoinductivity. This study develops a modified GBR membrane that can undergo progressive self-mineralization and matrix stiffening in situ. Increase in extracellular matrix stiffness provides the mechanical cues required for MSCs differentiation and expedites in-situ bone regeneration by inactivating the Hippo-YAP/TAZ signaling cascade.

Enabling Aqueous Processing for Low/No-Cobalt Lithium-Ion Battery Cathode Active Materials

Industrially, lithium-ion battery cathodes are manufactured through a wet slurry mixing and coating process. There is great interest in replacing the presently-used N-methyl-2-pyrrolidone (NMP) solvent with water due to the cost and toxicity associated with NMP. In this study, the modifications made to the active materials as a result of water exposure were studied and two materials, LiMn2O4 (LMO) and LiNi0.8Co0.15Al0.05O2 (NCA), were assembled in high-performing aqueous-processed cathodes for the first time.Five cathode active materials were the subject of this study: LiCoO2 (LCO), LiFePO4 (LFP), LMO, NCA, and LiNi0.5Mn0.3Co0.2O2 (NMC532). All materials exposed to DI water exhibited rapid increases in pH over the first 10 min, with stable pH values ranging from 9.0 (LFP and LMO) to 12.5 (NCA). Given that the protective aluminum oxide layer on the current collector breaks down at a pH of 8.5, corrosion is predicted for all materials, with NCA being the most extreme case. Pristine samples of the same five materials were submerged in water for 24 h, then the moisture was dried in a vacuum oven. The crystal structures of these materials (henceforth referred to as the wetted samples) were evaluated using X-ray diffraction and compared with pristine samples. No changes were observed in the crystal structure of any material as confirmed by Rietveld refinement. X-ray photoelectron spectroscopy was used to evaluate the changes of the surface composition of each wetted and pristine material.Based on inductively coupled plasma-mass spectrometry results, the amount of Li and transition metal leaching in water was found to be independent of time in excess of 1 h, and the amount of Li leaching in water for NCA was found to be five times that of NMC532 and more than 30 times that of the other materials. As a result, using a traditional aqueous slurry formulation (active material, carbon black, emulsion binder, carboxymethylcellulose thickener) resulted in a severely cracked and unusable NCA cathode. By including high-molecular weight polyacrylic acid (PAA), the adhesion of the cathode was restored. Half coin cells of this PAA-processed and an NMP-processed NCA cathode were constructed using punches with 1.7 mAh·cm-2 areal capacity and a charge and discharge rate of C/3 between 3.0-4.3 V. The initial capacity of the PAA-processed NCA cathode was slightly lower (176.3 mAh·g-1 to 185.2 mAh·g-1), though it did exhibit better capacity retention through 100 cycles (84.2% to 78.1%).

Lithium and transition metal dissolution due to aqueous processing in lithium-ion battery cathode active materials

Enabling aqueous processing for lithium-ion battery cathodes is essential as solvents like N-methyl-2-pyrrolidone (NMP) are expensive, hazardous, and being phased out of usage around the world. Using water as a solvent can reduce electrode manufacturing cost and environmental impact, but it presents unique challenges for cathodes such as Li and transition metal dissolution from the active material and current collector corrosion. In this study, the suitability of aqueous processing for five cathode active materials is evaluated: LiCoO2 (LCO), LiFePO4 (LFP), LiMn2O4 (LMO), LiNi0.80Co0.15Al0.05O2 (NCA), and LiNi0.5Mn0.3Co0.2O2 (NMC532). After three days of water exposure, NCA and NMC532 exhibit significantly greater pH values (11.5–12.5) than the Ni-free materials (9.0–10.5), though all pH values suggest corrosion of the Al substrate would occur. Surface compositions change to various extent while little change is observed in the crystal structures. The transition metal dissolution in water and electrolyte is relatively low for all materials, though the Li dissolution in water is high for NCA (~0.1 mg mL−1). Electrochemical testing in half coin cells reveals that high-molecular weight polyacrylic acid addition is able to modify the pH and provide adequate binding to the current collector to permit aqueous processing of NCA.

Development of potentially biocompatible hydrogels with cylindrical pores prepared from polyvinyl alcohol and low‐molecular weight polyacrylic acid

In the present work, blend hydrogels from PVA and two different low PAA molecular weights, Mw 1800 g/mol and 5000 g/mol were prepared through the freezing thawing (F‐T) physical crosslinking method. The obtained materials were fully characterized by means of scanning electron microscopy (SEM) in order to analyze their morphology, gel fraction (GF) to determine the crosslinking degree and Fourier transformed infrared spectroscopy (FTIR) to analyze the PVA‐PAA interactions. Thermal characterizations [thermogravimetric analysis (TGA) and dynamic scanning calorimetry (DSC)] were conducted to study the relevant thermal characteristics. Sorption tests at different pH values (4 and 7) obtained from different aqueous systems were also inquired. The effects of PAA contents (between 1 and 5 wt%) and Mw of the used PAA on the hydrogel final properties were analyzed and related to the most probably PVA‐PAA interactions. POLYM. ENG. SCI., 59:1479–1488 2019. © 2019 Society of Plastics Engineers

Recyclable nanoscale zerovalent iron (nZVI)-immobilized electrospun nanofiber composites with improved mechanical strength for groundwater remediation

Nanoscale zero-valent iron (nZVI), as a promising material, has been widely used in groundwater remediation. Membrane-supported nZVI can both avoid nZVI agglomeration for better reactivity and recycle nZVI/contaminants to lower the risk of secondary pollution. However, membrane mechanical strength is a critical property for long-term operation and the regeneration of nZVI membranes. This study tried to use a high molecular weight dual-crosslinking method to improve the mechanical strength of polymeric electrospun nanofiber membranes. Specifically, high molecular weight polyacrylic acid (PAA, Mw = 450,000) was dual-crosslinked by adding polyvinyl alcohol (PVA) as covalent cross-linker (named as M450k) and Fe(II) or Fe(III) as the ionic cross-linker (named as M450k-II and M450k-III). The results indicated that the M450k had better thermal resistance against membrane shrinkage, thus having larger surface areas and more –COOH groups to immobilize more nZVI particles. Besides, M450k-III had the highest tensile strength at 8.5 MPa, 5 times the figure for the mono-crosslinked low molecular weight membrane (M2k). In terms of nZVI immobilization and filtration performance, the Fe(II)-crosslinked membrane had better nZVI immobilization with the highest removal capacity at 463 mg/g while Fe(III)-crosslinked membrane had overwhelming mechanical strength with decent and stable removal capacity under multiple nZVI regenerations over 15 filtration cycles. Generally, the high molecular weight Fe(III)-crosslinked PAA-PVA electrospun nZVI showed better potential for long-term filtration process.

Polyacrylic Acid‐Based Coordination Supramolecular Elastomer with High Strength, Excellent Fatigue‐Resistance, and Self‐Recovery Properties

AbstractSupramolecular elastomers have attracted extensive attention due to their excellent mechanical properties. Herein, inspired by the concept of a dual cross‐linked network structure, a dual‐component coordination supramolecular elastomer is prepared via photopolymerization of three monomers combined with zinc ion (Zn2+)‐crosslinked low molecular weight polyacrylic acid (PAA). The covalent network of three monomers serves as a soft component forming the supporting network. The network of Zn2+ crosslinked low molecular weight PAA forms the hard component. The covalent network is crosslinked and locked by the coordinated network. This compact network contributes to improving the comprehensive mechanical properties. The optimal elastomer is that the molar ratio of carboxylic of low molecular weight PAA with Zn2+ is 1:0.5. The tensile and compression stress of the optimal elastomer are 4.08 and 6.90 MPa, respectively. The loading–unloading cycles can reach 1000 times without fracture. The self‐recovery ratios of the tensile and compression modes reaches 80% and 95%, respectively.

Comparative Evaluation of Compressive Strength of Ketac Molar, Fuji IX and Equia Forte

Glass Ionomers have been shown to be a very useful adjunct to restorative dentistry due to their properties such as; biocompatibility with body's hard tissue, long-term fluoride release, low thermal expansion coefficient, good adhesion to moist enamel and dentin without requiring an intermediate agent and low cytotoxicity. Compressive stress results when the body is subjected to two sets of forces in the same straight line but directed toward each other and it is an important property to be considered while choosing a restorative material. FUJI IX and Ketac Molar are two conventional packable high strength glass ionomer cements used to restore teeth in high stress bearing areas. Equia Forte which is a relatively new glass ionomer cement which can be used to restore teeth in high stress bearing areas. It containins ultrafine glass particles and a higher molecular weight Polyacrylic acid. the purpose of the study undertaken was to evaluate and compare the compressive strength of FUJI IX, Ketac Molar and EQUIA FORTE.

Preparation of superparamagnetic and flexible γ-Fe2O3 nanowire arrays in an anodic aluminum oxide template

Superparamagnetic and flexible Fe2O3 nanowire arrays were fabricated by the controlled electrostatic assembly of iron oxide nanoparticles and poly(dimethyldiallylammonium chloride) (PDADMAC) in an anodic aluminum oxide (AAO) template. The micrograph of iron oxide nanowire arrays was characterized by field emission scanning electron microscopy. The magnetic hysteresis loops obtained by a vibrating sample magnetometer confirm that the nanowire arrays have superparamagnetic properties. The filling ratio of iron oxide nanoparticles and polymers in the AAO template was affected by four factors, including the concentration of iron oxide nanoparticles, the pore diameter of the AAO template, the charge ratio of iron oxide nanoparticles and PDADMAC, and the molecular weight of polyacrylic acid. The effect of the AAO template on the diameter and length of the nanowire arrays was also analyzed. In addition, the nanowire arrays were shown to be flexible because of the presence of polymers. These nanowire arrays with superparamagnetic and flexural properties have potential applications in sensor probes.

Rapid biomimetic mineralization of collagen fibrils and combining with human umbilical cord mesenchymal stem cells for bone defects healing

Collagen biomineralization is regulated by complicated interactions between the collagen matrix and non-collagenous extracellular proteins. Here, the use of sodium tripolyphosphate to simulate the templating functional motif of the C-terminal fragment of non-collagenous proteins is reported, and a low molecular weight polyacrylic acid served as a sequestration agent to stabilize amorphous calcium phosphate into nanoprecursors. Self-assembled collagen fibrils served as a fixed template for achieving rapid biomimetic mineralization in vitro. Results demonstrated that, during the mineralization process, intrafibrillar and extrafibrillar hydroxyapatite mineral with collagen fibrils formed and did so via bottom-up nanoparticle assembly based on the non-classical crystallization approach in the presence of these dual biomimetic functional analogues. In vitro human umbilical cord mesenchymal stem cell (hUCMSC) culture found that the mineralized scaffolds have a better cytocompatibility in terms of cell viability, adhesion, proliferation, and differentiation into osteoblasts. A rabbit femoral condyle defect model was established to confirm the ability of the n-HA/collagen scaffolds to facilitate bone regeneration and repair. The images of gross anatomy, MRI, CT and histomorphology taken 6 and 12weeks after surgery showed that the biomimetic mineralized collagen scaffolds with hUCMSCs can promote the healing speed of bone defects in vivo, and both of the scaffolds groups performing better than the bone defect control group. As new bone tissue formed, the scaffolds degraded and were gradually absorbed. All these results demonstrated that both of the scaffolds and cells have better histocompatibility.

White/blue-emitting, water-dispersible CdSe quantum dots prepared by counter ion-induced polymer collapse

The synthesis and characterization of water-dispersible, luminescent CdSe/ZnS semiconductor quantum dots that exhibit nominal “white” fluorescence emission and have potential applications in solid-state lighting is described. The nanomaterials, prepared through counter ion-induced collapse and UV cross-linking of high-molecular weight polyacrylic acid in the presence of appropriate aqueous inorganic ions, were of ∼2–3nm diameter and could be prepared in gram quantities. The quantum dots exhibited strong luminescence emission in two bands, the first in the blue-region (band edge) of the optical spectrum and the second, a broad emission in the red-region (attributed to deep trap states) of the optical spectrum. Because of the relative strength of emission of the band edge and deep trap state luminescence, it was possible to achieve visible white luminescence from the quantum dots in aqueous solution and in dried, solid films. The optical spectroscopic properties of the nanomaterials, including ensemble and single-molecule spectroscopy, was performed, with results compared to other white-emitting quantum dot systems described previously in the literature.

Precipitation of biomimetic fluorhydroxyapatite/polyacrylic acid nanostructures

Ordered structures of fluorhydroxyapatite (FHA) nanoparticles that resemble the nanostructure of natural human enamel have been prepared. Wet precipitation in the presence of polyacrylic acid (PAA) was used, and the particle morphology was altered by varying several reaction conditions. High molecular weight PAA increased particle length from around 54nm to several hundred nanometres, while maintaining particle width at 15nm. PAA concentration and the order of mixing the reactants also influenced crystal morphology. Optimum conditions produced dense, aligned bundles of highly elongated nanorods, which are very similar to the hierarchical nanostructure of human tooth enamel.

Low Cost, Scalable and Selective Electrochemical TSV Fill Technology for 3D IC Interconnects

Physical and economical limitations for 2D scaling (so called “Moore’s Law”) prevents further increase of integration density to improve the performance of integrated circuits (IC). These challenges have stimulated the development of 3D through-silicon via (TSV) technology (so called “More than Moore”) in order to increase the speed and the bandwidth of the devices as well as to decrease the form factor and power consumption of integrated microsystems. However, the implementation of 3D TSV technology is limited by the high cost of 3D TSV fill (due to the use of expensive vapor deposition and chemical-mechanical processes) and its poor scalability (due to low conformality of physical and chemical vapor deposited films) to high TSV aspect ratios and smaller via sizes (to increase I/O). The objective of this investigation is to address the cost and scalability issues in order to enable cost-effective and reliable fill of high aspect ratio 3D TSVs. In this paper, we will review the low temperature and scalable process technology for 3D TSV fill employing the selective electrochemical through-via metal (Ni alloy/Cu or Co alloy/Cu) filling technology which is more economical because it will eliminate expensive chemical-mechanical polishing (CMP) process and replace expensive plasma-enhanced chemical vapor deposition (PE CVD) and physical vapor deposition (PVD) processes with low cost, lower temperature (<100 oC), more scalable (AR > 30:1) selective electrochemical process (LoCoSS process). LoCoSS process technology includes the following major electrochemical process steps: anodic oxidation to form isolation layer, selective electroless barrier deposition and selective electrochemical fill that can be implemented using one LoCoSS electrochemical processing tool instead of four POR processing tools utilizing different technologies – PE CVD isolation, PVD barrier/seed, Electrofill and CMP.The activation of thin continuous electroless barrier films (Ni or Co alloys) with high adhesion on the isolation surface (SiO2) is challenging. To overcome this technical risk, a novel nanoactivation process has been developed with the use of self-assembled monolayers [Si-(CH2)x-NH2-OH] and catalytic functionalized nanoparticles (Pd/Cu). To increase the adhesion of the deposited barrier films, the covalent bonding between substrate and the SAM binding layer has been engineered through the proper choice of the functional groups. Selective activation has been achieved through the mechanical removal of catalysts from the front surface (except inside the TSV’s) and the use of photosensitive TiO2/catalyst process. Besides, robust and defect-free fill of high aspect ratio TSV’s requires the development of electroless Cu superfill process with the use of suppressing additives in the plating solution such as high molecular weight polyacrylic acid (PAA) and polyethylene glycols (PEG). Selective electroless Cu plating into high aspect ratio TSV was successfully demonstrated with complete coverage of electroless barrier layer and low overplating on the field. Copper electroplating from NANO3D suppression-based plating solutions was also used to enable high speed and uniform plating of flat Cu bumps that can be used to interconnect chips in 3D microelectronics systems. LoCoSS technology could accelerate the mass-scale adoption of low cost and scalable TSV technology in semiconductor manufacturing. Implementation of our proprietary LoCoSS process will lower the cost of 3D ICs with the potential to reduce the cost by over 2X and increase scalability by over 3X for volume production. Besides, enabling low cost 3D ICs with our technology will allow heterogeneous system generation for next generation smart phones and other communication devices as well as increase of the bandwidth, memory capacity and decrease of the signal transmission delay within computing chips.

Graphene/silicon nanocomposite anode with enhanced electrochemical stability for lithium-ion battery applications

A graphene/silicon nanocomposite has been synthesized, characterized and tested as anode active material for lithium-ion batteries. A morphologically stable composite has been obtained by dispersing silicon nanoparticles in graphene oxide, previously functionalized with low-molecular weight polyacrylic acid, in eco-friendly, low-cost solvent such as ethylene glycol. The use of functionalized graphene oxide as substrate for the dispersion avoids the aggregation of silicon particles during the synthesis and decreases the detrimental effect of graphene layers re-stacking. Microwave irradiation of the suspension, inducing reduction of graphene oxide, and the following thermal annealing of the solid powder obtained by filtration, yield a graphene/silicon composite material with optimized morphology and properties.Composite anodes, prepared with high-molecular weight polyacrylic acid as green binder, exhibited high and stable reversible capacity values, of the order of 1000 mAh g−1, when cycled using vinylene carbonate as electrolyte additive. After 100 cycles at a current of 500 mA g−1, the anode showed a discharge capacity retention of about 80%. The mechanism of reversible lithium uptake is described in terms of Li–Si alloying/dealloying reaction. Comparison of the impedance responses of cells tested in electrolytes with or without vinylene carbonate confirms the beneficial effects of the additive in stabilizing the composite anode.

Ultra-stable hemoglobin–poly(acrylic acid) conjugates

Stabilization of proteins against thermal deactivation is a major challenge, and a simple, facile, novel chemical approach is described here to overcome this hurdle. We report here, for the first time, the successful synthesis of ultrastable protein nanoparticles consisting of met-hemoglobin (Hb) conjugated with low molecular weight polyacrylic acid (PAA, Mw 8000) to form discrete nanoparticles. Hb–PAA nanoparticles were not deactivated when subjected to prolonged thermal treatment such as steam sterilization conditions (122 °C, 40 minutes, 17–20 psi), while the unprotected Hb lost most of its activity when subjected to the same heating conditions. Several Hb–PAA derivatives which resist thermal inactivation, in a similar manner, are produced and characterized. Interestingly, the highest activity retention, after the above thermal treatment, was ∼100% for the untreated samples. This resistance to heat is attributed to the enhanced thermodynamic stability of the Hb–PAA conjugate and improved re-folding of the denatured state to the native form, facilitated by PAA conjugation to Hb. This is a unique approach to stabilize Hb against thermal inactivation, and it is a major breakthrough in the production of stable Hb-based nanomaterials that can be safely sterilized in an autoclave for biomedical/in vivo applications.

Effect of a low-molecular-weight polyacrylic acid on the coagulation of kaolinite particles

Kaolinite is of very fine particle size in nature and thus its dispersion plays a key role in the successful removal of kaolinite in iron ore flotation and selective flocculation processes. As the most widely used dispersant in the world, sodium silicate has been used as a standard dispersant in iron ore industry. However, in the author's previous work, the actual effect of sodium silicate on the colloid stability of kaolinite particles was found to be weak under the typical conditions of iron ore flotation and selective flocculation. In this work, the dispersive effect of a low molecular weight polyacrylic acid on kaolinite particles was systematically investigated through electrophoretic mobility and colloidal stability studies. The results demonstrate that interactions between polyacrylic acid and kaolinite take place over the entire pH range studied in this work, from pH 5 to 10.5, with stronger interactions observed at neutral and acidic pH. This indicates that polyacrylic acid adsorbs on both positively and negatively charged sites on kaolinite, although the presence of positively charged sites on the clay surfaces at low pH and in CaCl 2 and MgCl 2 solutions at high pH significantly enhances its interactions with kaolinite. The strong dispersive effect of polyacrylic acid on kaolinite in the presence of CaCl 2 and MgCl 2 shows that polyacrylic acid is a promising dispersant for kaolinite under the typical conditions of iron ore flotation and selective flocculation.

Insoluble complex formation between alpha-amylase from Aspergillus oryzae and polyacrylic acid of different molecular weight

The insoluble complex formation between alpha-amylase and the strong anionic polyelectrolyte polyacrylic acid was studied by using turbidimetric and enzymatic activity. The highest molecular weight polyacrylic acid (100,000 Da and 240,000 Da) proved to be suitable precipitating agents. They were insoluble at pH lower than 4–5, with a stoichiometric ratio polymer mol per protein mol of 1:52 and 1:154, respectively. Electrostatic interactions are not the only factor in the formation of insoluble complexes. High percentage of alpha-amylase enzymatic activity maintains throughout time, even in the presence of polyelectrolyte. The application of precipitation conditions found when applying a bovine homogenate showed that it is not suitable for purification even if it proved to be useful methodology for the concentration of the enzyme and can be used as a first step of purification.