Polyelectrolyte Cross-linking Research Articles

Sustainable Electrochemical Mechanical Polishing (ECMP) for 4H-SiC wafer using chemical-free polishing slurry with hydrocarbon-based solid polymer electrolyte

Large-diameter single-crystal silicon carbide (SiC) wafers with good surface quality are desirable to dramatically improve the performance of SiC-based power electronic devices. However, the preparation of such wafers using a strong oxidative polishing slurry has the limitations of low material removal rate (MRR) and high environmental impact. Electrochemical–mechanical polishing (ECMP) initiates surface removal by electrochemical oxidation without using harsh chemicals, making it an alternative with low environmental impact to conventional polishing. Herein, we propose the use of polystyrene sulfonic acid (PSS), a hydrocarbon-based polymer electrolyte without perfluoro compounds, for ECMP. The SiC surface was effectively oxidized by ECMP using PSS. The effects of the polyelectrolyte crosslinking treatment on the lifetime of polyelectrolyte-incorporated nonwoven cloths were investigated. The optimum electrolytic and mechanical conditions yielded high MRRs of 37 and 14 µm/h for 2- and 4-inch SiC wafers. Moreover, the surface morphologies of the growth face and nonfacet areas was discussed. The wafer-scale evaluation demonstrated the roughness reduction to 0.85 nm Sa (average) after 15-min ECMP of the 4-inch wafer. The polishing-induced residual stress was investigated using microscale and wafer-scale Raman mapping. Overall, the proposed ECMP process offers significant advantages in terms of speed, cost-effectiveness, and environmental impact.

Structural characterization and stability of microencapsulated flavonoids from Lycium barbarum L. leaves

Lycium barbarum L. leaves are rich in flavonoids, which have been proven to show poor stability and solubility in the external and gastrointestinal environment. To improve the stability and water-solubility of Lycium barbarum L. leaves flavonoids (LBLF), sodium alginate (SA) and chitosan (CS) were utilized as the wall materials to prepare the microcapsules of LBLF (M-LBLF) by polyelectrolyte cross-linking method. The spectrum of Fourier Transform Infrared spectroscopy (FT-IR) showed M-LBLF had an absorption peak at 1735 cm-1, which might be the electrostatic interaction between the positive and negative charges of SA and CS. X-ray diffraction (XRD) spectrum showed the diffraction peak at 2θ = 51.8° was due to the microencapsulation and transformation of the amorphous structural part into a crystalline state. As demonstrated by Differential Scanning Calorimetry (DSC), the M-LBLF displayed wider and higher endothermic peaks due to the electrostatic interaction between SA and CS. The release of main monomers from M-LBLF in different stages of the in vitro digestion were detected, and it was shown that M-LBLF could resist the digestion in simulated oral fluid (SOF) and gastric fluid (SGF), and enhance the slow-release ability of LBLF in simulated intestinal fluid (SIF), indicating that microencapsulation can improve the stability of LBLF and play a slow-release role.

All-aqueous emulsions as miniaturized chemical reactors in the food and bioprocess technology

All-aqueous emulsions are conventionally formed at bulk scale by mild shaking of aqueous two-phase systems. They can be used to carry out reactions both in droplets (compartmentalized) and on droplet surfaces in conditions free of synthetic surfactants and organic solvents. The use of all-aqueous emulsions for extractive bioconversion is a routine application; however, these emulsions hold many more promises. A renowned, rapidly evolving application is bio-microgel synthesis through biopolymer crosslinking within the emulsion internal phase. When polyelectrolyte crosslinking is achieved at the interface rather than in droplets, microcapsules can be formed, and when in situ colloidal particle generation at the droplet surface is obtained, colloidosomes are produced. The use of microfluidics to control the formation of all-aqueous emulsions offers many advantages in reactions monitoring and partitioning of reactants.

Effect of Multivalent Ions on Ionic Crosslinking of Polyelectrolytes Adsorbed on Particle

Effect of Multivalent Ions on Ionic Crosslinking of Polyelectrolytes Adsorbed on Particle

Reversible Control Method for Particle Dispersion and Flocculation using Ionic Crosslinking of Polyelectrolytes

Reversible Control Method for Particle Dispersion and Flocculation using Ionic Crosslinking of Polyelectrolytes

Preparation and Characterization of Chitosan/Alginate Polyelectrolyte Complex Prepared by Using Calcium Tripolyphosphate Ionic Gelator

The formation of polyelectrolyte complexes (PECs) between chitosan and alginate has been widely investigated for many pharmaceutical and biomedical uses. Ionotropic gelation resulted from the crosslinking of polyelectrolytes (PEs) in the presence of ionic crosslinkers to form hydrogels. The most widely used ionic crosslinker for chitosan is sodium tripolyphosphate (NaTPP); and Ca2+ ions for alginates. The use of these cross-linkers to prepare PECs of chitosan and alginates resulted in hydrogels of similar moieties: chitosan-chitosan and alginate-alginate rather than the sought for hybrid chitosan-alginate PECs. Calcium tripolyphosphate (CaTPP) is a single molecule ionic gelator of chitosan and alginate that have the capability of producing the true hybrid compound of chitosan/alginate polyelectrolyte complex. This paper reported the synthesis of calcium tripolyphosphate and the preparation of a hybrid chitosan/alginate PECs using this newly identified ionic gelator. The newly-synthesized ionic gelator was characterized using ICP-OES; the PECs thereof prepared were characterized using TGA and SEM. The degradation temperature of the prepared PECs is higher than the degradation temperatures of the individual chitosan and alginates. SEM image of the prepared PECs showed rougher surfaces compared to the images of the individual chitosan and alginate compound. Both TGA and SEM revealed the possibility of the newly prepared material to be of the PECs sought for.

Prolonged release of TGF-β from polyelectrolyte nanoparticle loaded macroporous chitin-poly(caprolactone) scaffold for chondrogenesis

Cartilage degeneration occurs when the catabolic factors overtakes the anabolic factors. The regeneration capability of damaged cartilage is poor due to its hypovascular and hypocellular tissue. Tissue engineering strategies aims in development of a suitable substrate that provide the required physical, chemical and biological cues to the proliferating cells to direct chondrogenesis. A macroporous polymeric blend scaffold of chitin and poly(caprolactone) (PCL) was fabricated by lyophilisation technique and characterized using Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric/Differential thermal Analysis (TG/DTA). The effect of prolonged release of Transforming growth factor-β (TGF-β) was studied by encapsulating it in chondroitin sulphate nanoparticles (nCS) incorporated in chitin-PCL scaffold. Chondroitin sulphate nanoparticles containing TGF-β (TGF-β-nCS) was developed by polyelectrolyte crosslinking using chitosan. Characterization of TGF-β-nCS by Dynamic Light Scattering particle sizer and SEM showed a 230±20nm sized spherical particles. Swelling and degradation studies of the composite scaffold showed its stability. Protein adsorption was enhanced in nanoparticle containing scaffold. The effect of TGF-β was well addressed by the increased attachment and proliferation of rabbit adipose derived mesenchymal stem cells (rASCs). The chondrogenic potential of rASCs in the presence of TGF-β releasing composite scaffold showed an increased proteoglycan deposition. These studies highlight the positive effects of chitin-PCL-TGF-β-nCS scaffold for cartilage regeneration.

Diffusion of Oligonucleotides from within Iron-Cross-Linked, Polyelectrolyte-Modified Alginate Beads: A Model System for Drug Release.

An analytical model to describe diffusion of oligonucleotides from stable hydrogel beads is developed and experimentally verified. The synthesized alginate beads are Fe(3+) -cross-linked and polyelectrolyte-doped for uniformity and stability at physiological pH. Data on diffusion of oligonucleotides from inside the beads provide physical insights into the volume nature of the immobilization of a fraction of oligonucleotides due to polyelectrolyte cross-linking, that is, the absence of a surface-layer barrier in this case. Furthermore, the results suggest a new simple approach to measuring the diffusion coefficient of mobile oligonucleotide molecules inside hydrogels. The considered alginate beads provide a model for a well-defined component in drug-release systems and for the oligonucleotide-release transduction steps in drug-delivering and biocomputing applications. This is illustrated by destabilizing the beads with citrate, which induces full oligonucleotide release with nondiffusional kinetics.

Dual layer composite nanofiltration hollow fiber membranes for low-pressure water softening

Nanofiltration (NF) membrane process has become increasingly attractive due to their unique characteristics to selectively remove specific compounds or ions. The most commonly NF membranes are negatively charged which is unsuitable for hardness removal. Therefore, the development of novel NF membranes with a positively charged skin has become a key issue for low pressure water softening.In this study, dual layer microporous hollow fiber membranes were fabricated using Torlon poly(amide-imide) (PAI) as the material of the selective outer layer and polyethersulfone (PES) as the material of the porous support inner layer. A positively charged NF-like selective layer was developed by a simple polyelectrolyte cross-linking using polyallylamine (PAAm). The newly developed (PAI–PAAm)–PES dual layer hollow fiber membranes show a salt water permeability of 15.8 L/m2 h bar and high Mg2+ and Ca2+ rejections of 94.2% and 92.3%, respectively, at operating pressure of 2 bar using a 3000 ppm TDS feed solution. This study provides a simple and effective approach to produce positively charged NF hollow fiber membranes for water softening applications with low energy consumption.

Support materials for yeast immobilization affect the concentration of metal ions in the fermentation medium

Hydrogels are potential absorbers of ions present in the medium, but they can also release some cations (e.g. calcium in calcium alginates). Polyelectrolytes such as alginic acid and poly(acrylic acid) strongly bind polyvalent metal ions. In this paper, the impact of some materials used for the immobilization of yeast, in particular the concentration of certain ions, especially those that play a significant role in the process of fermentation such as calcium, magnesium, zinc and manganese, was assessed. The support for the immobilization of yeast (calcium alginate and polyacrylate) significantly affected the concentration of metal ions in a model solution. Calcium alginate decreased the concentration of Mg2+, Zn2+ and Mn2+ in the solution by about 10–25%, and greatly increased the Ca2+ concentration. Polyacrylate, while swelling, decreased the concentration of cations present by up to 50%. Based on the results in this work, no supplementation of wort with divalent metal salts is advised, since it may lead to a stronger cross-linking of polyelectrolytes used, and consequently result in a slower fermentation. Similarly, the relatively high concentration of calcium ions, caused by ion exchange, did not appear to affect the fermentation process. Copyright © 2013 The Institute of Brewing & Distilling

Chemical Control of Yeast Cell Division by Cross‐Linked Shells of Catechol‐Grafted Polyelectrolyte Multilayers

The chemical control of cell division has attracted much attention in the areas of single cell-based biology and high-throughput screening platforms. A mussel-inspired cytocompatible encapsulation method for achieving a "cell-division control" with cross-linked layer-by-layer (LbL) shells is developed. Catechol-grafted polyethyleneimine and hyaluronic acid are chosen as polyelectrolytes for the LbL process, and the cross-linking of polyelectrolytes is performed at pH 8.5. Cell division is controlled by the number of the LbL nanolayers and cross-linking reaction. We also suggest a new measuring unit, t-2.0 OD 600, for quantifying "cell-division timing" based on microbial growth kinetics.

Nanoemulsions coated with alginate/chitosan as oral insulin delivery systems: preparation, characterization, and hypoglycemic effect in rats

This study aimed to prepare nanoemulsions coated with alginate/chitosan for oral insulin delivery. Uncoated nanoemulsions were prepared by homogenization of a water in oil in water (w/o/w) multiple emulsion that was composed of Labrafac® CC, phospholipid, Span™ 80 and Cremorphor® EL. Coating of the nanoemulsions was achieved based on polyelectrolyte cross-linking, with sequential addition of calcium chloride and chitosan to the bulk nanoemulsion dispersion that contained alginate. The particle size of the coated nanoemulsions was about 488 nm and the insulin entrapment ratio was 47.3%. Circular dichroism spectroscopy proved conformational stability of insulin against the preparative stress. In vitro leakage study indicated well-preserved integrity of the nanoemulsions in simulated gastric juices. Hypoglycemic effects were observed in both normal and diabetic rats. The relative pharmacological bioavailability of the coated nanoemulsion with 25 and 50 IU/kg insulin were 8.42% and 5.72% in normal rats and 8.19% and 7.84% in diabetic rats, respectively. Moreover, there were significantly prolonged hypoglycemic effects after oral administration of the coated nanoemulsions compared with subcutaneous (sc) insulin. In conclusion, the nanoemulsion coated with alginate/chitosan was a potential delivery system for oral delivery of polypeptides and proteins.

Fabrication of poly(amide-imide)-polyethersulfone dual layer hollow fiber membranes applied in forward osmosis by combined polyelectrolyte cross-linking and depositions

Delamination-free ultrafiltration (UF) dual layer hollow fibers have been successfully fabricated by dry jet-wet spinning technique. Two different polymers of poly(amide-imide) (PAI) and polyethersulfone (PES) were utilized as the selective layer on the outer side and the porous support layer on the inner side, respectively. The dual layer substrates were subsequently modified to develop a nanofiltration (NF)-like skin on the outer layer by polyethyleneimine (PEI) cross-linking followed by multilayer polyelectrolyte depositions. These membranes were characterized by a series of standard protocols in terms of membrane structure, permeability and salt rejection, and were applied in FO process.Experiments reveal that the dual-layer NF hollow fiber modified by polyelectrolyte cross-linking and depositions can achieve pure water permeability of 4.1l/m2.h.bar and a high rejection to MgCl2 up to 97%. In FO process, the dual-layer hollow fibers exhibited a water flux of 39 and 21lm−2h−1 in the orientations of active layer facing draw solution and feed water, respectively, by using 0.5M MgCl2 as draw solution and de-ionized (DI) water as feed at room temperature. It suggests that the combined treatment of polyelectrolyte cross-linking and deposition is an effective way to form a NF-like selective layer for FO dual-layer hollow fiber membranes.

The radiation crosslinking of polyelectrolytes based on polyacrylamide

The radiation crosslinking of polyelectrolytes based on polyacrylamide