Homo- and heteroflocculation of papermaking fines and fillers

The effects of cationic polyethylenimine (PEI) on the colloidal stability of anionic fines (microcrystalline cellulose or thermomechanical fines), fillers (clay) and their mixtures in deionized and tap water were investigated, using a photometric dispersion analyzer. Measurements confirmed that PEI flocculates all used materials by charge neutralization. As expected, higher additions of PEI lead to electrostatic stabilization of microcellulose and clay suspensions, but it was not possible to stabilize the suspension of fines using high additions of PEI. This is ascribed to the mechanical entanglements of fibrillar fines. In tap water, much more PEI is needed to reach optimum flocculation conditions than in deionized water. Heteroflocculation between PEI-coated clay and fines takes place with a rate which, for high fines concentration and a constant clay concentration, is independent of fines concentration. A theoretical model for the heteroflocculation of fines with PEI-coated clay has been developed, which explains the observed trends. In essence, clay particles can act as bridging agents for fines flocculation.     

Electrochemical Sensing of Uric Acid Using Glassy Carbon Modified with Multiwall Carbon Nanotubes Dispersed in Polyethylenimine

This work reports the advantages of using glassy carbon electrodes modified with multiwall carbon nanotubes (MWCNT) dispersed in polyethylenimine (PEI). The presence of MWCNTs wrapped by PEI largely facilitated the strong adsorption of uric acid (UA) and allowed its highly sensitive and selective quantification even in the presence of high excess of ascorbic acid. The selected conditions for the electrochemical sensing were 5 s accumulation at ?0.300 V under stirring and quantification in a 0.050 M phosphate buffer solution pH 7.40 by differential pulse voltammetry adsorptive‐stripping after medium exchange. The platform allowed the successful application in the quantification of UA in urine.     

Simultaneous extraction and preconcentration of copper,silver and palladium with modified alumina and their determination by electrothermal atomic absorption spectrometry

In the present work,an easy solid phase extraction method using alumina modified with polyethylenimine as a new adsorbent was applied to the simultaneous extraction of copper,silver,and palladium ions prior to their determination with electrothermal atomic absorption spectrometry.The analytical procedure involved the complex formation of these cations with polyethylenimine as a chelating agent in buffer media of pH 7.0.Under the optimum conditions,a preconcentration factor of200,150,and 200,precision of ±5.4%,±4.7%,and ±5.2%and linear calibration ranges of 15.0-140,4.0-93,and 7.5-125 ng/L(in original solution) for Cu,Ag,and Pd were obtained,respectively.Also detection limits of3.9,1.1,and 2.0 ng/L were obtained for Cu,Ag,and Pd,respectively.The proposed method was applied to the determination of copper,silver,and palladium in some real samples with satisfactory results.     

Application of pulsed-magnetic field enhances non-viral gene delivery in primary cells from different origins

Primary cell lines are more difficult to transfect when compared to immortalized/transformed cell lines, and hence new techniques are required to enhance the transfection efficiency in these cells. We isolated and established primary cultures of synoviocytes, chondrocytes, osteoblasts, melanocytes, macrophages, lung fibroblasts, and embryonic fibroblasts. These cells differed in several properties, and hence were a good representative sample of cells that would be targeted for expression and delivery of therapeutic genes in vivo. The efficiency of gene delivery in all these cells was enhanced using polyethylenimine-coated polyMAG magnetic nanoparticles, and the rates (17–84.2%) surpassed those previously achieved using other methods, especially in cells that are difficult to transfect. The application of permanent and pulsating magnetic fields significantly enhanced the transfection efficiencies in synoviocytes, chondrocytes, osteoblasts, melanocytes and lung fibroblasts, within 5 min of exposure to these magnetic fields. This is an added advantage for future in vivo applications, where rapid gene delivery is required before systemic clearance or filtration of the gene vectors occurs.     

Quantification of Quercetin Using Glassy Carbon Electrodes Modified with Multiwalled Carbon Nanotubes Dispersed in Polyethylenimine and Polyacrylic Acid

This work reports the highly sensitive detection of quercetin using glassy carbon electrodes modified with multiwall carbon nanotubes (MWCNT) dispersed in polyethylenimine and poly(acrylic acid). The adsorptive stripping with square wave voltammetric transduction allowed the detection of 7.5 nM quercetin after 1.0 min accumulation at open circuit potential. The amperometric detection at 0.150 V is reported as an easier and simpler alternative to determine quercetin, with detection limits of 0.2 µM. The careful selection of the working conditions also made possible the detection of submicromolar levels of quercetin in the presence of excess of rutin. The proposed methodology was successfully used to quantify quercetin in onion samples.     

Surface modification of an epoxy resin with polyamines via cyanuric chloride coupling

The presence of polyamine groups on the surface of dielectric resins potentially improves the adhesion with electrochemically deposited metals. In this article, first cyanuric chloride is covalently bound to the surface hydroxyl groups of the epoxy resin. The remaining reactive sites on the coupled cyanuric chloride molecule are then used to anchor polyamines. New data on the triazine coupling is presented. The surface reactions are monitored and characterized by means of ATR-IR, SEM-EDS, XPS and ToF-S-SIMS.     

Polyethylenimine Functionalized with Dopamine: Characterization and Electrocatalytic Properties

We report the chemical modification of polyethylenimine (PEI) by functionalization with dopamine (Do) using glutaraldehyde (Glu) as a linker (PEI‐Glu‐Do). The new polymer was characterized by FT‐IR spectroscopy, by derivative UV‐vis spectroscopy, and Cyclic Voltammetry. The PEI‐Glu‐Do demonstrated to have an important electrocatalytic activity allowing an important decrease in the overvoltages for the oxidation of NADH and a significant increase in its oxidation peaks currents. Different ratios of PEI:Do were assayed and the best response was obtained using PEI : Glu : Do 1 : 2 : 1. The new polymer represents an interesting and promising alternative for the electrochemical quantification of NADH and other analytes of clinical interest, as well as for the development of new electrochemical (bio)sensors.     

Nonenzymatic H2O2 Electrochemical Sensor Based on SnO2‐NPs Coated Polyethylenimine Functionalized Graphene

This paper demonstrated using polyethylenimine (PEI)‐functionalized graphene (Gr) incorporating tin oxide (SnO₂) hybrid nanocomposite as a platform for nonenzymatic H₂O₂ electrochemical sensor. The results of UV‐vis spectroscopy and X‐ray diffraction (XRD) confirmed the simultaneous formation of tin oxide (SnO₂) nanocomposite and reduction of graphene oxide (GO). Transmission electron microscopy (TEM) images showed a uniform distribution of nanometer‐sized tin oxide nanoparticles on the grapheme sheets, which could be achieved using stannous chloride (SnCl₂) complex instead of tin oxide as precursor. The electrochemical measurements, including cyclic voltammetry (CV) and amperometric performance (I‐t), showed that the PEI‐functionalized Gr supported SnO₂ (SnO₂‐PEI‐Gr) exhibited an excellent electrocatalytic activity toward the H₂O₂. The corresponding calibration curve of the current response showed a linear detection range of 9×10⁻⁶∼1.64×10⁻³ mol L⁻¹, while the limit of detection was estimated to be 1×10⁻⁶ mol L⁻¹. Electrochemical studies indicated that SnO₂ and functionalized Gr worked synergistically for the detection of H₂O₂.     

Influences of hyperbranched polyethylenimine on the reactive compatibilization of polycarbonate/polyamide blends

The influences of hyperbranched polyethylenimine(h PEI), which possesses many reactive amino end-groups, on the blending properties of bisphenol-A polycarbonate(PC) and amorphous polyamide(a PA) were systematically investigated. Scanning electron microscopy(SEM) and differential scanning calorimetry(DSC) were used to observe the effect of h PEI on morphologies of PC and a PA phases in bulk blends. While the interfacial fracture toughness between planar PC and a PA layers with and without h PEI was studied by using augmented double cantilever beam(ADCB) method. Results show that the compatibility in PC/a PA blends can be significantly improved by adding a small amount of h PEI, mainly due to the interchange reactions between the polymers leading to the formation of block copolymers, cross-linked polymers and molecules with other constitutions. The augmented double cantilever beam experiments showed that the reactive process drastically reinforced the interfacial adhesion between planar layers of PC and a PA. However, degradation takes place during annealing at 180 °C, which was responsible for the production of small molar mass species of PC.     

Core-shell type multiarm star poly(ε-caprolactone) with high molecular weight hyperbranched polyethylenimine as core: Synthesis, characterization and encapsulation properties

Core-shell type multiarm star copolymers with poly(ε-caprolactone) (PCL) as shells and hyperbranched polyethylenimine (PEI) as core have been successfully prepared by the Sn(Oct)₂ catalyzed ring-opening polymerization of ε-caprolactone (CL) using high molecular weigh PEIs directly as macroinitiators. The initiation efficiency is in the range of 91-95% for PEI with M_n = 10⁴ (PEI10K) and only around 60% for PEI with M_n = 2.5 × 10⁴ (PEI25K), leading to star polymers with an average arm number in the range of 155-276. The thermal property of the obtained multiarm star polymers were also investigated by DSC. The melting and crystallization temperatures of the star polymers increase as the PCL arm length increases when the PEI core is fixed. The fusion enthalpy, crystalline enthalpy and degree of crystallinity values of the star polymers with PEI10K core are less than those with PEI1.8K core. Due to the polarity difference between PCL arm and PEI core, the resulting multiarm star polymers can act as inverted micellar nanocapsules capable of extracting and encapsulating water soluble guests. Increasing the size and polarity of the hydrophilic PEI core of the star nanocapsules are two effective ways to enhance their hydrophilic guest encapsulation capacity. Increasing the hydrophobic PCL arm length can increase the molar ratio, whereas reduce the weight ratio of the encapsulated hydrophilic guests to the star nanocapsules. Unexpectedly, the obtained nanocapsules can entrap the bigger size hydrophilic congo red guests more than the smaller size methyl orange.