Cationic Polyelectrolyte Polyethylenimine Research Articles

Hybrid Zinc-Based Multilayer Systems with Improved Protective Ability against Localized Corrosion Incorporating Polymer-Modified ZnO or CuO Particles

Localized corrosion and biofouling cause very serious problems in the marine industries, often related to financial losses and environmental accidents. Aiming to minimize the abovementioned, two types of hybrid Zn-based protective coatings have been composed. They consist of a very thin underlayer of polymer-modified ZnO or CuO nanoparticles and toplayer of galvanic zinc with a thickness of ~14 µm. In order to stabilize the suspensions of CuO or ZnO, respectively, a cationic polyelectrolyte polyethylenimine (PEI) is used. The polymer-modified nanoparticles are electrodeposited on the steel (cathode) surface at very low cathodic current density and following pH values: 1/CuO at pH 9.0, aiming to minimize the effect of aggregation in the suspension and dissolution of the CuO nanoparticles; 2/ZnO at pH 7.5 due to the dissolution of ZnO. Thereafter, ordinary zinc coating is electrodeposited on the CuO or ZnO coated low-carbon steel substrate from a zinc electrolyte at pH 4.5–5.0. The two-step approach described herein can be used for the preparation of hybrid coatings where preservation of particles functionality is required. The distribution of the nanoparticles on the steel surface and morphology of the hybrid coatings are studied by scanning electron microscopy. The thickness of the coatings is evaluated by a straight optical microscope and cross-sections. The protective properties of both systems are investigated in a model corrosive medium of 5% NaCl solution by application of potentiodynamic polarization (PDP) curves, open circuit potential (OCP), cyclic voltammetry (CVA), and polarization resistance (Rp) measurements. The results obtained allow us to conclude that both hybrid coatings with embedded polymer-modified CuO or ZnO nanoparticles ensure enhanced corrosion resistance and protective ability compared to the ordinary zinc.

PH and charge reversal-driven nanoplatform for efficient delivery of therapeutics

Nanomedicine which delivers therapeutics to tumours holds great potential for cancer treatment. However, endosomal trapping and uncontrollable release usually limit the efficiency of nanomedicine. Herein, a smart mesoporous silica based nanoplatform was constructed, in which mesoporous silica nanoparticles (MSNs) serve as the core, capped with pH-induced charge-reversal polymer -PAH-cit- and cationic polyelectrolyte polyethyleneimine (PEI). The oppositely charged polymer can not only act as a gatekeeper for controlled release, but also mediated efficient endosomal escape of the therapeutics. Under the acidic endosomal environment, the hydrolysis of acid-cleavable bonds in PAH-Cit would trigger the charge reversal and endosomal escape of the nanoplatform for efficient drug release. Furthermore, the prepared nanoplatform demonstrated a higher tumor cell proliferation inhibition rate than free theruputics in vitro assays and significantly inhibited tumour growth in the 4T1 tumour model in mice. Therefore, our strategy offers a simple and general nanoplatform to delivery therapeutics to tumours with efficient endosomal escape and controlled release.

Composite coatings with polymeric modified ZnO nanoparticles and nanocontainers with inhibitor for corrosion protection of low carbon steel

Incorporation of zinc oxide (ZnO) nanoparticles and ZnO based nanocontainers with corrosion inhibitor Safranin into the matrix of standard zinc coatings is applied for preparation of coatings with improved corrosion protection for mild steel. A cationic polyelectrolyte polyethylenimine (PEI) is used to stabilize the ZnO suspension before electrodeposition of the ZnO nanoparticles on the steel surface. Encapsulation of Safranin is realized in polymer coatings on ZnO nanoparticles prepared using layer-by-layer assembly of polyacrylic acid (PAA) and PEI. The average size and surface charge of the PEI coated ZnO nanoparticles and ZnO based nanocontainers with inhibitor are identified using dynamic and electric light scattering methods and microelectrophoresis. The ZnO nanoparticles or ZnO nanocontainers are electrodeposited on steel (cathode) substrates at pH 7.5 to minimize the effect of ZnO dissolution. In a second step, ordinary zinc coatings are electrodeposited on the ZnO nanoparticles or ZnO nanocontainers covered steel samples from zinc sulfate electrolyte at pH 4.5-5.0. The surface morphology of the coatings and their corrosion behavior are studied by scanning electron microscopy and electrochemical methods potentiodynamic polarization and polarization resistance. The results show better corrosion protection of steel by composite coatings as compare to the bare zinc coating. The composite coating with inhibitor shows better protective characteristics in comparison with the other one. The two-step approach described herein can be used for preparation of composite coatings where preservation of particles functionality is required.

The structure and mass of heterogeneous thin films measured with dual polarization interferometry and ellipsometry

Optical techniques for the characterisation of thin films, such as Dual Polarisation Interferometry (DPI), Ellipsometry or Optical Waveguide Lightmode Spectroscopy (OWLS), usually apply a uniform single layer model to the analysis of thin films. Whilst this is the simplest approach, fitting a more realistic density profile would be preferable for heterogeneous films. The influence of a film's density distribution on the optically determined values, assuming a homogeneous isotropic model is thus investigated. New analytic formulae are proposed that give a good approximation to the measured averages for the thickness, refractive index and extinction coefficient of inhomogeneous light absorbing films. It is demonstrated that these equations are valid for optical waveguide techniques, such as DPI and agree closely with ellipsometry. The equations enable non-uniform density distributions of heterogeneous films to be studied and related to the experimentally measured values created using a slab model, without the need for instrument dependent modelling using the often more complicated Drude, Fresnel or Maxwell equations. A non-uniform density distribution model is applied, as an example, to the analysis of data obtained during the deposition of the cationic polyelectrolyte Polyethylenimine (PEI) on silica, measured by DPI and correlated with data obtained using a Quartz Crystal Microbalance with Dissipation (QCM-D). The equations presented are then extended to enable the calculation of the mass of different molecular species in composite films that absorb varying amounts of light. The ability to measure the mass of light absorbing molecules provides more information concerning surface morphology and removes an ambiguity concerning a film's composition, especially when different molecular species compete for sites on a surface.

Controllable fabrication of PS/Ag core-shell-shaped nanostructures

In this paper, based on the previous steps, a facile in situ reduction method was developed to controllably prepare polystyrene/Ag (PS/Ag) core-shell-shaped nanostructures. The crucial procedure includes surface treatment of polystyrene core particles by cationic polyelectrolyte polyethyleneimine, in situ formation of Ag nanoparticles, and immobilization of the Ag nanoparticles onto the surface of the polystyrene colloids via functional group NH from the polyethyleneimine. The experimental parameters, such as the reaction temperature, the reaction time, and the silver precursors were optimized for improvement of dispersion and Ag coat coverage of the core-shell-shaped nanostructures. Ultimately, the optimum parameters were obtained through a series of experiments, and well-dispersed, uniformly coated PS/Ag core-shell-shaped nanostructures were successfully fabricated. The formation mechanism of the PS/Ag core-shell-shaped nanostructures was also explained.

Adsorption of polyelectrolyte modified graphene to silica surfaces: Monolayers and multilayers

Exfoliated graphene particles stabilised by the cationic polyelectrolyte polyethyleneimine (PEI) were used in conjunction with an anionic polyelectrolyte, poly(acrylic acid), to construct multilayers using the layer-by-layer technique on a silica substrate. In the first adsorption step, the surface excess of the cationic graphene was dependent on the overall charge on the nanoparticle which in turn can be tuned through modifying solution pH as PEI has weakly ionisable charged amine groups. The adsorbed amount onto the silica surface increased as the solution pH increased. Subsequently, a layer of PAA was adsorbed on top of the cationic graphene through electrostatic interaction. The multilayer could be assembled through this alternate deposition, with the influence of solution conditions investigated. The pH of the adsorbing solutions was the chief determinant of the overall adsorbed amounts, with more mass added at the elevated pH of 9 in comparison with pH 4. Atomic force microscopy confirmed that the graphene particles were adsorbed to the silica interface and that the surface coverage of the disc-like nanoparticles was complete after the deposition of five graphene-polyelectrolyte bi-layers. Furthermore, the graphene nanoparticles themselves could be modified through the consecutive addition of the oppositely charged polymers. A multilayered assembly of negatively charged graphene sheets modified with a bi-layer of PEI and PAA was also deposited on a silica surface with adsorbed PEI.

Textured Ti<sub>3</sub>SiC<sub>2</sub> by EPD in a Strong Magnetic Field

We present a method for fabrication of textured MAX phase ceramics, particularly, Ti3SiC2; by EPD in a strong magnetic field (12T). Ti3SiC2 was dispersed in cationic polyelectrolyte-Polyethylenimine (PEI). Addition of 0.3-1dwb PEI resulted in high zeta potential values and suspension was found to be stable and of good fluidity. The optimized suspension parameters for EPD were determined as 10vol% Ti3SiC2 and 1dwb PEI in 50 % ethanolic water at pH ~ 7. X-ray diffraction analysis of the textured samples revealed that the preferred orientation of Ti3SiC2 grains parallel to the magnetic eld direction was along the a,b-axis. The Lotgering orientation factors on the textured top surface and textured side surface were determined as f (hk0) = 0.35 and f (00l) = 0.75, respectively.

Immobilized capillary adenosine deaminase microreactor for inhibitor screening in natural extracts by capillary electrophoresis

A novel strategy for the preparation of in-column adenosine deaminase (ADA) microreactor and rapid screening of enzyme inhibitors in natural extracts was demonstrated. In this approach, ADA was encapsulated in anionic polyelectrolyte alginate that was immobilized on the surface of fused-silica capillary via ionic binding technique with cationic polyelectrolyte polyethylenimine (PEI). On-line enzyme inhibition study was performed by capillary electrophoresis (CE). The substrate and product were baselined separated within 75 s. The enzyme activity was determined by the quantification of peak area of the product. Enzyme inhibition can be read out directly from the reduced peak area of the product in comparison with a reference electropherogram obtained in the absence of any inhibitor. The inhibition percentage was used to evaluate relative activity of ADA microreactor. A known ADA inhibitor, erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) was employed as a model compound for the validation of the inhibitor screening method, and the screening of ADA inhibitor in 19 traditional Chinese herbal medicines was performed.

Adsorption of polyelectrolyte multilayers on plasma-modified porous polyethylene

Hydrophilic and chemically reactive porous media was prepared by adsorbing functional polymers at the surface of sintered polyethylene membranes. Modification of the membrane was accomplished by first exposing the membrane to an oxygen glow discharge gas plasma to render electrostatic charge at the membrane surfaces. Cationic polyelectrolyte polyethylenimine (PEI) was adsorbed from solution to the anionically charged surface to form an adsorbed monolayer. The adsorption of a second anionic polyelectrolyte allowed further modification of the membrane surface with a polyelectrolyte bilayer complex. In this paper we probe the effect of polymer structure on the conformation and stability of the adsorbed polyelectrolyte monolayers and bilayers on the modified polyethylene surface. Using the wicking rate of deionized, distilled water through the porous membrane to gauge the interfacial energy of the modified surface, we show that the wicking rate of the multilayer membrane can be controlled by varying the chemistry of the adsorbing polyelectrolytes and their molecular weights.

Deposition and Wetting Characteristics of Polyelectrolyte Multilayers on Plasma-Modified Porous Polyethylene

Hydrophilic and chemically reactive porous media were prepared by adsorbing functional polymers at the surface of sintered polyethylene membranes. Modification of the membrane was accomplished by first exposing the membrane to an oxygen glow discharge gas plasma to introduce an electrostatic charge at the membrane surfaces. Cationic polyelectrolyte polyethylenimine (PEI) was adsorbed from solution to the anionic-charged surface to form an adsorbed monolayer. The adsorption of a second anionic polyelectrolyte onto the PEI layer allows further modification of the membrane surface to form a polyelectrolyte-bilayer complex. The conformation and stability of the adsorbed monolayers and bilayers comprising the modified surface are probed as a function of the polymer structure, charge density, and solubility. Using X-ray photoelectron spectroscopy analysis, we demonstrate that the presence of the polyelectrolyte multilayers drastically increases the density and specificity of the functional groups at the surface, more than what can be achieved through the plasma modification alone. Also, using the wicking rate of deionized, distilled water through the porous membrane to gauge the interfacial energy of the modified surface, we show that the membrane wicking rate can be controlled by varying the chemistry of the adsorbing polyelectrolytes and, to a lesser extent, by adjusting the polarity or ionic strength of the polyelectrolyte solution.

Contact Interactions between Individual Fibers of Cellulose and Its Derivatives: Mechanism of Cationic Surfactant Action

The effect of cationic surfactants (cetyltrimethylammonium bromide and tetrabutylammonium iodide) and cationic polyelectrolyte polyethylenimine on the coefficient of friction μ and adhesion force p(during shear and tensile testing, respectively) at the point contacts between the individual fibers of cellulose, viscose, and cellulose acetate was studied. The comparison of these data with the results of ζ-potential and adsorption measurements enabled us to relate the nonmonotonic dependence of parameters μ and pon the surfactant concentration to the changes in electrosurface properties and the hydrophilicity or hydrophobicity of the fibers. The specific free energy of interaction U[mJ/m2] was estimated for cellulose acetate fibers.