Deposition Of Polyelectrolyte Layers Research Articles

Optimization of Polymeric Membrane Characteristics through Thermal Treatment and Deposition of Polyelectrolyte Layers Using Response Surface Modeling

ABSTRACTImprovement in polyethersulfone membrane performance by employing thermal treatment and deposition of polyelectrolyte layers was proposed. High molecular weight polyelectrolytes were used in the formation of polyelectrolyte multilayers in the presence of various concentrations of supporting electrolyte. Interactions between the membrane thermal treatment duration and salt concentration in a polyelectrolyte solution were evaluated and optimized using response surface methodology. The predictive models showed good fittings between the experimental and model predicted values, which confirmed the precision and reliability of the regression models. Confirmation run was conducted using the thermal treatment duration of 17.07 min and 1.70 M of the supporting electrolyte concentration in the polyelectrolyte solution. The pure water permeability, NaCl rejection, MgSO4 rejection, Na2SO4 rejection, selectivity of NaCl/Na2SO4, and selectivity of MgSO4/Na2SO4 obtained were 6.51 L⋅m−2⋅h−1⋅bar−1, 45.41%, 69.14%, 85.79%, 3.84, and 2.17, respectively.

Preparation and characterization of polyacrylonitrile membranes modified with polyelectrolyte deposition for separating similar sized proteins

One of the challenges faced by ultrafiltration membranes is to separate proteins with a small difference in their molecular weights. Recently, some researchers tried to overcome this problem by using charged membranes. This study examined the use of layer by layer deposition of polyelectrolytes on the chemically-modified polyacyronitrile membrane to increase the selectivity of the ultrafiltration. The membranes were prepared by wet-phase inversion technique and polyethylenimine (PEI) and alginate (ALG) were chosen as cationic and anionic polyelectrolytes for the modification of the surfaces. Sieving coefficient data were obtained with myoglobin and lysozyme as model proteins. The influences of solution pH, ionic strengths of the protein and polyelectrolyte solution and the number of polyelectrolyte bilayers on both selectivity and throughput were investigated. The highest selectivity and throughput were achieved with the 1-bilayer PEI-ALG coated polyacrylonitrile (PAN) membrane. Increasing the number of coating bilayers or the ionic strength of the protein solution or adding salt into the polyelectrolyte coating solution decreased both the maximum selectivity and throughput of the modified membranes. ▸ Polyacyronitrile membranes were modified with polyelectrolyte deposition. ▸ Polyethylenimine and alginate were used as polyelectrolytes. ▸ The membranes were tested for the separation of myoglobin and lysozyme. ▸ The highest selectivity and throughput were achieved with the 1-bilayer coating.

Conditioning biomass hydrolysates by membrane extraction

Conditioning of biomass hydrolysates prior to fermentation is essential in the production of bioethanol. The removal of acetic acid, furfural and 5-hydroxymethylfurfural by membrane extraction has been investigated. Removal of these compounds is essential in order to maximize ethanol yields. The organic phase consisted of Alamine 336 in octanol. Ab initio calculations, coupled with the implicit continuum solvation method were performed in order to determine the free energies associated with extraction of acetic acid, furfural and 5-hydroxymethylfurfural from an aqueous to organic phase in the presence and absence of a tertiary amine. Due to complexation between amines and acetic acid, furfural and 5-hydroxymethylfurfural, extraction from an aqueous to organic phase becomes favorable. The formation of acetic acid dimers in octanol also appears to be favorable. Experimentally, layer by layer deposition of polyelectrolytes onto flat sheet polypropylene membranes has been conducted in order to improve the extraction performance during biomass conditioning. The resulting membranes have one hydrophilic surface while the other surface remains hydrophobic. The results obtained here indicate the importance of choosing an appropriate solvent and membrane surface chemistry that maximizes extraction of compounds that are toxic to the microorganisms during fermentation. Finally the advantages of using amphiphilic polymeric membranes are discussed.

Preparation of core-shell and hollow fibers using layer by layer (LbL) self-assembly of polyelectrolytes on electrospun submicrometer-scale silica fibers

Herein, fabrication of hollow fibers made of polyelectrolyte multilayers is reported. Silica submicrometer-scale fibers were fabricated by electrospinning and layer by layer deposition of polyelectrolytes were performed to coat silica fibers with polyelectrolyte multilayers, which were prepared by consecutive deposition of poly(ethyleneimine) and poly(styrene sulfonate sodium salt)/sodium dodecyl sulfate onto the surface of the silica fibers. In order to obtain hollow fibers, the core removal was carried out by introducing the core-shell fibers to a hydrofluoric acid solution. The hollow fibers were stable in hydrofluoric acid solution and displayed pH-dependent structural changes. SEM microscopy indicated the formation of the glass fibers and the fibers coated with polyelectrolyte multilayers (Silica—polyelectrolyte multilayers (PEM) fibers). The diameter of the core-shell fibers was increased after layer-by-layer coating. ATR-FTIR was performed for characterization of the glass fibers before and after layer-by-layer coating as well as after selective core removal. IR spectrum of the Silica-PEM fibers indicates C-H stretching modes of saturated hydrocarbons, confirming multilayers formation. Core removal was also confirmed by IR spectroscopy as Si-O-Si band disappears for the IR spectrum of the fibers after core-removal.

Effect of Layer-by-Layer Electrostatic Assemblies on the Surface Potential and Current Voltage Characteristic of Metal−Insulator−Semiconductor Structures

In the present Article, the Kelvin probe method for surface potential measurement is introduced to study polyelectrolyte multilayer coatings deposited on silicon plates. Metal-insulator-semiconductor (MIS) structures with polyelectrolyte layers as insulator were fabricated. The polyelectrolyte layer deposition on the surface of silicon plates led to a change of the current-voltage characteristics connected with resistance changes of the MIS structures. Poly(ethylenimine) (PEI) monolayer formation resulted in resistance decrease, and the following increase of the polyelectrolyte layer number led to MIS structure resistance increase. The results are interpreted as an interplay between accumulation of majority carriers (electrons) near the semiconductor surface and resistance increase due to insulating polyelectrolyte adsorption, and both effects can be discriminated by varying the polyelectrolyte layer thickness.

Kinetic evaluation of the effect of layer by layer deposition of polyelectrolytes on the stability of POPC liposomes

Layer by layer (LBL) assembly of poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) was used to coat positively as well as negatively charged liposomes. The adsorption of either polyelectrolyte onto the liposomal surface occurs by means of electrostatic and hydrophobic interactions, depending on the structure of the polymer. The stability of the surface-modified liposomes was evaluated by monitoring the rate of the breakdown induced by the addition of increasing amounts of octaethyleneglycol mono-n-dodecylether (C12E8). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) yielded insight into the morphology of the capsules before and after the impact with the surfactant.