Klaus Lunkwitz

Selective Interaction Between Proteins and the Outermost Surface of Polyelectrolyte Multilayers: Influence of the Polyanion Type, pH and Salt

Protein adsorption was studied by in-situ ATR-FT-IR spectroscopy of consecutively deposited polyelectrolyte multilayer systems terminated either with poly(ethyleneimine) (PEI) or polyanions, such as poly-(acrylic acid) (PAC), poly(maleic acid-co-propylene) (PMA-P) or poly(vinyl sulfate) (PVS). The influence of the polyanion type, pH and ionic strength was investigated. Negatively charged human serum albumin (HSA) was strongly repelled by multilayers terminated with weak polyanions (PAC, PMA-P), whereas moderate attraction was observed for those terminated with the strong polyanion PVS. Changing the pH from 7.4 to 5 resulted in enhanced HSA adsorption onto PAC-terminated multilayers. An increase in ionic strength diminished the attractive HSA adsorption onto PEI-terminated multilayers. For the PEI/PAC system, the biomedically relevant adsorption of human fibrinogen (FGN) is determined via its isoelectric point in accordance with three other proteins.

An in‐situ ATR‐FTIR study on polyelectrolyte multilayer assemblies on solid surfaces and their susceptibility to fouling

In-situ attenuated total reflection (ATR)-FTIR spectroscopy was used to monitor the consecutively alternating adsorption of polyethylenimine (PEI) and poly(acrylic acid) (PAC) onto both Si crystals (SiO) and CO2 plasma-treated polypropylene (PP) films. The vibration band vas(COO−) and v(CO) of PAC are diagnostic for the polyelectrolyte layer build-up and sensitive to protonation changes. Human serum albumine (HSA) adsorption experiments revealed a strong decrease of fouling for the PP films, which were modified with polyelectrolyte multilayers, in comparison to the unmodified ones.

Hydrophilization of microporous polypropylene Celgard membranes by the chemical modification technique

Microporous hydrophobic polypropylene (PP) membranes (Celgard® 2400 and 2500) were modified by the chemical modification technique to impart permanent hydrophilicity. The modification was carried out in two stages. In the first stage, the membranes were hydroxylated by treatment with aqueous potassium peroxydisulfate solution under a strong flow of nitrogen. In the second stage, the hydroxylated membranes were subjected to grafting of acrylamide using cerric ammonium nitrate as an initiator. Subsequently, acrylamide grafted PP membranes were partially hydrolyzed to have carboxvl functional groups at the membrane surfaces. Under given experimental conditions the grafting also took place within the pores of the microporous structure of hydrophobic PP Celgard® membranes. Modified membranes exhibited permanently wettable characteristics by aqueous solutions and appeared translucent when immersed in water. Contact angle measurements showed excellent wetting properties with water. In contrast to unmodified Celgard® membrane, the modified membranes exhibit water permeability even after repeated drying. Membranes were further characterized by FTIR and ESCA for the different types of functional groups.

Deposition of polylelectrolyte complex nano-particles at silica surfaces characterized by ATR-FTIR and SEM

Abstract We report on the adsorption of preformed polyelectrolyte complex (PEC) particles at silica surfaces. PEC dispersions were prepared by mixing poly(diallyldimethylammonium chloride) (PDADMAC) optionally with two maleic acid copolymers: sodium poly(maleic acid-co-propylen) (PMA-P) or sodium poly(maleic acid-co-α-methylstyrene) (PMA-MS). Stable colloid nanoparticles were formed as it was characterized by PCS and turbidity. ATR-FTIR spectroscopy was used to study the adsorbed amount of the PECs and SEM and AFM were applied for the lateral characterization of the PEC layers. The influence of surface pretreatment (i), polyanion (ii), pH (iii) and PEC centrifugation (iv) on the adsorption behavior was studied. Different pretreatments of the silicon substrate, i.e. cleaning in sulfuric acid, ‘piranha’ solution or multilayer deposition caused different adsorbed amounts, whereby additionally a linear dependence of the adsorbed amount on the bulk PEC concentration was found. Deposition of PEC-PDADMAC/PMA-P resulted in flat highly deformed adsorbed particles, whereas the adsorbed PEC-PDADMAC/PMA-MS formed spherical caps on the surface. The adsorbed amount obtained at pH=9 was significantly higher compared to that at pH=6. Centrifugation of the PEC dispersion resulted in a monodisperse coacervate fraction for PMA-MS containing PECs showing also a low polydispersity in the adsorbed state. Using silicon surfaces modified by polyanion terminating polyelectrolyte multilayers, the highest adsorbed amount of PECs was found, whereby additionally no deformation of the adsorbed PECs was observed. Furthermore consecutive deposition of oppositely charged PEC particles resulted in a complete surface coverage. From these findings we outline the potential of PEC nanoparticles, which might be compared in properties and applications to latex systems.

Deposition and properties of polyelectrolyte multilayers studied by ATR-FTIR spectroscopy

Abstract In-situ ATR-FTIR spectroscopy was adopted to study multilayer assemblies of oppositely charged polyelectrolytes consecutively deposited on plasma treated SiO surface. Two different polyelectrolyte systems were selected for this series of studies in order to address (i) conformational changes in polyelectrolyte multilayers as a response to the external stimuli and (ii) protein adsorption on preformed polyelectrolyte multilayers. The former phenomenon was examined for the polyelectrolyte pair of poly(acrylic acid) (PAA) and poly( l -lysine) (PLL), where PLL provides an advantage of detecting the early adsorption events due to its intense amide I band. Protein adsorption was followed on the multilayer assembly consisting of sodium alginate (SA), cellulose sulfate (CS) and poly(methylene-co-guanidine) (PMCG). These multilayers were used as a model system to simulate protein interactions with the membranes formed by polyelectrolyte complexation.

Microporous membranes from polyolefin-polyamide blend materials☆

An alternative method using established polymer processing and membrane formation processes to prepare hydrophilic membranes based on acid modified polyolefins is introduced. This process includes blend formation by reactive extrusion of functionalized polyolefins (polypropylene; PP) and a hydrophilic polyamide (PA). In a first step the pore formation is realized by extracting non-covalently bound polyamide. The resulting membranes are tested by pure water as well as protein filtration. The properties are discussed in terms of permeate flux, retention capability and fouling behavior.

Electrostatic self-assembled nanoarchitectures between polycations of integral type and azo dyes

Abstract The electrostatic self-assembling was successfully used to build-up new polycation/azo dye multilayers starting from a polycation of integral type containing 95 mol.% of N,N-dimethyl-2-hydroxypropyleneammonium chloride units in the main chain (PCA5) and two multicharged azo dyes: Direct Blue 1 (DB1) and Direct Red 80 (DR80). The build-up and the stability of the PCA5/azo dyes layered thin films, in dependence on the adsorption conditions and the dye structure, were followed by UV–Vis spectroscopy, the variation of the ζ potential in dependence on pH and by spectroscopic ellipsometry. The multilayer build-up in the presence of the neutral salts was correlated with the counterion influence on the macroion conformation. The surface charge and the pH corresponding to the isoelectric point were depending on the polycation adsorption conditions.

Ultrathin Films from Fluorine Containing Polymers: Fabrication and Characterization

Monolayers and ultrathin films of some fluorine containing polymers were prepared by the Langmuir-Blodgett (LB) technique. The polymers were obtained using two main synthetic approaches: firstly, polyamide (PA-1) and polyimide (PI-1) were prepared from direct polycondensation of 4,4′-hexafluoroisopropylidenediphthalic anhydride and 4,4′-hexafluoroisopropylidenedianiline in N-methyl-2-pyrrolidone (NMP). The thermogravimetric analysis (TGA) for PI-1 yielded 580°C by 1% weight loss. They formed stable monolayers with a collapse pressure of 62 mN/m and a collapse area of 0.20 nm2 per repeat unit (R.U.) in the case of PA-1, for PI-1 the collapse pressure was 60 mN/m associated with a collapse area of 0.23 nm2 per R.U. Secondly, poly[(maleic acid perfluorooctylamide-imide)-co-ethylene] (PAPE) with fluorinated side chains was synthesized from poly[(maleic anhydride)-co-ethylene]. They formed stable monolayers too. Multilayer depositions onto various substrates were possible for all the synthesized polymers. LB films were characterized by ultra-violet/visible spectroscopy (UV-Vis), surface plasmon resonance (SPR), dielectric spectroscopy and atomic force microscopy (AFM). Gas phase polymerization of tetrafluoropropyl methacrylate (TFPM) was carried out in the presence of macroinitiator, poly[octadecene-co-(maleic anhydride)] modified with tert-butyl hydroperoxide. Film thickness could be controlled on different hydrophobic substrates varying the reaction time.

Stimulation and binding properties of polyelectrolyte multilayers verified by ATR-FTIR spectroscopy

We report on the deposition and properties of multilayers composed of reactive polymers on planar surfaces. As reactive polymers the polycations poly(ethylene-imine), poly(L-lysine) (PLL), poly(allylamime) (PAA) and the polyanions poly(acrylate) (PAC), poly(vinylsulfate), poly(maleate-co-olefines) were used. ATR-FTIR spectroscopy was adopted to study deposition, binding and stimulation properties of polymer multilayers. The binding of charged species of different molecular size such as rhodanide anions and sodium oleate from solution was examined, whereby binding was found to be dependent on the charge of the outermost layer. For these two analytes a selectivity parameter Q, defined as the ratio between the adsorbed amount obtained at the negatively charged and that at the positively charged surface, respectively, was determined. Furthermore, swelling experiments on multilayer assemblies of PLL and PAC exposed to mixtures of ethanol/water (10 - 70% EtOH content) were carried out. Our experiments gave evidence, that the PLL layers showed a more significant increase in density than the PAC layers. The conformation of PLL incorporated into multilayers could be changed by pH variation.

Modifizierung von Polyaramid-Ultrafiltrationsmembranen durch Elektronenbestrahlung

Die Bestrahlung von Polyaramid-Ultrafiltrationsmembranen (PA-UF-Membranen; NADIR® UF-PA-5) mit energiereichen Elektronen ergab im Energiedosisbereich von D≈150 bis 200 kGy eine Erhohung des Ruckhaltevermogens R von 93 auf 98%. Entgegen der ublichen Erfahrung trat dabei keine Reduzierung des Permeatfluswertes JPVP auf. Durch ζ-Potentialmessungen und IR-spektroskopische Untersuchungen konnte der Einbau von zusatzlichen Carboxygruppen durch die Bestrahlung nachgewiesen werden, die diesen Effekt im wesentlichen verursachen. Electron beam irradition of polyaramide ultrafiltration membranes (PA-UF membranes; NADIR® UF-PA-5) led to an increase of retention R from 93% to 98% in the applied dose range between 150 and 200 kGy. Contrary to common findings, no reduction of permeate flux JPVP was observed. The formation of carboxy groups caused by electron beam irradiation was confirmed by ζ-potential measurements and ATR-FTIR spectroscopic investigations.