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PubMed2000

Adsorption of Polyelectrolyte-Nanoparticle Systems on Silica: Influence on Interaction Forces.

In this work, we have studied the interfacial properties of cationic polyelectrolyte (PE) and silica nanoparticle (NP) systems at macroscopic silica surfaces by means of ellipsometry. The influence of adsorbed layers on the interactions between silica surfaces was also investigated using the bimorph surface force apparatus. Added nanoparticles were observed to strongly swell the interfacial polyelectrolyte layers, an effect partly related to neutralization of charged polyelectrolyte groups. The effect was more pronounced for low charged than for highly charged polyelectrolytes. Overall, the presence of nanoparticles seemed to increase the repulsive interaction measured between silica surfaces. The force measured on approach was long range and quite strongly repulsive. On separation, an attractive bridging interaction was measured for polyelectrolyte-covered surfaces. For the low charged polyelectrolyte used in the study, the force turned repulsive on addition of nanoparticles. For the highly charged polyelectrolyte used, a change from a very strong attraction (involving a jump of the surfaces out of contact) to a very long-range elastic attractive force was observed on adding nanoparticles. The long-range elastic force indicates that polymer chains and nanoparticles form a transient network in the gap between the surfaces. The observed difference in the outward force curves may explain why the addition of nanoparticles appears to improve, e.g., shear-resistance and reflocculation characteristics of polymeric flocculants. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

The Effect of a Cationic Polyelectrolyte on the Forces between Two Cellulose Surfaces and between One Cellulose and One Mineral Surface.

The effect of a cationic polyelectrolyte, PCMA, on the forces between two cellulose surfaces and between one cellulose surface and one mica surface has been studied using the interferometric surface force apparatus (SFA). The cellulose surfaces were prepared by Langmuir-Blodgett deposition of trimethylsilyl cellulose onto hydrophobized mica. Prior to measurements the surfaces were desilylated to obtain pure cellulose. Introduction of a cationic polyelectrolyte into the solution drastically changed the interactions between the cellulose layers. It was found that the cationic polyelectrolyte does adsorb onto the cellulose surface, although the adsorbed amount is low. The adsorbed layer is very thin, as expected at a low electrolyte concentration. Before the adsorption has reached equilibrium, when only some polyelectrolyte had adsorbed, the adhesion between the surfaces was high, and it was noted that the cellulose layer was damaged on separation. After a longer adsorption time an electrostatic repulsion and no adhesion were observed between the polyelectrolyte-coated cellulose surfaces. An electrostatic repulsion was observed between cellulose and mica. When cationic polyelectrolyte was introduced to the system it overcompensated the charges on both surfaces, and the range and magnitude of the double-layer force was higher than without polyelectrolyte. The relevance of the results to flocculation mechanism and efficiency in cellulose systems is discussed. Copyright 2000 Academic Press.

Journal Article↗
PubMed2006

Kinetics of polyelectrolyte adsorption onto polystyrene latex particle studied using electrophoresis: effects of molecular weight and ionic strength.

The kinetics of the adsorption of a cationic polymer flocculant onto negatively charged polystyrene latex (PSL) particles were measured by means of electrophoresis as a function of the molecular weight of the polyelectrolyte and the ionic strength of the solution. In the experiment, the dispersion of bare PSL particles was mixed with a polyelectrolyte solution by means of end-over-end rotation in which the mixing intensity was evaluated in terms of the collision frequency between the colloidal particles. The rate of electrophoretic mobility of a PSL particle, which remained as a singlet, was measured against the mixing steps, which was equivalent to the time elapsed after the onset of flocculation. The shape of the kinetic curves is typical: a linear increase for a short period followed by a plateau, implying the saturation of the colloidal surface by the adsorbed polyelectrolyte. In the case of low ionic strength, the plateau value was dependent on the molecular weight of the polyelectrolyte. That is, a lower plateau value was detected when the molecular weight of the polyelectrolyte was smaller and its concentration was lower. However, the amount of adsorption was kinetically controlled only for the case of higher molecular weight. In the case of high ionic strength, the plateau value of electrophoresis was constant, regardless of the polyelectrolyte concentration and molecular weight. These data will ultimately be useful in further analysis of the flocculation behavior of colloidal particles with a polyelectrolyte.

Journal Article↗
PubMed2003

Synthesis and aqueous solution properties of polyelectrolyte-grafted silica particles prepared by surface-initiated atom transfer radical polymerization.

A range of polyelectrolyte-grafted silica particles have been prepared by grafting suitable initiators onto near-monodisperse, 304-nm-diameter silica particles using siloxane chemistry, followed by surface-initiated atom transfer radical polymerization (ATRP) of four ionic vinyl monomers, namely sodium 4-styrenesulfonate (SStNa), sodium 4-vinylbenzoate (NaVBA), 2-(dimethylamino)ethyl methacrylate (DAM), and 2-(diethylamino)ethyl methacrylate (DEA) in protic media. The resulting polyelectrolyte-grafted silica particles were characterized using dynamic light scattering (DLS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), helium pycnometry, and diffuse reflectance infrared Fourier transfer spectroscopy (DRIFTS). The TGA results indicated that the polyelectrolyte contents of the silica particles could be varied from 0.6% to 6.0% in weight. SEM studies revealed several surface morphologies for the grafted polyelectrolytes and XPS analysis of the particle surface also provided good evidence for surface grafting. Combined aqueous electrophoresis and DLS studies confirmed that these polyelectrolyte-grafted silica particles had pH-dependent colloid stabilities, as expected. Cationic polyelectrolyte-grafted silica particles were colloidally stable at low or neutral pH, but became aggregated at high pH. Conversely, anionic polyelectrolyte-coated silica particles became unstable at low pH. It was found that the rate of surface-initiated ATRP was substantially slower than the analogous solution polymerization. Finally, there was some evidence to suggest that, at least in some cases, a significant fraction of polymer chains became detached from the silica particles during polymerization.

Journal Article↗
PubMed2001

Effect of aluminum sulfate and cationic polyelectrolytes on the destabilization of emulsified wastes.

Emulsified oil in wastewater constitutes a severe problem in the different treatment stages. Aluminum salts have been traditionally used as coagulants in wastewater treatments. Polyelectrolytes are used to coagulate and flocculate colloidal systems. The performance of aluminum sulfate in comparison to polyelectrolytes (chitosan and polyacrylamide) as conditioning chemicals for an emulsion waste was tested, and the predominant mechanisms acting in each case were analyzed. Turbidimetry, jar test, colloidal titration and microscopy were used to test emulsion destabilization. Both charge neutralization and bridge formation were identified and confirmed as mechanisms of interaction of polyelectrolytes with waste constitutents. Charge neutralization would be more important for chitosan than for polyacrylamide treatment. A coincidence between the doses necessary to reach zero colloidal charge and minimum turbidity was observed for polyelectrolytes. The time necessary to produce system clarification was larger for aluminum sulfate than for polyelectrolytes; this time was shortened for higher aluminum sulfate concentration. The pH showed a marked effect on aluminum sulfate performance with the optimum at pH 6; polyelectrolyte action was practically not affected by pH. Polyelectrolyte addition produced the minimum turbidity for the same doses that zero colloidal charge; at higher doses, emulsion was restabilized and became turbid again. However, aluminum sulfate treatment did not produce emulsion restabilization.

Acrylic Resins↗
PubMedDate not supplied

Secondary structure of proteins adsorbed onto or embedded in polyelectrolyte multilayers.

The structural changes of bovine serum albumin (BSA) and hen egg white lysozyme (HEL) upon their adsorption onto the surface or their embedding into the interior of poly(allylamine hydrochloride)-(poly(styrenesulfonate) (PAH-PSS) multilayer architectures were investigated by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The presence of the polyelectrolytes seems, as previously observed for fibrinogen (J. Phys. Chem. B 2001, 105, 11906-11916), to prevent intermolecular interactions and, thus, protein aggregation at ambient temperature. The secondary structure of the proteins was somewhat altered upon adsorption onto the polyelectrolyte multilayers. The structural changes were larger when the charges of the multilayer outer layer and the protein were opposing. The adsorption of further polyelectrolyte layers onto protein-terminated architectures (i.e., embedding the proteins into a polyelectrolyte multilayer) did not cause considerable further changes in their secondary structures. The capacity of the polyelectrolyte architectures to delay the formation of intermolecular beta-sheets upon increasing temperatures was not uniform for the studied proteins. PSS in contact with HEL could largely prevent the heat-induced aggregation of HEL. In contrast, PAH had hardly any effect on the aggregation of BSA. The differences are explained on the basis of protein-polyelectrolyte interactions, affected mostly by the nature and the strength of the ionic interactions between the polyelectrolyte-protein contact surfaces.

Adsorption↗
PubMed2006

Electrophoresis of a spherical dispersion of polyelectrolytes in a salt-free solution.

The electrophoretic behavior of a spherical dispersion of polyelectrolytes of arbitrary concentration is analyzed theoretically under a salt-free condition, that is, the liquid phase contains only counterions which come from the dissociation of the functional groups of polyelectrolytes. We show that, in general, the surface potential of a polyelectrolyte increases nonlinearly with its surface charge. A linear relation exists between them, however, when the latter is sufficiently small; and the more dilute the concentration of polyelectrolytes, the broader the range in which they are linearly correlated. If the amount of surface charge is sufficiently large, counterion condensation occurs, and the rate of increase of surface potential as the amount of surface charge increases declined. Also, it leads to an inverse in the perturbed potential near the surface of a polyelectrolyte, and its mobility decreases accordingly. For a fixed amount of surface charge, the lower the concentration of polyelectrolytes and/or the lower the valence of counterions, the higher the surface potential. The qualitative behavior of the mobility of a polyelectrolyte as the amount of its surface charge varies is similar to that of its surface charge.

Journal Article↗
PubMed2004

On the monomer density of grafted polyelectrolyte brushes and their interactions.

Most of the modern theories of grafted polyelectrolyte brushes are valid only for moderate stretching of the polyelectrolyte. However, particularly at low ionic strength and high grafting densities, even a moderate charge of the polyelectrolyte can generate a strong stretching. A simple mean field model for strongly stretched grafted polyelectrolyte brushes is suggested, based on an approximate calculation of the partition function of a polyelectrolyte chain. It is shown that the average Boltzmann factor of a possible chain configuration can be approximated by the Boltzmann factor of a configuration with a constant monomer distribution, for which the free energy can be readily obtained. The monomer density in the brush and the interaction between two surfaces with grafted polyelectrolyte brushes could be calculated as a statistical average over all possible configurations. Some simple analytical results are derived, and their accuracy is examined. The dependence of the brush thickness on the electrolyte concentration is investigated, and it is shown that the trapping of a fraction of counterions in the brush influences strongly the thickness of the brush. When two surfaces with grafted polyelectrolyte brushes approach each other more rapidly than the ion diffusion parallel to the surface, the trapping of the counterions between the brushes can affect the interactions by orders of magnitude.

Electrolytes↗
PubMed2004

Cylindrical cell model for the electrostatic free energy of polyelectrolyte complexes.

Associative phase separation (complex coacervation) in a mixture of oppositely charged polyelectrolytes can lead to different types of (inter-)polyelectrolyte complexes (soluble micelles, macroscopic precipitation). In a previous report [Langmuir 2004, 20, 2785-2791], we presented a model for the electrostatic free energy change when (weakly charged) polyelectrolyte forms a homogeneous complex phase. The influence of ionization of the polymer on the electrostatic free energy of the complex was incorporated but the influence of complex density neglected. In the present effort, cylindrical cells are assumed around each polyelectrolyte chain in the complex, and on the basis of the Poisson-Boltzmann equation, the electrostatic free energy is calculated as a function of the complex density. After combination with Flory-Huggins mixing free energy terms and minimization of the total free energy, the equilibrium complex density is obtained, for a given ratio of polycations to polyanions in the complex. The analysis is used in an example calculation ofpolyelectrolyte film formation by alternatingly applying a polycation and a polyanion solution. The calculation suggests that the often observed exponential growth of a polyelectrolyte film when the polymer is weakly charged has a thermodynamic origin: the polyelectrolyte complex shifts repeatedly between two equilibrium states of different densities and compositions. However, when the polyelectrolytes are strongly charged the difference in the compositions between the two equilibrium states is very small, and exponential growth by an absorption mechanism is no longer possible.

Journal Article↗
PubMed2004

Structure formation in films of weakly charged block polyelectrolyte solutions.

A mean-field dynamic density functional theory is used to describe a phase diagram of concentrated solutions of weakly charged flexible block polyelectrolytes in a film. Electrostatics is taken into account by applying the local electroneutrality constraint (the Donnan membrane equilibrium approach). In the Donnan limit it is assumed that a salt added to the solution perfectly screens long-range electrostatic interactions. The phase diagram of a solution of a triblock polyelectrolyte in a film as a function of the solvent concentration and the charge of the polyelectrolyte (solvophilic) block is calculated for a given film thickness. The phase behavior of the block polyelectrolyte film arises from the interplay between surface-induced alignment and the electrostatically-driven structure formation. The observed mesoscopic structures (lamellar, perforated lamellar, cylindrical, micellar, and mixed phases) are oriented parallel to the surfaces for the considered case of morphologies unfrustrated by the film thickness. Structures with connections between parallel layers (bicontinuous, etc.) are not formed. As a result of surface-induced ordering, the region of ordered phases in a film is wider than in bulk and the phase boundary between ordered and disordered phases is more diffuse. As in the case of unconfined block polyelectrolyte solution, the solution in a film does not follow the lyotropic sequence of phases of such a block copolymer upon increase in the charge of the polyelectrolyte block. Upon changing the charge of the solvophilic copolymer block, transformations of copolymer morphology take place via change in curvature of polymeric domains. Due to confinement of a polyelectrolyte film, no swelling of solvophilic domains is observed.

Journal Article↗
PubMed2005

Behaviour of endothelial cells seeded on thin polyelectrolyte multilayered films: a new biological scaffold.

The surface modification using thin polyelectrolyte multilayered films was proposed as a new scaffold material for different cell lines. In this study, we evaluated the possible use of polyelectrolyte multilayers as surface modification for the development of endothelial cells. In order to control the behaviour of endothelial cells, cell viability by MTT assay was studied. Moreover, the endothelial cell phenotype was checked and the expression of a leukocyte adhesion molecule (ICAM-1) was quantified. The behaviour of the cells on two polyelectrolyte multilayers was compared to cells on polystyrene, and two polyelectrolyte monolayers (terminating the multilayer architectures). The results have shown a better cell viability on the polyelectrolyte multilayers, inducing a higher cell number compared to polyelectrolyte monolayers after 1 and 3 days of culture. Moreover, the cells showed a normal morphology of cytoskeleton. The phenotype of the endothelial cells was kept and a low level of leukocyte adhesion molecules was observed. In conclusion, the polyelectrolyte multilayers can be considered as a potential surface modification procedure to enhance the development of endothelial cells on hydrophobic substrate and which can be applied to vascular tissue engineering.

Biocompatible Materials↗
PubMed2006

Initial adhesion of endothelial cells on polyelectrolyte multilayer films.

Polyelectrolyte multilayer films were recently investigated to favour attachment of Human Vein Umbilical Endothelial Cells (HUVECs) on non-adhesive surfaces. In this study, we evaluated the initial adhesion of HUVECs after 3 h of seeding on two polyelectrolyte multilayer films ending by poly(D-lysine) (PDL) or poly(allylamine hydrochloride) (PAH). In order to obtain information about initial adhesion of HUVECs, cell morphology as well as the expression of beta1 integrins, specific receptors of adhesion, were evaluated after 3 h of seeding on polyelectrolyte multilayer films. The data were also compared to PDL or PAH monolayers (polyelectrolytes terminating the multilayer architecture). The expression of beta1 integrins was not different, whatever are the studied surfaces. However, HUVECs spreading on polyelectrolyte multilayer films, in particular on PAH ending film, was more important as compared to polyelectrolyte monolayers or glass. In conclusion, the best initial adhesion conditions of HUVECs on polyelectrolyte films could not be elucidated, moreover the results suggested also that beta1 integrins could only play a limited role.

Actins↗
PubMed1998

Effect of Ionic Strength on the Initial Dynamics of Flocculation of Polystyrene Latex with Polyelectrolyte.

The effect of ionic strength on the kinetics of flocculation of polystyrene latex (PSL) particles induced by addition of excess polyelectrolyte was studied. The flocculation experiment was performed in the standardized mixing flow generated by using an end-over-end rotation apparatus and by changing the ionic strength and polyelectrolyte concentration. We focused our attention on the initial process of flocculation, which is characterized by a remarkably high rate of flocculation (the first stage) followed by an abrupt decrease in the flocculation rate (the second stage). The combined measurements of the rate of flocculation and the electrophoretic mobility as a function of mixing steps revealed a transient state of polyelectrolyte adsorbing on the bare surface of PSL particles. Under the conditions of low ionic strength, the picture is consistent with that of kinetically controlled adsorption of polyelectrolyte, while, under high ionic strength, the evidence of kinetically controlled adsorption disappeared. However, even in the latter, the rate of flocculation in the first stage was a function of polyelectrolyte concentration. This is consistent with a picture of nonequilibrium flocculation. A crossover with respect to ionic strength can be ascribed to an increase in flexibility of polyelectrolytes at colloidal surfaces with an increase in ionic strength. Copyright 1998 Academic Press.

Journal Article↗
PubMed1991

Development of an equation for potentiometric titration of polyelectrolytes using a periodic lattice model. A numerical analysis of interactions among ionizable groups.

A numerical method is presented for analysing the potentiometric titration behavior of linear polyelectrolytes. A polyelectrolyte molecule is treated as a one-dimensional lattice containing a large number of lattice points, each of which has an identical ionizable group. In this method, the polyelectrolyte model lattice is divided into identical repeating unit cell systems with a finite number of ionizable groups to calculate the thermodynamic partition function of the system of polyelectrolyte solution. The electrostatic interaction between ionized groups adopted in the present study is given by the Debye-Hückel type screened Coulombic potential. The titration behavior as well as several thermodynamic quantities is derived by making a canonical ensemble summation of all states in a unit cell system under an appropriate periodic boundary condition. This method serves as a model of the two-step ionization often appearing in polyions with strong neighboring interactions such as homo- and copolymers of maleic acid. Several characteristics of the titration behavior of these polyelectrolytes are well reproduced by using a lattice model with pairwise intervals, including the effects of hydrogen bond formation and change in dielectric constant of the medium around an ionizable group. In addition, this method is valid for a more detailed analysis of the titration behavior of polyelectrolytes with various kinds of arrangements of charged groups.

Journal Article↗
PubMed2005

Polyelectrolyte-mediated surface interactions.

The current understanding of interactions between surfaces coated with polyelectrolytes is reviewed. Experimental data obtained with various surface force techniques are reported and compared with theoretical predictions. The majority of the studies concerned with interactions between polyelectrolyte-coated surfaces deal with polyelectrolytes adsorbed to oppositely charged surfaces, and this is also the main focus of this review. However, we also consider polyelectrolytes adsorbed to uncharged surfaces and to similarly charged surfaces, areas where theoretical predictions are available, but relevant experimental data are mostly lacking. We also devote sections to interactions between polyelectrolyte brush-layers and to interactions due to non-adsorbing polyelectrolytes. Here, a sufficient amount of both theoretical and experimental studies are reported to allow us to comment on the agreement between theory and experiments. A topic of particular interest is the presence of trapped non-equilibrium states that often is encountered in experiments, but difficult to treat theoretically.

Adsorption↗
PubMed2006

Preparation of insulin nanoparticles and their encapsulation with biodegradable polyelectrolytes via the layer-by-layer adsorption.

To develop a new polypeptide delivery system, insulin nano-aggregates with sizes of 100-230nm were prepared by the salting out method with NaCl and encapsulated via the layer-by-layer (LbL) adsorption to provide the insulin nanoparticles shelled with two oppositely charged polyelectrolytes. Poly(alpha,beta-l-malic acid) (PMA) and water-soluble chitosan (WSC) as the weak polyelectrolytes with good biodegradability and biocompatibility in vivo were chosen to be the encapsulating materials of the LbL adsorption. In the preparation of the insulin nano-aggregates, the NaCl concentration and pH in the medium obviously affected yield and particle size of the insulin nano-aggregates. After eight adsorption cycles of the polyelectrolytes on the insulin nano-aggregates, the insulin-polyelectrolyte nanoparticles with the sizes of 100-250nm were obtained with about 20% insulin loss. The insulin release from the nanoparticles was mostly pH-dependent owing to sensitivity of the weak polyelectrolytes to pH. Insulin was hardly released from the nanoparticles in a medium at pH 4-5 while it could be released at pH 7.4, corresponding to the pH of the human blood and the body fluid. A burst effect was also observed although it could be reduced via increasing the polyelectrolyte layers of PMA and WSC assembled on insulin nano-aggregates.

Adsorption↗
PubMed2004

Double layer interaction between two plates with polyelectrolyte brushes.

When polyelectrolyte chains are grafted to colloidal particles, the electric field between particles is affected by the charges of the chains. In some previous theoretical attempts, the charge density of the polyelectrolyte chains per unit length was considered constant, and its effect was accounted for by introducing an additional constant charge density into the unidimensional Poisson-Boltzmann equation, which was evaluated assuming that it is uniformly distributed in the polyelectrolyte volume of the brush. In this paper, a more detailed model is employed for the calculation of the electrical potential between two plates on which polyelectrolyte brushes are present. In this model, the polyelectrolyte chain is viewed as a rigid cylinder, on the surface of which charges are generated through the dissociation of ionizable sites and adsorption of the cations of the electrolyte. To each of the chains an atmosphere is attached which for simplicity is assumed cylindrical. In the brush region, the electrical potential is described by a two-dimensional Poisson-Boltzmann equation, while in the region free of polyelectrolyte chains by a unidimensional Poisson-Boltzmann equation. Such a model is physically suitable when the charges of the chains are sufficiently large for the repulsion they generate to ensure that the chains are fully extended. Such cases are quite frequent, because relatively low charges lead to an almost complete extension of the chains. In this paper, both the plate surface and the surface of the cylinders are considered charged. The effects of electrolyte concentration, pH, brush thickness and chain coverage density on the repulsion between plates are examined.

Journal Article↗
PubMed2006

Counterion release from adsorbed highly charged polyelectrolyte: an electrooptical study.

The adsorption of sodium poly(4-styrene sulfonate) on oppositely charged beta-FeOOH particles is studied by electrooptics. The focus of this paper is on the release of condensed counterions from adsorbed polyelectrolyte upon surface charge overcompensation. The fraction of condensed Na+ counterions on the adsorbed polyion surface is estimated according to the theory of Sens and Joanny and it is compared with the fraction of condensed counterions on nonadsorbed polyelectrolyte. The relaxation frequency of the electrooptical effect from the polymer-coated particle is found to depend on the polyelectrolyte molecular weight. This is attributed to polarization of the layer from condensed counterions on the polyion surface, being responsible for creation of the effect from particles covered with highly charged polyelectrolyte. The number of the adsorbed chains is calculated also assuming counterion condensation on the adsorbed polyelectrolyte and semiquantative agreement is found with the result obtained from the condensed counterion polarizability of the polymer-coated particle. Our findings are in line with theoretical predictions that the fraction of condensed counterions remains unchanged due to the adsorption of highly charged polyelectrolyte onto weakly charged substrate.

Journal Article↗