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PubMed2004

Release of a dye from hydrogen-bonded and electrostatically assembled polymer films triggered by adsorption of a polyelectrolyte.

The absorption of dyes within hydrogen-bonded and electrostatically assembled multilayers and subsequent release of the dyes from the films were studied in situ using FTIR-ATR. Multilayers were composed of poly(methacrylic acid), PMAA, and poly(ethylene oxide), PEO (hydrogen-bonded multilayers), or of PMAA and 22% quarternized copolymer of N-ethyl-4-vinylpyridium bromide and 4-vinylpyridine, Q22 (electrostatically stabilized multilayers). After multilayer deposition, the solution pH was changed to produce excess charge within the films. Dyes with charge opposite to the excess charge of the film (Rhodamine 6G for hydrogen-bonded films or Bromophenol Blue for electrostatically assembled multilayers) were then allowed to absorb within multilayers. In both systems, the dyes were uniformly included within the films. The top layers largely affected the loading capacity of the multilayers, suggesting weaker binding of the dyes with the top layers. Dye release into a 0.01 M phosphate buffer was significantly smaller as compared to release in the presence of 0.05-0.5 mg/mL solutions of adsorbing polymers whose charge was the same as the excess charge within the films. We found that with the PMAA/PEO films, dye release did not depend on the concentration of polymer in solution, but was largely controlled by the amount of charge accumulated within the adsorbing polymer layer on the top of the film. For electrostatically stabilized PMAA/Q22 systems, dye release increased with increasing concentration of Q22 in solution, suggesting a significant contribution of the competition of solution species in the release mechanism. Our findings contribute to the understanding of interactions of small molecules with polymer multilayers and might have ramifications for novel applications of multilayer films as new materials for the controlled delivery of chemicals.

Journal Article↗
PubMed2004

Electroactive core-shell nanocluster films of heme proteins, polyelectrolytes, and silica nanoparticles.

Novel protein core-shell nanocluster films were assembled layer by layer on solid surfaces. In the first step, positively charged heme protein hemoglobin (Hb) or myoglobin (Mb) and negatively charged poly(styrenesulfonate) (PSS) were alternately adsorbed on the surface of SiO2 nanoparticles, forming core-shell SiO2-(protein/PSS)m nanoclusters. In the second step, the SiO2-(protein/PSS)m nanoclusters and polycationic poly(ethylenimine) (PEI) were assembled layer by layer on various solid substrates, forming [[SiO2-(protein/PSS)m]/PEI]n films. Various techniques were used to characterize the nanoclusters and monitor the film growth. [[SiO2-(protein/PSS)m]/PEI]n films at pyrolytic graphite (PG) electrodes exhibited well-defined, chemically reversible cyclic voltammetric reduction-oxidation peaks characteristic of the heme Fe(III)/Fe(II) redox couples. The proteins in the films retained near native conformations in the medium pH range, and the films catalyzed electrochemical reduction of oxygen and hydrogen peroxide. Advantages of the nanocluster films over the simple [SiO2/protein]n layer-by-layer films include a larger fraction of electroactive protein and higher specific biocatalytic activity. Using this approach, biocatalytic activity can be tailored and controlled by varying the number of bilayers deposited on the nanoparticle cores and the number of nanocluster layers on electrodes.

Electrochemistry↗
PubMed2004

Synthesis and nanostructure of strong polyelectrolyte brushes in amphiphilic diblock copolymer monolayers on a water surface.

We synthesized an ionic amphiphilic diblock copolymer, poly(hydrogenated isoprene)-b-poly(styrenesulfonic acid) (PIp-h2-b-PSS), by living anionic polymerization, and the nanostructure of its monolayer spread on a water surface was directly investigated by the in situ X-ray reflectivity technique. The monolayer of the diblock copolymer on a water surface had a smooth hydrophobic PIp-h2 layer on water and a "carpet"/polymer brush double layer in a hydrophilic sodium polystyrene sulfonate (PSSNa) layer under the water. The surface pressure dependence and PSSNa chain length dependence of the PIp-h2 layer thickness and the brush nanostructure were quantitatively studied. The effect of salt concentration in the subphase was also investigated in aqueous solutions containing 0-2 M NaCl. The salt effect on monolayer structure occurred at around 0.2 M. The thickness of the PSS brush layer decreased at salt concentrations above 0.2 M, while no structural change was observed below 0.2 M. This critical salt concentration is thought to be related to the balance of ionic concentrations inside the brush and in bulk solution.

Journal Article↗
PubMed2005

Facile synthesis of mesoporous silica sublayer with hierarchical pore structure on ceramic membrane using anionic polyelectrolyte.

A facile method for introducing mesoporous silica sublayer onto the surface of a ceramic membrane for use in liquid-phase separation is described. To reduce the electrostatic repulsion between the mesoporous silica sol and the ceramic membrane in highly acidic conditions (pH < 2), thus facilitating the approach of hydrolyzed silica sol to the surface of the membrane, poly(sodium 4-styrenesulfonate) (Na+PSS-, denoted as PSS-) was used as an ionic linker. The use of PSS- led to a significant reduction in positive charge on the ceramic membrane, as confirmed by experimental titration data. Consistent with the titration results, the amount of mesoporous silica particles on the surface of the ceramic membrane was low, in the absence of PSS- treatment, whereas mesoporous silica sublayer with hierarchical pore structure was produced, when 1 wt % PSS- was used. The results show that mesoporous silica grows in the confined surface, eventually forming a multistacked surface architecture. The mesoporous silica sublayer contained uniform, ordered (P6 mm) mesopores of ca. 7.5 nm from mesoporous silica as well as macropores ( approximately mum) from interparticle voids, as evidenced by transmission electron microscopy and scanning electron microscopy analyses. The morphologies of the supported mesoporous silica could be manipulated, thus permitting the generation of uniform needlelike forms or uniform spheroid particles by varying the concentration of PSS-.

Journal Article↗
PubMed2005

Direct comparison of atomic force microscopic and total internal reflection microscopic measurements in the presence of nonadsorbing polyelectrolytes.

We have investigated the structural and depletion forces between silica glass surfaces in aqueous, salt-free solutions of sodium poly(styrene sulfonate). The interaction forces were investigated by two techniques: total internal reflectance microscopy (TIRM) and colloid probe atomic force microscopy (AFM). The TIRM technique measures the potential energy of interaction directly, while the AFM is a force balance. Comparison between the data sets was used to independently calibrate the AFM data since the separation distances cannot be unequivocally determined by this technique. Oscillatory structural forces are excellent for this work since they give multiple reference points against which to analyze. Comparison of the data from the two techniques highlighted significant uncertainties in the AFM data. At low polymer concentrations, a significant uncertainty in the apparent zero separation distance was seen as a result of the AFM cantilever reaching an apparent constant compliance region prior to any real contact between the surfaces. Further complications arising from the number and position of the measured minima were also seen in the dilute polymer concentration regime as a result of hydrodynamic drainage between the approaching surfaces in the AFM perturbing the delicate structural components in the fluid.

Journal Article↗
PubMed2005

Nonspherical assemblies generated from polystyrene-b-poly(L-lysine) polyelectrolyte block copolymers.

This report describes the aqueous solution self-assembly of a series of polystyrene(m)-b-poly(L-lysine)n block copolymers (m = 8-10; n = 10-70). The polymers are prepared by ring-opening polymerization of epsilon-benzyloxycarbonyl-L-lysine N-carboxyanhydride using amine terminated polystyrene macroinitiators, followed by removal of the benzyloxycarbonyl side chain protecting groups. The critical micelle concentration of the block copolymers determined using the pyrene probe technique shows a parabolic dependence on peptide block length exhibiting a maximum at n = approximately 20 (m = 8) or n = approximately 60 (m = 10). The shape and size of the aggregates has been studied by dynamic and static light scattering, small-angle neutron scattering (SANS), and analytical ultracentrifugation (AUC). Surprisingly, Holtzer and Kratky analysis of the static light scattering results indicates the presence of nonspherical, presumably cylindrical objects independent of the poly(L-lysine)n block length. This is supported by SANS data, which can be fitted well by assuming cylindrical scattering objects. AUC analysis allows the molecular weight of the aggregates to be estimated as several million g/mol, corresponding to aggregation numbers of several 10s to 100s. These aggregation numbers agree with those that can be estimated from the length and diameter of the cylinders obtained from the scattering results.

Journal Article↗
PubMed2005

Wormlike micelles mediated by polyelectrolyte.

Aqueous solutions of the anionic surfactant potassium oleate (K-oleate) were studied using small-angle neutron scattering (SANS), steady-state rheology, and cryogenic transmission electron microscopy (cryo-TEM). The micellar structural changes induced by the addition of potassium chloride (KCl) and sodium polystyrenesulfonate (PSS) of different molecular weights were investigated. Upon addition of KCl, a transition from spherical to wormlike micelles was detected from the SANS data and confirmed by the cryo-TEM pictures. The rheological measurements revealed a strong dependence of the low-shear viscosity on the concentration of salt: a broad maximum in the viscosity curve was observed upon addition of KCl, characteristic of the growth of micelles into long worms, followed by branching. The addition of PSS to salt-free solutions of K-oleate had a significant effect on the scattering patterns, revealing partial growth of the spherical micelles into rodlike micelles. In contrast, in the presence of high salt concentrations, addition of PSS to solutions of wormlike micelles did not bring any noticeable modifications in the scattering. However, in the same salt conditions, a clear effect was observed on the low shear viscosity upon addition of PSS, which was found to depend significantly on molecular weight. This suggests a novel way of impacting the viscosity of solutions of wormlike micelles.

Micelles↗
PubMed2005

A model of polyelectrolyte conductance in moist solvents as a basis of water sensors.

The conductance of interpenetrated polymer networks (IPNs) containing quaternary amino groups was studied in cyclohexane, toluene, ethyl ether, ethyl acetate, and tetrahydrofurane as a function of water content by electrochemical impedance spectroscopy. IPNs were then used as sensitive materials to detect water traces in organic solvents with promising results for the construction of a moisture sensor. The detection onset for water concentration increased with the dielectric constant of the solvent. Different IPN-based sensors in the same solvent showed a detection limit at lower water concentration if their characteristic plot [conductance/relative humidity (RH%) in air] was shifted toward lower RH%. This suggests that the composition of this class of polymers can be tuned to achieve the best performance for each solvent.

Journal Article↗
PubMed2006

Adhesion of single polyelectrolyte molecules on silica, mica, and bitumen surfaces.

In a recent study (Energy Fuels 2005, 19, 936), a partially hydrolyzed polyacrylamide (HPAM) was used as a process aid to recover bitumen from oil sand ores. It was found that HPAM addition at the bitumen extraction step not only improved bitumen recovery but also enhanced fine solids settling in the tailings stream. To understand the role of HPAM, single-molecule force spectroscopy was employed for the first time to measure the desorption/adhesion forces of single HPAM molecules on silica, mica, and bitumen surfaces using an atomic force microscope (AFM). Silicon wafers with an oxidized surface layer and newly cleaved mica were used, respectively, to represent sand grains and clays in oil sands. The force measurements were carried out in deionized water and in commercial plant process water under equilibrium conditions. The desorption/adhesion forces of HPAM obtained on mica, silica, and bitumen surfaces were approximately 200, 40, and 80 pN in deionized water and approximately 100, 50, and 40 pN in the plant process water, respectively. The measured adhesion forces together with the zeta potential values of these surfaces indicate that the polymer would preferentially adsorb onto clay surfaces rather than onto bitumen surfaces. It is the selective adsorption of HPAM that benefits both bitumen recovery and tailings settling when the polymer was added directly to the bitumen extraction process at an appropriate dosage.

Acrylic Resins↗
PubMed2006

Steric and bridging interactions between two plates induced by grafted polyelectrolytes.

If colloidal particles are grafted with a polymer, then the grafted chains can provide steric repulsion between them. If some of the grafted polymer chains are also adsorbed to a second particle, then a bridging force is generated as well. For uncharged plates and polymer, the following contributions to the free energy of the system have been taken into account in the calculation of the interaction force: (i) the Flory-Huggins expression for the mixing free energy of the grafted chains with the liquid; (ii) the entropy loss due to the connectivity of the polymeric segments; (iii) the van der Waals interactions between the segments and the plates; and (iv) the free energy of adsorption of the polymer segments of the grafted chains on the other plate. For charged plates, the electrostatic free energy as well as the free energy of the electrolyte are included in the total free energy of the system. By minimizing the free energy with respect to the segment concentration and, when it is the case, with respect to the electrical potential, equations for the segment number density distribution and for the electrical potential are obtained, on the basis of which the interactions between two plates grafted with polymer chains that can be also adsorbed on the other plate were calculated. The interaction thus obtained includes steric and bridging forces.

Journal Article↗
PubMed2006

Controlled association in suspensions of charged nanoparticles with a weak polyelectrolyte.

The properties of high-pH suspensions of mixtures of silica with low-molecular-weight samples of the water-soluble polymer polyethylenimine (PEI) have been studied. At pH > 10 and low ionic strength, silica nanoparticles are stabilized by a negative surface charge, and PEI has only a very low positive charge. The adsorption of PEI induces a localized positive charge on the segments of polymer closest to the silica surface. The parts of the molecule furthest away from the surface have little charge because of the high pH of the medium. The polymer-covered particle remains negatively charged, imparting some electrostatic stabilization. Suspensions of silica and low-molecular-weight PEI are low-viscosity fluids immediately after mixing, but aggregation occurs leading to the eventual gelation (or sedimentation at lower concentrations) of these mixtures, indicating colloidal instability. The gelation time passes through a minimum with increasing surface coverage. The rate of gelation increases exponentially with molecular weight: for molecular weight > or = 10,000 Da PEI, the instability is so severe that uniform suspensions cannot be produced using simple mixing techniques. The gelation rates increase rapidly with temperature, ionic strength, and reduction in pH. The rate of gelation increases with increasing particle concentration at low surface coverage but decreases at high coverage as a consequence of a small increase in pH. Gels are broken by application of high shear into aggregates that re-gel more rapidly than the original discrete coated particles.

Journal Article↗
PubMed2006

Meta-linked poly(phenylene ethynylene) conjugated polyelectrolyte featuring a chiral side group: helical folding and guest binding.

A water soluble, meta-linked poly(phenylene ethynylene) featuring chiral and optically active side groups based on L-alanine (mPPE-Ala) has been studied by using absorption, fluorescence, and circular dichroism spectroscopy. Studies of mPPE-Ala in methanol/water solvent mixtures show that the polymer folds into a helical conformation, and the extent of helical folding increases with the volume % water in the solvent. The presence of the helical conformation is signaled by the appearance of a broad, excimer-like visible fluorescence band, combined with a strong bisignate circular dichroism signal in the region of the pi,pi absorption of the polymer backbone. The circular dichroism signal exhibits negative chirality, suggesting that the left-handed (M-form) of the helix is in enantiomeric excess. Binding of the metallointercalator [Ru(bpy)2(dppz)]2+ (where bpy = 2,2-bipyridine and dppz = dipyrido[3,2-a:2',3'-c]phenazine) with the helical polymer is accompanied by the appearance of the orange-red photoluminescence from the metal complex. This effect is directly analogous to that observed when [Ru(bpy)2(dppz)]2+ binds to DNA via intercalation, suggesting that the metal complex binds to mPPE-Ala by intercalating between the pi-stacked phenylene ethynylene residues. Cationic cyanine dyes also bind to the periphery of the helical polymer in a manner that is interpreted as "groove binding". A circular dichroism signal is observed that is believed to arise from exciton coupling within the chiral cyanine dye chromophore aggregate that is formed as the dye molecules are oriented by the helical mPPE-Ala "template".

Journal Article↗
PubMed2006

Light-scattering study of polyelectrolyte complex formation between anionic and cationic nanogels in an aqueous salt-free system.

We studied complex formation in an aqueous salt-free system (pH approximately 3 and at 25 degrees C) between nanogel particles having opposite charges. Anionic gel (AG) and cationic gel (CG) particles consist of lightly cross-linked N-isopropylacrylamide (NIPA) copolymers with 2-acrylamido-2-methylpropane sulfonic acid and with 1-vinylimidazole, respectively. The number of charges per particle was -4490 for AG and +20 300 for CG, as estimated from their molar masses (3.33 MD for AG and 11.7 MD for CG) by static light scattering (SLS) and their charge densities (1.35 mmol/g for AG and 1.74 mmol/g for CG) by potentiometric titration. The complexes were formed through the addition of AG to CG and vice versa using a turbidimetric titration technique. At the endpoint of the titration, the aggregate formed was a complex based upon stoichiometric charge neutralization: CG(n)()(+) + xAG(m)()(-) --> CG(n)()(+) (AG(m)()(-))(x)() where x = (n)()/(m)(). At different stages of the titration before the endpoint, the resulting complexes were examined in detail using dynamic light scattering, SLS, and electrophoretic light scattering (ELS). The main results are summarized as follows: (i) When AG with a hydrodynamic radius (R(h)) of 119 nm is added to CG (R(h) approximately 156 nm), the (R(h)) of the complex size decreases from 156 to 80 nm. (ii) In contrast to this (R(h)) change, the molar mass increases from 11.7 MD to 24 MD with increasing amounts of added AG. (iii) Upon addition of CG to AG, the complex formed has the same size ((R(h)) approximately 80 nm) and the same molar mass (55 +/- 2.5 MD) until 55 +/- 5% of AG has been consumed in the complexation. To understand these results, we used the following two models: the random model (RM), in which the added AG particles uniformly bind to all of the CG particles in the system via a strong electrostatic attraction, and the all-or-none model (AONM), in which part of the AG particles in the system preferably bind to the added CG particles to neutralize their electric charges but the other AG particles are uncomplexed and remain in the system. The complex formations upon addition of AG to CG and CG to AG were elucidated in terms of RM and AONM, respectively.

Acrylamides↗
PubMed2006

Unraveling the spatial distribution of immunoglobulins, enzymes, and polyelectrolytes within layer-by-layer self-assembled multilayers. Ellipsometric studies.

The ellipsometric characterization of a layer-by-layer electrostatically self-assembled multilayer of polyphenol oxidase and alkaline phosphatase with the polycation poly(dimethyldiallylammonium chloride) built on an immunologic layer formed by immunoglobulin G (IgG) and glucose oxidase-conjugated anti-IgG (IgG-GOD) on glassy carbon is reported. The step-by-step evolution of the psi-Delta ellipsometric angles was followed during film growth. Two optical models, named the three-layer film model and reorganization film model, were employed and found suitable for ellipsometric data interpretation. A comparative analysis of film optical properties, film thickness, and ellipsometric mass assessed from both models is also presented.

Alkaline Phosphatase↗
PubMed2006

Robust ion-permselective multilayer films prepared by photolysis of polyelectrolyte multilayers containing photo-cross-linkable and photolabile groups.

The azobenzene-containing polyanion PAC-azoBNS was alternately assembled with the polycation diazoresin (DAR) to construct photo-cross-linkable multilayer films of PAC-azoBNS/DAR that contain photolabile groups of azobenzene. Upon mild UV irradiation, the interaction between PAC-azoBNS/DAR multilayers was converted from electrostatic interaction to covalent bonds. Because of the free carboxylic acid groups presented in the film, the photo-cross-linked multilayer film favors the selective permeation of positively charged species. After photolysis of the photo-cross-linked PAC-azoBNS/DAR films with intense UV irradiation, azobenzene groups decompose to produce imine groups, and a photo-cross-linked robust film containing free carboxylic acid and imine groups was fabricated. The resultant film allows the permeation of negatively charged species and meanwhile shows a pH-switchable permselectivity for positively charged species. Because of the covalently cross-linking structure, the photolyzed cross-linked PAC-azoBNS/DAR film shows high reversible switching behavior and has high stability in solution with high ionic strength.

Journal Article↗
PubMed2006

Novel method for the estimation of the binding isotherms of ionic surfactants on oppositely charged polyelectrolytes.

One of the most important characteristics of the polyelectrolyte/surfactant interaction is the binding isotherm of the surfactant because it provides basic thermodynamic information about the binding mechanism. However, the amount of the surfactant bound to the polymer may crucially affect the surface properties of these systems via changing the thermodynamic activity of the components. Therefore, a knowledge of the binding isotherms can also be useful in tuning the efficiency of commercial products. However, the determination of these isotherms is still subject to significant experimental difficulties. In this letter, we offer a novel method for the estimation of binding isotherms based on electrokinetic measurements. The technique provides a simple and quick way to estimate the bound amount of surfactant that might be useful in both fundamental and industrial research. In principle, the proposed method could also be extended to the determination of the binding isotherms of small ligands on biomacromolecules.

Journal Article↗