Polyelectrolyte Complexes In Solution Research Articles

Impact of Star Polyacid Branching on Polymer Diffusion within Multilayer Films

A series of linear and star poly(acrylic acids) (LPAA and star PAAs) were synthesized to explore the effect of molecular architecture on the stratification and polymer dynamics of electrostatic layer-by-layer (LbL) films. Studies of LbL deposition of LPAA and star PAAs with poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) at acidic pH showed an ∼30% increase in film dry thickness with increased polymer branching. Consistent with a greater mass of star polymer deposited within the films, in situ ellipsometric measurements of PAA uptake from solution revealed ∼3.5-fold greater diffusion coefficients for 8-arm PAA in comparison to linear PAA. For comparison, the dynamics of the linear PDMAEMA partner was explored via neutron reflectometry (NR) studies of stacked multilayers containing hydrogenated and deuterated polycations, hPDMAEMA and dPDMAEMA. The stacked multilayers deposited from low-ionic-strength solutions were stratified, exhibiting interfacial widths between hydrogenated and deuterated stacks of ∼15 and 10 nm for films constructed with star and linear PAAs, respectively, suggesting relatively low mobility of the polycation in both assemblies. Further exposure of these films to 0.5 M sodium chloride solutions enhanced the mobility of PDMAEMA, revealing an order magnitude faster diffusion of PDMAEMA in films of 8-arm PAA relative to linear PAA. The faster diffusion of polymers within films of star polyacids was correlated not only with the compactness of star polymers but also with an ∼2-fold lower ionization of assembled 8-arm PAA as determined by Fourier transform infrared spectroscopy and thus a lower number of polycation–polyacid ionic contacts in the case of star polymers as compared to their linear counterparts. The significant influence of molecular architecture on the number of polymer–polymer contacts was further confirmed by isothermal titration calorimetry studies of polyelectrolyte complexes in solution.

The Anomalous Influence of Polyelectrolyte Concentration on the Deposition and Nanostructure of Poly(ethyleneimine)/Poly(acrylic acid) Multilayers.

The deposition and nanostructure of polyelectrolyte (PEL) multilayers (PEMs) of branched poly(ethyleneimine)/poly(acrylic acid) (PEI/PAA) onto silicon substrates was studied in terms of the dependence of pH and the PEL concentration (cPEL) in the individual adsorption steps z. Both a commercial automatic dipping device and a homebuilt automatic stream coating device (flow cell) were used. Gravimetry, SFM, transmission (TRANS) and in situ attenuated total reflection (ATR) FTIR spectroscopy were used for the quantitative determination of the adsorbed amount, thickness, chemical composition and morphology of deposited PEMs, respectively. Firstly, the combination of pH = 10 for PEI and pH = 4 for PAA, where both PEL were predominantly in the neutral state, resulted in an extraordinarily high PEM deposition, while pH combinations, where one PEL component was charged, resulted in a significantly lower PEM deposition. This was attributed to both PEL conformation effects and acid/base interactions between basic PEI and acidic PAA. Secondly, for that pH combination an exponential relationship between PEM thickness and adsorption step z was found. Thirdly, based on the results of three independent methods, the course of the deposited amount of a PEM-10 (z = 10) versus cPEL in the range 0.001 to 0.015 M at pH = 10/4 was non-monotonous showing a pronounced maximum at cPEL = 0.005 M. Analogously, for cPEL = 0.005 M a maximum of roughness and structure size was found. Fourthly, related to that finding, in situ ATR-FTIR measurements gave evidence for the release of outermost located PEI upon PAA immersion (even step) and of outermost PAA upon PEI immersion (odd step) under formation of PEL complexes in solution. These studies help us to prepare PEL-based films with a defined thickness and morphology for interaction with biofluids in the biomedical and food fields.

Robust “one-component” chitosan-based ultrathin films fabricated using layer-by-layer technique

“One-component” chitosan-based multilayer films have been formed and characterized for the first time. Two derivatives of chitosan containing oppositely charged strong ionic groups were synthesized for that purpose. Low molecular weight chitosan was modified by glycidyltrimethylammonium chloride to obtain the cationic form (CCh) of the polymer. The anionic form of chitosan (ACh) was obtained by sulfonation of carboxymethylchitosan with trimethylamine-sulfur trioxide. The two derivatives of chitosan were used to prepare stable multilayer polyelectrolyte films through a layer-by-layer (LbL) deposition technique. The films revealed smooth surfaces and linear growth of the thickness during LbL adsorption as measured by atomic force microscope (AFM). Contact angle measurements revealed a very hydrophilic nature of the formed films. In contrast, the hybrid films, made of one of the chitosan derivatives and the synthetic oppositely charged polyelectrolyte, demonstrated non-linear growths and much higher surface roughnesses. So far, the multilayer films built of natural polymers like chitosan and alginate as well as the mentioned hybrid films have shown difficulties in regular formation related to the differences in polymer backbones and/or the charge distribution along them. The approach proposed here omits the inherent entropic barrier and leads to the controlled formation of robust “one-component” multilayer films. The entropy-driven formation of such films was also supported by the calorimetric studies on the model polyelectrolyte complexes in solution. Thanks to biocompatibility and bacteriostatic properties of chitosan and its derivatives, CCh/ACh multilayer films may be potentially useful for many biomedical and environmental protection applications.

Rheological properties of concentrated aqueous solutions of anionic and cationic polyelectrolyte mixtures

The rheological properties of aqueous solutions of poly(acrylic acid), poly(diallyldimethyldiammonium chloride), and their mixtures at 25°C have been studied. The concentrated solutions of the mixtures contain 18 wt % of both polymers taken at different ratios. The ratio of cationogenic and anionogenic groups φ varied from 0 to 0.4 is taken as a criterion for selection of mixture composition. An increase in φ, reflecting a more intense formation of polyelectrolyte complexes in solution, is accompanied by a significant rise in the low-frequency loss modulus and, especially, in the storage modulus, as well as by an increase in viscosity over the entire studied range of shear rates. This behavior may be explained by the presence of an additional spatial structure with junctions formed by interacting complementary charged groups. In the general case, the formation of poly(acrylic acid)-poly(diallyldimethyldiammonium chloride) polyelectrolyte complexes is said to take place in solution. The excess of rheological characteristics of mixture solutions over the corresponding characteristics of poly(acrylic acid) solutions is found to be the power function of parameter φ. The additional spatial network derived from polyelectrolyte complexes and occurring in solution is destroyed at lower shear stresses than is the network of intermolecular entanglements. At high shear stresses, orientational effects may cause phase separation of the systems owing to a change in the hydrophilic-hydrophobic balance between complexes of poly(acrylic acid) with poly(diallyldimethyldiammonium chloride) and water.

The influence of ionic strength, electrolyte type and preparation procedure on formation of weak polyelectrolyte complexes

The influence of ionic strength, electrolyte type and preparation procedure on formation of weak polyelectrolyte complexes formed by mixing aqueous solutions of poly(dimethylaminoethyl methacrylate) (PAMA) and poly(acrylic acid) (PAA) was investigated. For that purpose, nephelometric, electrokinetic and microcalorimetric measurements were performed. The influence of preparation procedure on formation of polyelectrolyte complexes was much more pronounced at lower ionic strength (50 mmol dm −3) than at higher ionic strength (200 mmol dm −3). The effect of KCl, NaNO 3 and phosphate buffer on weak polyelectrolyte complex formation is discussed. The obtained results are compared with earlier studies of effects of electrolyte type and ionic strength on multilayers formed by alternate adsorption of PAMA and PAA at silica surface. It has been shown that the formation of polyelectrolyte multilayers on metal oxide surface is largely governed by the phase behaviour of polyelectrolyte complexes in solutions and that the presence of different salts influences in similar manner both polyelectrolyte complex formation and polyelectrolyte multilayer formation process.

Where Polyelectrolyte Multilayers and Polyelectrolyte Complexes Meet

We summarize existing knowledge and present some new results on the relationship between polyelectrolyte multilayer (PEM) growth and phase behavior of polyelectrolyte complexes (PECs) in solution. Detailed understanding of competition between surface and solution as applied to PEMs requires selective labeling of polymers and/or the application of techniques that allow chemically specific monitoring of film components, such as in-situ ATR−FTIR spectroscopy. The trends observed with multilayers directly follow from the properties of PECs in solution. Effects of a number of parameters, such as the type of interacting polyelectrolyte chains, the ratio of their lengths, and ionic strength and pH of deposition solutions, on the likelihood of the multilayer stability or erosion are considered. Polycations with high density of primary amino groups and polyanions with SO3- or SO4- groups show the strongest interpolyelectrolyte binding, resulting in inhibited chain exchange within PECs and/or PEMs. With weakly boun...

Phase separation in solutions of polyelectrolyte complexes: The decisive effect of a host polyion

Boundaries of the existence of insoluble polyelectrolyte complexes in solutions of nonequimolar mixtures of quaternary polyamines and polycarboxylates of various degrees of polymerization have been determined with turbidimetric titration. It has been shown that in salt-free media the position of critical points expressed as the ratio between the charge numbers of polymer components in a mixture depends on the chemical nature of the host polyelectrolyte (polycation or polyanion) but does not depend on either the nature of the guest polyelectrolyte or the degree of polymerization of mixture components. Upon addition of a low-molecular-mass polyelectrolyte, the heterogeneous region widens. The shorter the host polyelectrolyte relative to the guest polyelectrolyte, the more pronounced this effect. Based on the thermodynamic state of the systems under examination, an explanation of this effect is confirmed by the velocity sedimentation data.

Polyelectrolyte Complexes in Solution and in Bulk

AbstractFor Abstract see ChemInform Abstract in Full Text.

Time-dependent conformational changes of polyelectrolyte complexes in solution

Changes in the conformation of the polyelectrolytes when contacted with oppositely charged polyelectrolytes or when subjected to shifts in solution conditions (pH), have been studied in this work along with reversibility of the changes using fluorescence spectroscopy. While changes due to both of the above are marked, they are measurably different from each other. Thus, the extent of coiling of the complexes formed between the anionic polyelectrolyte, maleicacid anhydride–propene and the cationic polyelectrolytes was much higher than that achieved by the change in pH alone. Also, while the changes due to pH shifts were fast and reversible, that due to complexation between oppositely charged ones involved first a rapid uncoiling followed by slow recoiling to a new structure. Interestingly, shifting the coiled conformation to an even more coiled one resulted in a new reversible state, but shifting to a stretched state by complexation led to a somewhat irreversible structure. Also maximum interaction obtained between the anionic and one cationic polyelectrolyte was markedly higher than that between the former and another cationic polymer. These observations using fluorescence spectroscopy was consistent with that obtained by the potentiometric titration. The study clearly shows the importance of the manner in which the polyelectrolytes are equilibrated to desired solution conditions. These results are interpreted here in terms of deprotonation/protonation of the polyelectroytes upon pH change and complexation with oppositely charged ones resulting in screening of charges as well as stiffening.

Salt-Induced Multilayer Growth: Correlation with Phase Separation in Solution

We report salt-induced phase separation of polyelectrolyte complexes in solution correlates with deposition of polymer multilayers at a surface. Multilayer growth was followed in situ using FTIR-ATR (Fourier transform infrared spectroscopy by attenuated total reflection). The polymer system was quaternized poly(4-vinylpyridine) (QPVP) and poly(methacrylic acid) (PMAA), with various ratios of PMAA to QPVP chain lengths. In solution, phase diagrams were produced for QPVP/PMAA mixtures containing excess of PMAA or QPVP, in both cases showing salt-induced phase separation. These phase diagrams controlled deposition of PMAA or QPVP chains at the surface and explained a bell-shaped dependence of the multilayer thickness on the salt concentration. The order of chain removal (occurring at the step of QPVP or PMAA deposition) could also be predicted from the phase state of QPVP/PMAA mixtures in solution. Finally, we show that, by using short equilibration times with solution, robust multilayers can be produced at surfaces even in conditions when multilayer deposition is aggravated by desorption of polymer chains.

Polyelectrolyte complexes of soluble poly-2-[(methacryloyloxy)ethyl]trimethylammonium chloride and its hydrogels with poly(acrylic acid)

The complex formation of poly-2-[(methacryloyloxy)-ethyl]trimethylammonium chloride (PMADQUAT) with poly(acrylic acid) (PAA) of different molecular weights has been studied in aqueous solutions by potentiometric, viscometric, turbidimetric and FTIR spectroscopic methods. The formation of insoluble non-stoichiometric polyelectrolyte complexes has been shown. The stability of polyelectrolyte complexes in solutions of different pH and ionic strength has been evaluated. The formation of polyelectrolyte complexes between hydrogels of PMADQUAT and linear PAA of different molecular weights has been studied. It was shown that the molecular weight of PAA considerably affects the kinetics of interaction as well as the final state of gel–polymer complex.

Conformational Behavior of Polyelectrolyte Complexes at the Solid/Liquid Interface

Conformation of polymers at solid/liquid interface is an important property that determines their effectiveness in processes such as dispersion, deposition, adhesion, and wettability. In this work, conformational behavior of pyrene labeled poly(maleic acid-co-propylene), MS−P*, in solution and at the alumina surface and its changes upon perturbation in solution pH or addition of a second oppositely charged polymer than the ones in solution were studied using fluorescence spectroscopy. Conformation of this weak polyanion, both in solution and at the solid/liquid interface was found to be strongly pH-dependent. The degree of coiling on alumina depended on the solution state immediately before the adsorption. The conformation of the polymers in solution and on the solid were the same above pH 4, but, interestingly, the adsorbed polymer was more stretched at low pH. When the polymer is in the coiled form, changes in pH caused partial conformational adjustments of the adsorbed species. However, in the stretched form, the adsorbed polymer was unable to adopt the coiled conformation on the surface even with pH perturbation. Addition of polycations, poly(ethyleneimine) and poly(diallyldimethylammonium) chloride, to systems containing the preadsorbed polyanion led to conformational changes due to the formation of complexes between them at the surface. While the polyelectrolyte adsorbed in the stretched form undergoes very little conformational rearrangement, the re-conformation of the polymer adsorbed in the coiled form depends on the charge density of the second polymer and the solid. These results are compared with the behavior of polyelectrolyte complexes in solution and analyzed to elucidate possible conformational dynamics of polymers at interfaces.

Biological polyelectrolyte complexes in solution and confined on patterned surfaces

In the first part of this paper we describe recently discovered structures in self-assemblies of charged membranes complexed with the biological polyelectrolyte DNA. These complexes are currently used in medical applications of non-viral gene delivery. The second part of the paper will describe entirely new experiments where liquid crystal and biological polymers are confined on lithographically prepared patterned surfaces to produce oriented self-assemblies for structural studies and confinement induced new phases. While the focus of the paper will be on DNA, other important biological polyelectrolytes include filamentous actin (F-actin), intermediate filaments, and microtubules with varying physical and chemical molecular properties, are also discussed.