Influence of chain charge and complexation on the overlap and entanglements formation in poly(acrylic acid) salt-containing aqueous solutions

Dilute-semidilute regime crossover in aqueous solutions of partly neutralized poly(acrylic acid) and of its complex with tetradecyltrimethylammonium bromide was studied by light scattering and viscometry methods. The chain charge growth causes the decrease of overlap concentration (c*) and the increase of the entanglements formation concentration (ce), hence, the semidilute unentangled regime of solution expands. Complexation of the polyelectrolyte with an oppositely charged surfactant leads to c* increase and to ce decrease. It is shown that in semidilute entangled solutions the surfactant acts as an effective structuring agent because of the binding of polyelectrolyte chains via surfactant micelles.     

Preparation of stable electroneutral nanoparticles of sodium dodecyl sulfate and branched poly(ethylenimine) in the presence of pluronic F108 copolymer

Mixing of polyelectrolyte solutions with solutions of oppositely charged surfactants usually leads to phase separation in a certain concentration range. However, since the charge-neutralized polyelectrolyte/surfactant nanoparticles might be utilized as versatile nanocarriers of different substances, it would be desirable to prevent their aggregation for some applications. As it was revealed in earlier investigations, the complete suppression of precipitation may be achieved only in mixtures of ionic surfactants and appropriate copolymer polyelectrolytes with nonionic and ionic blocks. In this work, we present a method that could prevent phase separation in mixtures of homopolyelectrolytes and oppositely charged surfactants. Specifically, it is shown that nonaggregating electroneutral nanocomplexes of branched poly(ethylenimine) (PEI) and sodium dodecyl sulfate (SDS) can be prepared in the presence of the amphiphilic triblock copolymer Pluronic F108, provided that an adequate mixing protocol is used for preparation of the PEI/SDS/F108 mixtures.     

Controlled phase separations in solutions of soluble polyelectrolyte complex of DIVEMA (copolymer of divinyl ether and maleic anhydride)

Copolymer of divinyl ether and maleic anhydride (DIVEMA) is known to possess some anti-tumor and immune-stimulating activity and use as a drug carrier in anti-tumor drug delivery systems. Samples of DIVEMA of different degrees of polymerization were synthesized and characterized. Interaction of the hydrolyzed water-soluble DIVEMA polyanions with poly(N-ethyl-4-vinylpyridinium) cations (PEVP) has been studied. According to the potentiometry data, almost all carboxylic groups of the polyanions were able to form ion pairs with PEVP. In aqueous and water-salt solutions, formation of either soluble or insoluble polyelectrolyte complexes occurred depending on pH, ratio of the oppositely charged groups, and degree of polymerization of PEVP and/or DIVEMA. The phase separations followed general rules revealed by studying mixtures of PEVP and polycarboxylic acids. However in the case of DIVEMA, a significant broadening of the region for insoluble complexes at the expense of the region of soluble complexes was established. The data obtained demonstrate plausible advantages of the complex formation as the non-covalent modification of the polymeric carrier that endow DIVEMA with the ability for reversible soluble-insoluble transformation, in particular at physiological pH and ionic strength.     

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.     

Polyelectrolyte complex nanoparticles from chitosan and poly(acrylic acid) and Polystyrene‐block‐poly(acrylic acid)

Interpolymer polyelectrolyte complexes of chitosan (CS) with poly(acrylic acid) homopolymers and polystyrene‐block‐poly(acrylic acid) diblock copolymers were prepared and characterized. The influence of the positive/negative charge balance (charge ratio), pH, and ionic strength were thoroughly studied by dynamic light scattering. The existence of a strong polyelectrolyte effect was also highlighted in this study. Domains of stability, in which nanoparticle sizes are smaller than 100 and 200 nm for complexes of CS with the homopolymer and copolymer, respectively, were identified and confirmed by scanning electron microscopy and atomic force microscopy. The charged nature of the surface of the nanoparticles was evidenced by Zeta potential measurements. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

On the stability of (highly aggregated) polyelectrolyte complexes containing a charged-block-neutral diblock copolymer

Using light scattering and cryogenic transmission electron microscopy, we show that highly aggregated polyelectrolyte complexes (HAPECs) composed of poly([4-(2-aminoethylthio)butylene] hydrochloride)49-block-poly(ethylene oxide)212 and poly(acrylic acid) (PAA) of varying lengths (140, 160, and 2000 monomeric units) are metastable or unstable if the method of preparation is direct mixing of two solutions containing the oppositely charged components. The stability of the resulting HAPECs decreases with decreasing neutral-block content and with increasing deviation from 1:1 mixing (expressed in number of chargeable groups) of the oppositely charged polyelectrolytes, most probably for electrostatic reasons. The difference between the metastable and stable states, obtained with pH titrations, increases with increasing PAA length and increasing pH mismatch between the two solutions with the oppositely charged components.     

Effect of a low-molecular-weight salt on colloidal dispersions of interpolyelectrolyte complexes

Colloidal dispersions of an interpolyelectrolyte complex were prepared by mixing dilute aqueous solutions of poly(dimethyldiallylammonium chloride) and the sodium salt of the alternating copolymer of maleic acid propene in amounts providing about a threefold excess of the charged groups of the cationic polyelectrolyte over those of the anionic polyelectrolyte. These dispersions were examined by means of analytical sedimentation, quasielastic light scattering, and laser Doppler microelectrophoresis. The experimental results obtained suggest that the particles of the interpolyelectrolyte complex are multicomplex aggregates bearing cationic charge. Such aggregates were assumed to consist of a hydrophobic core formed by coupled oppositely charged macromolecules and a hydrophilic shell formed by cationic macromolecules. Hydrodynamic and electrophoretic properties of these aggregates were found to be rather sensitive to variations in the ionic strength of the surrounding medium: with rising salt concentration, their sedimentation coefficient and hydrodynamic size increase, these increases becoming more strongly pronounced at higher salt concentrations, whereas their electrophoretic mobility gradually decreases. The salt effects revealed suggest that the aggregation level of the particles of the interpolyelectrolyte complex rises in response to an increase in the ionic strength of the surrounding medium. This phenomenon was associated with the salt-induced decrease of the stabilizing effect of the hydrophilic shells that protect such particles from progressive aggregation. Received: 15 May 1998 Accepted in revised form: 28 August 1998     

Pervaporation and properties of chitosan-poly(acrylic acid) complex membranes

Polyelectrolyte complex membranes between chitosan as a cationic polyelectrolyte and poly(acrylic acid) as an anionic species were prepared by blending two polymer solutions in different ratio. Characterization of chitosan-poly(acrylic acid) complex membrane was investigated by Fourier transform-infrared (FT-IR), wide angle X-ray diffractometer, dielectric analyzer. Their mechanical properties were studied by universal testing machine. The swelling of polyelectrolyte membranes was studied. Thermal properties of polyelectrolyte membranes from chitosan and poly(acrylic acid) by varying blend ratios showed a shift in transition temperatures of polyelectrolyte complexes. Polyelectrolyte complex membranes from chitosan and poly(acrylic acid) had pH sensitive characteristics as determined by FT-IR studies and swelling behaviors. Pervaporation performances were investigated with various organic mixtures; water-ethanol, water-isopropanol, methanol-methyl t-butyl ether mixtures. An increase of poly(acrylic acid) content in the polyelectrolyte complex membranes affected the swelling behavior and pervaporation performance of water-ethanol mixture. Permeation flux decreased and the water concentration in the permeate was close to 100% upon increasing the feed alcohol concentration.     

Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide)

Interpolymer complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide) was studied by fluorescence spectroscopy and viscometry in dilute aqueous solutions. Changes in chain conformation and flexibility due to the interpolymer association are reflected in the intramolecular excimer fluorescence of pyrene groups covalently attached to the polymer chain. Both poly(acrylamide) and hydrolysed poly(acrylamide) form stable complexes with poly(acrylic acid) at low pH. The molecular weight of poly(acrylic acid) and solution properties such as pH and ionic strength were found to influence the stability and the structure of the complexes. In addition, the polymer solutions mixing time showed an effect on the mean stoichiometry of the complex. The intrinsic viscosity of the solutions of mixed polymers at low pH suggested a compact polymer structure for the complex.     

Electrostatic self-assembly of neutral and polyelectrolyte block copolymers and oppositely charged surfactant

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.     

Layer-by-layer assembly of salt-containing polyelectrolyte complexes for the fabrication of dewetting-induced porous coatings

The layer-by-layer (LbL) assembly of salt-containing nonstoichiometric polyelectrolyte complexes (PECs) with oppositely charged uncomplexed polyelectrolyte for the fabrication of dewetting-induced porous polymeric films has been systematically investigated. Salt-containing poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) complexes (noted as PAH-PAA) with a molar excess of PAH were LbL assembled with polyanion poly(sodium 4-styrenesulfonate) (PSS) to produce PSS/PAH-PAA films. The structure of the PAH-PAA complexes is dependent on the concentration of NaCl added to their aqueous dispersions, which can be used to tailor the structure of the LbL-assembled PSS/PAH-PAA films. Porous PSS/PAH-PAA films are fabricated when salt-containing PAH-PAA complexes with a large amount of added NaCl are used for LbL assembly with PSS. In-situ and ex-situ atomic force microscopy measurements disclose that the dewetting process composed of pore nucleation and pore growth steps leads to the formation of pores in the LbL-assembled PSS/PAH-PAA films. The present study provides a facile way to fabricate porous polymeric films by dewetting LbL-assembled polymeric films comprising salt-containing PECs.     

Specific features of nonstoichiometric interpolymer complexes of poly(acrylic acid) and poly(ethylene glycol) as protectors of copper nanoparticles in aqueous sols

Advantages of interpolymer complexes for use as amphiphilic protectors of nanoparticles during the formation and stabilization of sols are considered. The effects of the ratio of poly(acrylic acid) and poly(ethylene glycol) and the molecular mass of poly(ethylene glycol) on the mean size and size distribution of copper nanoparticles in sols formed via the reduction of divalent copper ions in mixed aqueous solutions of these polymers are investigated. It is shown that sols of metal nanoparticles with small sizes and narrow size distributions are formed even when poly(ethylene glycols) with chain lengths below the “critical” chain length and a small PEG-to-PAA base-molar ratio are used. This is evidence for efficient protection of the formed copper nanoparticles by the interpolymer complex PEG-PAA under conditions of its instability and for self-organization of oligomeric PEG chains in complex macromolecular shields of nanoparticles.     

Light-scattering study of polyelectrolyte complexes: Heparin with partially aminoacetalized poly(vinyl alcohol) in aqueous solution

The structure of soluble polyelectrolyte complexes composed of heparin (Hep) and partially aminoacetalized poly(vinyl alcohol) (PVAA) in aqueous solution was investigated by light scattering. The pH was fixed at 3.2 while the ionic strength and mixing ratio were varied. At high ionic strength (0.5), polyelectrolyte complexes were not formed owing to the screening effect of simple salts on polyion charges. At low ionic strength (0.005), polyelectrolyte complexes formed were stable and dispersed when either the polycation or the polyanion was in great excess, whereas the complexes became unstable and coagulated when the concentrations of polycation and polyanion approached each other. At intermediate ionic strength (0.1), when PVAA was in excess, complex formation was similar to that at low ionic strength (0.005); but with an excess of Hep, polyelectrolyte complexes with similar structure (i.e., roughly spherical with average diameters about 2,700 Å) were formed over a wide range of mixing ratio. This observation is of interest in connection with the physiological activity of Hep in vivo.     

Hydrogel composites of neutral and slightly charged poly (acrylamide) gels with incorporated bentonite. Interaction with salt,linear polyelectrolytes and ionic surfactants

The swelling behavior in the solutions of sodium chloride, linear polyelectrolytes and ionic surfactants of the composites based on clay mineral bentonite (BENT) embedded in neutral and slightly charged poly(acrylamide) (PAAm) gels is studied. Negatively charged flat clay particles incorporated into polymer gel adsorb oppositely charged surfactant and linear polyelectrolyte and attract the charged chains of cationic polymer matrix. The results of SAXS study manifest the formation of lamella structure of the cationic surfactant adsorbed by the clay plates. The gels loaded with the clay show a strong response to changes in the nature and the composition of the ionic environment.     

Counterions in poly(allylamine hydrochloride) and poly(styrene sulfonate) layer-by-layer films

The amount of counterions in layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) has been determined with X-ray photoelectron spectroscopy (XPS) for films prepared from solutions with various NaCl concentrations. Sodium and chloride counterions are present in LBL films produced from salt solutions, which are located at the surface and in the bulk of the films. The percentage of bulk counterions increases with the ionic strength of the polyelectrolyte before reaching a constant value. The bulk sodium/sulfur percentage ratios tend to 0.8 for samples washed with pure water and for samples washed with NaCl aqueous solutions, while the bulk chlorine/nitrogen percentage ratios tend to 0.5 for the same samples. The ratio between the percentages of polyelectrolyte ionic groups lies close to unity for all samples, indicating that counterions do not contribute to charge compensation in the polyelectrolyte during the adsorption process. The presence of counterions in LBL films is explained by Manning condensation near the polyelectrolyte ionic groups, leading to inter-polyelectrolyte ionic bondings via ionic networks. It is believed that condensation leads to the formation of NaCl crystallites in these LBL films, which was confirmed by X-ray diffraction measurements.     

On the stability of the polymer brushes formed by adsorption of ionomer complexes on hydrophilic and hydrophobic surfaces

We have studied the effect of normal forces and shear forces on the stability and functionality of a polymer brush layer formed upon adsorption of polymeric micelles on hydrophilic and hydrophobic surfaces. The micelles consist of oppositely charged polyelectrolyte blocks (poly(acrylic acid) and poly(N-methyl 2-vinyl pyridinium iodide), and a neutral block (poly(vinyl alcohol)) or neutral grafts (poly(ethylene oxide)). The strength of the attachment of the micellar layers to various substrates was evaluated with Atomic Force Microscopy. Flow cell experiments allowed for the evaluation of long-term stability of coatings in lateral flow. Fixed angle optical reflectometry was used to quantify protein (BSA) adsorption on the micellar layers after their exposure to flow. The results show that adsorbed micellar layers are relatively weakly attached to hydrophobic surfaces and much stronger to hydrophilic surfaces, which has a significant impact on their stability. Adsorbed layers maintain their ability to suppress protein adsorption on hydrophilic surfaces but not on hydrophobic surfaces. Due to the relatively weak attachment to hydrophobic surfaces the structure of adsorbed layers may easily be disrupted by lateral forces, such that the complex coacervate-brush structure no longer exists.     

Water-soluble hydrogen-bonding interpolymer complex formation between poly(ethylene glycol) and poly(acrylic acid) grafted with poly(2-acrylamido-2-methylpropanesulfonic acid)

Comb-type copolymers of poly(acrylic acid) grafted with poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPSA) side chains form with poly(ethylene glycol), at low pH, water-soluble hydrogen-bonding interpolymer complexes. Turbidimetry, viscometry, and dynamic light scattering measurements suggest that compact, negatively charged, colloidal nanoparticles are formed at pH<3.75. The influence of the structure of the graft copolymers and of the ionic strength of the solution on the size of these nanoparticles was investigated. It was found that their hydrodynamic radius decreases by increasing the molecular mass of the PAMPSA side chains of the graft copolymer and increases with increasing the ionic strength of the solution.     

Polyelectrolyte complexation between poly(methacrylic acid,sodium salt) and poly(diallyldimethylammonium chloride) or poly[2‐(methacryloyloxyethyl) trimethylammonium chloride]

Polyelectrolyte complexes between poly(methacrylic acid, sodium salt) and poly(diallyldimethylammonium chloride) (PDADMAC) or poly[2‐(methacryloyloxyethyl)trimethylammonium chloride] (PMOETAC) form gels, liquid phases, or soluble complexes depending on charge ratio, total polymer loading, polymer molecular weight, and ionic strength. Increasing the ionic strength of the medium led most polyelectrolyte pairs to transition from gel through liquid complexes (complex coacervate) to soluble complexes. These transitions shift to higher ionic strengths for higher molecular weight polymers, as well as for PMOETAC compared to PDADMAC. The complex phases swelled with increasing polymer loading, ultimately merging with the supernatant phase at a critical polymer loading. The isolated liquid complex phases below and above this critical loading were temperature‐sensitive, showing cloud points followed by macroscopic phase separation upon heating. Incorporating 5 mol % lauryl methacrylate into the polyanion led to increased complex yield with PDADMAC, and increased resistance to ionic strength. In contrast, incorporating 30 mol % of oligo(ethylene glycol) methacrylate into the polyanion led to decreased complex yield, and to lower resistance to ionic strength. Two polyelectrolyte systems that produced liquid complexes were used to encapsulate hydrophobic oils, and in one case were used to demonstrate the feasibility of crosslinking the resulting capsule walls. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4129–4143, 2007     

Studies on the interaction of poly(4-vinylpyridiniumchloride) with poly(sodiumphosphate) in an aqueous solution by conductometry

A reaction between poly(4-vinylpyridiniumchloride) and poly(sodiumphosphate) in the presence and absence of NaCl and NaBr salts was studied in aqueous solution by conductometry. The interaction of polycation and polyanion gave insoluble polyelectrolyte complex which contained polycation and polyanion in unit mole ratio in a salt-free solution. A deviation from stoichiometry was observed at high polyion concentration and in the presence of NaCl and NaBr salts. The resultant complex showed swelling property in different solvent mixtures. A maximum degree of swelling was obtained in the solvent mixture of NaBr + water and NaBr + water + acetone. Furthermore, polyelectrolyte complex sorbed salts from aqueous electrolyte solutions. The sorption of salts increased with increasing salt concentration. © 1996 John Wiley & Sons, Inc.     

Complexation of linear and poly(ethylene oxide)‐grafted poly(methacryl oxyethyl trimethylammonium chloride) with poly(ethylene oxide‐block‐sodium methacrylate)

The interactions between oppositely charged polyelectrolytes were studied in saline aqueous solutions as functions of the temperature and the salt and polymer concentrations. The polyanion was a diblock copolymer composed of a poly(ethylene oxide) block and a poly(sodium methacrylate) block. Two polycations were used, the homopolymer poly(methacryl oxyethyl trimethylammonium chloride) and its poly(ethylene oxide)‐grafted analogue. By dynamic light scattering and turbidity measurements, it was observed that the salt concentration, temperature, and counterion size had a significant effect on the formation of the polymer complexes in aqueous solutions. At a fixed salt concentration and a fixed temperature, it was possible to form completely soluble complexes of an ionic polymer in aqueous solutions between poly(ethylene oxide)‐grafted poly(methacryl oxyethyl trimethylammonium chloride)and the polyanion with a poly(ethylene oxide) block at a 1:1 anion/cation ratio. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1904–1914, 2003