Stoichiometric polyelectrolyte complexes as comb copolymers

The collapse behavior of a single comblike copolymer chain has been studied by Monte Carlo simulations. It has been supposed that the solvent is good for the side chains but the solvent quality for the backbone chain changes. It has been shown that depending on the structural parameters of the comb copolymer (the lengths of the backbone and side chains, grafting density of the side chains) various thermodynamically stable morphologies of the collapsed backbone chain can be realized. In addition to ordinary spherical globule we have observed elongated structures as well as necklace-like conformations. The proposed model can be used to describe conformational behavior of stoichiometric complexes between block copolymers with a polyelectrolyte short block and oppositely charged linear homopolymers.     

Stoichiometric polyelectrolyte complexes of ionic block copolymers and oppositely charged polyions

Micellization in dilute solutions of diblock copolymers with a polyelectrolyte and a hydrophilic nonionic blocks and oppositely charged polyions is studied using mean-field theory. In aqueous solutions the micelle core consists of the polyelectrolyte complex (PEC) while the corona is formed by hydrophilic blocks of the block copolymers. Describing PEC as a globule in the framework of the Lifshitz [Zh. Eksp. Teor. Fiz. 55, 2408 (1968)] globule theory we calculate the surface tension of the micellar core/solvent interface as a function of the polyion degree of ionization, solvent quality, and concentration of low-molecular-mass salt. The equilibrium aggregation number of starlike micelles formed by block copolymers and homopolymers of opposite charge at stoichiometric mixture compositions is found as a function of the system parameters. It is shown that micelles disintegrate upon addition of salt.     

Two-phase structure of polyelectrolyte gel/surfactant complexes

The behavior of lightly cross-linked polyelectrolyte hydrogel swelling in the solution of oppositely charged surfactants is studied theoretically. It is shown that if there is a lack of surfactant in the solution intragel separation into two phases differing in swelling ratios and surfactant content can take place. The surfactant ions concentrate and form micelles in a part of the gel and this part collapses while the rest of the gel remains swollen. The two-phase region widens with an increase of ionization degree of the gel subchains.     

Nanostructures of polyelectrolyte gel–surfactant complexes

Small‐angle X‐ray scattering was used to investigate the nanostructures of complexes formed by slightly crosslinked anionic copolymer gels of poly(sodium methacrylate‐co‐N‐isopropylacrylamide) [P(MAA/NIPAM)] with cetyltrimethylammonium bromide (CTAB), and didodecyldimethylammonium bromide (DDAB), respectively, at room temperature (∼ 23°C). Several highly ordered supramolecular structures were observed in the polyelectrolyte gel–surfactant complexes. In P(MAA/NIPAM)–CTA systems, in sequence with decreasing charge density of the P(MAA/NIPAM) copolymer chains, structures of the Pm3n space group cubic, face‐centered cubic close packing of spheres, and hexagonal close packing of spheres were determined at a charge content of ≥ 75, 67, and 50%, respectively. The spheres and rods in these structures were the spherical and cylindrical micelles formed by the self‐assembly of CTA cations with their paraffin chains inside. Both the aggregation number and the size of the micelles decreased with a decreasing charge density of the copolymer chains. In the P(MAA/NIPAM)–DDA systems, the bilayer lamellar structures formed at charge contents ≥ 75% transferred to bicontinuous cubic structures of the Ia3d space group at charge contents of 50–67%. The rods in the Ia3d cubic structures were formed by the self‐assembly of double‐tailed DDA cations with polar moieties inside. The formation of these highly ordered structures were driven by both electrostatic and hydrophobic interactions of the charged copolymer chains/surfactants and the surfactants/surfactants inside the charged gels. The structures became less ordered by further decreasing the charge content of the P(MAA/NIPAM) chains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2165–2172, 1999     

Stabilization of bioderived surfactant/polyelectrolyte complexes through surfactant conjugation to the biopolymer

Mixtures of oppositely charged surfactants and polyelectrolytes self-assemble into a variety of nanostructured complexes. With the view of developing simpler and cleaner alternatives to synthetic nanomaterials, self-assembled nanostructures can be prepared from bioderived surfactant/polyelectrolyte mixtures. These complexes can be designed to vary their phase behavior and structure in response to external stimuli, and are simpler and cleaner to prepare than conventional synthetic copolymers (e.g., block or graft). Yet, some potential applications of surfactant/polyelectrolyte complexes are limited by their lower stability. Here, we overcome this limitation by covalently coupling the surfactant head group to the polymer chain. Visual observations and small-angle X-ray scattering (SAXS) reveal that covalent coupling dramatically improves stability at both the macroscopic and mesoscopic lengthscales. This suggests that, through covalent conjugation, stability of nanostructured surfactant/biopolymer complexes can be made to rival that of synthetic copolymers, thereby extending their use to applications that require long-lasting nanostructured materials.     

Layer-by-layer adsorption of polyelectrolyte and surfactant and adsorption of their complexes on solid surface

The capillary electrokinetics method (measurement of streaming potential and current in a capillary with a radius of 5–7 μm made of fused quartz) is employed to study the structure formation at interfaces between quartz and solutions containing a cationic polyelectrolyte (poly(diallyldimethylammonium chloride) with molecular mass M = 100000−200000) and an anionic surfactant (sodium dodecyl sulfate). The kinetics of surface layer formation is studied upon the layer-by-layer adsorption of the components and the adsorption of their complexes at the same component ratios. It is established that the formation time and the electrokinetic potentials of the surface layers are almost independent of the procedure of their formation. In the case of the layer-by-layer adsorption, the first layers of the polyelectrolyte appear to be virtually undeformed, thus indicating that molecules with a planar conformation prevail in the adsorption layer. Surfactant adsorption enhances the deformation (layer loosening), which decreases with time (layer aging). Layers formed from the complexes have a denser (less deformable) structure. Variations in the electrokinetic potentials of the layers during the long-term pumping of a background electrolyte solution through a capillary witnesses the prevailing desorption of the anionic surfactant, with the desorption being noticeably more pronounced for the layers resultant from the adsorption of the complexes.     

Role of the preparation procedure in the formation of spherical and monodisperse surfactant/polyelectrolyte complexes

Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed.     

Self-assembly in ternary systems: cross-linked polyelectrolyte,linear polyelectrolyte and surfactant

The competitive interactions in ternary systems consisting of a slightly cross-linked polyelectrolyte hydrogel and the mixture of linear polyelectrolyte and micelle forming surfactant both oppositely charged relative to the polyelectrolyte network were studied. It was shown that the equilibrium in the competitive reactions depends on the linear polyion charge density and the length of the surfactant aliphatic radical. Dependency on these characteristics the interpolyelectrolyte complex formed by cross-linked and linear polyelectrolytes can uptake surfactant ions from water solution transforming into the cross-linked polyelectrolyte-surfactant complex and releasing the linear polyelectrolyte or vice versa. The ternary systems of this kind are perspective to design the novel family of delivery constructs.     

聚电解质复合物研究进展

本文介绍了聚电解质复合物的制备及研究方法，对影响聚电解质复合物形成及其结构的因素进行了阐述，简要介绍了其性能并对其应用前景作了展望。     

Chitosan based polyelectrolyte complexes

Polyelectrolyte complexes (PECs) are formed through the electrostatic interactions between polymers carrying opposite charges. Here are presented results of basic studies on the PECs of chitosan with other polysaccharides such as sodium alginate, carboxymethyl cellulose, polygalacturonic acid and κ‐carrageenan. An extensive study on chitosan/carboxymethyl cellulose membranes, regarding its swelling characteristics and water vapour sorption is offered. Also the interaction of chitosan with polyacrylic acid has been examined from the thermodynamic point of view.     

Soluble polyelectrolyte complexes of biopolymers

This review analyzes the papers reflecting the state of the art and achievements in the field of experimental investigations of solutions of polyelectrolyte complexes containing biopolymers, specifically oligomeric enzymes, cationic polysaccharide chitosan, or DNA. The analysis shows that the use of soluble complexes is promising for solving urgent practical problems. The development of methods for suppressing thermal aggregation of globular proteins without any substantial loss in functional activity, for imparting chitosan the ability to dissolve under physiological conditions and to form polyelectrolyte complexes, and for creating dual-action dendrimer carriers that can simultaneously deliver genetic material and drugs to cells are among the most significant directions.     

Calorimetric determination of surfactant/polyelectrolyte binding isotherms

Mixing of oppositely charged surfactants and polyelectrolytes in aqueous solutions leads to cooperative surfactant adsorption onto the polyelectrolyte chains. Experimental determination of surfactant/polyelectrolyte binding isotherms is usually done using custom-built surfactant-ion-specific electrodes. As an alternative, we present an indirect isotherm approximation method that uses conventional isothermal titration calorimetry (ITC). The calorimetric data is fitted to the two-binding-state Satake-Yang adsorption model, which quantifies the extent of binding in terms of the binding constant (Ku) and the cooperativity parameter (u). This approach is investigated using two surfactant/polyelectrolyte mixtures: sodium perfluorooctanoate (FC7) and N,N,N-trimethylammonium derivatized hydroxyethyl cellulose (UCARE Polymer JR-400), whose binding behavior follows the Satake-Yang model, and dodecyltrimethylammonium bromide (DTAB) and poly(styrenesulfonate) (NaPSS), whose behavior deviates dramatically from the Satake-Yang model. These studies demonstrate that, in order to apply the indirect ITC method of binding isotherm determination, the surfactant/polyelectrolyte adsorption process must have no more than two dominant binding states. Thus, the technique works well for the FC7/JR-400 mixture. It fails in the case of the DTAB/NaPSS adsorption, but its mode of failure offers insight into the multiple-binding-state adsorption mechanism.     

Characterization and biodegradation of chitosan-alginate polyelectrolyte complexes

Polyelectrolyte complexes (PECs) have been the focus of an expanding number of studies for their wide use. This study investigated the characteristics and biodegradation of chitosan-alginate PECs prepared by freeze-drying a precipitate from sufficient mixtures of the two polymers. The analyses of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) suggested that the partial protonated amine groups of chitosan reacted with the carboxylate groups of alginate and thus strong PECs were formed. After incubating in lysozyme solution, the PECs showed high ability of enzyme adsorption, and low degradation rate in spite of different degrees of deacetylation of chitosan, due to the strong interaction between chitosan and alginate and the hindrance of closely adsorbed lysozyme.     

Stepwise disproportionation in polyelectrolyte complexes

Structural properties and the topology of polyelectrolyte complexes (PECs) formed in solution have been investigated under different conditions by Monte Carlo simulations using a coarse-grained model. The extension of individual polyions has been characterized by their radius of gyration, whereas the composition of the complexes has been investigated by their net charge and their internal topological structure by a novel analysis describing how the shorter polycations link to monomers of the longer polyanion. Conditions have been found at which the polyanion and a given number of polycations form distinguishable complexes differing in (i) the polyanion conformation and (ii) the fraction of polycations being in extended and collapsed states. Thus, at equilibrium, these PECs display a stepwise variation of the degree of intrachain disproportionation within the polyanion (also referred to as intrachain segregation), concomitant with the interchain disproportionation of the polycations, which is in agreement with previous theoretical predictions. The coexistence of the different polyelectrolyte complex structures appears, generally, at mixing ratios close to but different from charge equivalence and, as a consequence, broad polyelectrolyte size distributions are commonly obtained.     

Solubilization of phenols in surfactant/polyelectrolyte systems

The properties of the microheterogeneous systems formed by mixtures of cetyltrimethylammonium bromide (CTAB) and an alternating copolymer of maleic acid and styrene, MAS, and their anionic monoesters, MAS-n with n=2, 4, 6, 8, were investigated. The fluorescence of pyrene was used to sense the polarity of the polymer/CTAB aggregates. Measurements of the ratio III/I in pyrene fluorescence spectra indicate that the polymer/CTAB aggregates are more hydrophobic than normal micelles. A series of p-alkyl substituted phenols were employed to probe the solubilization ability of these aggregates. The distribution constant K(S) of phenol, p-methylphenol, p-ethylphenol, and p-propylphenol between water and MAS-n/CTAB aggregates and the corresponding free energy of transfer Deltamicro(0)(t) have been determined using the pseudo-phase model. The results show that the distribution is mainly determined by the phenol structure, and a linear free energy relationship has been found between Deltamicro(0)(t) and the structure of phenols. On the other hand, an increase in the number of methylene groups in the side alkyl chain has no effect on Deltamicro(0)(t). The results are discussed and compared with those obtained for ionic micelles.     

Hydrodynamic size and charge of polyelectrolyte complexes

Polyelectrolyte complexes have a wide range of applications for surface modification and flocculation and sorption of organic molecules from solutions. As an example, complexes between poly(diallyl dimethyl ammonium chloride) and poly(styrene sulfonate) have been investigated by diffusion and electrophoresis NMR. The formation of primary or soluble complexes is monitored. The hydrodynamic size is characterized by the hydrodynamic radius, calculated from the diffusion coefficient determined by pulsed field gradient NMR. In the combination with electrophoresis NMR, the effective charge of the molecules and complexes is determined. The hydrodynamic size of the primary complex is smaller than that of the pure polyelectrolyte of the larger molecular weight, in the present case poly(styrene sulfonate), in solution, since charges are compensated by the oppositely charged polyelectrolyte and hence the repelling forces diminish. The effective charge of the complexes is drastically reduced.     

Low-valence palladium complexes: Stoichiometric reactions and catalysis

New data on the structure and reactivity of palladium clusters are surveyed. The mechanisms of stoichiometric and catalytic reactions of the palladium cluster complexes with alkenes, alcohols, aldehydes, formic acid, CO, and phenol are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 807–815, March, 1998.     

Formation of surfactant and polyelectrolyte gel particles in aqueous solutions

Mixing of oppositely charged surfactants and polyelectrolytes in aqueous solutions can lead to associative phase separation, where the concentrated phase assumes the form of a viscous liquid, gel, or precipitate. This phenomenon can lead to the formation of gel-like particles whose size and polydispersity can be controlled. Here we present phase behavior and structural studies of gel-like particles formed by mixing drops of N,N,N-trimethylammonium derivatized hydroxyethyl cellulose (JR-400) polyelectrolyte solution with oppositely charged anionic and catanionic surfactant solutions composed of sodium perfluorooctanoate (FC₇) and cetyltrimethylammonium bromide (CTAB). Gel formation apparently occurs due to the collapse of the polyelectrolyte chains upon the adsorption of surfactant. This process results in the release of simple ions and water, and yields dense gel-like beads. The diameter of these beads ranges approximately from 200 to 4000 μm. Both the effects of solution composition and the method of preparation are studied by optical and confocal microscopy, and are linked to the structure and stability of the bead. Our observations suggest that the structure of the resulting particles is governed by the solution composition and the method of preparation, while the particle stability is governed by phase behavior alone.     

Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR

A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO(45)MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 A. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO(45)MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.     

Adsorption of oppositely charged polyelectrolyte/surfactant complexes at the air/water interface: formation of interfacial gels

The adsorption and complexation of polystyrene sulfonate (a highly charged anionic polyelectrolyte) and dodecyltrimethylammonium bromide (a cationic surfactant) at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously, the solution electromotive force is measured and used to track the polymer-surfactant interactions in the bulk solution. We find that surface gelation occurs above the critical aggregation concentration in solution but before bulk precipitation of the polymer-surfactant complexes. Furthermore, we reveal that strong readsorption of polymer-surfactant complexes occurs during the resolubilization of the precipitated complexes at high surfactant concentrations (i.e., >critical micelle concentration). Seemingly overlooked in the past, this readsorption significantly influences the surface rheological properties and foam-film drainage of these systems.