Formation and transformations of polyelectrolyte gel-ampholyte dendrimer-surfactant ternary complexes

The reactions of complex gels formed via the sorption of a poly(propylenimine) ampholyte dendrimer of the fourth generation by oppositely charged lightly cross-linked polyelectrolyte hydrogels with ionogenic micelle-forming surfactants have been studied. The sorption of surfactant ions likely charged relative to the complexed ampholyte dendrimer by complex gels is associated with two parallel chemical reactions controlled by the concentration of the surfactant and pH which give rise to the formation of network-dendrimer-surfactant tertiary complexes. The reactions of complex gels with surfactant ions likely charged relative to the network polyelectrolyte make it possible at different solution pHs to prepare both negatively and positively charged hydrogels reinforced by disperse particles of the dendrimer-surfactant complex.     

水溶性聚电解质—表面活性剂复合物的聚集行为

聚电解质在溶液中与相反电荷的表面活性剂通过解电作用与疏水作用可形成聚电解质－表面活性剂复合物，依据反应条件生成的复事物可以是水溶性也可以是非水溶性的。水溶性的聚电解质－表面活性剂复合物由于有许多工业应用，因此近几十上来水溶性聚电解质－表面活性剂复合物的形成和结构已爱到人们的广泛重视。本文对水溶性聚电解质－表面活性剂复合物的聚集过程、聚集结构作了简要概述，此外对荧光光谱在这一领域的应用进行了重点介绍     

Polymer/surfactant interactions at the air/water interface

The development of neutron reflectometry has transformed the study and understanding of polymer/surfactant mixtures at the air/water interface. A critical assessment of the results from this technique is made by comparing them with the information available from other techniques used to investigate adsorption at this interface. In the last few years, detailed information about the structure and composition of adsorbed layers has been obtained for a wide range of polymer/surfactant mixtures, including neutral polymers and synthetic and naturally occurring polyelectrolytes, with single surfactants or mixtures of surfactants. The use of neutron reflectometry together with surface tensiometry, has allowed the surface behaviour of these mixtures to be related directly to the bulk phase behaviour. We review the broad range of systems that have been studied, from neutral polymers with ionic surfactants to oppositely charged polyelectrolyte/ionic surfactant mixtures. A particular emphasis is placed upon the rich pattern of adsorption behaviour that is seen in oppositely charged polyelectrolyte/surfactant mixtures, much of which had not been reported previously. The strong surface interactions resulting from the electrostatic attractions in these systems have a very pronounced effect on both the surface tension behaviour and on adsorbed layers consisting of polymer/surfactant complexes, often giving rise to significant surface ordering.     

The combination of ionic surfactants with polyelectrolytes-a new material for membranes?

The combination of two oppositely charged polyelectrolytes results in polyelectrolyte complexes. The simultaneous interfacial reaction between the different polyions leads to formation of polyelectrolyte complex membranes. Some of these have a very good performance in the membrane process pervaporation, especially for dehydration of organic liquids. The combination of a polyelectrolyte with an ionic surfactant of opposite charge results like-wise membranes but with other separation properties. The differences between the two types of membranes, formed from cellulosesulfate in combination with cationic polyelectrolytes or cationic surfactants, will be discussed.     

Lysozyme in catanionic surfactant mixtures

We investigate the competition between the associations of oppositely charged protein-surfactant complexes and oppositely charged surfactant complexes. In all systems examined, the most favorable complexation is the one between the two oppositely charged surfactant ions, despite the strong binding known, for example, dodecyl sulfate, DS-, to lysozyme. Thus, the phase behavior of the catanionic system is dominating the features observed also in the presence of protein. The phase behavior of the dilute protein-free dodecyltrimethylammonium chloride-sodium dodecyl sulfate-water system is presented and used as a basis for the discussion on the different solubilization mechanisms. Our results show that the mechanism for resolubilization of a protein-surfactant salt is fundamentally different when it is caused by addition of a second surfactant than when it is accomplished by an excess of the first surfactant. The competition between lysozyme and cationic amphiphiles as hosts for the anionic surfactants was studied experimentally and analyzed quantitatively. Aggregates with C12 cationic surfactants are clearly preferred by the anionic surfactants, while for C10 and particularly C8 a clear excess of cationic surfactant has to be added to completely dissolve the complex salt lysozyme-anionic surfactant.     

The interaction between sodium alkyl sulfate surfactants and the oppositely charged polyelectrolyte, polyDMDAAC, at the air-water interface: the role of alkyl chain length and electrolyte and comparison with theoretical predictions

The effect of alkyl chain length and electrolyte on the adsorption of sodium alkyl sulfate surfactants and the oppositely charged polyelectrolyte, polyDMDAAC, at the air-water interface has been investigated by surface tension and neutron reflectivity. The variations in the patterns of adsorption and surface tension behavior with alkyl chain length and electrolyte are discussed in the context of the competition between the formation of surface active surfactant/polyelectrolyte complexes and polyelectrolyte/surfactant micelle complexes in solution. A theoretical approach based on the law of mass action has been used to predict the surface effects arising from the competition between the formation of polyelectrolyte/surfactant surface and solution complexes and the formation of free surfactant micelles. This relatively straightforward model is shown to reproduce the principal features of the experimental results.     

Monte Carlo simulations of cross-linked polyelectrolyte gels with oppositely charged macroions

The volume and structural changes upon replacement of oppositely charged network counterions for oppositely charged macroions in cross-linked polyelectrolyte gels have been investigated by Monte Carlo simulations using a coarse-grained model. Initially, the gel deswells, but after an approximately equivalent amount of macroions, the gel starts to swell again. The deswelling effect is greatest for small and highly charged macroions. The role of different network properties on the deswelling has also been examined. The initial deswelling is understood in terms of a replacement of confined counterions with macroions, thereby reducing the osmotic pressure originating from the counterions. At these conditions, macroions are located near network nodes with various degrees of network chains wrapping them. At charge equivalence, a profound change in the network structure has appeared. At these conditions, the cohesive electrostatic interaction and the excluded volume effect of the macroions strongly influence the equilibrium volume of the gel. Our model system reproduces many characteristic experimental observations of polyelectrolyte gels containing oppositely charged surfactants.     

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.     

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.     

Effect of Phase Transitions in the Solutions of the Complexes of Ionic Surfactants with Oppositely Charged Polyelectrolytes on the Molecular Mobility of Surfactant Ions inside Intracomplex Micelles

The effect of phase transitions in the solutions of the complexes of surfactants and oppositely charged polyelectrolytes of different chemical natures on the molecular mobility of the surfactant ions inside the intracomplex micelles was studied by the spin probe method. It was found that, irrespective of the fact whether the solutions of the polyelectrolyte–surfactant complexes are true solutions, colloidal dispersions, or thixotropic gels, the molecular mobility of the surfactant ions inside the complex micelles and, consequently, the local structure of the intracomplex micelles, remain unchanged upon both a change in the complex composition and transition of complexes from solution to the precipitate.     

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.     

Aggregation of ionic amphiphils in dilute solutions controlled by oppositely charged polyelectolyte templates

Formation and structure of water-soluble complexes of poly(acrylic acid) (PA) and poly(diallyldimethylammonium chloride) (PDADMAC) with oppositely charged surfactants have been studied by elastic and quasi-elastic laser light-scattering and high-speed sedimentation technique. It was experimentally shown that generation of intracomplex micellar phase is the necessary condition for formation of such complexes. Minimum aggregation number of the surfactant ions in the complex micelle was found to be determined by the chemical nature of the polymer.     

Interactions of polyelectrolyte brushes with oppositely charged surfactants

Using Brownian dynamics simulations, we study the effect of the charge ratio, the surfactant length, and the grafting density on the conformational behavior of the complex formed by the polyelectrolyte brush with oppositely charged surfactants. In our simulations, the polyelectrolyte chains and surfactants are represented by a coarse-grained bead-spring model, and the solvent is treated implicitly. It is found that varying the charge ratio induces different morphologies of surfactant aggregates adsorbed onto the brush. At high charge ratios, the density profiles of surfactant monomers indicate that surfactant aggregates exhibit a layer-by-layer arrangement. The surfactant length has a strong effect on the adsorption behavior of surfactants. The lengthening of surfactant leads to a collapsed brush configuration, but a reswelling of the brush with further increasing the surfactant length is observed. The collapse of the brush is attributed to the enhancement of surfactants binding to polyelectrolyte chains. The reswelling is due to an increase in the volume of adsorbed surfactant aggregates. At the largest grafting density investigated, enhanced excluded volume interactions limit the adsorption of surfactant within the polyelectrolyte brush. We also find that end monomers in polyelectrolyte chains exhibit a bimodal distribution in cases of large surfactant lengths and high charge ratios.     

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.     

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.     

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.     

Interplay of ionic and nonionic interactions in weakly charged polyelectrolytes

We describe the results of theoretical and experimental studies of the regular heterogeneities on a nanometer scale which are formed in the systems containing weakly charged polyelectrolytes due to the competition of ionic and hydrophobic interactions. In particular, we consider the effect of microphase separation in poor solvent polyelectrolyte solutions and gels and nano-self-assemblies emerging in the complexes of polyelectrolyte gels with oppositely charged surfactants. The practically important application connected with metal nanoparticles formation in regular microstructures in polyelectrolyte systems is considered as well.     

The Interaction between High-Molecular-Weight Flocculents and Ionic Surfactants

The interaction between the anionic and cationic polyelectrolytes of various molecular masses and charges and the ionic surfactants in aqueous and salt solutions is studied by viscometry, conductometry, light scattering, and electrophoresis. Oppositely charged molecules of surfactant and polymer form strong complexes due to the forces of electrostatic attraction that is manifested in a significant decrease in the viscosity and light transmission, as well as in the relative reduction in solution conductivity. As the surfactant/polyelectrolyte ratio increases, the forming complexes precipitated and then dissolved again. In the case of strongly charged polyelectrolytes, the partial dissolution of precipitates was observed preceding the wide region of destabilization. In this region, the value of surfactant/polyelectrolyte charge ratio reaches 3–4. The interaction between the cationic surfactants and anionic polyelectrolyte increases with the lengthening of alkyl radical, thus indicating the presence of cooperative interactions between the surfactant molecules bonded to polymer and the important role of relevant hydrophobic interactions. As a result, the interaction between the high-molecular-weight anionic polyelectrolytes and anionic surfactants containing aromatic core takes place in some cases.     

Surfactant polymer interactions between strongly interacting cationic surfactants and anionic polyelectrolytes from conductivity and turbidity measurements

The interactions between oppositely charged surfactant/polymer mixtures have been studied using conductivity and turbidity measurements. The dependence of aggregation phenomenon on the chain length and head group modifications of conventional cationic surfactants, i.e., hexadecyl- (HTAB), tetradecyl- (TTAB), and dodecyltrimethylammonium bromides (DTAB) and dimeric cationic surfactants, i.e., decyl- (DeDGB) and dodecyldimethylgemini bromides (DDGB), is investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolytes at critical aggregation concentration (cac). The cac values are considerably lower than the critical micelle concentration (cmc) values for the same surfactant. After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in aqueous polyelectrolyte than in pure water. Among the conventional and dimeric cationic surfactants, DTAB and DeDGB, respectively, have been found to have least interactions with oppositely charged polyelectrolytes.     

Electrostatic binding of oppositely charged surfactants to spherical polyelectrolyte brushes

We use Brownian dynamics (BD) simulations to investigate the formation and structural characteristics of the complex between a spherical polyelectrolyte brush (SPB) and oppositely charged surfactants. Increasing the amount of added surfactants leads to a collapsed conformation of the SPB and the number of adsorbed surfactants exhibits a linear dependence. Nevertheless, the surfactant uptake into the SPB does not increase with further addition of surfactants. It is found that the surfactant length has a strong influence on the SPB conformation and the adsorption properties of surfactant. Upon changing the surfactant length from 3 to 11, the SPB undergoes a swelling-deswelling-reswelling conformational transition. The brush deswelling is due to the increase in the surfactant uptake. The increasing size of adsorbed aggregates is a main reason for reswelling of the SPB. A non-linear relationship between the brush thickness and the grafting density is observed. Especially at intermediate grafting densities, increasing the number of grafted chains has a weak effect on the brush thickness. We also find that a completely collapsed brush conformation occurs at high surfactant/SPB charge ratios or large surfactant lengths, while the brush layer is in a partly collapsed or extended state at an intermediate charge ratio and surfactant length.