Counterion release from adsorbed highly charged polyelectrolyte: an electrooptical study

The adsorption of sodium poly(4-styrene sulfonate) on oppositely charged beta-FeOOH particles is studied by electrooptics. The focus of this paper is on the release of condensed counterions from adsorbed polyelectrolyte upon surface charge overcompensation. The fraction of condensed Na+ counterions on the adsorbed polyion surface is estimated according to the theory of Sens and Joanny and it is compared with the fraction of condensed counterions on nonadsorbed polyelectrolyte. The relaxation frequency of the electrooptical effect from the polymer-coated particle is found to depend on the polyelectrolyte molecular weight. This is attributed to polarization of the layer from condensed counterions on the polyion surface, being responsible for creation of the effect from particles covered with highly charged polyelectrolyte. The number of the adsorbed chains is calculated also assuming counterion condensation on the adsorbed polyelectrolyte and semiquantative agreement is found with the result obtained from the condensed counterion polarizability of the polymer-coated particle. Our findings are in line with theoretical predictions that the fraction of condensed counterions remains unchanged due to the adsorption of highly charged polyelectrolyte onto weakly charged substrate.     

Ion induced lamellar-lamellar phase transition in charged surfactant systems

We propose a model for the liquid-liquid (L(alpha)-->L(alpha(') )) phase transition observed in osmotic pressure measurements of certain charged lamellae-forming amphiphiles. The model free energy combines mean-field electrostatic and phenomenological nonelectrostatic interactions, while the number of dissociated counterions is treated as a variable degree of freedom that is determined self-consistently. The model, therefore, joins two well-known theories: the Poisson-Boltzmann theory for ionic solutions between charged lamellae and the Langmuir-Frumkin-Davies adsorption isotherm modified to account for charged adsorbing species. Minimizing the appropriate free energy for each interlamellar spacing, we find the ionic density profiles and the resulting osmotic pressure. While in the simple Poisson-Boltzmann theory the osmotic pressure isotherms are always smooth, we observe a discontinuous liquid-liquid phase transition when the Poisson-Boltzmann theory is self-consistently augmented by the Langmuir-Frumkin-Davies adsorption. This phase transition depends on the area per amphiphilic head group, as well as on nonelectrostatic interactions of the counterions with the lamellae and interactions between counterion-bound and counterion-dissociated surfactants. Coupling the lateral phase transition in the bilayer plane with electrostatic interactions in the bulk, our results offer a qualitative explanation for the existence of the L(alpha)-->L(alpha(') ) phase transition of didodecyldimethylammonium bromide (DDABr), but the transition's apparent absence for the chloride and the iodide homologs. More quantitative comparisons with experiment require better understanding of the microscopic basis of the phenomenological model parameters.     

The aqueous phase behavior of polyion-surfactant ion complex salts mixed with nonionic surfactants

The aim of this work was to study intermolecular interactions in systems containing charged polyion (polyacrylate, PA(-)), charged surfactant (C(16)TA(+)) and nonionic surfactant (C(12)E(5) or C(12)E(8)). To achieve this we have created four different phase diagrams using two different so-called complex salts, C(16)TAPA(25) and C(16)TAPA(6000), both consisting of positively charged surfactant (C(16)TA(+)) with polyacrylate (PA(-)) as counterions (no simple salt). The difference between the salts is the length of the polyion (25 or 6000 monomers). Both are insoluble in water. The results revealed that decreasing polyion length and increasing the PEO chain length of the nonionic surfactant were important factors for increasing the solubility of the complex salt. We also found that the curvature effects are quite small at low water content when gradually exchanging C(12)E(8) for either one of the complex salts while there is a gradual change in curvature for the systems containing C(12)E(5). Another interesting observation was the possibility for relatively large amounts of complex salt to be incorporated into a V(1) (Ia3d, bicontinuous) phase in the C(12)E(8)-containing systems. This gives rise to several questions regarding arrangements and dynamics of the polyion in this phase. In the dilute regime several different liquid crystalline phases can coexist with a dilute liquid phase containing the nonionic surfactant.     

Phase behavior of aqueous polyion-surfactant ion complex salts: effects of polyion charge density

The effect of varying the fraction of charged monomer units of the polyion in aqueous polyion-oppositely charged surfactant complex salts has been investigated. The complex salts used were based on cetyltrimethylammonium (C16TA+) with three different polymeric counterions: poly(acrylate) (PA-) or poly(acrylate) copolymerized with either dimethylacrylamide (PA-/DAM) or N-isopropylamide (PA-/NIPAM). The charge density of the polyion was varied by either adding poly(acrylic) acid (PAA) to the C16TAPA complex salt (annealed charges) or by varying the fraction of uncharged units in the C16TAPA/DAM or C16TAPA/NIPAM complex salts (quenched charges). The formed phases were studied visually between crossed polarizers and by small angle X-ray scattering (SAXS). Both types of complex salts (annealed and quenched) formed hexagonal phases at high fractions of charged monomers and low water contents. Upon increasing the water content, a cubic phase of the Pm3n space group was found. Upon further addition of water, a miscibility gap with the cubic phase in equilibrium with pure water was found. Decreasing the fraction of charged monomers in the annealed complex salt resulted in an increase of the curvature of the surfactant aggregates. Only at very low (<0.05) fractions of charged monomers did the packing of the surfactant aggregates lose long-range order, and eventually, the miscibility gap disappeared. For the quenched complex salts, the changes upon decreasing the fraction of charged monomers in the polyion were similar, but the loss of long-range order occurred at much higher fractions of charged monomers. The average surfactant aggregation number in the surfactant aggregates, which was similar for the annealed and quenched systems, decreased when the fraction of charged monomers was decreased.     

Polyion interchange reactions of interpolyelectrolyte complexes in aqueous solutions and gels

Cooperative coupling reaction between two opposite charged polyelectrolytes results in formation of polyelectrolyte complexes (IPEC). This reaction is very fast and diffusion controlled. Whether IPECs formed by linear polyions are soluble or limitary swellable in aqueous media is decided by their composition, namely, by a ratio of oppositely charged polyions as well as by a water phase composition (the nature and the concentration of a simple salt, pH, the presence and the concentration of organic additives etc.). The most important intrinsic property of IPECs is their ability to participate in interchange (exchange and substitution) reactions with competing polyions. The kinetics and the position of equilibria in these reactions are controlled by the low molecular salt concentration, the nature of small counterions, DP of interaction polyelectrolytes, as well as by their linear charge density. IPECs can be formed also by interacting linear and opposite charged networks. It is shown that linear polyelectrolytes dissolved in aqueous solution can penetrate unexpectedly fast into oppositely charged cross-linked polyelectrolyte gels to form “snake-in-cage” composites representing IPECs of corresponding polyion segments. It is proved that the mechanism consists in “relay-race” transfer of linear polyion segments from one segment of the polyelectrolyte network to the other via interpolyelectrolyte exchange reaction. The driving force for the fast transport of linear polyions into the gel is produced by coupling reaction between two polyelectrolytes proceeding on solution/gel interface.     

Dynamic octopus amphiphiles as powerful activators of DNA transporters: differential fragrance sensing and beyond

We report the design, synthesis and evaluation of dynamic "octopus" amphiphiles with emphasis on their efficiency as activators in synthetic membrane-based sensing systems. Previously, we found that the in situ treatment of charged hydrazides with hydrophobic aldehydes or ketones gives amphiphilic counterion activators of polyion transporters in lipid bilayers, and that their efficiency increases with the number of their hydrophobic tails. Herein, we expand this series to amphiphiles with one cationic head (guanidinium or ammonium) and four exchangeable hydrophobic tails. These results, with the highest number of tails reported to date, confirm that dynamic octopus amphiphiles provide access to maximal activity and selectivity. Odorants, such as muscone, carvone, or anisaldehyde are used to outline their usefulness in differential sensing systems that operate based on counterion-activated DNA transporters in fluorogenic vesicles. The enhanced ability of octopus amphiphiles to enable the discrimination of enantiomers as well as that of otherwise intractable ortho, meta, and para isomers and short cyclo-/alkyl tails is demonstrated. These findings identify dynamic octopus amphiphiles as being promising for application to differential sensing, "fragrant" cellular uptake, and slow release.     

Monte Carlo studies of polyelectrolyte solutions. Effect of polyelectrolyte charge density

The influence of the polyion charge density on the osmotic behavior of linear polyelectrolytes is studied by the Monte Carlo method and by the modified Poisson-Boltzmann equation. The polyion is assumed to be either a uniformly or discretely charged cylinder placed along the axis of the cylindrical cell containing only counterions. As a result, osmotic saturation is observed at high polyion charge density. In simulations of solutions with divalent counterions the maximum in the osmotic pressure versus degree of ionization is observed in analogy with recent studies of spherical and planar systems. The correlation between the osmotic coefficient and the acceptance rate observed in simulations is reported.     

Phase behavior of amphiphiles at liquid crystals/water interface: A coarse-grained molecular dynamics study

We present a coarse-grained molecular dynamics simulation study of phase behavior of amphiphilic monolayers at the liquid crystal （LC）/water interface. The results revealed that LCs at interface can influence the lateral ordering of amphiphiles. Particularly, the amphiphile tails along with perpendicularly penetrated LCs between tails undergo a two-dimension phase transition from liquid-expanded into a liquid-condensed phase as their area density at interface reaches 0.93. While, the liquid-condensed phase of the monolayer never appears at oil/water interface with isotropic shape oil particles. These findings reveal the penetration of anisotropic LC can promote ordered lateral organization of amphiphiles. Moreover, we find the phase transition point is shifted to lower surface coverage of amphiphiles when the LCs have larger affinity to the amphiphile tails.     

Synthesis and hierarchical self-assembly of cavity-containing facial amphiphiles

The synthesis and aggregation behavior of cavity-containing facial amphiphiles is described. The molecules consist of a glycoluril-based rigid cavity functionalized with two water-soluble benzoate groups. By specific molecular recognition processes in water, the amphiphilic hosts self-assemble in a hierarchical process to form arrays of molecules. Depending on the counterions, these arrays can be assembled into well-defined aggregates of mesoscopic size. The size and shape of the aggregates can be tuned by variations in the size and substitution pattern of the cavities of the host molecules.     

A unified analytical treatment of the acid-dissociation equilibria of weakly acidic linear polyelectrolytes and the conjugate acids of weakly basic linear polyelectrolytes

 The influence of added sodium chloride concentration levels on the acid-dissociation equilibria of a weakly acidic linear polyelectrolyte and a conjugate acid of weakly basic linear polyelectrolyte has been investigated potentiometrically by use of polyacrylic acid (PAA) and poly(N-vinylimidazole) (PVIm) as examples of polyelectrolytes. Both equilibria are strongly influenced by the degree of dissociation of the polyacids as well as the concentration levels of sodium chloride due to an electrostatic effect originating from the negatively or positively charged polymer surfaces. These have been analyzed in a unified manner by taking accounts of two-phase properties of the charged linear polyions. Distribution of counterions and coions between a polyelectrolyte phase formed around the polymer skeleton and a bulk solution phase has been rationalized by a Donnan’s relation. Introduction of a volume term for the polyelectrolyte phase permits definition of averaged concentrations of mobile ions in the vicinity of the polyion molecules, which enables us to define hypothetical intrinsic acid-dissociation constants in the polyion domain. The intrinsic constants estimated by extrapolation of apparent acid-dissociation constants at zero-charge state are in good agreement with the acid-dissociation constants of the monomer analogs of the polymers, i.e., acetic acid for PAA and imidazole for PVIm, respectively. The difference between the apparent and intrinsic acid-dissociation constants for PVIm was much higher than that for PAA at defined degree of dissociation of the polyacids, even though the separations of the functionalities fixed on the linear polymers are approximately equal to each other. Received: 4 February 1997 Accepted: 26 May 1997     

Phase behavior of polyion-surfactant ion complex salts: effects of surfactant chain length and polyion length

The aqueous phase behavior of a series of complex salts, containing cationic surfactants with polymeric counterions, has been investigated by visual inspection and small-angle X-ray scattering (SAXS). The salts were alkyltrimethylammonium polyacrylates, CxTAPAy, based on all combinations of five surfactant chain lengths (C6, C8, C10, C12, and C16) and two lengths of the polyacrylate chain (30 and 6 000 repeating units). At low water contents, all complex salts except C6TAPA6000 formed hexagonal and/or cubic Pm3n phases, with the hexagonal phase being favored by lower water contents. The aggregate dimensions in the liquid crystalline phases changed with the surfactant chain length. The determined micellar aggregation numbers of the cubic phases indicated that the micelles were only slightly aspherical. At high water contents, the C6TAPAy salts were miscible with water, whereas the other complex salts featured wide miscibility gaps with a concentrated phase in equilibrium with a (sometimes very) dilute aqueous solution. Thus, the attraction between oppositely charged surfactant aggregates and polyions decreases with decreasing surfactant chain length, and with decreasing polyion length, resulting in an increased miscibility with water. The complex salt with the longest surfactant chains and polyions gave the widest miscibility gap, with a concentrated hexagonal phase in equilibrium with almost pure water. A decrease in the attraction led to cubic-micellar and micellar-micellar coexistence in the miscibility gap and to an increasing concentration of the complex salt in the dilute phase. For each polyion length, the mixtures for the various surfactant chain lengths were found to conform to a global phase diagram, where the surfactant chain length played the role of an interaction parameter.     

On the phase behavior and structural properties of polyelectrolyte solutions

Correlations between structural properties and phase behavior of polyelectrolyte solutions were discussed along the line of the work reported by Châtellier and Joanny [Joanny JF, Châtellier X. J Phys France II 1996;6:1669]. A multicomponent system made of polyions, salt ions and counterions was considered under poor solvent conditions. Unlike this reference, partial structure factors were derived from the celebrated Zimm’s formula written in the matrix form including the effects of finite chain length. These effects were found to generate significant shifts in phase diagrams and qualitative changes in structural properties. The presence of a charged solid surface was briefly discussed. Here also, the phase diagram was found to shift with an increasing amount as the polyion chain length decreased.     

The Formation and Salt Induced Melting of a Highly Viscoelastic Mixture of Two Oppositely Charged Polyelectrolytes

A quick and convenient route to prepare a highly viscoelastic mixture of two oppositely charged polyelectrolytes is presented. The investigation was essentially performed at a fixed total polyelectrolyte concentration. The phase behaviour was studied at varying ratios between the two oppositely charged polyions. The mixtures phase separated associatively at mixing ratios in the vicinity of overall charge neutrality, while by screening the attractive forces with NaCl the precipitate could be dissolved. At certain mixing ratios off charge neutrality the mixtures were highly viscoelastic single-phase solutions in the absence of screening electrolyte. When NaCl was added to such a solution the viscoelasticity decreased strongly since the attractive forces between the oppositely charged polyions were screened. Therefore, by contacting an initially salt free mixture of polyions with a brine solution of known concentration, the diffusion of salt into the polyion matrices could be monitored by following the rheology of the mixture as a function of the contact time. It is shown that the transport of NaCl inside the polyion matrices was diffusion controlled.     

Phase transfer of hydrophilic, cyclodextrin-modified gold nanoparticles to chloroform solutions.

The preparation and characterization of gold nanoparticles (approximately 3 nm in diameter) capped with thiolated alpha- and beta-cyclodextrins (alpha and beta-CD) is described. The CD-capped nanoparticles are hydrophilic and bind ferrocene derivatives as evidenced by electrochemical and (1)H NMR spectroscopic measurements. The binding interactions of the CD-capped nanoparticles with a series of five alkyldimethyl(ferrocenylmethyl)ammonium ions (the alkyl group is propyl for compound 1, heptyl for 2, dodecyl for 3, hexadecyl for 4, and docosyl for 5) can be utilized for the phase transfer of the hydrophilic, CD-capped nanoparticles into a nonpolar chloroform phase. Only 3, 4, and 5 act as effective phase transfer agents, since 1 and 2 do not have enough amphiphilic character. The structure of the aggregates formed upon transfer of the CD-capped nanoparticles to the chloroform solution is postulated to resemble that of reverse micelles, as the nanoparticles template the peripheral arrangement of the cationic ferrocene amphiphiles, counterions and water molecules around their surfaces.     

Spermine‐Functionalized Perylene Bisimide Dyes—Highly Fluorescent Bola‐Amphiphiles in Water

A series of four spermine‐functionalized perylene bisimide dyes without linkers ( 1 ) and with linkers ( 2 – 4 ) between the chromophore and the polyamine was synthesized. Protonation of the spermine moieties resulted in the formation of highly water‐soluble dyes with up to six positively charged ammonium ions. The aggregation behavior of these strongly fluorescent bola‐amphiphiles was studied in pure water as solvent by UV/Vis and fluorescence spectroscopy, and an astonishingly high fluorescence quantum yield of up to Φ_fl=0.90 was observed for PBI 1 . Atomic force microscopy and transmission electron microscopy were applied for the visualization of the aggregates on surfaces. Molecular modeling studies were performed by force‐field calculations to explore the aggregate morphologies, which also provided valuable information on the influence of the additional alkylcarbonyl linkers. Our detailed spectroscopic and microscopic investigations revealed that the excellent optical properties of perylene bisimide chromophores can be used even in pure deionized water if their aggregation is efficiently suppressed.     

Electron paramagnetic resonance study of amphiphiles partitioning behavior in desiccation-tolerant moss during dehydration

Desiccation tolerance is a crucial characteristic for desert moss surviving in arid regions. Desiccation procedure always induces amphiphiles transferring from the polar cytoplasm into lipid bodies. The behavior of amphiphiles transferring can contribute to the enhancement of desiccation tolerance and the reduction of plasma membrane integrity simultaneously. The effects of amphiphiles partitioning into the lipid phase during water loss has been studied for pollen and seeds using electron paramagnetic resonance (EPR) spectroscopy. However, desiccation-tolerant high plants occur among mosses, several angiosperms and higher plants seeds or pollens. They have different strategies for survival in dehydration and rehydration. A desiccation-tolerant moss Tortula desertorum was used to investigate the behaviors of amphiphilic molecules during drying by spin label technology. There are small amount of amphiphilic probes partitioning into membrane during moss leaves dehydration, comparing with that in higher plants. Cytoplasm viscosity changed from 1.14 into glass state only dehydration less than 60 min. Moss leaves lost plasma membrane integrity slightly, from 0.115 to 0.237, occurred simultaneously with amphiphiles partition. The results showed the more advantages of mosses than higher plants in adapting fast dehydration. We propose that EPR spin label is feasible for studying the amphiphiles partitioning mechanisms in membrane protection and damage for desiccation-tolerant mosses.     

Lyotropic smectic layering of side-on polysoaps in water

 The synthesis and characterization of lyotropic smectic amphiphilic side-on polymers are described. The amphiphile consists of a rigid, aromatic core with two terminal ethyleneoxide chains of various lengths and is laterally attached to a polysiloxane backbone; the length of the spacer has also been varied. The phase behavior of the monomeric amphiphiles and side-on polymers are determined by polarizing microscopy and ²H-NMR measurements. In water, most of the low molecular weight surfactants show restricted lyotropic properties, namely lyotropic smectic phases. The packing restriction of the amphiphiles is due to their geometric anisometry. All side-on polymers exhibit only lyotropic smectic phases. The phase regime of the polymer mesophase with respect to the monomers depends on the spacer length. In contrast to surfactants having a flexible hydrophobic group, these amphiphiles align spontaneously parallel to an external magnetic field, leading to perfect lyotropic smectic monodomains. Received: 21 May 2001 Accepted: 27 August 2001     

Increased layer interdiffusion in polyelectrolyte films upon annealing in water and aqueous salt solutions

As-deposited films of multilayered polyelectrolytes are considered to be non-equilibrium structures. Due to the strong attraction between oppositely charged polyions, polyelectrolyte interdiffusion is thought to be suppressed during the adsorption process. Equilibration is promoted by a decrease of the electrostatic attraction between polyion pairs. We have used neutral impact collision ion scattering spectroscopy to investigate the influence of polyelectrolyte multilayer annealing in water and aqueous 1 M NaCl solutions at different temperatures (20 and 70 degrees C) on the increase in interpenetration of a single polyelectrolyte layer throughout the whole film. The multilayers were composed of poly(4-vinylpyridinium) and poly(4-styrenesulfonate). Contrast between neighboring layers was established by labelling the layer in question with the heavy atom ruthenium. It is found that both temperature and salt increase layer interpenetration, whereas salt has a stronger influence than temperature. From numerical simulations polyelectrolyte diffusion coefficients were evaluated for the different annealing conditions. The influence of temperature and salt on the equilibration of the film is interpreted in terms of increased screening of polyion charges and binding of small counterions to polyion monomeric units.     

Entropic effects in the electric double layer of model colloids with size-asymmetric monovalent ions

The structure of the electric double layer of charged nanoparticles and colloids in monovalent salts is crucial to determine their thermodynamics, solubility, and polyion adsorption. In this work, we explore the double layer structure and the possibility of charge reversal in relation to the size of both counterions and coions. We examine systems with various size-ratios between counterions and coions (ion size asymmetries) as well as different total ion volume fractions. Using Monte Carlo simulations and integral equations of a primitive-model electric double layer, we determine the highest charge neutralization and electrostatic screening near the electrified surface. Specifically, for two binary monovalent electrolytes with the same counterion properties but differing only in the coion's size surrounding a charged nanoparticle, the one with largest coion size is found to have the largest charge neutralization and screening. That is, in size-asymmetric double layers with a given counterion's size the excluded volume of the coions dictates the adsorption of the ionic charge close to the colloidal surface for monovalent salts. Furthermore, we demonstrate that charge reversal can occur at low surface charge densities, given a large enough total ion concentration, for systems of monovalent salts in a wide range of ion size asymmetries. In addition, we find a non-monotonic behavior for the corresponding maximum charge reversal, as a function of the colloidal bare charge. We also find that the reversal effect disappears for binary salts with large-size counterions and small-size coions at high surface charge densities. Lastly, we observe a good agreement between results from both Monte Carlo simulations and the integral equation theory across different colloidal charge densities and 1:1-electrolytes with different ion sizes.