Polyelectrolyte-surfactant Complexes Research Articles

Nanostructured polyelectrolyte-surfactant complex pervaporation membranes for ethanol recovery: the relationship between the membrane structure and separation performance

Polyelectrolyte-surfactant complexes (PESCs) were fabricated through the interaction of poly(acrylic acid) and four different cationic surfactants or their mixtures. PESC membranes were prepared by solution casting method and were applied in ethanol recovery from aqueous solution via pervaporation. Elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), water contact angle (CA) measurement, differential scanning calorimetry (DSC) and X-ray scattering were employed to characterize the composition, structure and properties of PESCs. The results reveal that the investigated PESCs are similar in hydrophobicity but different in hierarchical nanostructures. In separating 5 wt% ethanol/water mixture, PESC membranes with high crystallinity will have both low flux and ethanol selectivity because of the high packing density and low permeability of crystalline regions. Meanwhile, the hierarchical nanostructures of PESC membranes change under pervaporation environment as was revealed by in situ synchrotron radiation X-ray scattering measurement. That is, the crystalline region could melt at high temperature in swelling state, thus consequently enhancing the ethanol selectivity.

Structural behaviour of sodium hyaluronate in concentrated oppositely charged surfactant solutions.

This work discusses the polyelectrolyte sodium hyaluronate (HA) and its polyelectrolyte/surfactant complexes (PESCs) with tetradecyltrimethylammonium bromide (TTAB) in the semi-dilute regime of HA and at high concentrations of TTAB. The structure and flow properties in the surfactant excess region were studied by light scattering and small angle neutron scattering (SANS) as well as by rheology. The unique behaviour of HA to maintain its high viscosity was observed even at very high TTAB concentrations of 496 mM and this effect was systematically studied in the concentration range from 1 to 25 mM HA. From the data, it could be concluded that: (1) extended rod-like structures of the PESCs prevent molecular dissolution of HA by TTAB. (2) HA and TTAB micelles interact rather weakly as seen by a low fraction of bound micelles. (3) At very high TTAB concentrations a decompaction of PESCs (fractal dimension Df going from 2.0 to 1.2) occurs with increasing HA concentration but (4) both the entanglement of HA and the structure of the micelles are not affected.

Solvent Effects on the Structure-Property Relationship of Redox-Active Self-Assembled Nanoparticle-Polyelectrolyte-Surfactant Composite Thin Films: Implications for the Generation of Bioelectrocatalytic Signals in Enzyme-Containing Assemblies.

The search for strategies to improve the performance of bioelectrochemical platforms based on supramolecular materials has received increasing attention within the materials science community, where the main objective is to develop low-cost and flexible routes using self-assembly as a key enabling process. Important contributions to the performance of such bioelectrochemical devices have been made based on the integration and supramolecular organization of redox-active polyelectrolyte-surfactant complexes on electrode supports. Here, we examine the influence of the processing solvent on the interplay between the supramolecular mesoorganization and the bioelectrochemical properties of redox-active self-assembled nanoparticle-polyelectrolyte-surfactant nanocomposite thin films. Our studies reveal that the solvent used in processing the supramolecular films and the presence of metal nanoparticles not only have a substantial influence in determining the mesoscale organization and morphological characteristics of the film but also have a strong influence on the efficiency and performance of the bioelectrochemical system. In particular, a higher bioelectrochemical response is observed when nanocomposite supramolecular films were cast from aqueous solutions. These observations seem to be associated with the fact that the use of aqueous solvents increases the hydrophilicity of the film, thus favoring the access of glucose, particularly at low concentrations. We believe that these results improve our current understanding of supramolecular nanocomposite materials generated via polyelectrolyte-surfactant complexes, in order to use the processing conditions as a variable to improve the performance of bioelectrochemical devices.

Temperature dependence of solution properties of anionic polyelectrolyte-cationic surfactant complexes in ethanol

Abstract Stoichiometric polyelectrolyte-surfactant complexes, PSCs, were prepared from poly(acrylate), PA - , and poly(styrenesulfonate), PSS - , anions and dodecyltrimethylammonium cations, DTA + , and their properties were investigated by density and viscosity measurements in ethanol solutions in dependence on concentration and temperature. The measured densities were used to calculate the apparent molar volumes of the repeat units of DTAPA and DTAPSS complexes. Apparent molar volumes at infinite dilution, so as the reduced viscosities, in ethanol solutions are only weakly dependent on temperature. Through features typical for polyelectrolytes, viscosity curves suggest some small dissociation of complexes in ethanol. Light scattering, LS, measurements performed in the angular range from 50 to 150° did not reveal so called slow relaxation mode, which is typical for strongly charged polyelectrolytes in aqueous solutions without or with only a low amount of added salt. Size distributions were therefore calculated from the measured correlation functions. They were multimodal at all angles and for both PSCs, identifying 3 populations: particles with average hydrodynamic radii (i) below 10 nm, (ii) in the range 20–30 nm, and (iii) in the range 200–300 nm. Analysis of angular dependency of LS intensity for the largest particle population enabled the determination of the radius of gyration and the shape parameter ρ of these species. Large sizes, ρ values (ρ = 1.6 and 1.9 for DTAPA and DTAPSS, respectively), and the Kratky plots of the scattering data suggest that these particles are associates of more than one PSC (reverse micelle). Dynamic vapor sorption experiments with thin films of the studied PSCs show that the DTAPSS complex absorbs at the most 35% of water per its weight, whereas the DTAPA one absorbs considerably more (around 75%). Different structure of complexes was taken as responsible for large differences in water uptake.

Structure and dynamics of polyelectrolyte surfactant mixtures under conditions of surfactant excess

Oppositely charged polyelectrolyte (PE) surfactant mixtures can self-assemble into a large variety of mesoscopic structures, so-called polyelectrolyte surfactant complexes (PESCs). These structures directly affect the macroscopic behavior of such solutions. In this study, we investigated mixtures of the cationically charged PE JR 400 and the anionic surfactant SDS with the help of different neutron scattering and fluorescence methods. While an excess of PE charges in semi-dilute solutions causes an increase of viscosity, it has been observed that an excess of surfactant charges reduces the viscosity while precipitation is observed at charge equilibrium. The increase in viscosity had been investigated before and was attributed to the formation of cross links between PE chains. In this publication we focus our attention on the reduction of viscosity which is observed with an excess of surfactant charges. It is found that the PE chains form relatively large and densely packed clusters near the phase boundary on the surfactant rich side, thereby occupying less space and reducing the viscosity. For even higher surfactant concentrations, individual surfactant decorated PE chains are observed and their viscosity is found to be similar to that of the pure PE.

Layer-by-Layer Assembly of Fluorine-Free Polyelectrolyte-Surfactant Complexes for the Fabrication of Self-Healing Superhydrophobic Films.

Fluorine-free self-healing superhydrophobic films are of significance for practical applications because of their extended service life and cost-effective and eco-friendly preparation process. In this study, we report the fabrication of fluorine-free self-healing superhydrophobic films by layer-by-layer (LbL) assembly of poly(sodium 4-styrenesulfonate) (PSS)-1-octadecylamine (ODA) complexes (PSS-ODA) and poly(allylamine hydrochloride) (PAH)-sodium dodecyl sulfonate (SDS) (PAH-SDS) complexes. The wettability of the LbL-assembled PSS-ODA/PAH-SDS films depends on the film structure and can be tailored by changing the NaCl concentration in aqueous dispersions of PSS-ODA complexes and the number of film deposition cycles. The freshly prepared PSS-ODA/PAH-SDS film with micro- and nanoscaled hierarchical structures is hydrophilic and gradually changes to superhydrophobic in air because the polyelectrolyte-complexed ODA and SDS surfactants tend to migrate to the film surface to cover the film with hydrophobic alkyl chains to lower its surface energy. The large amount of ODA and SDS surfactants loaded in the superhydrophobic PSS-ODA/PAH-SDS films and the autonomic migration of these surfactants to the film surface endow the resultant superhydrophobic films with an excellent self-healing ability to restore the damaged superhydrophobicity. The self-healing superhydrophobic PSS-ODA/PAH-SDS films are mechanically robust and can be deposited on various flat and nonflat substrates. The LbL assembly of oppositely charged polyelectrolyte-surfactant complexes provides a new way for the fabrication of fluorine-free self-healing superhydrophobic films with satisfactory mechanical stability, enhanced reliability, and extended service life.

Development of Cetylpyridinium-Alginate Nanoparticles: A Binding and Formulation Study

In this study the development of stable polyelectrolyte-surfactant complex nanoparticles composed of alginate and cetylpyridinium chloride (CPC), with and without ZnCl2, for therapeutic use, is investigated. The mechanism of CPC binding by alginate was analyzed using a cetylpyridinium cation (CP+) selective membrane electrode. The cooperative nature of the interaction between CP+ and alginate was underlined by the sigmoidal shape of the binding isotherms. The presence of salts was shown to weaken interactions and, moreover, ZnCl2 reduced the cooperativity of binding. The CP+ cations in the form of micellar associates acted as multivalent crosslinkers of the alginate chains where stable dispersions of CP-alginate nanoparticles were formed in water at CP+/alginate charge ratios from 0.2 to 0.8. Characterization of the nanoparticles showed hydrodynamic diameters from 140 to 200nm, a polydispersity index below 0.2, a negative zeta potential and spherical morphology. The entrapment efficiency of CPC was ∼94%, the loading capacity more than 50% and prolonged release over 7days were shown. The formulations with noted charge ratios resulted in stable CP-alginate nanoparticles with a potential of treating periodontal disease.

Nanoscopic Terraces, Mesas, and Ridges in Freely Standing Thin Films Sculpted by Supramolecular Oscillatory Surface Forces.

Freely standing thin liquid films containing supramolecular structures including micelles, nanoparticles, polyelectrolyte-surfactant complexes, and smectic liquid crystals undergo drainage via stratification. The layer-by-layer removal of these supramolecular structures manifests as stepwise thinning over time and a coexistence of domains and nanostructures of discretely different thickness. The layering of supramolecular structures in confined thin films contributes additional non-DLVO, supramolecular oscillatory surface forces to disjoining pressure, thus influencing both drainage kinetics and stability of thin films. Understanding and characterizing the spontaneous creation and evolution of nanoscopic topography of stratifying, freely standing thin liquid films have been long-standing challenges due to the absence of experimental techniques with the requisite spatial (thickness <10 nm) and temporal resolution (<1 ms). Using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols developed herein, we visualize and characterize size, shape, and evolution kinetics of nanoscopic mesas, terraces, and ridges. The exquisite thickness maps created using IDIOM protocols provide much needed and unprecedented insights into the role of supramolecular oscillatory surface forces in driving growth of such nanostructures as well as in controlling properties and stability of freely standing thin films and, more generally, of colloidal dispersions like foams.

Influence of Corona Structure on Binding of an Ionic Surfactant in Oppositely Charged Amphiphilic Polyelectrolyte Micelles.

Interaction of polystyrene-block-poly(methacrylic acid) micelles (PS-PMAA) with cationic surfactant N-dodecylpyridinium chloride (DPCl) in alkaline aqueous solutions was studied by static and dynamic light scattering, SAXS, cryogenic transmission electron microscopy (cryo-TEM), isothermal titration calorimetry (ITC), and time-resolved fluorescence spectroscopy. ITC and fluorescence measurements show that there are two distinct regimes of surfactant binding in the micellar corona (depending on the DPCl content) caused by different interactions of DPCl with PMAA in the inner and outer parts of the corona. The compensation of the negative charge of the micellar corona by DPCl leads to the aggregation of PS-PMAA micelles, and the micelles form colloidal aggregates at a certain critical surfactant concentration. SAXS shows that the aggregates are formed by individual PS-PMAA micelles with intact cores and collapsed coronas interconnected with surfactant micelles by electrostatic interactions. Unlike polyelectrolyte-surfactant complexes formed by free polyelectrolyte chains, the PMAA/DPCl complex with collapsed corona does not contain surfactant micelles.

Adsolubilization phenomenon perceived in chitosan beads leading to a fast and enhanced malachite green removal

Chitosan (CS) is a well recognized cationic polyelectrolyte, widely used as an adsorbent. However, CS hydrogel bead lacks its ability to adsorb cationic dyes because of the obvious repulsion between cationic CS and the dye of same charge. In this work CS hydrogel beads are modified by sodium dodecyl sulfate (SDS), an anionic surfactant, under various conditions to improve its efficiency for the adsorption of malachite green (MG), a cationic dye. In the first part, the complex forming ability of surfactant (at <<CMC) with counter ion polyelectrolyte is utilized to fabricate modified chitosan beads, which are designated as surfactant–polyelectrolyte-complex (SPEC). In the second part of the adsorbent preparation, micelle aggregation behavior of surfactant (at >>CMC) is used to modify the surface charges and solubilization properties of the modified adsorbent. These beads are called as chitosan–surfactant–core–shell (CSCS). The mechanism of formation for both is discussed. Besides these modified beads, the CS–SDS composite material (CSC) is also prepared. The adsorptive removal of MG by all the prepared beads has been evaluated. The CSCS beads are found to be the best (adsorption capacity: 360mg/g) for MG removal. Such an enhanced adsorption is believed to be due to ‘adsolubilization’ of MG on surfactant bilayer, which has been realized for the first time in CS bead support. The kinetics of removal also is much faster compared to CS beads. The efficiency of CSC for MG removal is higher compared to that of CS beads. The adsorption behavior of CS beads in binary mixture of MG and SDS has also been examined.

Extinction coefficients and refractive index increments of complex salts between cetylpyridinium cations and poly(styrenesulfonate) anion

Abstract Polyelectrolyte–surfactant complexes, PSCs, are widely used and studied. In this data article, we report an easy preparation procedure of the complex salt formed between cetylpyridinium cations and poly(styrenesulfonate) anion complemented by values of its molar extinction coefficient and specific refractive index increment in aqueous solutions at various charge ratios between the surfactant (S) and the polyion (P) charges (S/P). These complexes have superior solubility in water. The molar extinction coefficient increases linearly with S/P, whereas the specific refractive index increment does not depend on S/P. These data are useful for the spectrophotometric determination of concentration and for molar mass determination by light scattering, respectively. They were already used in measurements of several thermodynamic and transport properties (Kogej, 2010) and of molar mass values of the soluble PSCs (Prelesnik et al., 2011) where the knowledge of precise concentration is crucial.

Self‐Healing Poly(acrylic acid) Hydrogels: Effect of Surfactant

SummaryPhysical poly(acrylic acid) gels were prepared by micellar copolymerization of hydrophilic monomer acrylic acid with large hydrophobic monomer stearyl methacrylate (C18) in solutions of worm‐like anionic surfactant (sodium dodecyl sulfate, SDS) and cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) micelles. Hydrophobe content of the monomer mixtures was 2 mol.% and total monomer concentration in gels was 20 w/v%. Gelation reactions were monitored by rheometry using oscillatory deformation tests. Hydrogel samples were also subjected to uniaxial elongation and compression tests after preparation and swelling. The physical gels with SDS and CTAB showed similar properties as long as they are at the state of preparation, such as insoluble in water and exhibit time‐dependent dynamic moduli, high Young's modulus, high fracture stress, high elongation ratios at break. Also self‐healing was evidenced by mechanical measurements. Physical gels formed in SDS solution were stable, exhibited high equilibrium swelling ratios and SDS progressively extracted from the network in water. On the other hand, gels with CTAB formed a complex and resulted in shrinkage after gels were immersed in a large excess of water because both electrostatic interactions between the charged components and hydrophobic interactions between the polymer backbone and the alkyl chains of the surfactant are important in driving the self‐assembly of molecules to form ordered structures. These structures of the polyelectrolyte surfactant complexes have unusual mechanical properties. Also, the hydrogel samples with CTAB self‐healed via heating and surfactant treatment of the damaged areas withstand up to 1.05 MPa stresses and rupture at a stretch of 800%.

Surfactant-Mediated Polyelectrolyte Self-Assembly in a Polyelectrolyte–Surfactant Complex

Self-assembly and dynamics of a polyelectrolyte (PE)–surfactant complex (PES) are investigated using molecular dynamics simulations. The complexation is systematically studied for five different PE backbone charge densities. At a fixed surfactant concentration the PES complexation exhibits pearl necklace to agglomerated double spherical structures with a PE chain decorating the surfactant micelles. The counterions do not condense on the complex but are released in the medium with a random distribution. The relaxation dynamics for three different length scales, the polymer chain, segmental, and monomer, show distinct features of the charge and neutral species; the counterions are fastest followed by the PE chain and surfactants. The surfactant heads and tails have the slowest relaxation due to their restricted movement inside the agglomerated structure. At the shortest length scale, all the charge and neutral species show similar relaxation dynamics confirming Rouse behavior at monomer length scales. Overa...

Self- and co-assembly of amphiphilic gradient polyelectrolyte in aqueous solution: Interaction with oppositely charged ionic surfactant

Association behavior of the biocompatible amphiphilic cationic gradient polyelectrolyte poly[(2-methyl-2-oxazoline)-grad-(2-phenyl-2-oxazoline)-mod-(ethylene imine)] (HPPhMeOx) prepared by partial hydrolysis of the gradient copolymer poly[(2-methyl-2-oxazoline)-grad-(2-phenyl-2-oxazoline)] and the interaction of HPPhMeOx with the anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solutions were investigated by scattering techniques (SANS, DLS) and by atomic force microscopy. SANS measurements revealed that large particles with the hydrodynamic radius of ca. 500nm observed in HPPhMeOx aqueous solutions by DLS are formed by a network of physically crosslinked compact hydrophobic domains with the mean radius of ca. 10nm. Upon addition of sodium dodecyl sulfate (SDS), the size of the domains increases at low amounts of the added SDS due to hydrophobic interaction of the single surfactant ions with the aggregates. Further addition of SDS leads to the formation of the co-assembled polyelectrolyte–surfactant complex manifested in SANS by the presence of the correlation peak from the densely packed SDS micelles as well as by partial disruption of the domains.

Molecular Dynamics Simulations of Adsorption of Poly(acrylic acid) and Poly(methacrylic acid) on Dodecyltrimethylammonium Chloride Micelle in Water: Effect of Charge Density.

We have investigated the interaction of dodecyltrimethylammonium chloride (DoTA) micelle with weak polyelectrolytes, poly(acrylic acid) and poly(methacrylic acid). Anionic as well as un-ionized forms of the polyelectrolytes were studied. Polyelectrolyte-surfactant complexes were formed within 5-11 ns of the simulation time and were found to be stable. Association is driven purely by electrostatic interactions for anionic chains whereas dispersion interactions also play a dominant role in the case of un-ionized chains. Surfactant headgroup nitrogen atoms are in close contact with the carboxylic oxygens of the polyelectrolyte chain at a distance of 0.35 nm. In the complexes, the polyelectrolyte chains are adsorbed on to the hydrophilic micellar surface and do not penetrate into the hydrophobic core of the micelle. Polyacrylate chain shows higher affinity for complex formation with DoTA as compared to polymethacrylate chain. Anionic polyelectrolyte chains show higher interaction strength as compared to corresponding un-ionized chains. Anionic chains act as polymeric counterion in the complexes, resulting in the displacement of counterions (Na(+) and Cl(-)) into the bulk solution. Anionic chains show distinct shrinkage upon adsorption onto the micelle. Detailed information about the microscopic structure and binding characteristics of these complexes is in agreement with available experimental literature.

Formation of redox-active self-assembled polyelectrolyte–surfactant complexes integrating glucose oxidase on electrodes: Influence of the self-assembly solvent on the signal generation

In this work the effects of the self-assembly solvent on the structure and electrochemical behavior of redox-active polyelectrolyte–surfactant complexes cast on electrode supports from aqueous and DMF solutions are presented. The complex studied is formed by complexation of osmium complex-modified polyallylamine (OsPA) with dodecyl sulfate (DS) surfactants. The structure of the films was characterized by GISAXS, showing that films present a lamellar mesostructure. However, when they are exposed to humid environments, films cast from aqueous solutions (OsPA–DSaq) undergo a structural transition that ultimately leads to the disappearance of the mesostructural order. On the other hand, OsPA–DS films cast from DMF solutions (OsPA–DSorg) revealed no significant changes upon exposure to humid environments. Both types of films were exposed to glucose oxidase (GOx), showing similar adsorption characteristics. Notwithstanding these similarities in GOx and content, OsPA–DSaq films revealed a more sensitive bioelectrocatalytical response to glucose as compared to OsPA–DSorg films.

Polycation-sodium lauryl ether sulfate-type surfactant complexes: influence of ethylene oxide length.

Polyelectrolyte-surfactant complexes (PESC) are a class of materials which form spontaneously by self-assembly driven by electrostatic and hydrophobic interactions. PESC containing sodium lauryl ether sulfates (SLES) have found wide application in hair care products like shampoo. Typically, SLES with only one or two ethylene oxide (EO) groups are used for this application. We have studied the influence of the size of the EO block (ranging from 0 to 30 EO groups) on complexation with two model polycations: linear polyDADMAC and branched PEI. PESC size and electrostatic properties were determined during stepwise titration of buffered polycation solutions. The critical aggregation concentration (CAC) of PESC was determined by surface tension measurements and fluorescence spectroscopy. For polyDADMAC, there is no influence of the size of the EO block on the complexation behavior; the stiff polycation governs the structure formation. For PEI, it was seen that the EO block size does affect the structure of the complexes. The CAC value of the investigated complexes turns out to be rather independent of the EO block size; however, the CMC/CAC ratio decreases with increasing size of the EO block. This latter observation explains why the Lochhead-Goddard effect is most effective for small EO blocks.

The effect of the molecular mass of poly(N,N-diallyl-N,N-dimethylammonium chloride) on the particle size of its polyelectrolyte-surfactant complexes with sodium dodecylsulfate

The formation of polyelectrolyte-surfactant complexes of poly(N,N-diallyl-N,N-dimethylammonium chloride) of various molecular masses with sodium dodecylsulfate has been studied with the use of turbidity titration and laser diffraction-scattering. It has been shown that the molecular mass of the polycation has a significant influence on the boundary compositions of the system, which are related to the appearance of a complex phase, and on the particle size of the complex.

Polymer–surfactant complexes for microencapsulation of vitamin E and its release

Microencapsulation of vitamin E directly from oil-in-water (o/w) emulsions was carried out by means of a novel practically relevant approach. For the first time, a preformed polyelectrolyte–surfactant complex (sodium polystyrene sulfonate/dodecyl trimethyl ammonium bromide) was simultaneously used as an electrosteric emulsion stabilizer and as a charged precursor for the following build up of microcapsules. Subsequently, a layer-by-layer technique was applied to emulsions leading to the formation of core–shell microcapsules with oily cores and polyelectrolyte shells. The effect of the complexes on the process of emulsion formation and on the stability and characteristics of the resulting emulsions was investigated by measurements of dynamic and equilibrium interfacial tension, size distribution (DLS) and interfacial charge (zeta-potential). The resulting microcapsules were characterized by confocal laser scanning microscopy (CLSM), Cryo-SEM, size distribution and zeta-potential measurements on each stage of the shell assembly. The release kinetics of vitamin E was monitored during the consecutive steps of the encapsulation procedure using UV–vis spectroscopy and showed the progressive enhancement of sustainability.The developed approach may be promising for the practical use in the cosmetic and food industry.

Properties of polyelectrolytes prepared by polymerization of ionogenic monomers in micellar solutions of sodium dodecyl sulfate

The properties of polyelectrolytes obtained by the free radical and template polymerization of N-ethyl-N,N-dimethyl-N-methacryloyloxyethylammonium bromide, trimethylmethacryloyloxyethylammonium methyl sulfate, and [N-benzyl-N,N-dimethyl-N-(methacryloyloxyethyl)]ammonium chloride in micellar solutions of sodium dodecyl sulfate were studied by static and dynamic light scattering, viscosimetry, and differential refractometer. It was shown that the solubility of the polymerization products, being polyelectrolyte—surfactant complexes, is determined by the composition of the reaction mixture and chemical nature of the monomer. The introduction of a surfactant into the polymerization medium noticeably decreases the molecular weight of the formed polymers.