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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.

In arthropods, the determination of two important parameters of digestive juices, i.e. the total surfactant concentration and the critical micelle concentration (CMC), is challenging due to small sample volumes and low surfactant concentrations. In this work, we report a successful implementation of potentiometric titrations using the surfactant ion-selective electrode (SISE) and the pyrene fluorescence method (PFM) for the determination of the total surfactant concentration and CMC in the digestive juice of terrestrial isopod crustaceans Porcellio scaber. Pooled digestive juice extracts of four (SISE) or two (PFM) animals were used per measurement run. In both cases, digestive juice extracts in 100 μL of deionized water were sufficient for one measurement run. The total surfactant concentration of P. scaber digestive juice was determined to be 9.2 ± 3.5mM and the CMC was approximately 90 μM. Our work presents an important improvement towards easy CMC determination in small volume samples in comparison with the commonly used stalagmometric technique, where much larger sample volumes are usually needed. To date, the total surfactant concentration was not measured in the digestive juices of arthropods other than Homarus vulgaris, Astacus leptodactylus and Cancer pagurus, for which complex separation and analytical techniques were required. Our results obtained by SISE and PFM therefore present the first successful quantification of surfactants and their CMC in small volumes of arthropod digestive juice without prior separation or purification techniques.

The polyelectrolyte matrix tablets loaded with an oppositely charged drug exhibit complex drug-release mechanisms. In this study, the release mechanism of a cationic drug doxazosin mesylate (DM) from matrix tablets based on an anionic polyelectrolyte λ-carrageenan (λ-CARR) is investigated. The drug release rates from λ-CARR matrices are correlated with binding results based on potentiometric measurements using the DM ion-sensitive membrane electrode and with molecular characteristics of the DM-λ-CARR-complex particles through hydrodynamic size measurements. Experiments are performed in solutions with different ionic strength and with the addition of an anionic surfactant sodium dodecyl sulphate (SDS). It is demonstrated that in addition to swelling and erosion of tablets, the release rates depend strongly on cooperative interactions between DM and λ-CARR. Addition of SDS at concentrations below its critical micelle concentration (CMC) slows down the DM release through hydrophobic binding of SDS to the DM-λ-CARR complex. On the contrary, at concentrations above the CMC SDS pulls DM from the complex by forming mixed micelles with it and thus accelerates the release. Results involving SDS show that the concentration of surfactants that are naturally present in gastrointestinal environment may have a great impact on the drug release process.

Nanostructured polyanilines (PANI) with various morphology were synthesized by polymerization of aniline with ammonium peroxodisulfate in acidic aqueous medium containing ionic liquids (ILs) with imidazolium, pyridinium and quaternary ammonium cations. The influence of the type of IL and the aniline/IL mole ratio on the morphology and properties of formed PANIs was investigated. ILs added to reaction mixture control the PANI morphology toward nanowires or various complex two- and three-dimensional structures in contrast to the morphology of agglomerated granular particles that is typical of PANIs prepared in the absence of IL. The UV–Vis, IR and Raman spectra of PANIs showed that the used ILs do not affect the chemical structure of PANI, which indicates that they do not affect the formation of PANI molecules but only their assembling during polymerization. The DLS measurements indicate that ILs as well as their mixtures with an oxidant and aniline form in 1 M HCl ordered micellar structures. The micellar structures most likely act as soft templates that assemble growing PANI chains and/or aniline molecules into particular nanostructures and/or their precursors. The fact that the structure of PANI nanoparticles is, in general, a function of the type of IL and IL/aniline concentration ratio, indicates that the architecture of micelles depends on the same variables.

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.

Investigations dealing with association behaviour and structure formation in oppositely charged polyelectrolyte-surfactant mixtures in aqueous solutions are reviewed. Discussion is limited to a selection of vinyl based anionic polyelectrolytes that, when completely ionized, posses the same structural value of the linear charge density parameter. Particular emphasis is placed on the role of polymer chain properties in aggregates with surfactants. Chain characteristics are varied by changing the nature of the charged group, its ionization degree - when possible, the spatial distribution of these groups along the chain, i.e. the tacticity, and the hydrophobic character of other substituents attached to the chain. Quantitative information on the degree of binding in the form of binding isotherms is obtained using surfactant-sensitive membrane electrodes and microstructures of polyelectrolyte-surfactant complexes are determined by synchrotron small angle X-ray scattering. Considerable differences in the degree of binding (including the critical association concentration, CAC, values) and in structures are found. It is concluded that strong interactions in these systems arise from the electrostatic attraction, but this only forms the basis for initial extensive accumulation (anchoring) of surfactant ions in the vicinity of the polyion chain. When this is accomplished, additional specific interactions and effects may come into play. The most powerful of these interactions, the hydrophobic association between the chain and the micelle core, were found in polystyrenesulfonate, PSS, solutions. Other properties are less influential but still lead to CAC values that differ by more than one order of magnitude. These differences are explained by taking into account the chain conformation, flexibility, and hydrophobic character. Specific interactions between PSS and cetylpyridinium, CP, cations result in a soluble non-stoichiometric PSS-CP complex that could be characterized by measuring various solution properties as a function of polymer concentration and degree of complexation. The review is supplemented by including studies of complexation between the spherical fullerene hexamalonate anion and cationic surfactants, which demonstrate a high association tendency with characteristics similar to those found in binding of surfactants by linear polyelectrolytes.

Structural properties of complexes of poly(acrylate) anion (PA) and the cationic surfactants dodecylpyridinium (DPC) and cetylpyridinium chloride (CPC) were investigated by synchrotron X-ray scattering at various degrees of neutralization αN of poly(acrylic acid) (HPA) and at a fixed surfactant:polymer molar ratio. In all scattering curves, one broad (PA−DPC complexes, all αN-values, and PA−CPC complexes, αN = 0) or several sharp peaks (PA−CPC complexes, αN > 0) were observed, pointing to a high degree of ordering in these systems. The fundamental type of organization of surfactant is in the form of polymer-induced micelles that are clustered around the polymer. The multiple reflections in the case of PA−CPC complexes point to a Pm3n cubic structure. The calculated values of structural parameters indicate a larger degree of ordering in complexes at low αN-values (i.e., at αN < 0.5) than that at higher ones. This suggests that the binding of the surfactant by the polyelectrolyte is influenced by factors ot...

Mixtures of natural and biodegradable surfactants and ionic polysaccharides have attracted considerable research interest in recent years because they prosper as antimicrobial materials for medical applications. In the present work, interactions between the lysine-derived biocompatible cationic surfactant Nε-myristoyl-lysine methyl ester, abbreviated as MKM, and the sodium salt of hyaluronic acid (NaHA) are investigated in aqueous media by potentiometric titrations using the surfactant-sensitive electrode and pyrene-based fluorescence spectroscopy. The critical micelle concentration in pure surfactant solutions and the critical association concentration in the presence of NaHA are determined based on their dependence on the added electrolyte (NaCl) concentration. The equilibrium between the protonated (charged) and deprotonated (neutral) forms of MKM is proposed to explain the anomalous binding isotherms observed in the presence of the polyelectrolyte. The explanation is supported by theoretical model calculations of the mixed-micelle equilibrium and the competitive binding of the two MKM forms to the surface of the electrode membrane. It is suggested that the presence of even small amounts of the deprotonated form can strongly influence the measured electrode response. Such ionic-nonionic surfactant mixtures are a special case of mixed surfactant systems where the amount of the nonionic component cannot be varied independently as was the case for some of the earlier studies. © 2015 American Chemical Society., This work was partially supported by the Slovenian Research Agency, ARRS, through the Physical Chemistry program P1-0201, program P2 0118, and project L2-4060. LP generously thanks the Spanish Plan National I+D+I MAT2012-38047-C02-02.

The poly(acrylate) (PA)/surfactant and poly(methacrylic acid) (PMA)/surfactant complexes were investigated by synchrotron X-ray scattering at various degrees of neutralization, α, of the polyion and at a fixed surfactant to polyion charge ratio. At low α-values, the surfactant organizes into polymer-induced micelles that are attracted by the polymer through hydrophobic interactions. This is followed by a formation of a Pm3n cubic structure at higher α-values as a consequence of very strong electrostatic attractions between the polyion and charged surfactant aggregates. From the position of the maxima in the scattering curves, the characteristic distance d was obtained. In PA/surfactant complexes, d varies linearly with α. This is an indication of a smooth expansion of the PA chain upon neutralization. In PA/dodecylpyridinium chloride (DPC) solutions, d increases from 30.2 A at α = 0 to 36.6 A at α = 1, and correspondingly d increases from 44.1 to 51 A in the PA/CPC case. The d-value at α = 0 almost matche...

values), NaPSS/CPC (S/P < 1), and NaPA(NaPMA)/DPC (S/P < 1) complexes produced a micellelike organization of the surfactant along the polyion chain. The NaPSS-induced micelle is smaller in size than the ordinary one because of the inclusion of the aromatic rings on the PSS chain into the hydrophobic interior of the micelle. The size of the ordered elements in complexes with the hydrophilic NaPA and NaPMA corresponds to the radius of an ordinary globular micelle together with the thickness of the polyelectrolyte chain that surrounds it. (2) In NaPSS/CPC precipitate (S/P g 1), a hexagonal phase is observed with a unit cell parameter equal to 39.5 A. (3) The multiple reflections in the scattering curves of NaPA(NaPMA)/DPC complexes with S/P g 1 and of NaPA(NaPMA)/CPC ones for all S/P values point to some cubic structure. The cell constants of these mesophases correspond approximately to 2.5 diameters of a globular surfactant micelle. (4) In addition to a cubic phase, a well-pronounced hexagonal phase with a unit cell parameter of 40.5 A develops in the NaPA/CPC case with S/P g 1.

Synchrotron X-ray scattering was used for the structural investigation of complexes between anionic polyelectrolytes and cetylpyridinium chloride (CPC). According to the Bragg peaks, different types of ordering are proposed. Cetylpyridinium chloride in conjunction with carrageenan forms bilayers connecting rigid polysaccharide chains. In the presence of poly(styrenesul-fonate), several micelles are bound to one chain. They appear rather small in size due to specific interactions with this polyion. In poly(acrylate)/CPC and poly(methacrylate) /CPC solutions, a cubic structure is indicated.

The osmotic coefficient, the apparent molar volume, and the electrical conductivity of aqueous solutions of the homologous series of decyl-, undecyl-, dodecyl-, tridecyl-, tetradecyl-, pentadecyl-, and hexadecylpyridinium bromides (CnPyBr) have been determined at 25 °C. From these data the variation of the critical micelle concentration (cmc) with the chain length of the surfactant has been obtained. Measurements were performed usually at concentrations from well below to well above the cmc. From osmotic coefficient and conductivity measurements, the degree of counterion binding to micelles, β, has been calculated. It has been found that the values of β are rather insensitive to the chain length, and as expected, the values determined from transport measurement are lower than those from the osmotic pressure measurements. From the apparent molar volumes the aggregation numbers of alkylpyridinium bromides have been estimated, following simple geometrical considerations suggested by Tartar and Tanford.

Micelle formation of alkyltrimethylammonium surfactants (CnTMAB) in aqueous sodium poly(styrenesulfonate) (NaPSS) solutions was studied by fluorescence and conductivity measurements at 25 °C. The dependence of the aggregation phenomena on the chain length of the surfactant (n = 12, 14, 16, 18) and on the ionic strength of solutions was investigated. The critical aggregation concentration (cac) decreases with increasing hydrophobicity of the surfactant but remains approximately unchanged for C16TMAB and C18TMAB. The cac values are considerably lower than the critical micellization concentration (cmc) values for the same surfactant. The decrease is in the range from about three orders of magnitude for C12EDMAB in water to approximately 10 times for C18TMAB in 0.01 M NaBr. Furthermore, the cac for C12EDMAB and C14TMAB in NaPSS was found to increase slightly with increasing NaBr concentration but much less than, for instance, in sodium poly(acrylate) solutions. No significant effect of NaBr on cac values for ...

Mixtures of polyelectrolytes and oppositely charged surfactants show very rich phase behavior that is influenced by surfactant-ion and polyion properties and by water content. A general feature is associative phase separation as a result of strong electrostatic interactions, whereas the effect of eventual more specific interactions (e.g., hydrophobic) has not been thoroughly investigated. In this paper, we report a detailed study on phase behavior and structures in poly(styrenesulfonate anion) (PSS(-))-cetyltrimethylammonium cation (CTA(+))-water mixtures that are characterized by a hydrophobic interaction between the styrene groups of PSS(-) and the micelle interior. Structures of various phases were determined by small-angle X-ray scattering, and results indicated the presence of a disordered micellar and an ordered hexagonal phase; no cubic phase was found. The general conclusion is that the highlighted hydrophobic interaction promotes dissolution of CTAPSS when the polyion salt is added and provides further stabilization of the dense phase when the surfactant salt is added.

Polyelectrolyte–surfactant mixtures have attracted considerable research interest in the past decades due to their widespread appearance in nature and technology. Many different systems have been studied with the purpose to identify the key features that effect their behavior and performance. In this chapter, we review our studies on polyelectrolyte–surfactant interactions in a particular system involving a strong polyelectrolyte, poly(styrenesulfonate), PSS, and oppositely charged surfactants. The interest in PSS is due to its concealed hydrophobic character related to benzene rings in its functional groups. Owing to this feature, PSS interacts strongly with oppositely charged surfactants through electrostatic and additional hydrophobic interactions, which involve solubilization of hydrophobic groups of PSS in surfactant micelles. We demonstrate that this characteristic has an important effect on binding isotherms, critical association concentration values, and free energy changes associated with the binding process, so as on the solubility and structure of the ensuing polyelectrolyte–surfactant complexes (PSCs). Good solution stability of PSCs involving PSS enabled the determination of several solution properties of soluble PSCs.

Complexes formed between a cationic surfactant cetylpyridinium chloride, CPC, and an anionic polyelectrolyte sodium poly(styrenesulfonate), NaPSS, in aqueous 0.1 M NaCl solutions were studied by static and dynamic light scattering and by ζ-potential measurements in a broad region of surfactant cation, CP(+), to polyanion, PSS(-), charge ratio, S/P. Two NaPSS samples were used, NaPSS-L with a lower molar mass, M(w) = 1.4 × 10(5) g/mol, and NaPSS-H with a considerably higher M(w) (= 2.6 × 10(6) g/mol), to elucidate the effect of the polyion chain length on the behavior of the aggregates. In the polyelectrolyte-rich regime (S/P1), CPPSS complexes are soluble up to rather high S/P values (around 0.72, irrespective of the polyion chain length), which is attributed to a specific interaction between the hydrophobic benzene groups on the polyion and the surfactant micelle, which leads to a less efficient charge screening. The addition of surfactant causes chain contraction. The obtained data suggest a pronounced effect of the NaPSS chain length on the structural properties of the CPPSS complexes. The CPPSS-L complexes are small and dense (the radius of gyration, R(g), is 7.3 nm at S/P = 0.7), and their shape is close to spherical. In contrast, the CPPSS-H complexes (R(g) around 73 nm at S/P = 0.7) have no well-defined structure and reveal a stronger tendency toward intermolecular association when the nominal charge of the complex is reduced, although they remain pretty monodisperse. A model of a temporary network-like association in which surfactant micelles serve as cross-links for polyion chains is proposed to explain the behavior in CPPSS-H solutions. The forces responsible for such labile intermolecular association are weak, in contrast to strong specific interaction involved in the formation of the primary complex. The redissolution of the complex by adding excess surfactant (S/P1: the surfactant-rich regime) depends strongly on the polyion chain length and is a slow process, taking several days (CPPSS-L) or even weeks (CPPSS-H). It is achieved only at very high S/P values (around 240 and 2400 in the CPPSS-L and CPPSS-H cases, respectively) by hydrophobic binding of surfactant to the CPPSS complex. The predominating species in these solutions are free surfactant micelles. Similarly, a large excess of NaCl (almost 390 and 690 mol per 1 mol of CPPSS-L and CPPSS-H, respectively) is needed to disintegrate the stoichiometric CPPSS (S/P = 1) complex into free polyion chains and free surfactant micelles.

The interaction of cationic surfactant cetylpyridinium chloride, CPC, with giant lipid vesicles prepared from 1-palmitoyl-2-oleoylphosphatidylcholine, POPC, was examined at various concentrations of the lipid component. The lipid concentration was determined by a spectrophotometric method. The potentiometric method based on surfactant-selective electrode was used for the determination of surfactant concentration in the external water solution. From these results, moles of surfactant incorporated in the membrane per mole of lipid (parameter beta) and two kinds of partition coefficients were calculated. Their values were found to be considerably larger than the available literature data. A three stage process of surfactant-induced solubilization of lipid vesicles was observed. First, stable mixed bilayers form, which become saturated with CPC at a value beta(sat) larger than 0.8, which then gradually disintegrate. Just prior to the breakdown of the vesicular structure, formation of ellipsoidal vesicles was observed by optical microscopy. This phenomenon was attributed to the cooperative incorporation of surfactant into the bilayer. Fluorescence measurements have shown that the second stage in the solubilization process of POPC by the C16 chain-length surfactant does not involve mixed micelles. These are formed only in the third stage, which is the complete solubilization of POPC bilayers. The corresponding critical micellization concentration decreases with increasing concentration of the lipid component.