Preparation of stable electroneutral nanoparticles of sodium dodecyl sulfate and branched poly(ethylenimine) in the presence of pluronic F108 copolymer

Effect of Dilution on the Nonequilibrium Polyelectrolyte/Surfactant Association

Polyelectrolyte (PE)/surfactant (S) mixtures play a distinguished role in the efficacy of shampoos and toiletries primarily due to the deposition of PE/S precipitates on the hair surface upon dilution of the formulations. The classical interpretation of this phenomenon is a simple composition change during which the system enters the two-phase region. Recent studies, however, indicated that the phase properties of PE/S mixtures could be strongly affected by the applied solution preparation protocols. In the present work, we aimed at studying the impact of dilution on the nonequilibrium aggregate formation in the sodium poly(styrenesulfonate) (NaPSS)/dodecyltrimethylammonium bromide (DTAB)/NaCl system. Mixtures prepared with hundredfold dilution of concentrated NaPSS/DTAB/NaCl solutions in water were compared with those ones made by rapid mixing of dilute NaPSS/NaCl and DTAB/NaCl solutions. The study revealed that the phase-separation concentration range as well as the composition, morphology, and visual appearance of the precipitates were remarkably different in the two cases. These observations clearly demonstrate that the dilution/deposition process is also related to the nonequilibrium phase properties of PE/S systems, which can be used to modulate the efficiency of various commercial applications.

Supramolecular assembly of a thermoresponsive steroidal surfactant with an oppositely charged thermoresponsive block copolymer

Supramolecular rearrangements are crucial in determining the response of stimuli sensitive soft matter systems such as those formed by mixtures of oppositely charged amphiphiles. Here mixtures of this kind were prepared by mixing the cationic block copolymer pAMPTMA₃₀-b-pNIPAAM₁₂₀ and an anionic surfactant obtained by the modification of the bile salt sodium cholate. As pure components, the two compounds presented a thermoresponsive self-assembly at around 30-35 °C; a micelle formation in the case of the copolymer and a transition from fibers to tubes in the case of the bile salt derivative. When both were present in the same solution they associated into mixed aggregates that showed complex thermoresponsive features. At room temperature, the core of the aggregate was comprised of a supramolecular twisted ribbon of the bile salt derivative. The block copolymers were anchored on the surface of this ribbon through electrostatic interactions between their charged blocks and the oppositely charged heads of the bile salt molecules. The whole structure was stabilized by a corona of the uncharged blocks that protruded into the surrounding solvent. By increasing the temperature to 30-34 °C the mixed aggregates transformed into rods with smooth edges that associated into bundles and clusters, which in turn induced clouding of the solution. Circular dichroism allowed us to follow progressive rearrangements of the supramolecular organization within the complex, occurring in the range of temperature of 20-70 °C.

Adsorption of poly(ethylene oxide)-containing amphiphilic polymers on solid-liquid interfaces: Fundamentals and applications

The adsorption of amphiphilic molecules of varying size on solid-liquid interfaces modulates the properties of colloidal systems. Nonionic, poly(ethylene oxide) (PEO)-based amphiphilic molecules are particularly useful because of their graded hydrophobic-hydrophilic nature, which allows for adsorption on a wide array of solid surfaces. Their adsorption also results in other useful properties, such as responsiveness to external stimuli and solubilization of hydrophobic compounds. This review focuses on the adsorption properties of PEO-based amphiphiles, beginning with a discussion of fundamental concepts pertaining to the adsorption of macromolecules on solid-liquid interfaces, and more specifically the adsorption of PEO homopolymers. The main portion of the review highlights studies on factors affecting the adsorption and surface self-assembly of PEO-PPO-PEO block copolymers, where PPO is poly(propylene oxide). Block copolymers of this type are commercially available and of interest in several fields, due to their low toxicity and compatibility in aqueous systems. Examples of applications relevant to the interfacial behavior of PEO-PPO-PEO block copolymers are paints and coatings, detergents, filtration, and drug delivery. The methods discussed herein for manipulating the adsorption properties of PEO-PPO-PEO are emphasized for their ability to shed light on molecular interactions at interfaces. Knowledge of these interactions guides the formulation of novel materials with useful mesoscale organization and micro- and macrophase properties.

Impact of Polyelectrolyte Chemistry on the Thermodynamic Stability of Oppositely Charged Macromolecule/Surfactant Mixtures

The complexation between hexadecyl- and dodecyltrimethylammonium bromides (CTAB and DTAB) with sodium poly[(vinyl alcohol)-co-(vinyl sulfate)] (PVAS) copolymer of low charge density has been investigated using pyrene fluorescence spectroscopy, electrophoretic mobility, turbidity, and dynamic light scattering measurements. The results indicate that the binding of the cationic surfactant occurs in three steps. At low surfactant concentrations, the cationic amphiphile binds to the vinyl sulfate groups. Above charge neutralization, surfactant binding may occur on the surface of the hydrophobic vinyl sulfate/CnTAB nanoassemblies. At even higher concentrations, the surfactant binds on the nonionic vinyl alcohol units of the polyion which reswells the PVAS/CnTAB complexes and makes them highly soluble in water. In earlier studies on oppositely charged ionic surfactants and homopolyelectrolytes the impact of mixing protocols was found remarkable, especially at surfactant excess, where these systems can be trapped in the charge stabilized colloidal dispersion state. In contrast, in the case of PVAS/CnTAB mixtures the effect of mixing is less pronounced and diminishes with increasing ionic strength or decreasing alkyl chain length of the surfactant. These findings are rationalized by taking into account the different binding mechanism of surfactants on oppositely charged homopolyelectrolytes and double hydrophilic copolymers.

Elegant cooperativity of noncovalent interactions in effective removal of Cu–EDTA from water via stepwise addition of polymer and surfactant

The elegant cooperativity of electrostatic interaction, coordinating interaction, and hydrophobic effects allows facile flocculation of Cu–EDTA through the stepwise addition of polyethyleneimine (PEI) and sodium dodecyl sulphate (SDS).

Fine-tuning the nonequilibrium behavior of oppositely charged macromolecule/surfactant mixtures via the addition of nonionic amphiphiles

The various commercial applications of oppositely charged polyelectrolytes (P) and ionic surfactants (S) with added nonionic amphiphiles initiated intensive research on the polyion/mixed surfactant interaction. A large group of earlier studies revealed that one of the major effects of the nonionic cosurfactants is the suppression of the associative phase separation of P/S systems. In contrast, recent studies indicated that in the dilute surfactant concentration range the added uncharged amphiphile enhances the precipitation concentration range. In order to rationalize these observations, the mixtures of poly(diallyldimethylammonium chloride) (PDADMAC), sodium dodecyl sulfate (SDS), and dodecyl maltoside (C12G2) are investigated using a variety of experimental methods. It is shown that the nonionic cosurfactant has two distinct and competing impacts on the mixed surfactant binding onto the polyions. The composition dependent variation of the chemical potentials of the amphiphiles determines which of these effects is the dominant one, explaining the seemingly diverse earlier observations and their interpretations. We also demonstrate that the nonionic amphiphile affects considerably the nonequilibrium features of polyion/ionic surfactant complexation. Namely, the presence of the uncharged surfactant can destabilize the colloidal dispersion of P/S nanoparticles formed in the two-phase composition range. However, at the same concentration range highly stable dispersions of polyion/mixed surfactant nanoparticles can be produced through the application of a new two-step solution preparation technique. This method is based on the order of addition effect of the two surfactants which can be utilized in future scientific and industrial applications.

The impact of nonionic surfactant additives on the nonequilibrium association between oppositely charged polyelectrolytes and ionic surfactants

The effect of uncharged surfactant additives on the oppositely charged polyion/ionic surfactant complexation is usually described as a direct equilibrium association between the polyelectrolyte molecules and free mixed micelles analogous to the polyion/colloidal particle interactions. This approach predicts that the binding of the ionic surfactant to the polyelectrolyte molecules can be completely suppressed by increasing the nonionic-to-ionic surfactant ratio. In the present work, it is shown that the addition of nonionic surfactants to poly(diallyldimethylammonium chloride)/sodium dodecyl sulfate mixtures considerably enhances the binding of the anionic surfactant to the polycation in the dilute surfactant concentration regime. The dynamic light scattering, turbidity, electrophoretic mobility and fluorescence spectroscopic measurements are consistent with the synergic binding of the ionic and nonionic surfactants to the polyelectrolyte molecules. The enhanced surfactant binding could be utilized for the preparation of stable colloidal dispersions of novel polyion/mixed surfactant nanoparticles over a wide composition range provided that adequate mixing protocols are used. These results clearly indicate that the nonionic surfactant additives can be successfully used to tune the nonequilibrium association of oppositely charged macromolecules and amphiphiles.

Effect of linear nonionic polymer additives on the kinetic stability of dispersions of poly(diallyldimethylammonium chloride)/sodium dodecylsulfate nanoparticles

In this article, the impact of different neutral polymers on the kinetic stability of charge-stabilized poly(diallyldimethylammonium chloride) (PDADMAC)/sodium dodecylsulfate (SDS) colloidal dispersions is analyzed using dynamic light scattering, electrophoretic mobility, turbidity, and coagulation kinetics measurements. Poly(ethyleneoxide) (PEO), poly(vinylpyrrolidone) (PVP), and dextran of comparable molecular masses as well as a higher-molecular-weight dextran sample were tested as nonionic additives. The light scattering and mobility data indicate that the PEO and PVP molecules may adsorb on the surface of the PDADMAC/SDS nanoparticles formed in the presence of excess surfactant. The primary effect of these additives is manifested in enhanced coagulation of the PDADMAC/SDS nanoparticles due to bridging at lower polymer concentrations and depletion flocculation at higher polymer concentrations. These findings are in sharp contrast to the earlier published effect of the same nonionic polymers on the poly(ethyleneimine) (PEI)/SDS colloidal dispersions, which can be sterically stabilized at appropriate PEO or PVP concentrations. However, the adsorption of the investigated dextran samples is negligible on the PDADMAC/SDS nanoparticles. Therefore, dextran molecules may cause only depletion flocculation in the PDADMAC/SDS system in the vicinity of the critical overlap concentration.

Nanoparticles with a bicontinuous cubic internal structure formed by cationic and non-ionic surfactants and an anionic polyelectrolyte

Nanoparticles with an internal structure have been prepared by dispersing under dilute conditions poly(acrylic acid) with a polymerization degree n = 6000 (PAA6000) together with a cationic surfactant hexadecyltrimethylammonium hydroxide (C16TAOH) and the non-ionic surfactant penta(ethylene glycol) monododecyl ether (C12E5) in water. The nanoparticles are formed at different mixing ratios in the corresponding two-phase regions (liquid crystalline phase/dilute isotropic phase) of the C16TAPA6000 complex salt/C12E5/water ternary phase diagram. The particles consist of polyacrylate PA6000– polyions, C16TA+ surfactant ions, and C12E5. Their internal ordering was identified by small-angle X-ray scattering (SAXS) to be either bicontinuous cubic with the Ia3d crystallographic space group or normal hexagonal depending upon the amount of C12E5. The bicontinuous cubic phase, to our knowledge never observed before in polyelectrolyte–surfactant particle systems, was inferred by SAXS experiments. The data also showed that this structure is thermoresponsive in a reversible manner. The bicontinuous cubic space group transforms from Ia3d to Im3m as the temperature decreases from 25 to 15 °C. According to dynamic light scattering and electrophoretic mobility measurements, the particles have a well-defined size (apparent hydrodynamic radii RH in the range of 88–140 nm) and carry a positive net charge. The size of the nanoparticles is stable up to 1 month. The faceted nanoparticles are visualized by cryogenic transmission electron microscopy that also reveals their coexistence with thread-like C12E5 micelles.

Solution behavior of normal and reverse triblock copolymers (pluronic L44 and 10R5) individually and in binary mixture

Solution properties of pluronics L44 or L [(PEO)(10)(PPO)(23)(PEO)(10)] and 10R5 or R [(PPO)(8)(PEO)(22)(PPO)(8)] were studied individually as well in their binary mixtures in aqueous medium. The critical micelle concentration (CMC), critical micelle temperature, and cloud point (CP) were determined. Ideal and nonideal behaviors of their mixtures in the formation of CMC and CP were observed; the energetics of the studied processes were determined. Spectrophotometry, isothermal titration calorimetry and dynamic light scattering (DLS) methods were used for evaluations. Morphologies of the dispersed L, R, and their mixtures along with their polydispersities were determined from DLS measurements. Atomic force microscopy was also employed. The interfacial properties of L and R were investigated forming Langmuir monolayers in a surface balance. The surface pressures (π) generated by the compounds were moderate, the area per molecule was higher for R than L. R has shown antibacterial activity against both gram positive and gram negative bacteria whereas L was inactive in this respect.