Nonstoichiometric polymer-surfactant complexes obtained in a lamellar lyotropic medium

Abstract

The addition of a polyelectrolyte to lamellar media formed by an oppositely charged surfactant often leads to the coexistence of several phases without macroscopic phase separation, which makes their characterization difficult. Here, the effect of the polydiallyldimethylammonium chloride (PD) on the lamellar liquid crystal formed by the anionic surfactant Aerosol OT (AOT) and water is investigated. Small-angle X-ray scattering results are discussed regarding the changes in the lamellar spacing as a function on the PD or AOT concentrations. In most of the samples, two lamellar phases, without macroscopic phase separation, are detected. One of them is a typical swollen phase, while the other is a collapsed phase, which corresponds to the polymer-surfactant complex. At concentrations of polymer up to 3 wt%, the two lamellar phases coexist; however, at a critical concentration higher than 3 wt%, the swollen phase becomes isotropic, and a macroscopic phase separation takes place. A simple model is proposed to calculate the composition of the phases when macroscopic phase separation does not occur. The results thus calculated show that generally the polymer-surfactant complexes are nonstoichiometric containing a lesser amount of polymer than ideally expected.

Composition and Structural Transitions of Polyelectrolyte–Surfactant Complexes in the Presence of Fatty Acid Studied by NMR and Cryo-SEM

“…However, the diffusion data (Figure horizontal axis and Table ) reveals that the water of components A–C all have a diffusion rate fairly close to that of pure water (2.3 × 10 –9 m 2 /s), meaning that water is able to move quite freely in at least one direction but is hindered in other directions as seen from the reduced T 2 relaxation times. Hence, two possibilities are tubelike or sheetlike structures, which agree well with the ordered microstructures (surfactant lamellar structures and hexagonal/cubic tubes/cylinders) seen in the literature. − Assuming that the direction of the channels between them will predominantly follow the direction of the applied magnetic field gradient ( z direction), which also follows the vertical axis of the sample tube, water will seem to diffuse freely.…”

“…Figure shows cryo-SEM images of complexes below (A1-4) and above (B1-4) CMC′ with different scaling. With the exception of the LA containing sample above CMC′ (B3+4), the images show a network of fibers presumably corresponding to the polyelectrolyte-stabilized surfactant aggregates previously seen with SAXS. − Below CMC′ both samples have networks of fibers (A2 + 4); however, the pattern of the fibrous network seems more random in the LA-containing sample (A4). Furthermore, the widths of the fibers are more uniform in the absence of LA at about 0.7–0.8 μm (A2).…”

“…10 Studies where oppositely charged polyelectrolytes are incorporated into lamellar lyotropic systems have shown how the surfactant phase is destabilized when macroscopic phase separation occurs and therby can form a collapsed lamellar structure upon interaction with a polyelectrolyte. 9,11 Similar microstructures are also seen in small compact complexes (size in the nanometer to micrometer range) formed in solution below the surfactant concentration where the precipitate is formed. 12,13 However, structural information beyond such ordered morphologies is necessary for a more complete structural picture of the water-insoluble polyelectrolyte−surfactant complexes.…”

“…Such structures are considered to be polyelectrolyte-stabilized surfactant phases and greatly depend on the properties of the polyelectrolyte and surfactant . Studies where oppositely charged polyelectrolytes are incorporated into lamellar lyotropic systems have shown how the surfactant phase is destabilized when macroscopic phase separation occurs and therby can form a collapsed lamellar structure upon interaction with a polyelectrolyte. , Similar microstructures are also seen in small compact complexes (size in the nanometer to micrometer range) formed in solution below the surfactant concentration where the precipitate is formed. , …”

“…There are several studies describing polyelectrolyte–surfactant insoluble complexes in the absence of a third component, where mainly small-angle X-ray scattering (SAXS) − has yielded valuable mesoscopic-scale structural information in cases where more ordered lamella and hexagonal or cubic structures are present. Such structures are considered to be polyelectrolyte-stabilized surfactant phases and greatly depend on the properties of the polyelectrolyte and surfactant .…”