Polyelectrolyte-Induced Peeling of Charged Multilamellar Vesicles

Abstract

We study mixtures of charged surfactants, which alone in solution form uni-and multilamellar vesicles, and oppositely charged polyelectrolytes (PEs). The phase behavior is investigated at fixed surfactant concentration as a function of the PE-to-surfactant charge ratio x. We find that, for x > 0, aggregates form. Light microscopy and Xray scattering experiments show that the isoelectric point plays a crucial role since the morphology and the microscopic structure of the aggregates are different before (x ≤ 1) and after the isoelectric point (x > 1). To better understand the dynamics for the formation of PE/surfactant complexes, we perform light microscopy experiments where we follow in real-time the effect of a PE solution on one multilamellar vesicle (MLV). We find that the PE induces a peeling of the bilayers of the MLV one by one. The peeling is accompanied by strong shape fluctuations of the MLV and leads ultimately to a pile of small aggregates. This novel phenomenon is analyzed in detail and discussed in terms of PE-induced tension, and pore formation and growth in a surfactant bilayer. *

Real-Time Observation of Polyelectrolyte-Induced Binding of Charged Bilayers

“…We note that the effect of a weak polyelectrolyte gradient on a MLV has been reported previously. 45 However, the novel confocal microscopy pictures given in Figure 3 show unambiguously a single event, which provides a compelling evidence for a peeling mechanism. …”

“…36,45 The confocal pictures of a GUV interacting with a PE solution (Figure 1) provide a dynamic observation for the formation of these complexes. In this part, we discuss the experimental findings on the formation of DDAB/PE complexes, when polyelectrolyte molecules interact with a MLV.…”

Role of the Preparation Procedure in the Formation of Spherical and Monodisperse Surfactant/Polyelectrolyte Complexes

“…Figure 3 shows the SAXS results for complexes formed using the "mixing" and "diffusion" procedures, at different charge ratios. As described previously, [27] for the "mixed" samples, the SAXS patterns depend on the charge ratio. For x 1, two peaks are observed at q 0 % 2.06 nm À1 and q 1 % 2q 0 % 4.12 nm À1 (the inset of Figure 3 (top) is the enlargement at large values of q, revealing the peak at q 1 .).…”

“…Our observations are similar to what has been discussed previously. [27] Extremely polydisperse complexes are formed for all x. For instance, for x = 1/3, the complexes size ranges from 0.8 to 14.7 mm.…”

“…[22][23][24][25][26] We note that the concentration of polyelectrolyte has a major effect on the behavior of oppositely charged surfactant bilayers at a mesoscopic scale. Diluted polyelectrolyte solution induces a peeling of the successive surfactant bilayers that constitute a multilamellar vesicle, [27] while a more concentrated polyelectrolyte solution induces novel structural transitions of the charged surfactant bilayers. [28] Notable studies by other groups include, in particular, the work of Berret et al who found that neutral/polyelectrolyte diblock copolymers and oppositely charged surfactants in aqueous solution associate into colloidal aggregates that have an original core-shell microstructure, with a core made up of by densely packed surfactant micelles connected by the polyelectrolyte blocks.…”