Self-Organization of the Ternary Didecyldimethylammonium Bromide/Octyl-β-d-glucopyranoside/Water System

Abstract

The spontaneous and thermodynamically stable mixed vesicles constituted by a double-chain cationic surfactant with 10 carbon atoms hydrophobic tail, didecyldimethylammonium bromide (di-C(10)DMAB), and a nonionic single-chain surfactant, octyl-beta-d-glucopyranoside (OBG), have been characterized in aqueous media by means of a series of experimental techniques, as well as a theoretical approach. Conductivity data allow for the determination of the concentrations at which the monomer-to-vesicle (CVC) and/or vesicle-to-micelle (CMC) transitions occur. Electrophoretic mobilities, obtained from laser-doppler-electrophoresis experiments, permit the determination of zeta-potentials and, from them, the surface charge density of the vesicle aggregates. Cryogenic transmission electron microscopy (cryo-TEM) provides pictures of the vesicles, their size and shape being, thus, determined. Finally, the sensitivity of the emission spectra of some fluorescent probes, such as the cationic TNS and the nonionic PRODAN, to the polarity of the environment, allow for a complete study of different pre- and post-vesicle microdomains, of variable rigidity and micropolarity. This, in turn, yield interesting information about the vesicle surface and bilayer, as well as, about the existence of clusters and/or nanoaggregates prior to the formation of vesicles, as was proposed by us in a previous paper.

Spectrofluorimetric Characterization of Mixed Nanoaggregates Comprising a Double-Chain Cationic Surfactant and a Cationic or Non-Ionic Single-Chain Surfactant

“…An aliquot of 10 lL of TNS stock solution was mixed with 3.85 mL of the mixed surfactant solution, while an aliquot of 155 lL of the PRODAN stock solution was mixed with 3.00 mL of the mixed surfactant solution, the ethanol being previously evaporated with nitrogen in this case. As a result, probe concentrations are kept constant at [TNS] ¼ 2.07 lM and/or [PRODAN] ¼ 5.02 lM, and surfactant concentrations range from pre-to post-vesicle values, 22,[25][26][27] at each molar fraction of the ternary system. All surfactant/probe solutions thus prepared were firstly stirred for 2-3 hours and subsequently allowed to equilibrate more than 60 hours, prior to obtaining the spectra.…”

“…2 molar fraction, previously reported for these mixed systems from conductivity experiments. 22,[25][26][27] Experimental emission spectra were analyzed, after conversion of wavelength to frequency, by deconvolution into overlapping Gaussian curves with a commercial nonlinear least-squares multi-peaks fitting procedure that uses an iterative Marquardt-Levenberg fitting algorithm. The fluorescence data were thus deconvoluted into the optimum number of reproducible components, based on the photophysical data of probe emission, the center, width, and amplitude of each Gaussian curve being the adjustable parameters.…”

“…It is well known that the mixture of a single-chain surfactant with a double-chain surfactant/water system drives the formation of a variety of mixed aggregates, whose selforganization pattern depends very much on the composition of the mixed system and/or the total surfactant concentration. Four domains have been documented in the literature: [22][23][24] (1) the pre-vesicle domain, where only the presence of monomers is expected; (2) the mixed vesicles domain, at total surfactant concentration above the critical mixed vesicle concentration (CVC*); (3) a region where the mixed micelles start to form and coexist with mixed vesicles, above the critical mixed micelle concentration (CMC*); and (4) the mixed micelles domain (the mixed vesicles are disrupted and solubilized by the mixed micelles), above the total critical mixed micelle concentration (CMC Ã tot ). Our previous works, aimed mainly at investigating what happens in the extremely diluted and very diluted region, i.e., the pre-vesicle and vesicle domains, respectively, have shown that a series of colloidal aggregates appear even at [S] tot , CVC*.…”

“…Our previous works, aimed mainly at investigating what happens in the extremely diluted and very diluted region, i.e., the pre-vesicle and vesicle domains, respectively, have shown that a series of colloidal aggregates appear even at [S] tot , CVC*. 22,25 In particular, the critical concentrations, surface charge, size, and shape of the vesicle and pre-vesicle nanoaggregates constituted by di-decyldimethylammonium bromide, di-C 10 DMAB, or di-dodecyldimethylammonium bromide, di-C 12 DMAB, and a cationic (dodecylethyldimethylammonium bromide, C 12 EDMAB) or nonionic (octyl-b-D-glucopyranoside, OBG) single-chain surfactant have been fully analyzed and reported. 22,[25][26][27] With this information, we face in the present work the analysis of the characteristics of the interior and surface of these aggregates by means of the steady-state fluorescence emission of TNS and PRODAN, properly solubilized within them.…”

Double Inversion of Emulsions By Using Nanoparticles and a Di‐Chain Surfactant

“…The existence of a network of flocculated particles is also evident within the water drops. Finally, for o/w emulsions at high surfactant concentrations (Figure 4 f), the interface is covered with close‐packed particles and the continuous aqueous phase contains either aggregated excess surfactant (white object) probably in the form of vesicles14 or ice crystal artifacts.…”