Electrochemical, Microscopic, and Spectroscopic Characterization of Prevesicle Nanostructures and Vesicles on Mixed Cationic Surfactant Systems

Abstract

Several experimental techniques (conductivity, zeta potential, transmission electronic microscopy, and steady-state fluorescence spectroscopy) have been used to study the formation of mixed colloidal aggregates consisting of a cationic double-chain surfactant, di-dodecyldimethylammonium bromide (di-C12DMAB), and a single-chain alkyltrimethylammonium bromide with 10 and/or 14 carbon atoms (decyltrimethylammonium bromide, C10TAB, and/or tetradecyltrimethylammonium bromide, C14TAB). Special interest has been devoted to the prevesicle domain, within which the formation of aggregated nanostructures was first reported in our laboratory. For that purpose, studies have been carried out on the very dilute region by means of conductivity experiments, confirming the existence of two critical aggregation concentrations in that concentration domain: the so-called mixed critical aggregate concentration, CAC, and the mixed critical vesicle concentration, CVC. By carrying out TEM experiments on negatively stained samples, we were surprised to find a number of aggregates without a clear aggregation pattern and with a variety of sizes and shapes at concentrations below CAC, where only monomers were expected. However, the nanoaggregates found at concentrations between CAC and CVC, also by TEM microscopy, show a clear and ordered "fingerprint"-like aggregation pattern similar to the liquid-crystalline phases reported for DNA-liposome complexes and/or DNA packed with viral capsids. Finally, at total surfactant concentrations above CVC, the aggregates were confirmed, by means of cryo-TEM micrographs and zeta potential measurements, to be essentially unilamellar spherical vesicles with a medium polydispersity and a net-averaged surface density charge of around 12 x 10(-3) C m(-2). The fluorescence emission of two probes, TNS (anionic) and PRODAN (nonionic), allows for the analysis of the micropolarity and microviscosity of the different microenvironments present in aqueous surfactant solutions where the above-mentioned vesicle and prevesicle aggregates are present.

Charge Regulation as a Stabilization Mechanism for Shell-Like Assemblies of Polyoxometalates

“…[10] if R 1. Reported experimental values of j j are close to 6 kT for micelles [12] and highly charged colloids [13] in aqueous media, but also smaller values have been observed depending upon (bare) charge density and ionic strength [8,14,15]. Inserting Eq.…”

Effect of hydrophilic ionic liquid on the micellar properties of aqueous Tween-20

“…The aggregation number (N agg ) of Tween-20 micelles in the presence of different wt% of [C 5 mim][BF 4 ] was obtained by fluorescence quenching of pyrene using a cosurfactant cetylpyridinium chloride (CPC) as quencher according to the following equation [36][37][38]. 4 ].…”

Effect of added ionic liquid on aqueous Triton X-100 micelles

“…2-(p-Toluidino)naphthalene-6-sulfonate (TNS, Scheme S2 of supporting materials) is a fluorescence probe, which apart from wavelength shift, contrary to PyCHO, demonstrates a dramatic increase in fluorescence quantum yield upon encountering hydrophobic environment (∼200-fold increase in φ F in 1-octanol versus water) [92,93]. Fig.…”