We report on small-angle neutron scattering and cryo-transmission electron microscopy of complexes made from polyelectrolyte-neutral block copolymers and surfactants. Two block copolymer/surfactant systems have been investigated. In the first system, the polyelectrolyte block is negatively charged (poly(sodium acrylate), molecular weight 5 000 g/mol) and the neutral block is a poly(acrylamide) chain of molecular weight 30 000 g/mol. This copolymer is studied in solution in the presence of a cationic surfactant, dodecyltrimethylammonium bromide (DTAB). In the second system, the polyelectrolyte block is positively charged (poly(trimethylammonium ethylacrylate), molecular weight 11 000 g/mol) and the neutral block is again a poly(acrylamide) of molecular weight 30 000 g/mol. This copolymer is studied in solution with an anionic surfactant, sodium dodecyl sulfate (SDS). We show that the diblocks copolymers associate with oppositely charged surfactants into colloidal complexes which have a core−shell microstructure. For the two systems investigated, we have found that the core is constituted from densely packed surfactant micelles, presumably connected by the polyelectrolyte chains. Within the complexes, the DTAB or SDS micelles have the same aggregation number as in aqueous solutions above the cmc. The outer part of the complex is a corona formed by the neutral poly(acrylamide) chains. The microstructure of the core has been inferred from a strong forward neutron scattering and the appearance of a structure peak at high wave vectors (q 0 ∼ 0.16 Å-1). Using a model of aggregation of colloids developed for latex−silica nanocomposites and based on a Monte Carlo algorithm, we have simulated the internal structure of the aggregates. The model assumes spherical cages containing from one to several hundreds of micelles in a closely packed state. The agreement between the model and the data is remarkable. This allows us to conclude that the structure peak at q 0 ∼ 0.16 Å-1 is associated with the hard-sphere interactions between micelles in the core.

Surfactant oligomers are made up of x (g2) amphiphilic moieties connected at the level of, or close to, the headgroups by spacer group(s). This paper examines the effect of the degree of oligomerization x on the self-assembling of cationic surfactant oligomers at interfaces and in the bulk. The quaternary ammonium bromide surfactant oligomers investigated are made up of dodecyldimethyl-and dodecylmethylammonium bromide moieties connected by short polymethylene spacers -(CH2)s-(of carbon number s). The properties investigated are the surface occupied by the surfactant at the air/solution and silica/solution interfaces, the critical micellization concentration (cmc), the micelle ionization degree at the cmc, the micelle micropolarity and microviscosity, and the microstructure and rheology of the solution. As x is increased, the surfactant layers at interfaces become more dense, the cmc decreases, the micelle microviscosity increases, the micelle shape for oligomers with s ) 3 changes from spherical (x ) 1) to wormlike (x ) 2), branched wormlike (x ) 3), and ring like (x ) 4). Last the zero-shear viscosity of the oligomer aqueous solutions starts to increase very rapidly and by orders of magnitude at surfactant concentrations above a value C* that decreases as x is increased. On the contrary the micelle ionization degree at the cmc and micelle micropolarity are nearly independent of x. These results are discussed in terms of surfactant packing parameter. They emphasize once more the possibilities offered by surfactant oligomers in obtaining surfactant organized assemblies with new architectures and solutions with improved and adjustable properties.

BackgroundRecently, much progress has been made to develop more physiologic in vitro models of the respiratory system and improve in vitro simulation of particle exposure through inhalation. Nevertheless, the field of nanotoxicology still suffers from a lack of relevant in vitro models and exposure methods to predict accurately the effects observed in vivo, especially after respiratory exposure. In this context, the aim of our study was to evaluate if exposing pulmonary cells at the air-liquid interface to aerosols of inhalable and poorly soluble nanomaterials generates different toxicity patterns and/or biological activation levels compared to classic submerged exposures to suspensions. Three nano-TiO2 and one nano-CeO2 were used. An exposure system was set up using VitroCell® devices to expose pulmonary cells at the air-liquid interface to aerosols. A549 alveolar cells in monocultures or in co-cultures with THP-1 macrophages were exposed to aerosols in inserts or to suspensions in inserts and in plates. Submerged exposures in inserts were performed, using similar culture conditions and exposure kinetics to the air-liquid interface, to provide accurate comparisons between the methods. Exposure in plates using classical culture and exposure conditions was performed to provide comparable results with classical submerged exposure studies. The biological activity of the cells (inflammation, cell viability, oxidative stress) was assessed at 24 h and comparisons of the nanomaterial toxicities between exposure methods were performed.ResultsDeposited doses of nanomaterials achieved using our aerosol exposure system were sufficient to observe adverse effects. Co-cultures were more sensitive than monocultures and biological responses were usually observed at lower doses at the air-liquid interface than in submerged conditions. Nevertheless, the general ranking of the nanomaterials according to their toxicity was similar across the different exposure methods used.ConclusionsWe showed that exposure of cells at the air-liquid interface represents a valid and sensitive method to assess the toxicity of several poorly soluble nanomaterials. We underlined the importance of the cellular model used and offer the possibility to deal with low deposition doses by using more sensitive and physiologic cellular models. This brings perspectives towards the use of relevant in vitro methods of exposure to assess nanomaterial toxicity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-016-0171-3) contains supplementary material, which is available to authorized users.

Formation of a dominant population of closed loops in wormlike micellar systems, theoretically predicted but never reported so far, is achieved with a new cationic surfactant tetramer. The contour length distribution N(L) of the closed-looped micelles is determined by transmission electron microscopy at cryogenic temperature. At large contour lengths, the distribution observed scales as N(L) ∝ L -5/2, as expected from ring−chain equilibrium polymerization theory. At small contour lengths, the rigidity-dependent ring closure probability provides a direct estimate of the persistence length. These results re-emphasize the new possibilities offered by surfactant dimers (gemini) and oligomers in obtaining new morphologies in self-assemblies.