Characterization of the Interactions between an Unassociated Cationic Pyrene-Labeled Gemini Surfactant and Anionic Sodium Dodecyl Sulfate.

The gemini surfactant PyO-3-12, made of two dimethylammonium bromides joined by a propyl linker and bearing a dodecyl pendant on one side and a 1-pyrenemethoxyhexyl group on the other side, was employed to probe the interactions between positively charged PyO-3-12 and negatively charged sodium dodecyl sulfate (SDS). PyO-3-12 was selected for its ability to respond to the polarity of its local environment through the fluorescence intensity ratio I1/I3 of the first-to-third fluorescence peaks of the pyrene monomer and the local pyrene concentration [Py]loc through the IE/IM ratio of the pyrene excimer-to-pyrene monomer fluorescence intensity. Furthermore, analysis of the fluorescence decays of aqueous solutions of PyO-3-12 and SDS yielded a measure of the internal dynamics, local concentration, and state (associated vs unassociated) of PyO-3-12 in solution. By following these parameters for aqueous solutions prepared with a constant PyO-3-12 concentration of either 1, 4, or 16 µM and SDS concentrations ranging from 0 to 200 mM, six SDS concentration regimes were identified to describe the interactions between PyO-3-12 and SDS in pure water. Sharp transitions of the parameters describing the fluorescence of pyrene marked the boundaries between the different regimes. Perhaps the most important transition was the one defining the formation of the PyO-3-12/SDS aggregates, which was completed at the equicharge point, implying that they were constituted of 1 meq of PyO-3-12 and 2 meq of SDS. The low I1/I3 ratio obtained for the PyO-3-12/SDS aggregates suggested that they were multilamellar aggregates, which would shield the pyrenyl labels from polar water. The formation of these multilamellar aggregates was confirmed by transmission electron microscopy (TEM), which demonstrated the existence of multilamellar vesicles, whose presence increased with decreasing PyO-3-12 concentration. This study suggests that the combination of pyrene excimer formation and TEM provides an interesting experimental means to probe the assemblies generated from oppositely charged surfactants at surfactant concentrations, which are much lower than their critical micelle concentration.

Vanishing nematic order beyond the pseudogap phase in overdoped cuprate superconductors.

During the last decade, translational and rotational symmetry-breaking phases-density wave order and electronic nematicity-have been established as generic and distinct features of many correlated electron systems, including pnictide and cuprate superconductors. However, in cuprates, the relationship between these electronic symmetry-breaking phases and the enigmatic pseudogap phase remains unclear. Here, we employ resonant X-ray scattering in a cuprate high-temperature superconductor [Formula: see text] (Nd-LSCO) to navigate the cuprate phase diagram, probing the relationship between electronic nematicity of the Cu 3d orbitals, charge order, and the pseudogap phase as a function of doping. We find evidence for a considerable decrease in electronic nematicity beyond the pseudogap phase, either by raising the temperature through the pseudogap onset temperature T* or increasing doping through the pseudogap critical point, p*. These results establish a clear link between electronic nematicity, the pseudogap, and its associated quantum criticality in overdoped cuprates. Our findings anticipate that electronic nematicity may play a larger role in understanding the cuprate phase diagram than previously recognized, possibly having a crucial role in the phenomenology of the pseudogap phase.