Bicontinuous microemulsion as confined reaction media for the synthesis of plasmonic silver self-assembled hierarchical superstructures

Effect of equilibration time on the structural gradient in the vertical direction for bicontinuous microemulsions in Winsor-III and -IV systems

Bicontinuous microemulsions (BMEs), self-assembly systems consisting of oil and water nanodomains separated by surfactant monolayers, have many applications. However, changes in structure and properties of BMEs in the vertical direction can affect BMEs' utility. This study's objective was to determine the effect of equilibration time (τeq) on structural changes in the vertical direction for bicontinuous phases of Winsor-III (WIII) systems in situ or after being isolated, for D2O + H2O/1-dodecane/sodium dodecyl sulfate (SDS)/1-pentanol/NaCl at 22 °C. Small-angle neutron scattering (SANS) measurements were performed using a vertical stage sample environment that precisely aligned samples in the neutron beam. SANS data were fitted by the Teubner-Strey (TS) model and changes in TS-derived parameter values were observed. For 10 min ≤ τeq ≤ 4 h, the effective activity of the bicontinuous phase's surfactant monolayers increased with time at all vertical positions. At short equilibration (τeq = 10 min), small but significant amounts of water and oil were transiently emulsified near the WIII upper liquid-liquid interface. WIII systems underwent a relaxation process after being transferred to narrow 1 mm pathlength cells, resulting in a decrease of surfactant activity for the top half of the bicontinuous phase. For isolated bicontinuous phases, results suggest that SDS was desorbed from the BMEs by quartz near the bottom, while near the top, the water concentration near was relatively high. The results suggest that WIII systems should equilibrate for at least 4 hours after being prepared and transferred to a container that differs in cross sectional area and surfactant behavior in BMEs can change near interfaces.

Hierarchical Nanobiosensors at the End of the SARS-CoV-2 Pandemic

Nanostructures have played a key role in the development of different techniques to attack severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Some applications include masks, vaccines, and biosensors. The latter are of great interest for detecting diseases since some of their features allowed us to find specific markers in secretion samples such as saliva, blood, and even tears. Herein, we highlight how hierarchical nanoparticles integrated into two or more low-dimensional materials present outstanding advantages that are attractive for photonic biosensing using their nanoscale functions. The potential of nanohybrids with their superlative mechanical characteristics together with their optical and optoelectronic properties is discussed. The progress in the scientific research focused on using nanoparticles for biosensing a variety of viruses has become a medical milestone in recent years, and has laid the groundwork for future disease treatments. This perspective analyzes the crucial information about the use of hierarchical nanostructures in biosensing for the prevention, treatment, and mitigation of SARS-CoV-2 effects.

Interplay of Polarity and Confinement in Asymmetric Catalysis with Chiral Rh Diene Complexes in Microemulsions

Microemulsions provide a unique opportunity to tailor the polarity and liquid confinement in asymmetric catalysis via nanoscale polar and nonpolar domains separated by a surfactant film. For chiral diene Rh complexes, the influence of counterion and surfactant film on the catalytic activity and enantioselectivity remained elusive. To explore this issue chiral norbornadiene Rh(X) complexes (X=OTf, OTs, OAc, PO2 F2 ) were synthesized and characterized by X-ray crystallography and theoretical calculations. These complexes were used in Rh-catalyzed 1,2-additions of phenylboroxine to N-tosylimine in microemulsions stabilized either exclusively by n-octyl-β-D-glucopyranoside (C8 G1 ) or a C8 G1 -film doped with anionic or cationic surfactants (AOT, SDS and DTAB). The Rh(OAc) complex showed the largest dependence on the composition of the microemulsion, yielding up to 59 % (90 %ee) for the surfactant film doped with 5 wt% of AOT as compared to 52 % (58 %ee) for neat C8 G1 at constant surfactant concentration. Larger domains, determined by SAXS analysis, enabled further increase in yield and selectivity while the reaction rate almost remained constant according to kinetic studies.

From Nanoparticle Heteroclusters to Filament Networks by Self-Assembly at the Water-Oil Interface of Reverse Microemulsions

Surface self-assembly of spherical nanoparticles of sizes below 10 nm into hierarchical heterostructures is under arising development despite the inherent difficulties of obtaining complex ordering patterns on a larger scale. Due to template-mediated interactions between oil-dispersible superparamagnetic nanoparticles (MNPs) and polyethylenimine-stabilized gold nanoparticles (Au(PEI)NPs) at the water-oil interface of microemulsions, complex nanostructured films can be formed. Characterization of the reverse microemulsion phase by UV-vis absorption revealed the formation of heteroclusters from Winsor type II phases (WPII) using Aerosol-OT (AOT) as the surfactant. SAXS measurements verify the mechanism of initial nanoparticle clustering in defined dimensions. XPS suggested an influence of AOT at the MNP surface. Further, cryo-SEM and TEM visualization demonstrated the elongation of the reverse microemulsions into cylindrical, wormlike structures, which subsequently build up larger nanoparticle superstructure arrangements. Such WPII phases are thus proven to be a new form of soft template, mediating the self-assembly of different nanoparticles in hierarchical network-like filaments over a substrate during solvent evaporation.