Oversaturating Liquid Interfaces with Nanoparticle-Surfactants

Assemblies of nanoparticles at liquid interfaces hold promise as dynamic "active" systems when there are convenient methods to drive the system out of equilibrium via crowding. To this end, we show that oversaturated assemblies of charged nanoparticles can be realized and held in that state with an external electric field. Upon removal of the field, strong interparticle repulsive forces cause a high in-plane electrostatic pressure that is released in an explosive emulsification. We quantify the packing of the assembly as it is driven into the oversaturated state under an applied electric field. Physiochemical conditions substantially affect the intensity of the induced explosive emulsification, underscoring the crucial role of interparticle electrostatic repulsion.

Revealing Two Distinct Formation Pathways of 2D Wurtzite-CdSe Nanocrystals Using In Situ X-Ray Scattering

Understanding the mechanism underlying the formation of quantum-sized semiconductor nanocrystals is crucial for controlling their synthesis for a wide array of applications. However, most studies of 2D CdSe nanocrystals have relied predominantly on ex situ analyses, obscuring key intermediate stages and raising fundamental questions regarding their lateral shapes. Herein, the formation pathways of two distinct quantum-sized 2D wurtzite-CdSe nanocrystals - nanoribbons and nanosheets - by employing a comprehensive approach, combining in situ small-angle X-ray scattering techniques with various ex situ characterization methods is studied. Although both nanostructures share the same thickness of ≈1.4 nm, they display contrasting lateral dimensions. The findings reveal the pivotal role of Se precursor reactivity in determining two distinct synthesis pathways. Specifically, highly reactive precursors promote the formation of the nanocluster-lamellar assemblies, leading to the synthesis of 2D nanoribbons with elongated shapes. In contrast, mild precursors produce nanosheets from a tiny seed of 2D nuclei, and the lateral growth is regulated by chloride ions, rather than relying on nanocluster-lamellar assemblies or Cd(halide)2 -alkylamine templates, resulting in 2D nanocrystals with relatively shorter lengths. These findings significantly advance the understanding of the growth mechanism governing quantum-sized 2D semiconductor nanocrystals and offer valuable guidelines for their rational synthesis.

Optimizing surfactant removal from a soft-templated ordered mesoporous carbon precursor: an in situ SAXS study

In situ small-angle X-ray scattering (SAXS) was employed to identify critical parameters during thermal treatment for template removal of an ordered mesoporous carbon precursor synthesized via a direct soft-templating route. The structural parameters obtained from the SAXS data as a function of time were the lattice parameter of the 2D hexagonal structure, the diameter of the cylindrical mesostructures and a power-law exponent characterizing the interface roughness. Moreover, detailed information on contrast changes and pore lattice order was obtained from analysis of the integrated SAXS intensity of the Bragg and diffuse scattering separately. Five characteristic regions during heat treatment were identified and discussed regarding the underlying dominant processes. The influence of temperature and O₂/N₂ ratio on the final structure was analyzed, and parameter ranges were identified for an optimized template removal without strongly affecting the matrix. The results indicate that the final structure and controllability of the process are optimum for temperatures between 260 and 300°C with a gas flow containing 2 mol% of O₂.

Scalable Electrically Conductive Spray Coating Based on Block Copolymer Nanocomposites

Currently available conductive inks present a challenge to achieving electrical performance without compromising mechanical properties, scalability, and processability. Here, we have developed blends of carbon black and the commercially available triblock copolymer (BCP), poly(styrene-ethylene-butylene-styrene)-g-maleic anhydride (SEBS-g-MAH) (FG1924G, Kraton), that can be readily applied as a conductive coating via a spray-coating process, for a wide range of insulating materials (fabric, wood, glass, and plastic). Simple but effective mechanical and chemical modifications of the ingredients can increase the electrical conductivity (∼100 S/m) by an order of magnitude more than previously reported for carbon black composites; moreover, the coatings display excellent mechanical flexibility (tensile strain ε ∼ 5.00 mm/mm). To correlate electrical conductivity and nanoscale structural changes with mechanical deformation, small-angle X-ray scattering (SAXS) during in situ tensile testing was performed. We show that the nanocomposite can be produced using low-cost ingredients (∼$ 10/kg), ensuring scalability for fabrication of large-scale devices without specialized material synthesis. Equally important, the phase behavior of block copolymers can enable recovery from physical damage via thermal annealing, which is critical for product longevity.