Pd x Au100–x nanoparticle (NP) catalysts with well-defined morphologies and compositions can be rapidly prepared using a simple microwave-assisted synthetic approach. Common Pd­(II) and Au­(III) precursors are coreduced in ethylene glycol to give small and nearly monodisperse (2.5 ± 0.6 nm) NPs with homogeneously alloyed structures in less than 300 s at 150 °C. A comparison of the nucleation and growth processes responsible for the formation of PdAuNPs by microwave and conventional methods revealed faster and more reproducible product formation under microwave-assisted heating. Pd-rich NPs were rapidly formed, into which Au atoms were subsequently incorporated to give the alloyed NPs. The value of x in the Pd x Au100–x NPs obtained can be finely controlled, allowing the surface electronic structure of the NPs to be broadly tuned. This permits model heterogeneous reaction studies, in which catalytic reactivity can be directly related to Pd:Au composition. Vapor-phase alkene hydrogenation studies using a series of PdAuNPs with varying compositions revealed that Pd59Au41NPs were catalytically the most active. Detailed theoretical studies of the entire hydrogenation reaction catalyzed at randomly alloyed PdAu surfaces were performed using a density functional theory (DFT) approach. Local ensemble effects and longer range electronic effects in the alloys were considered, leading to a prediction for optimal hydrogenation activity by Pd57Au43NPs. PdAuNPs obtained from microwave-assisted syntheses were also found to be more highly active than analogous NPs prepared conventionally. Quantitative solution-state 1H NMR studies suggest that significantly less PVP was incorporated into PdAuNPs synthesized under microwave heating.

Small-angle X-ray scattering analyses reveal that the hydrated diblock oligomer n -C 16 H 23 (OCH 2 CH 2 ) 20 -OH (C 16 E 20 or Brij 58) forms lyotropic liquid crystals (LLCs) exhibiting face-centered cubic (FCC), body-centered cubic (BCC), Frank–Kasper (FK) A15, and cylindrical (H I ) morphologies over the concentration range 30–65 wt % amphiphile. Heating LLCs comprising 54–59 wt % C 16 E 20 drives the temperature-dependent phase transition sequence: A15 → BCC → H I . However, rapidly quenching the resulting H I phase from 70 to 25 °C initially forms a BCC phase that isothermally transforms into a complex, tetragonal FK σ phase comprising 30 quasispherical micelles. The metastability of this micellar σ phase is shown to depend on the sample cooling rate, thermal quench depth, and isothermal annealing temperature. We rationalize the preference for the A15 structure at 25 °C in terms of minimizing unfavorable water/hydrophobic contacts, while maximizing local particle sphericity. The symmetry breaking transition kinetics in these micellar LLCs apparently stem from the temperature-dependent activation barriers for phase nucleation and growth, which are intimately coupled to the time scales for micelle reconfiguration by amphiphile chain exchange and their spatial rearrangement. These findings highlight how thermal processing influences nucleation and growth of the self-assembled morphologies of intrinsically reconfigurable, soft spherical particles.

Implementation of next-generation Li-ion batteries based on high-voltage cathodes requires the development of new electrolytes that are stable over wide electrochemical potential windows. High lithium-ion transference number (t Li+) electrolytes, in which most of the ionic current is carried by Li+, offer additional opportunities to improve the efficiencies of such batteries by minimizing unproductive anion motion. Herein, we report the synthesis and characterization of solution electrolytes based on poly­(lithium bis­(nonenylmalonato)­borate) (P­(LiBNMB)) with molecular weights M n = 2.7–55 kg/mol and dispersities Đ = M w/M n = 1.6–3.2. Cyclic voltammetry studies reveal that propylene carbonate (PC) solutions of P­(LiBNMB) are electrochemically stable up to 5.2 V (versus Li/Li+). Electrochemical impedance spectroscopy (EIS) studies indicate that the total ionic conductivities of these P­(LiBNMB)/PC solution electrolytes with [Li+] ≈ 0.10 M are nearly M n-invariant with σ = 0.31–0.39 mS/cm. Complementary ion diffusivity measurements by 1H and 7Li NMR diffusion ordered spectroscopy (DOSY) and potentiostatic polarization also reveal that they exhibit high t Li+ = 0.77–0.98. Thus, semidilute solutions of oligomeric salts comprising as few as 21 monomer units unexpectedly display t Li+ > 0.90 with σ = 0.34 mS/cm.

Aqueous lyotropic liquid crystals (LLCs) are structured soft materials with long range crystallographic order, which derive from minimal hydration of amphiphilic molecules in water. In certain composition windows, amphiphiles self-assemble into quasispherical micelles that pack on body-centered cubic (BCC), face-centered cubic (FCC) and hexagonally close packed (HCP) lattices [1]. Herein, we describe investigations of the aqueous LLC phase behavior of polyethylene-poly(ethylene oxide) (PE-PEO) diblock polymers using temperature-dependent small-angle X-ray scattering (SAXS). With increasing polymer concentration, we show that these aqueous LLCs self-assemble into FCC, BCC, and Frank-Kasper (FK) A15 phases (Cr3Si structure type). Upon heating the A15 phase, we find that it undergoes a transition to a BCC phase that gives way to a hexagonally-packed cylindrical micelle phase (H) at high temperatures. Quenching the H phase to room temperature drives formation of a FK σ phase, which transforms into the original A15 structure after several months. These findings suggest that various, complex intermediate phases may form in LLCs depending on their thermal histories. We discuss the formation of these phases in the context of a delicate balance between minimization of free energy at the local micelle length scale against the global LLC unit cell scale. The specific observations of FK A15 and  phases, both periodic approximants of dodecagonal quasicrystals, suggest the possibility that suitable processing of these aqueous LLCs may lead to soft liquid quasicrystals. In view of recent discoveries of dodecagonal quasicrystals and their approximants in other soft systems[2-5], our discovery provides a new context for understanding the factors driving periodic and quasiperiodic order in soft materials.