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Undercooling metals relies on frustration of liquid–solid transition mainly by an increase in activation energy. Passivating oxide layers are a way to isolate the core from heterogenous nucleants (physical barrier) while also raising the activation energy (thermodynamic/kinetic barrier) needed for solidification. The latter is due to composition gradients (speciation) that establishes a sharp chemical potential gradient across the thin (0.7–5 nm) oxide shell, slowing homogeneous nucleation. When this speciation is properly tuned, the oxide layer presents a previously unaccounted for interfacial tension in the overall energy landscape of the relaxing material. We demonstrate that 1) the integrity of the passivation oxide is critical in stabilizing undercooled particle, a key tenet in developing heat‐free solders, 2) inductive effects play a critical role in undercooling, and 3) the magnitude of the influence of the passivating oxide can be larger than size effects in undercooling. [ABSTRACT FROM AUTHOR]

Undercooling metals relies on frustration of liquid–solid transition mainly by an increase in activation energy. Passivating oxide layers are a way to isolate the core from heterogenous nucleants (physical barrier) while also raising the activation energy (thermodynamic/kinetic barrier) needed for solidification. The latter is due to composition gradients (speciation) that establishes a sharp chemical potential gradient across the thin (0.7–5 nm) oxide shell, slowing homogeneous nucleation. When this speciation is properly tuned, the oxide layer presents a previously unaccounted for interfacial tension in the overall energy landscape of the relaxing material. We demonstrate that 1) the integrity of the passivation oxide is critical in stabilizing undercooled particle, a key tenet in developing heat‐free solders, 2) inductive effects play a critical role in undercooling, and 3) the magnitude of the influence of the passivating oxide can be larger than size effects in undercooling. [ABSTRACT FROM AUTHOR]

Abstract: A facile method is reported for rapid, room‐temperature synthesis of block copolymers (BCP) of complex morphology and hence nontraditional spherical assembly. The use of solvated electrons generates radical anions on olefinic monomers, and with a felicitous choice of monomer pairs, this species will propagate bimechanistically (via radical and the anion) to form BCPs. Molecular weight of the obtained BCP range from Mw = 97 000–404 000 g mol−1 (polydispersity index, PDI = 1.4–3.0) depending on monomer pairs. The composition of the blocks can be controlled by changing monomer ratio, with the caveat that yield is affected. Detailed characterization by 2D nuclear magnetic resonance spectroscopy, differential scanning calorimetry (DSC), and analysis of the mechanisms involved indicate the structure of obtained block copolymers to be at least a triblock with a complex central unit. Evaluating trends in the Hammett parameter segregates monomer pairs into “armed and disarmed” groups with respect to radical or anionic polymerization akin to oligosaccharides synthesis. [ABSTRACT FROM AUTHOR]

Cover Picture: Stabilization of Undercooled Metals via Passivating Oxide Layers (Angew. Engineering composition across a thin surface oxide layer of a metal particle, and stabilizing it with appropriate ligands, leads to a sharp surface stress that frustrates solidification. Engineering composition across a thin surface oxide layer of a metal particle, and stabilizing it with appropriate ligands, leads to a sharp surface stress that frustrates solidification. [Extracted from the article]

Energy landscape, inductive effect, metastability, phase transformation, stable undercooling Es bildet sich ein unterkühltes flüssiges Metallteilchen, was ein neues Konzept für das gezielte Engineering der Energielandschaft eines Materials unter Verwendung einer dünnen Oberflächenschicht aufzeigt, wie Martin Thuo et al. in ihrem Forschungsartikel auf S. 5993 beschreiben. Keywords: energy landscape; inductive effect; metastability; phase transformation; stable undercooling EN energy landscape inductive effect metastability phase transformation stable undercooling 5633 5633 1 03/03/21 20210308 NES 210308 B Kühle Frustration b . [Extracted from the article]

In article number 1903687, Martin Thuo and co-workers describe a unique heat-free approach for the fabrication of conductive metallic interconnects on diverse types of substrates. This method hinges on undercooled metal particles fabricated by encapsulating molten metal in thin shells to enable solidification. Heat-free solder, interconnects, liquid metal, multimaterial manufacturing, undercooled. [Extracted from the article]

Exploiting interfacial excess (Γ), Laplace pressure jump (ΔP), surface work, and coupling them to surface reactivity have led to the synthesis of undercooled metal particles. Metastability is maintained by a core–shell particle architecture. Fracture of the thin shell leads to solidification with concomitant sintering. Applying Scherer's constitutive model for load‐driven viscous sintering on the undercooled particles implies that they can form conductive traces. Combining metastability to eliminate heat and robustness of viscous sintering, an array of conductive metallic traces can be prepared, leading to plethora of devices on various flexible and/or heat sensitive substrates. Besides mechanical sintering, chemical sintering can be performed, which negates the need of either heat or load. In the latter, connectivity is hypothesized to occur via a Frenkel's theory of sintering type mechanism. This work reports heat‐free, ambient fabrication of metallic conductive interconnects and traces on all types of substrates. [ABSTRACT FROM AUTHOR]