Haoran Wang

Governing partial differential equations (PDEs) play a critical role in materials research and applications, as they describe essential physics underlying materials behaviour. Traditionally, these equations are developed through phenomenological modelling of experimental results or first principle analysis based on conservation laws. In addition, molecular dynamics (MD) simulations capture atomistic-scale behaviour with detailed physics. However, translating atomistic insights into continuum-scale governing equations remains a significant challenge. Empowered by recent advances in data-driven modelling, we develop a computational framework to learn governing PDEs directly from atomistic simulation data. The framework integrates numerical differentiation of MD data with the identification of constitutive relationships. It proves effective and efficient in learning governing PDEs from noisy and limited MD datasets, without requiring prior knowledge of the final PDEs. Using this framework, we identify a nonlinear PDE governing solid-state diffusion in nickel–hydrogen alloys. This PDE reveals a highly concentration-dependent diffusivity that varies over an order of magnitude. Our data-driven computational framework paves the way for cross-scale constitutive modelling.

An organophosphine-controlled diversity-oriented synthesis of chromone inden-1-one-fused cyclopentadienylides and C-acylated 2-((chromone-3-yl)methylene)-indandiones is reported. Key attributes of the methodology are the in situ generation of an allylic P-ylide and subsequent regio- and chemoselective intramolecular cyclization reactions that preferentially result in the aforementioned chromone adducts.

Over the past decade, there has been a significant advancement in understanding the mechanics of silicon (Si) electrodes in lithium (Li)-ion batteries. Much of this interest in Si electrodes as ideal anode materials for high-capacity Li-ion batteries stems from its theoretical specific capacity of 4200 mAh g⁻¹, which is an order-of-magnitude higher than that of conventional graphite electrodes (372 mAh g⁻¹). However, the high capacity of Li ions is also accompanied by a ∼300% volume expansion of the Si electrode during Li intercalation, which results in massive cracking of the electrode and capacity fade. In this review article, we summarize recent progress in elucidating the underlying fracture and failure mechanics of Si electrodes using multiscale computations and experiments, spanning the quantum, atomistic, microscopic, and macroscopic length scales. We focus on four fundamental mechanics issues: (i) the mechanical properties and fracture behavior of lithiated Si electrodes; (ii) the interfacial mechanics between Si thin-film electrodes and current collectors; (iii) the deformation and failure mechanics of the solid electrolyte interphase; and (iv) the design of Si electrodes for improved mechanical performance. Current challenges and possible future directions for the field of mechanics of materials in pursuit of high-capacity rechargeable batteries are also discussed.

Continuum models describing ideal nematic solids are widely used in theoretical studies of liquid crystal elastomers. However, experiments on nematic elastomers show a type of anisotropic response that is not predicted by the ideal models. Therefore, their description requires an additional term coupling elastic and nematic responses, to account for aeolotropic effects. In order to better understand the observed elastic response of liquid crystal elastomers, we analyse theoretically and computationally different stretch and shear deformations. We then compare the elastic moduli in the infinitesimal elastic strain limit obtained from the molecular dynamics simulations with the ones derived theoretically, and show that they are better explained by including nematic order effects within the continuum framework.

We report on the chemical lithiation of long microscale helices composed of densely packed amorphous silicon (aSi) nanofibrils, fabricated by glancing angle deposition (GLAD) through e-beam evaporation. In situ electron microscopy and companion finite element modeling demonstrate that the nanofibrillar structure of the aSi helices allows for 2 orders of magnitude faster effective rates for Li diffusion (D₀ = 10^–10 cm²/s) compared to solid aSi nanowires, while also averting fragmentation during lithiation. More importantly, it is shown that specific helical geometries can accommodate large, lithium-induced, volumetric expansions without shape distortion. A major advantage of the helical nanostructures is that the compressive force generated due to lithiation-induced expansion is an order of magnitude smaller than in straight nanocolumns that permanently buckle during lithiation. Thus, GLAD-fabricated films composed of dense periodic microscale helices with properly designed coil geometries are highly suitable for robust, high-capacity Li⁺ anodes.

It is important to observe the metallic vapor dissipation after interrupting a vacuum arc, for getting a deeper understanding of dielectric recovery processes, especially for DC interruptions. The object of this paper is to obtain two dimensional density distribution of copper vapor in a forced vacuum arc extinction. The method of laser-induced fluorescence (LIF) using a pulse laser with a central wavelength at 324.8 nm was adopted here. Meanwhile, an ICCD was used to capture the 510.6 nm fluorescence signal with an exposure time of 50 ns. The fluorescence can be distinguished from 125μs (the moment of arc extinction) to 375μs with a time interval of 25μs. As a result, we could obtain the relative density distribution of ground-state copper metal vapor after the arc extinction. The results show that on the condition of CuCr25 contacts the metal vapor was evenly distributed in the gap and rapidly spread over time. The density of the copper vapor between the contacts dropped to less than 10% of the initial stage 200μs after arc extinction. On the contrary, on the condition of CuCr50, higher copper metal vapor density at the moment of arc extinction was observed. It seems that the higher Cr content in the Cu-Cr contacts will lead to producing more metal vapor around current zero.