In two-dimensional interfacial assemblies, there is an interplay between molecular ordering and interface geometry, which determines the final morphology and order of entire systems. Here we present the interfacial phenomenon of spontaneous facet formation in a water droplet driven by designed peptide assembly. The identified peptides can flatten the rounded top of a hemispherical droplet into a plane by forming a macroscopic two-dimensional crystal structure. Such ordering is driven by the folding geometry of the peptide, interactions of tyrosine and crosslinked stabilization by cysteine. We discover the key sequence motifs and folding structures and study their sequence-specific assembly. The well-ordered, densely packed, redox-active tyrosine units in the YYACAYY (H-Tyr-Tyr-Ala-Cys-Ala-Tyr-Tyr-OH) film can trigger or enhance chemical/electrochemical reactions, and can potentially serve as a platform to fabricate a molecularly tunable, self-repairable, flat peptide or hybrid film.
A volume expansion of up to ~310% occurs upon the lithiation of silicon in Si-coated nickel inverse opal anodes, which causes (de)lithiation-induced mismatch stresses and strains between the Si and Ni during battery cyclical (dis)charging. These (de)lithiationinduced mismatch strains and stresses are modeled via sequentially coupled diffusionand stress-based finite element (FE) analysis, which takes the mechanical contact between the Si and Ni phases into account, as well as the complex geometry and material properties of the Si-coated Ni inverse opal anode system. During lithiation, compressive strains are developed in the Ni scaffold since the Si active layer expands. A rapid recovery of these lithiation-induced mismatch strains occurs during subsequent delithiation, though full recovery is not achieved. Strain histories upon multiple (de)lithiation cycles vary with the choice of various mechanical contact conditions employed between the two phases, since the mechanical contact properties determine how the contacted phases interact mechanically. The numerically predicted strains are compared with experimental strain data collected in operando using X-ray diffraction. The simulated strain histories agree with the measured data, enabling the possibility of predicting mechanical performance and eventual degradation using only numerical modeling. In particular, the FE model indicates that plastic deformation occurs first in the lithiated Si active layer, then in the Ni scaffold.
Tin alloy-based anodes supported by inverse-opal nanoscaffolds undergo large volume changes from (de)lithiation during cyclic battery (dis)charging, affecting their mechanical stability. We perform continuum mechanics-based simulation to study the evolution of internal stresses and strains as a function of the geometry of the active layer(s): (i) thickness of NiSn single layer (30 and 60 nm) and (ii) stacking sequence of NiSn and amorphous Si in bilayers (60 nm thick). For single NiSn active layers, a thinner layer displays higher strains and stresses, which are relevant to mechanical stability, but causes lower strains and stresses in the Ni scaffold. For NiSn-Si bilayers, the stacking sequence significantly affects the deformation of the active layers and thus its mechanical stability due to different lithiation behaviors and volume changes.
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