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1. Amorphous entangled active matter

   https://doi.org/10.1039/D2SM01573K  

   Savoie, William; Tuazon, Harry; Tiwari, Ishant; Bhamla, M. Saad; Goldman, Daniel I. (March 2023, Soft Matter)

   The design of amorphous entangled systems, specifically from soft and active materials, has the potential to open exciting new classes of active, shape-shifting, and task-capable ‘smart’ materials. However, the global emergent mechanics that arise from the local interactions of individual particles are not well understood. In this study, we examine the emergent properties of amorphous entangled systems in an in silico collection of u-shaped particles (“smarticles”) and in living entangled aggregate of worm blobs ( L. variegatus ). In simulations, we examine how material properties change for a collective composed of smarticles as they undergo different forcing protocols. We compare three methods of controlling entanglement in the collective: external oscillations of the ensemble, sudden shape-changes of all individuals, and sustained internal oscillations of all individuals. We find that large-amplitude changes of the particle's shape using the shape-change procedure produce the largest average number of entanglements, with respect to the aspect ratio ( l / w ), thus improving the tensile strength of the collective. We demonstrate applications of these simulations by showing how the individual worm activity in a blob can be controlled through the ambient dissolved oxygen in water, leading to complex emergent properties of the living entangled collective, such as solid-like entanglement and tumbling. Our work reveals principles by which future shape-modulating, potentially soft robotic systems may dynamically alter their material properties, advancing our understanding of living entangled materials, while inspiring new classes of synthetic emergent super-materials. 

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2. A continuum of amorphous ices between low-density and high-density amorphous ice

   https://doi.org/10.1038/s42004-024-01117-2  

   Eltareb, Ali; Lopez, Gustavo E; Giovambattista, Nicolas (February 2024, Communications Chemistry)

   Abstract Amorphous ices are usually classified as belonging to low-density or high-density amorphous ice (LDA and HDA) with densitiesρ_LDA ≈ 0.94 g/cm³andρ_HDA ≈ 1.15−1.17 g/cm³. However, a recent experiment crushing hexagonal ice (ball-milling) produced amedium-density amorphous ice (MDA,ρ_MDA ≈ 1.06 g/cm³) adding complexity to our understanding of amorphous ice and the phase diagram of supercooled water. Motivated by the discovery of MDA, we perform computer simulations where amorphous ices are produced by isobaric cooling and isothermal compression/decompression. Our results show that, depending on the pressure employed, isobaric cooling can generate a continuum of amorphous ices with densities that expand in between those of LDA and HDA (briefly, intermediate amorphous ices, IA). In particular, the IA generated atP ≈ 125 MPa has a remarkably similar density and average structure as MDA, implying that MDA is not unique. Using the potential energy landscape formalism, we provide an intuitive qualitative understanding of the nature of LDA, HDA, and the IA generated at different pressures. In this view, LDA and HDA occupy specific and well-separated regions of the PEL; the IA prepared atP = 125 MPa is located in the intermediate region of the PEL that separates LDA and HDA. 

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3. Prestressed elasticity of amorphous solids

   https://doi.org/10.1103/PhysRevResearch.4.043181  

   Zhang, Shang; Stanifer, Ethan; Vasisht, Vishwas V.; Zhang, Leyou; Del_Gado, Emanuela; Mao, Xiaoming (December 2022, Physical Review Research)

   Prestress in amorphous solids bears the memory of their formation and plays a profound role in their mechanical properties. Here we develop a set of mathematical tools to investigate mechanical response of prestressed systems, using stress rather than strain as the fundamental variable. This theory allows microscopic prestress to vary for the same bond or contact configuration and is particularly convenient for nonconservative systems, such as granular packings and jammed suspensions, where there is no well-defined reference state, invalidating conventional elasticity. Using prestressed nonconservative triangular lattices and a computational model of amorphous solids, we show that drastically different mechanical responses can show up in amorphous materials at the same density, due to nonconservative interactions which evolve over time, or different preparation protocols. In both cases, the information is encoded in the prestress of the network and not visible at all from the configurations of the network in the case of nonconservative interactions. 

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4. Emergent Elasticity in Amorphous Solids

   https://doi.org/10.1103/PhysRevLett.125.118002  

   Nampoothiri, Jishnu N.; Wang, Yinqiao; Ramola, Kabir; Zhang, Jie; Bhattacharjee, Subhro; Chakraborty, Bulbul (September 2020, Physical Review Letters)

   null (Ed.)
5. Fracture universality in amorphous nanowires

   https://doi.org/10.1016/j.jmps.2023.105210  

   Zhao, Kun; Wang, Yun-Jiang; Cao, Penghui (April 2023, Journal of the Mechanics and Physics of Solids)