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Temperature Triggered Self-Unfolding Carbon Loops

Steven Cranford (Northeastern University)

Soft Materials and Structures

Wed 1:30 - 2:50

Barus-Holley 158

Self-unfolding items provide a practical convenience, wherein ring-like frames are buckled and contorted into a smaller state. Flexible rings that fold up on themselves into stacks of interlinked loops are most recognizable in such items as pop-up tents and laundry baskets. A recent investigation has determined that the way these rings behave depends on a single characteristic known as overcurvature, or how much more curved the rings are than a circle of the same circumference. Induced buckling/folding as a designed mechanism has been proposed for systems ranging from stretchable electronics, to responsive polymer membranes, to hollow shell structures, typically accounting for the intrinsic balance between bending and strain energies. Here, we focus on the smallest possible foldable system – a closed chain of carbon atoms – to investigate the limits of stability of such folded ring-structures at the atomistic scale. Synthetic assembly of molecular structures with mono-atomistic control represents a milestone in materials physics, enabling piecewise engineering of new nanoscale architectures. Carbyne – or linear acetylenic carbon - is a one-dimensional carbon allotrope composed of sp-hybridized carbon atoms, consisting of alternating single-triple bonds (polyyne). Due to their potential use in atomic-scale circuits, there has been particular interest in their novel electronic properties. While described by a 1D molecular chain, the potential for folding can serve to extend the accessible design space (similar to the self-folding of peptides to form protein structures). Understanding of the stability and mechanics of folded carbyne loops can serve to modify transport properties, or act as triggering mechanisms in active molecular systems. Here, we explore the stability of carbyne loops as a function of chain length, temperature and curvature, and delineate an effective “phase” diagram between folded and unfolded states as a function of temperature.