|Title||Controlled fragmentation of multimaterial fibres and films via polymer cold-drawing|
|Publication Type||Journal Article|
|Year of Publication||2016|
|Authors||Shabahang, S, Tao, G, Kaufman, JJ, Qiao, Y, Wei, L, Bouchenot, T, Gordon, AP, Fink, Y, Bai, Y, Hoy, RS, Abouraddy, AF|
|Pagination||529 - +|
|Keywords||behavior, blends, composites, elastic properties, matrix, mechanical-properties, neck propagation, phosphate-glasses, silkworm silk, stress transfer|
Polymer cold-drawing(1-4) is a process in which tensile stress reduces the diameter of a drawn fibre (or thickness of a drawn film) and orients the polymeric chains. Cold-drawing has long been used in industrial applications(5-7), including the production of flexible fibres with high tensile strength such as polyester and nylon(8,9). However, cold-drawing of a composite structure has been less studied. Here we show that in a multimaterial fibre(10,11) composed of a brittle core embedded in a ductile polymer cladding, cold-drawing results in a surprising phenomenon: controllable and sequential fragmentation of the core to produce uniformly sized rods along metres of fibre, rather than the expected random or chaotic fragmentation. These embedded structures arise from mechanical-geometric instabilities associated with 'neck' propagation(2,3). Embedded, structured multimaterial threads with complex transverse geometry are thus fragmented into a periodic train of rods held stationary in the polymer cladding. These rods can then be easily extracted via selective dissolution of the cladding, or can self-heal by thermal restoration to re-form the brittle thread. Our method is also applicable to composites with flat rather than cylindrical geometries, in which case cold-drawing leads to the break-up of an embedded or coated brittle film into narrow parallel strips that are aligned normally to the drawing axis. A range of materials was explored to establish the universality of this effect, including silicon, germanium, gold, glasses, silk, polystyrene, biodegradable polymers and ice. We observe, and verify through nonlinear finite-element simulations, a linear relationship between the smallest transverse scale and the longitudinal break-up period. These results may lead to the development of dynamical and thermoreversible camouflaging via a nanoscale Venetian-blind effect, and the fabrication of large-area structured surfaces that facilitate high-sensitivity bio-detection.