Polymer cold-drawing1,2,3,4 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 applications5,6,7, including the production of flexible fibres with high tensile strength such as polyester and nylon8,9. However, cold-drawing of a composite structure has been less studied. Here we show that in a multimaterial fibre10,11 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’ propagation2,3. 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.
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We thank E.-H. Banaei, L. N. Pye, F. Tan, A. Schülzgen, C. Jollivet, C. Cariker, A. Schulte, M. Lodge, M. Ishigami, E. Duenas, C. Burchett, M. Finke, Y. Xu, S. Dai, H. Ren and X. Wang for technical assistance. We also thank M. Rein, F. Sorin, M. Kolle, A. Dogariu, D. N. Christodoulides and B. E. A. Saleh for discussions. The authors acknowledge the University of Central Florida Stokes Advanced Research Computing Center for providing computational resources and support that have contributed to results reported here. We also thank Simulia, Inc. for providing the license of the ABAQUS software package. This work was supported by the US Air Force Office of Scientific Research (AFOSR) under contract FA-9550-12-1-0148 and AFOSR MURI contract FA9550-14-1-0037, and the US National Science Foundation (CMMI-1300773). This work was supported in part by the MIT MRSEC through the MRSEC Program of the National Science Foundation under award number DMR-1419807.
Real time videos of the cold-drawing of a 20 μm diameter As2Se3 glass fibre contained in PES cladding of 1 mm outer diameter. 7 different experiments are shown in this video, where the dimensions of each fibre are the same, but the cold-drawing speed and fibre pre-stress are varied.
Animation of cold-drawing-induced fragmentation process for cylindrical fibres; details of the simulations can be found in Methods.
Real time videos of the cold-drawing of a 300 nm thick layer of As2Se3 glass embedded in a 1mm wide, 350 μm thick PES cladding. 6 different experiments are shown in this video, where the dimensions of each fibre are the same, but the cold-drawing speed and fibre pre-stress are varied. This video was replaced on 10 June 2016 as the original video was corrupted.
Animation of cold-drawing-induced fragmentation process for flat fibres; details of the simulations can be found in Methods.
A 1-mm-wide flat PES fibre containing six cylindrical 20-mm-diameter As2Se3 cores is cold-drawn in real time, with a pre-stress of 30 g and at a speed of 20 mm/min. Two segments of the video show two different zooms of the fibre.
About this article
Advanced Materials Technologies (2019)