Abstract
Controlling stresses in materials presents many unusual opportunities for their engineering applications. The potential for current approaches is severely limited by the intrinsic tie between the stress and the geometric shape. Here, we report a material concept that allows stress management in a highly efficient digital manner while decoupling the stress and the geometric shape. This is realized in a dynamic covalent shape memory polymer network, for which the elastic shape memory sets the baseline stress level and maintains the geometric shape while the plasticity enabled by the dynamic bond exchange allows stress tuning. With a digital gray scale photothermal mechanism, any arbitrarily defined stress distribution can be created in a free-standing polymer film. The naturally invisible stresses can be further visualized as mechanical colors under polarized light, revealing its potential for encoding hidden information. Our approach expands the technological potential in many areas for which stresses are relevant.
Highlights
Controlling stresses in materials presents many unusual opportunities for their engineering applications
Mechanical stresses are ubiquitous in materials. They are often detrimental to mechanical properties, well-controlled stresses can lead to unusual opportunities in various technological areas including flexible electronics[1,2], four-dimensional (4D) printing[3,4,5], microfabrication[6], and actuators[7,8,9]
We report a digital photothermal mechanism enabled by laser printing that allows unparalleled freedom in stress manipulation in a dynamic covalent shape memory polymer network, critically without altering its free-standing geometric shape
Summary
Controlling stresses in materials presents many unusual opportunities for their engineering applications. The digital photothermal effect permits spatiotemporal stress control via plasticity enabled by dynamic covalent bond exchange[16,17,18,19,20,21,22,23,24,25], whereas the elasticity-based shape memory mechanism ensures its geometric stability regardless of the stress[16,17,18,19,20] This leads to a two-dimensional (2D) film of any arbitrarily distributed stress which is invisible under regular light but can be visualized under polarized light due to the birefringence. Our approach of digital stress manipulation in a free-standing polymer expands the technological potential in areas for which stresses are relevant
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