Mechanochromic Polymer Film with High Sensitivity toward Tensile Strain by the Post-Curing Ring-Closure Induced Pre-Stretching.

Abstract

Mechanochromic materials has received broad research interests recently, owing to its ability to monitor the in-situ stress/strain in polymer materials in a straight forward way. However, one major setback that hinder the practical application of these materials is their low sensitivity toward tensile strain. Here we show a new strategy for pre-stretching of the mechanochromic agent in a polymer film on the molecular scale, which can effectively enhance the mechanochromic sensitivity of a polymer film toward tensile strain. In-situ fluorescent measurement during tensile test showed an early activation of the mechanochromic agent at tensile strain as low as 50%. The pre-stretching effect is realized by firstly inducing ring-opening of the mechanochromic agent by molecular functionalization, and then compelling the ring-closure process in the cured film by elevated temperature. This post-curing ring-closure process will result in pre-stretched mechanochromic agent in a crosslinked network. The mechanism for mechanochromic activation of polymer films with different composition was elaborated by visco-elastic measurements, and the effect of pre-stretching was further confirmed by polymer films with other compositions. Combined with the simplicity of the method developed, we believe this work will offer an alternative strategy to enhance the sensitivity of different mechanochromic agents toward tensile strain. This article is protected by copyright. All rights reserved.