Carbon dots-polyurethane composites with anisotropic enhanced fluorescence for strain sensing

Abstract

Strain sensors have emerged as indispensable tools for measuring mechanical deformation, playing a vital role in structural health monitoring, motion detection in wearable devices, and precision force control in industrial robotics. A new type of nontoxic low-cost strain sensor is reported here, whose fluorescence intensity is instantly responsive to the external strain applied over a large range (up to 250% strain). Highly stretchable fluorescent composites of carbon dots (CDs) and polyurethane (PU) are fabricated via a scalable green chemistry method by conveniently dispersing CDs in the aqueous solution of PU. It is discovered that, upon tensile deformation, the fluorescence peak of the CD-PU film remains non-shifted but displays enhanced fluorescence intensity. The observed fluorescence responses to strain are ascribed to the enlarged inter-particle distance of CDs along the tensile direction, although a higher degree of aggregation results from the other two axes. The fluorescence-dependence on the anisotropic patterns of CDs in solid state points to a new mechanism to overcome aggregation-induced quenching by controlling the distribution behaviors of the fluorescent species.