Asymmetric Dichroic Colors in Stretchable Film with Embedded Au/Ag Alloy Nanoparticles.

We present a new type of stretchable dichroic film in which Au and Ag alloy nanoparticles (NPs) are dispersed in polydimethylsiloxane (PDMS). The alloy NPs are synthesized with different atomic compositions and sizes to modulate their plasmonic resonance frequencies and absorption and scattering cross sections. The PDMS dichroic film in which 100 nm alloy NPs with a Au/Ag ratio of 7:3 are dispersed shows exotic optical properties under tensile strain. When 40% tensile strain is applied, the film exhibits a strain-sensitive transmission and strain-insensitive reflection behavior in which the transmittance is increased up to 2.6 times, whereas the reflectance remains unchanged. Moreover, we demonstrate a stretchable anticounterfeiting film and a flexible dichroic sculpture fabricated with the PDMS composite. This work demonstrates a new type of plasmonic application that has great potential in various applications, such as special-purpose optical films, security patterns, and smart windows.