Visualization of strain in elastic silicone polymers using fluorescence energy transfer

There is an urgent need to develop new methods for assessing strain in polymers without damaging the material’s intrinsic properties. The disadvantages of current methods include: high costs; impregnation of the polymer with bulky mechanical devices; inability to measure in several dimensions; and interaction with electromagnetic radiation. In this paper, a method to detect strain in elastic polymers that is based on energy transfer between two fluorophores is presented. By incorporating donor and acceptor dyes in poly(dimethylsiloxane) (PDMS) and monitoring the change in emission spectral profile, evidence of strain is gathered. We first demonstrate the successful doping of the elastomer with the dyes fluorescein and rhodamine B by using different optical techniques. PDMS strips containing the two dyes are fabricated and their emission spectral profile upon stretching is analyzed using a spectrometer. As the strip is extended, the distance between donor and acceptor molecules increases, resulting in a decline in energy transfer efficiency. This is manifested by intensification of emission from fluorescein, accompanied by a decline in emission from rhodamine B. The effect of dye incorporation on the polymer’s elastic properties is explored with an extensometer. Next, strain in samples is visualized using a simple digital camera and basic image-processing methods. Finally, a gradual flexibility PDMS is manufactured and the nonuniform distribution of strain in it is charted.