A tensile stage for high resolution synchrotron-based infrared microspectroscopy at MIRAS

For the study of thin films and fibres under load, a uniaxial tensile stage has been developed for synchrotron-based polarized Fourier-transform infrared (FTIR) microspectroscopy. One of the advantages compared to commercial available stages is its compact design at the sample position (<20 mm thickness) and the large field of view on the sample for transmission and reflection geometry. In addition, the stage is mounted on a base plate, which can be rotated between -15° and +193° in the sample plane, in order to rotate the sample relative to the inherent polarization of the incoming infrared light from the synchrotron light source. Preliminary in situ tensile load experiments conducted at MIRAS beamline of the ALBA synchrotron were done on 3D printed thermoplastic polyurethane (TPU) polymer thin films. The samples could be mapped in transmission geometry under tensile load achieving high spatial resolution up to 10 micros using the intense IR source of the synchrotron light. Making use of polarized synchrotron-based infrared light, it was possible to show the alignment of different vibrational bands parallel and orthogonal to the stretching direction. The v(C=O) absorbance bands decrease upon stretching using parallel polarized infrared light, while the v(C=C) bands are increasing in intensity, revealing the orientation of v(C=O) bonds orthogonal to the stretching direction during stretching. The experiments highlight the unique instrumentation capabilities of the tensile stage for in situ measurement of molecular distributions and chemical bond orientations as a function of sample displacement and applied load.