STUDY OF IMPULSE POLYMER RHEO-OPTICS BY STEP-SCAN FT-IR TIME-RESOLVEDSPECTROSCOPY

The applicability of step-scan impulse/response FT-IR spectroscopy to the rheo-optical study of polymer films is demonstrated by spectral me asurements with isotactic polypropylene. A novel piezoelectrically dri ven microrheometer is employed to apply repetitive impulses to a polym er sample while time-domain spectra are recorded by step-scan FT-IR sp ectroscopy, The traditional advantages of Fourier transform spectrosco py are retained while providing a second multiplex advantage for the c haracterization of the time-dependence of the sample response, Reprodu cible results, consistent with the frequency-domain literature data an d having good signal-to-noise ratio, are obtained. The spectral change s due to molecular reorientation are found to be essentially as fast a s the mechanical stretching, also consistent with frequency-domain res ults. To our knowledge, this is the first reported step-scan FT-IR tim e-domain rheo-optical measurement. This technique appears to be applic able to a variety of polymer samples, The advantages of time-domain me asurements over frequency-domain measurements are briefly discussed.