Noninvasive imaging of molecular dynamics in heterogeneous materials

The macroscopic properties of microscopically heterogeneous materials are often determined by specific molecular changes within constitutive microdomains. In particular, the electrooptical properties of a class of composites termed polymer-dispersed liquid crystals (PDLCs) are established by the orientation dynamics of the component liquid crystals (LCs) and the dissolved species dictated by applied electric fields. We demonstrate the accessibility of spatially resolved molecular dynamics in the millisecond time regime by developing a time-resolved Fourier transform infrared (FTIR) spectroscopic imaging technique. Applying this approach to PDLCs, we determine the molecular reorientation dynamics to be a strong function of spatial position. The liquid crystal and polymer segmental dynamics correlate through dipole-dipole interactions, demonstrating that chemical factors other than surface anchoring interactions contribute significantly to the electrooptical characteristics of polymer-LC composites. The morphologically specific dynamics and molecular interactions are determined noninvasively and without addition of foreign materials or molecular labeling.