Technique: Dielectric Relaxation Spectroscopy
Dielectric relaxation spectroscopy is utilized in our lab to probe the molecular dynamics of small volume polymer samples and self-assembled monolayers. Observable motions include segmental reorientation, including that associated with glass transitions, and intermolecular rotation (such as observed in side chains). Typically samples are measured on interdigitated electrodes with an ultra-sensitive capacitance bridge. Capacitance and dissipation factor, tan(δ), are measured as a function of temperature (as illustrated below) over a broad temperature range (from liquid He to ~ 400K). Relaxation peaks occur in the spectrum when a dipole-active motion within the sample is occurring at a rate similar to the frequency of the applied electric field. We utilize a narrow band of frequencies (as opposed to the more common broad-band technique), within which very sensitive measurements can be made, and tune the dynamics within the sample by changing the temperature. The interdigitated electrode configuration enables measurement of very small volume samples, such as one-molecule-thick films (monolayers) or small volumes of polymer.
