Condensed Exponential Correlation Functions in Multicomponent Polymer Blends Measured by X-ray Photon Correlation Spectroscopy

X-ray photon correlation spectroscopy experiments were conducted on bicontinuous microemulsion and lamellar phases in polystyrene/polyisoprene/poly(styrene-b-isoprene) blends. Regardless of the microstructure, the scattering intensity autocorrelation function at low temperatures in the vicinity of the primary X-ray scattering peak, g2(q,t) (q is the scattering vector), was found to be a condensed exponential, i.e., g2(q,t) ∼ exp{−[t/τ(q)]α}with α > 1. This is in direct contrast to previous observations of exponential and stretched exponential correlation functions (α ≤ 1) in microstructured materials comprising polymers as well as small molecules. At higher temperatures, more conventional stretched exponential correlation functions are recovered. We suggest that condensed exponential relaxation functions may be related to the spontaneous breakup of microsctructure.