Single Molecule Measurements of Dielectric Domains in Polymers

Single molecule (SM) spectroscopies reveal phenomena obscured by ensemble measurements.  Monitoring the fluorescence of a single molecule can provide information on the nanoscale structure of the supporting lattice, as the fluorescence of a dye is solvent dependent.    This is of particular interest for deducing the structure of soft and complex matter which possesses both static and dynamic heterogeneity.  One hypothesis that has come of previous SM studies which monitored the rotation of fluorophores embedded in polymer films is that super-cooled polymers are comprised of domains that interchange at varying rates.  The existence of domains is an important consideration in the design of organic electronics especially if charge is moving inhomogeniously due to these domains.  To determine the existence of “dielectric domains” a highly solvochromatic fluorophore, nile red, is doped into polymer films to probe the local dielectric constant by monitoring the color of the dye using confocal microscopy.  This method is used to determine the distribution of dielectric constants in several polymer films (amorphous polycarbonate, poly methyl methacrylate, and a ferroelectric polymer) and correspondence with the ensemble measurement will be tested. The influence of an external poling field will be used to determine the degree of domain rearrangement possible within the films. These experiments are important in understanding both the structure of polymer films as well as how much the structure can be manipulated by electric fields to produce better devices.