Ultrafast Dynamics of Styrene Microemulsions, Polystyrene Nanolatexes, and Structural Analogues of Polystyrene

摘要

The ultrafast optically heterodyne-detected optical-Kerr-effect is used to compare the dynamics of styrene neat and in dodecane solution with those of styrene dispersed as the oil phase in a oil-in-water microemulsion. The dynamics in the microemulsion are similar to those of the neat liquid, both on the ultrafast and picosecond time scales, but there is also evidence for additional inhomogeneous broadening in the microemulsion. The styrene in the microemulsion was photopolymerized to yield isolated latex particles. The effect of polymerization on the ultrafast dynamics is dramatic. The picosecond diffusive response seen for the monomer is suppressed, whereas the ultrafast spectral density shifts to higher frequency in the polymer. Similar dynamics are seen for polystyrene in solution. This behavior is further analyzed through an investigation of the ultrafast dynamics of solutions of toluene, bibenzyl, a polystyrene oligomer, and polystyrene itself. It is concluded that the shift to higher frequency in the spectral density corresponds to the opening of additional intramolecular relaxation pathways in the larger more flexible molecules. It is found that both molecular and intramolecular librational dynamics are sensitive to their environment.