Events

Seminar "Coherence-Correlations-Complexity", Dept. of Theoretical Physics, Wrocław University of Technology

Complex dynamics of photo-switchable guest molecules in all-optical poling close to glass transition: kinetic Monte Carlo modelling

prof. Antoni C. Mituś

Katedra Fizyki Teoretycznej WPPT PWr

We study theoretically the kinetics of non-interacting photo-switchable guest molecules (model azo-dye) dispersed in host (model polymer matrix) in the all-optical poling process close to the glass transition temperature Tg. We modify kinetic Monte Carlo model used in our previous studies of nonlinear optical processes in host-guest systems. The polymer matrix is simulated using the bond-fluctuation model. The kinetics of multiple trans-cis-trans cycles is formulated in terms of transition probabilities which depend on local free volume in the matrix and its dynamics. Close toTg the build-up of polar order, monitored in terms of angular probability den sity functions, follows a power-law in time while the evolution of the nonlinear susceptibilities related to second harmonic generation effect follows the stretched-exponential law. This complex dynamics of guest molecules implies the presence of dynamic heterogeneities of the matrix in space and time which spread the complexity from the matrix to the otherwise simple dynamics of non-interacting guest molecules. A qualitative physical picture of mosaic-like states - intertwined areas of free- and hindered angular motion of guest molecules - is proposed and the role of related short and longer scales in space for the promotion of complex dynamics of guest molecules is discussed. A brief comparison of the theory to available experimental data is given.