A THEORY FOR ELECTRIC DICHROISM AND BIREFRINGENCE DECAYS AND DEPOLARIZED DYNAMIC LIGHT-SCATTERING OF WEAKLY BENDING RODS

When a weakly bending rod consisting of discrete subunits is partially oriented in a weak electric field by an independent induced dipole me chanism, the off-field decay of its dichroism or birefringence reflect s the same mutual-rotational correlation function that is manifested i n its forward depolarized dynamic light scattering. An analytical theo ry of that mutual-rotational correlation function is developed by exte nding a previous theory for self-rotational correlation functions of s ubunits in macromolecules with mean local cylindrical symmetry, and th e result is formulated in terms of a previous normal mode theory for d iscrete weakly bending rods. Results from this analytical theory are c ompared with those of Brownian dynamics simulations with generally goo d agreement. By dissecting the analytical theory, explanations are fou nd both for the unexpectedly small fraction of total relaxing amplitud e that appears in the rapid initial transient due to bending and for t he absence of the relaxation time of the longest bending mode from tha t initial relaxation.