Birefringence, deformation, and scattering of segmentally flexible macromolecules under an external agent. Steady-state properties in an electric field

Segmentally flexible macromolecules are composed of a few rigid subunits jo ined by semiflexible joints. When such macromolecules are exposed to an ext ernal agent, they become oriented and deformed, and this fact can be monito red by birefringence, and scattering. In this paper, we present a theoretic al treatment of deformation and scattering of segmentally flexible macromol ecules in an external agent that complements existing treatments of birefri ngence. We treat in detail the case in which the external agent is an elect ric field, particularizing for the case of a macromolecule with two cylindr ically symmetric subunits. We focus on the steady-state behavior of the mol ecule in the field, studying the effect of arbitrarily high field strengths , which can be simulated using a Monte Carlo procedure. We show how the dep endence of birefringence and deformation on field strength can be related t o the electrooptical properties of the macromolecule and its flexibility. P articular attention is paid to macromolecular deformation expressed in term of the gyration tensor, whose components can be determined from separate s cattering experiments with different scattering geometries. A joint discuss ion of deformations and birefringence provides a nexus between the techniqu es of electric birefringence and electric-field light scattering.