In biochemistry, flow birefringence is a hydrodynamic technique for measuring the rotational diffusion constants (or, equivalently, the rotational drag coefficients. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion The birefringence of a solution sandwiched between two concentric cylinders is measured as a function of the difference in rotational speed between the inner and outer cylinders. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray The flow tends to orient an ellipsoidal particle (typically, a protein, virus, etc. ) in one direction, whereas rotational diffusion (tumbling) causes the molecule to become disoriented. The equilibrium between these two processes as a function of the flow provides a measure of the axial ratio of the ellipsoidal particle.
In Hydrodynamics, the Perrin friction factors are multiplicative adjustments to the translational and rotational friction of a rigid spheroid relative to the corresponding frictions