DYNAMIC SCATTERING FUNCTION FOR DIBLOCK COPOLYMER CHAINS IN DILUTE-SOLUTIONS

The quasielastic scattering function of a diblock copolymer chain in d ilute solution has been evaluated according to the Rouse-Zimm theory ( valid for Gaussian,chains with preaveraged hydrodynamic interactions), and also through Brownian dynamics simulations which include net repu lsions between units of different; type (A or B) and fluctuating hydro dynamic interactions. Opposite contrast factors are defined for the A and B units (i.e., the solvent refractive index is assumed to be inter mediate with respect to those of A and B). Both types of calculations agree in the main features: The scattering function can be expressed a s a sum of exponential terms, whose relative contributions are complet ely different from the ones calculated from the Pecora analysis for ho mopolymer chains. For small or moderate values of the scattering varia ble, close to the peak for the total scattering intensity, a single ex ponential is obtained, but its exponent depends both on the translatio nal diffusion coefficient, and on the chain first internal relaxation time.