Computer simulations of hyperbranched polymers in shear flows

Brownian dynamics simulations of hyperbranched polymers with different degr ees of branching have been performed under the influence of simple shear fl ow. Hydrodynamic and excluded-volume interactions have been taken into acco unt explicitly. Shear-thinning effects have been observed for all simulated degrees of branching. As the molecular weight of highly branched structure s increases, the zero shear rate intrinsic viscosity reaches a maximum and begins to fall similar to the intrinsic viscosity behavior of perfectly bra nched dendrimers. In the absence of shear, static structure factors, S(k), for hyperbranched polymers with the smallest number of monomers studied res emble those of a three-arm star. As the number of monomers increases and as the degree of branching increases, the S(k) curves for the hyperbranched p olymers begin to illustrate features associated with S(k) curves for hard s pheres. Further insight into the shape and interior density of these struct ures is obtained through the ratio of the radius of gyration, R-g,, to the hydrodynamic radius, Rh. The ratio R-g/R-h is observed to approach unity as the number of monomers and the degree of branching increase.