SCATTERING FROM SOLUTIONS OF STAR POLYMERS

We study the scattering intensity of dilute and semi-dilute solutions of star polymers. The star conformation is described by a model introd uced by Daoud and Cotton. In this model, a single star is regarded as a spherical region of a semi-dilute polymer solution with a local, pos ition dependent screening length. For high enough concentrations, the outer sections of the arms overlap and build a semi-dilute solution (a sea of blobs) where the inner parts of the actual stars are embedded. The scattering function is evaluated following a method introduced by Auvray and de Gennes. In the dilute regime there are three regions in the scattering function: the Guinier region (low wave vectors, qR muc h less than 1) from where the radius of the star can be extracted, the intermediate region (1 much less than qR f(2/5)) that carries the sig nature of the form factor of a star with f arms: I(q) N similar to q(- 10/3); and a high wavevector zone (qR much greater than f(2/5)) where the local swollen structure of the polymers gives rise to the usual q( -5/3) decay. In the semi-dilute regime the different stars interact st rongly, and the scattered intensity acquires two new features: a liqui d peak that develops at a reciprocal position corresponding to the sta r-star distances; and a new large wavevector contribution of the form q(-5/3) originating from the sea of blobs.