MESOSCOPIC PHYSICS OF SWOLLEN POLYMER NETWORKS - STATICS AND DYNAMICS

We investigate in this paper the origin of the ''butterfly'' patterns that were discovered during small-angle-neutron-scattering studies of uniaxially stretched gels and rubbers and of polymer blends in extensi onal flow. We present a general formalism for both gels and liquids wh ich shows that when material parameters such as shear modulus or visco sity are allowed to depend on the internal degrees of freedom (e.g., t he monomer concentration), then butterfly patterns are naturally encou ntered in the isointensity contours of the structure factor. We also s how that for higher strains (or strain rates for liquids), one encount ers strain-induced decomposition. The dynamics of strain and of flow-i nduced decomposition are shown to be closely similar. To test the theo retical description, we compute the inelastic-light-scattering spectru m and the time evolution of the small-angle neutron-scattering cross s ection.