Nature of viscoelasticity in lamellar block copolymers: Contraction correlated to strain localization

We determined the local strain profile in sheared lamellar block copolymers . A trilayer model, based on elastic brushes separated by viscous interpene tration zones, captures the rheological response of these materials and pro vides a measure of the relative contributions of elastic versus viscous str ain. The elastic chain distortions were evident from a reversible lamellar contraction, as measured from in situ small-angle x-ray scattering. The con traction was directly correlated to the elastic strain from our trilayer mo del; three distinct diblock copolymers conform to the predicted relationshi p, thus suggesting universal behavior.