Experimental studies of stress-diffusion coupling in semi-dilute polymer solutions. I. 'Viscoelastic length' and viscoelastic effects on early stage spinodal decomposition

We investigated the viscoelastic effects on the early stage spinodal decomp osition (SD) in semi-dilute polymer solutions where the coupling between st ress and diffusion plays an important role. The so-called viscoelastic leng th, xi (ve), within which the stress suppresses the growth of the concentra tion fluctuations, was quantitatively evaluated experimentally. The evaluat ed value was found out to be about 10 times larger than the radius of gyrat ion of polymer. We measured the interdiffusion coefficient, the cooperative diffusion coefficient, the zero-shear viscosity, and the plateau modulus i n the one phase region and evaluated xi (ve) independently from the SD expe riment. The value xi (ve) obtained in the early stage SD agrees well with t hat estimated from the diffusion and viscoelasticity measurements, confirmi ng the validity of the Doi-Onuki theory. (C) 2001 Elsevier Science Ltd. All rights reserved.