DIFFUSION OF TRACER MOLECULES WITHIN SYMMETRICAL DIBLOCK COPOLYMERS

Forced Rayleigh scattering has been used to investigate tracer diffusi on of a tetrahydrothiophene-indigo derivative (TTI), a photochromic dy e molecule, in a macroscopically isotropic lamellar poly(styrene-b-iso prene) diblock copolymer of relative high molecular weight. As anticip ated from the large difference of segmental mobility between the const ituent blocks, three relaxation processes termed fast, intermediate, a nd slow, respectively, have been observed as a function of temperature and grid spacing for the decay curve of scattered light from the phot oinduced grating in the experiments. The fast process exhibits a q(2) dependence, which is characteristic of Fickian diffusion, whereas the slow process is independent of q. Model calculations have identified t he nature of these two processes. In addition, the role of the size of the grid spacing chosen in these experiments, relative to the lamella r period of the microstructure, has been elucidated. A means of extrac ting diffusion coefficients for TTI in PI and PS lamellae from the exp erimental results has been demonstrated. A comparison of the diffusion coefficients obtained from the PI and PS lamellae in the block copoly mer with those of TTI diffusion in PI and PS homopolymers revealed dif ferences in the temperature dependence between the homogeneous and mic rostructured materials.