Ce. Eastman et Tp. Lodge, SELF-DIFFUSION AND TRACER DIFFUSION IN STYRENE 2-VINYLPYRIDINE BLOCK-COPOLYMER MELTS, Macromolecules, 27(20), 1994, pp. 5591-5598
Forced Rayleigh scattering (FRS) has been used to probe self-diffusion
and tracer diffusion in unentangled, symmetric diblock copolymer melt
s. Two poly(styrene-b-2-vinylpyridine) (PS-PVP) diblocks, with M(w) =
1.1 x 10(4) and 2.2 x 10(4), were synthesized anionically and end-labe
led with a photochromic o-nitrostilbene derivative, and two PS homopol
ymers, with M(w) = 1.4 x 10(4) and 2.5 x 10(4), were labeled with the
same dye, randomly along the chain. Rheological measurements demonstra
ted that the lower M(w) diblock was in the disordered state and the hi
gher M(w) diblock was in the ordered (lamellar) state, over the measur
ement temperature range (110-210-degrees-C). The ordered samples were
quenched, in the sense that no attempt was made to induce a preferred
orientation to the lamellae. The self-diffusion coefficients of the tw
o copolymers superpose, when scaled by the ratio of molecular weights,
as expected for disordered Rouse chains, thus indicating that the lam
ellar order has little effect on the overall mobility. Similarly, the
copolymer and homopolymer self-diffusion coefficients are nearly ident
ical, for equal total M(w). This result is interpreted as reflecting u
nhindered motion of the copolymer chains in the lamellar planes. Trace
r diffusion measurements for the homopolymers and the lower M(w) copol
ymer in the ordered copolymer matrix also showed little difference fro
m the corresponding self-diffusion coefficients but were qualitatively
consistent with perturbation theory. In all cases, the FRS signals we
re well-described by single exponential decays, possibly suggesting th
at diffusion through the lamellae is not greatly retarded relative to
diffusion in the lamellar planes and/or that the orientational correla
tion length of the lamellae is small.