156,900 research outputs found
Random Isotropic Structures and Possible Glass Transitions in Diblock Copolymer Melts
We study the microstructural glass transitions in diblock-copolymer melts
using a thermodynamic replica approach. Our approach performs an expansion in
terms of the natural smallness parameter -- the inverse of the scaled degree of
polymerization, which allows us to systematically study the approach to
mean-field behavior as the degree of polymerization increases. We find that in
the limit of infinite long polymer chains, both the onset of glassiness and the
vitrification transition (Kauzmann temperature) collapse to the mean-field
spinodal, suggesting that the spinodal can be regarded as the mean-field
signature for glass transitions in this class of systems. We also study the
order-disorder transitions (ODT) within the same theoretical framework; in
particular, we include the leading-order fluctuation corrections due to the
cubic interaction in the coarse-grained Hamiltonian, which has been ignored in
previous works on the ODT in block copolymers. We find that the cubic term
stabilizes both the ordered (body-centered-cubic) phase and the glassy state
relative to the disordered phase. While in melts of symmetric copolymers the
glass transition always occurs after the order-disorder transition (below the
ODT temperature), for asymmetric copolymers, it is possible that the glass
transition precedes the ordering transition.Comment: An error corrected in the referenc
- …