Iw. Hamley et al., Lamellar-to-gyroid transition in a poly(oxyethylene)-poly(oxybutylene) diblock copolymer melt, PCCP PHYS C, 1(9), 1999, pp. 2097-2101
The transition from the lamellar (lam) to the gyroid (gyr) phase in the mel
t of a poly(oxyethylene)-poly(oxybutylene) (EB) diblock copolymer was shown
to proceed via an intermediate perforated lamellar (pl) structure. The tra
nsition was studied starting from a shear-oriented lamellar phase using syn
chrotron small-angle X-ray scattering (SAXS) with simultaneous rheology. Th
e transition occurred with a continuous variation of q*, the position of th
e principal peak position, although the slope of q* as a function of temper
ature increased in the region of the transition (pl state). In the intermed
iate state, the variation of q* with T was shown to be much stronger than t
hat of the radius of gyration of EB diblocks. It was observed that the gyr
phase developed from an oriented pi phase precursor as an isotropic distrib
ution of grains. This indicates that growth of this structure did not occur
epitaxially on a macroscopic scale. Finally, density images corresponding
to lam, hexagonal perforated lamellar and gyr structures were generated usi
ng a single wavenumber approximation, based on the SAXS evidence that diffr
action patterns are dominated by the first Fourier component.