We have considered the stability of lamellar, cylindrical, and spherical morphologies of a ternary melt system of A homopolymers, B homopolymers, and AB diblock copolymers in the weak segregation limit. We have extended the mean field analysis by including composition fluctuations in a one-loop self-consistent approximation. We find rich binary and ternary phase diagrams with multiphase equilibria which are highly sensitive to parameter variations. The order-disorder transition points (N) ODT are shifted upward relative to the mean field theory ͑MFT͒ transition points and all second order MFT microphase separation transitions are changed to first order. Composition fluctuations modify the MFT microphase separation and macrophase separations differently. As a consequence, the MFT Lifshitz critical point is destroyed. This implies that observation of the scattering function by itelf does not suffice to infer the existence of Lifshitz critical points. We demonstrate this in a quantitative comparison between our results and experiments.

We have studied thermal composition fluctuations of a ternary symmetric homopolymer/diblock copolymer system of PEE/PDMS/PEE-PDMS ͓PEE and PDMS being poly͑ethyl ethylene͒ and poly͑dimethyl siloxane͒, respectively͔ in its disordered state with small angle neutron scattering for concentration ⌽ of diblocks up to 15%. The phase diagram shows three characteristic regimes; ͑1͒ below the Lifshitz concentration ⌽ LL Х9%; ͑2͒ in the very near vicinity of the Lifshitz concentration; and ͑3͒ above ⌽ LL . In the regime ͑1͒ of low diblock content the maximum neutron intensity is obtained at Qϭ0 and phase separation into macroscopic large domains is observed at low temperatures. With increasing diblock content the thermal fluctuations indicate a crossover from 3d-Ising to isotropic Lifshitz critical behavior with critical exponents of the susceptibility ␥ ϭ(1.62Ϯ0.01) and correlation length ϭ(0.99Ϯ0.04) appreciably larger than in the 3d-Ising case. In the structure factor this crossover is accompanied by a strong reduction of the Q 2 term leading to the dominance of the Q 4 term; the restoring force of the thermal fluctuations is strongly reduced as the Q 2 term is proportional to the surface energy. Near the Lifshitz critical temperature a further crossover was observed leading to the appreciably larger critical exponents ␥ϭ(2.44Ϯ0.08) and ϭ(1.22Ϯ0.08) and a stabilization of the disordered regime visible through a decrease of the phase boundary by nearly 10 K. This crossover is interpreted by the formation of fluctuation induced inhomogeneous diblock distribution at the interface of the thermal fluctuations. ͑2͒ In the intermediate regime between 9% and 12% diblock content the Lifshitz line was crossed twice upon increasing the temperature from low to high temperatures; at low and high temperatures the structure factor S(Q) shows diblock character ͑maximum of S(Q) at Q 0͒ while at intermediate temperature blendlike character ͑maximum of S(Q) at Qϭ0͒. At low temperatures a transition to a bicontinuous microemulsion phase is proposed. ͑3͒ At diblock content of 15% a weak order-disorder transition was observed. The data in the Lifshitz critical range and larger than the Lifshitz line could be interpreted by a recently developed theory of Kielhorn and Muthukumar who considered the effect of thermal fluctuations in ternary homopolymer/diblock copolymer samples and from which the Flory-Huggins parameter could be evaluated.

Crystallization kinetics in a homogeneous copolymer of ethene and 1-octene with appended long chain branches has been investigated in real time by means of time-resolved light scattering under H V (cross-polarized) and V V (parallel-polarized) optical alignments using a CCD camera system, simultaneous small angle-X-ray and wide angle X-ray measurements using synchrotron radiation and differential scanning calorimetry (DSC). The data show that in the case of crystallization at large supercooling, a significant fraction of the crystallinity develops after the spherulites have become volume filling. The fraction of crystallinity that develops after primary crystallization increases with crystallization temperature. This opens up a challenge to explore the extent to which this behavior is universal in other crystallizable ethylene copolymers as well.

The effect of a patterned surface on the phase separation kinetics of a thin polymer film has been investigated using the Cahn–Hilliard–Cook model in three dimensions with the addition of a short range surface potential. We have observed pattern-induced spinodal waves perpendicular to the surface creating “checkerboard”-like composition fluctuations for a wide range of patterns used in this study. The number of such layers strongly depends on the magnitude of the thermal noise. For sufficiently thin films, where the film thickness is smaller than the spinodal wavelength, spinodal decomposition can be arrested if the surface potential and the characteristic size of the pattern are chosen accordingly, enabling the transfer of surface patterns to the film material. The kinetic pathways through which the equilibrium states are reached delicately depend on the particular pattern, its size, and the film thickness.