The equilibrium phase behavior of 43 linear poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock copolymer melts, with molecular weights that place these materials near the order-disorder transition, is reported. Ordered phase morphologies were characterized using small-angle X-ray scattering, transmission electron microscopy, dynamic mechanical spectroscopy, and static birefringence measurements. Interpretation of these results was aided by a modeling technique that facilitates resolution of reciprocal and real-space experimental data, leading to definitive three-dimensional morphological structures. Three distinct multiply continuous network morphologies are identified across a range of compositions between 0.1 e f O e 0.3, situated between two-domain and three-domain lamellae, where fO represents the volume fraction of O blocks. Two cubic network phases, Q 230 (core-shell double gyroid, Ia3 hd space group symmetry) and Q 214 (alternating gyroid, I4132 space group symmetry), flank an orthorhombic network phase, denoted O 70 (Fddd space group symmetry), which is positioned around the isopleth composition fS ≈ fI. These results provide a powerful strategy for designing network phases in linear ABC triblock copolymers when χAB ≈ χBC < χAC, where χ represents the Flory-Huggins interaction parameter.

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Monolayer arrays of polystyrene−poly(2-vinylpyridine) diblock copolymer cylinders with excellent orientational order and a very low density of dislocations are prepared by cooling slowly from above the bulk order−disorder temperature (ODT) ∼212 °C within silicon oxide channels one cylinder spacing a in depth and 2 μm in width. The translational order of this array, however, is short range with a correlation length of ∼12a. If such an array is heated to a temperature above the glass transition temperature of the block copolymer (100 °C) but well below the ODT, a finite density of thermally generated dislocations is observed, which leads to a decrease in the translational correlation length and an appearance of quasi-long-range orientational order such that the orientational correlation function g 2(r) decays as a power law, i.e., g 2(r) ≈ (r/a)-η 2 ( T ). The state of disorder at any given temperature appears to be an equilibrium one since cylinder arrays with similar dislocation densities and correlation functions can be obtained either by heating from the well-ordered state or by cooling slowly directly to the final temperature and holding at that temperature for a sufficient time. Above a temperature of 195 °C, the orientational order becomes short range (g 2(r) decaying exponentially with r), and a large density of disclinations is observed in addition to the dislocations. The cylinder array becomes isotropic above this temperature, which is ∼20 °C below the bulk ODT. These results are in qualitative agreement with the theory of Toner and Nelson which describes the thermal generation of disorder and ultimate melting of a two-dimensional smectic.

We investigate the effect of surface energy and chain architecture on the orientation of microdomains in relatively thick films (600−800 nm) of lamellar and cylindrical block copolymers of poly(cyclohexylethylene) (C) and poly(ethylene) (E). The E block has 26 ethyl branches per 1000 backbone carbon atoms. Melt surface energies of the C and E blocks are 22.3 and 20.9 mJ/m2, respectively. Grazing-incidence small-angle X-ray scattering (GISAXS), scanning force microscopy (SFM), and cross-sectional transmission electron microscopy (TEM) show that cylindrical and lamellar CEC triblock copolymers orient their microdomains normal to the surface throughout the film thickness. However, a lamellar CE diblock copolymer prefers a parallel orientation of the lamellae relative to the surface with an E surface layer. Moreover, a cylindrical CEBC triblock copolymer where the EB block has 125 ethyl branches per 1000 backbone carbon atoms leads to EB cylinder domains that always orient parallel to the surface. In this case the lower surface energy EB block dominates the surface. Calculations using self-consistent-field theory allow us to interpret the experimental results in terms of the entropic cost of forming a wetting layer comprised entirely of looping blocks. Thus, in triblock copolymers, parallel orientations are only stabilized when the midblock has the lower surface energy, and the difference in surface energies of the two blocks is large enough to compensate for this conformational penalty, which is absent in diblock copolymers.