Since the discovery of the Frank−Kasper (FK) phase a decade ago, single-component block copolymer systems have offered unique opportunities to explore the structural and phase-transition properties of topologically close-packed FK phases composed of point-particle motifs. Here, we present the formation of complex low-symmetry phases and their thermodynamic stability using high-χ and high-ε linear diblock copolymers, where χ and ε are the Flory−Huggins interaction parameter and conformational asymmetry between the two blocks, respectively. A series of polydimethylsiloxane-b-poly(2,2,2-trifluoroethyl acrylate) (PDMS-b-PTFEA) copolymers are prepared by tuning the volume fraction (f PTFEA ) of a minor PTFEA block. The packing structures of PDMS-b-PTFEAs are mapped in the space of temperature versus f PTFEA using X-ray scattering measurements. In addition to the packing structures reported earlier, we identify another A15 phase at higher f PTFEA close to a hexagonally packed cylinder (HEX) phase and establish the phase sequence of HEX−A15−σ−C14−BCC with decreasing f PTFEA . Theoretical calculation of relative freeenergy densities confirms the experimental phase sequence of the composition-dependent sphere-packing structures. Interestingly, the domain sizes of three-dimensional (3D) sphere-packing structures are nearly temperature-invariant compared to that of a twodimensional HEX structure, and we attribute this dimensional stability to the strong enthalpic effects in the formation of 3D packing structures and the geometrical characteristics of spherical domains. Our results demonstrate that the interaction parameter χ, together with the known role of conformational asymmetry ε, serves as the primary thermodynamic parameter for selecting and stabilizing various low-symmetry packing structures in sphere-forming linear diblock copolymer systems.

We present material substitutions and optical characterization of block copolymer (BCP)-templated gyroid structures that are obtained from a volume-asymmetric polystyrene-b-poly­(methyl methacrylate) (PS-b-PMMA). In addition to the structural analyses reported earlier, we elucidate the optical responses to the nonaffine gyroid planes, in which the PMMA channels are complexed with Al2O3 by sequential infiltration synthesis and the organic components are further eliminated to produce an inorganic air–Al2O3 gyroid film. Grazing-incidence small-angle X-ray scattering measurements show that three-dimensional gyroid lattices are retained in both in-plane and out-of-plane directions through these material substitution processes. Our BCP-templated gyroid films respond to the middle UV wavelength from 200 to 300 nm, and peculiar optical reflectance peaks correlate with the unforbidden {110} diffraction spots. Together with the red- and blue-shifts of the reflectance peaks by the component substitutions, the air–Al2O3 gyroid structure reveals the high-amplitude spectrum due to the large refractive-index difference between channel and matrix.

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Upon exposure to UV light (120 mW/cm 2 , λ = 365 nm), a trans−cis isomerization occurs in a cylinder-forming, azobenzene-containing block copolymer of polydimethylsiloxane-b-poly((4(phenyldiazenyl)phenoxy)hexyl acrylate) (PDMS-b-PPHA) that enables the generation of monodomains of healable, long-range ordered arrays of nanoscopic domains over macroscopic distances. The trans−cis isomerization gives rise to a significant increase in the dielectric constant (from 6.52 to 19.8 at 100 Hz, photodielectric behavior) and a dramatic decrease in the T g (from 54 to 1 °C, photoplastic behavior) of the PPHA block. By combining these characteristics with an in-plane electric field, macroscopic monodomains of near-perfectly aligned cylindrical microdomains are achieved at low temperatures, and a damage repair is clearly uncovered, where the 300 nm wide scratches can be completely healed at 40 °C, leaving a smooth, uniformly thick film where the continuity and orientation of the aligned microdomains are restored. Subsequent exposure to visible light causes a cis−trans isomerization, increasing the matrix T g to 54 °C, producing highly oriented and aligned PDMS cylindrical microdomains in a PPHA matrix.