Selective segregation of surfactant molecules to one domain type of block copolymers in the melt leads to the formation of hierarchical structures. Here we show that combining an organometallic, Pd−pincer-based surfactant (Pd−SCS) with a polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer leads to hierarchical structures due to weak stacking interactions between the Pd−pincer complex and the pyridine units. These structures feature a different morphological behavior than analogous systems, including the formation of perforated lamellae (PL) over a wide range of surfactant filling fractions and a distinct swelling anisotropy behavior of the copolymer chains by the added surfactant molecules. The results suggest that the strength of interaction between the surfactant and the compatible block influences the degree of segregation between the blocks. This study lays the foundations for the creation of organized, hierarchical arrays of inorganic nanoclusters that are periodic on two different length scales.
■ INTRODUCTIONBlock copolymers (BCPs) phase separate into a variety of useful morphologies with periodicities on the scale of tens of nanometers. For this reason, BCPs can serve, for example, as nanoreactors for nanoparticle synthesis 1−11 and as templates for the arrangement of nanoparticles, 12−43 among other applications. 44−47 The classical morphologies of diblock copolymers are alternating lamellae, cylinders and spheres of the minority block embedded in a matrix of the majority block. As the copolymer composition varies from symmetric, the phase is dictated by two competing thermodynamic factors: the tendency to minimize interfacial area between the domains, which favors the formation of curved interfaces with constant mean curvature, 48 and avoiding chain packing frustration, which prefers the creation of uniform thickness domains (i.e., where all chains are stretched to the same extent). 49−52 At the intermediate segregation regime (15 < χN < 60), this leads to the formation of additional phases with complex morphologies between the lamellar and cylindrical phases, which offer lower curvatures than that of cylinders: the stable gyroid phase, the long-lived, metastable perforated lamellae (PL) phase (i.e., parallel layers interconnected by cylindrical channels that perforate the minority phase of separate layers), 53−61 and the thermodynamically unstable double diamond phase. 49−52 Unlike the classical phases, these complex phases cannot achieve minimal surface area and avoid packing frustration at the same time. Hence, their interfaces deviate from constant mean curvature; the extent of the deviation was found to correlate with stability. 49−52 Because of the packing frustration, the metastable PL morphology is accessible mainly under shearing 53,[55][56][57][58]62,63 or under the influence of surface fields (i.e., near the substrate). 64 Selective inclusion of filler molecules (either small molecules 65,66 or homopolymers corresponding to one of the blocks 48,60,67−74 ) can relieve pac...