Grain shapes and growth kinetics during self‐assembly of block copolymers

Abstract

ABSTRACT:With block copolymer equilibrium phase behavior becoming increasingly better understood, a more detailed description of ordering kinetics is feasible. This article highlights recent experimental observations that provide new insight into ordering kinetics and grain structures when a block copolymer liquid is first cooled below the order-disorder transition. Measurements have been made on several concentrated poly(styreneb-isoprene) solutions, with concentrations and temperatures adjusted to access the cylinder, lamellar, and gyroid phases. A diverse set of grain types were observed using polarized optical microscopy (POM). Cylinder grains were either oblate ellipsoids or spherulites, whereas the lamellar phase formed prolate ellipsoidal grains, twinned ellipsoidal grains, twofold twinned grains, and spherulites. The orientation of the cylinders and lamellae within the grains were unambiguously identified. The shapes of the ellipsoidal and twinned grains were dictated by the relative interfacial tensions of the available growth surfaces with respect to the disordered state. Grain growth front velocities were also quantified before grain impingement, and consistent values were obtained among different grains for a given sample and quench temperature. The experimental growth velocities were compared to an expression derived by Goveas and Milner. There was good agreement in terms of the temperature dependence, and the absolute magnitude was predicted with some success. The rates of nucleation and overall conversion to the ordered phase were also determined.

Cooperative Assembly of Block Copolymers with Deformable Interfaces: Toward Nanostructured Particles

“…Similarly, non-spherical structures in small domain of multi-component polymer film were also observed in previous reports, in which embedded grains of lamellar or cylindrical morphology were produced by selfassembly at the specific temperature due to the different interfacial tension between block copolymer domain and polymer matrix. [36,37] In summary, we have demonstrated a novel and simple route for synthesizing functional particles with unique nanostructures via block copolymer assembly in emulsion droplets. In the range of D/L 0 from 4 to 30, their shapes and internal nanostructures depend on the commensurability of the block copolymer and the interfacial affinities of the constituent blocks, which were controlled by using a mixture surfactant of two types of amphiphilic block copolymers.…”

Beyond native block copolymer morphologies

“…83,84 However, a polygrain structure is observed experimentally unless special measures taken to promote long-range order. The energetic degeneracy of grain orientations, nucleation and propagation of domain order from sample boundaries, 85,86 and the statistical distribution of grain sizes and shapes 43,[87][88][89][90] reflect the significant importance of initial ordering pathways. Moreover, once microphase separation has taken place, both domain and grain boundaries themselves create large energy barriers to further chain rearrangement, 90,91 inhibiting defect annihilation and leading to kinetically trapped states.…”

Implications of Grain Size Variation in Magnetic Field Alignment of Block Copolymer Blends

“…[20]. Studies of grain growth kinetics have been conducted by Balsara et al [21][22][23] and Lodge et al [24,25]. They observed growth velocities which scaled with the undercooling in good agreement with ordered front propagation velocities predicted by the theory of Goveas and Milner [26].…”