The Gyroid: A New Equilibrium Morphology in Weakly Segregated Diblock Copolymers

Abstract

We report the identification of a new equilibrium microdomain morphology in an intermediate to weakly segregated diblock copolymer melt. A polystyrene-polyisoprene (SI) diblock copolymer consisting of 37 wt % styrene and of total Afw = 27 400 was observed to transform from the lamellar morphology (in equilibrium at low annealing temperatures) to a new morphology at annealing temperatures approximately 50 °C below the order-disorder transition (ODT). The transformation was observed to be thermoreversible. Investigation of the new morphology via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) revealed the new structure to have remarkable three-dimensional long-range order, to belong to the cubic space group Ia3d, and to possess a bicontinuous cubic microstructure. From computer simulations of model structures and comparison with microscopy results, we propose models for the new morphology based on the triply periodic G minimal surface (gyroid) discovered by Schoen;1 similar morphologies have been observed in a variety of microphase-separated surfactant-water systems. Blends of this diblock with various short-chain homopolymers were used to investigate the compositional extent of the region of IaZd stability on the phase diagram; the results indicate that the Ia3d phase is stable over a wide range of minority component volume fractions.ogy, the ordered bicontinuous double diamond (OBDD), in a strongly segregated melt;3 the new structure has since been observed in a variety of block copolymer systems.4-6Recently, Olmsted and Milner7 have developed methods for calculating the free energy of bicontinuous morphologies in the strong segregation limit. A variety of new structures not predicted by the early theories have been observed in the weak segregation regime, including the lamellar-catenoid,8'9 hexagonally modulated lamellae, and hexagonally packed lamellae.10 As part of a study on block copolymer thermal behavior, Gobran11 observed an unusual microphase-separated morphology in a polystyrene-polyisoprene (SI) diblock copolymer. After casting from toluene, the sample formed a lamellar phase; upon heating to temperatures above 120

Biomimetic block copolymer particles with gated nanopores and ultrahigh protein sorption capacity

“…The transition from lamella to gyroid phases was observed for the first time in self-assembled BCP nanoporous particles. This transition has been mostly previously observed for diblock copolymers in melts [32][33][34] . (3) Gyroid to Schwarz P structure transition (Fig.…”

A Re-Evaluation of the Morphology of a Bicontinuous Block Copolymer−Ceramic Material

“…38 Consequently, for pure block copolymers only 3-fold networks have been predicted [39][40][41] or observed. 5,[42][43][44] Chain stretching in a 4-fold or 6-fold node can be reduced by the presence of a second component that occupies the center of the node. For example, adding homopolymer to the minority phase of a diblock copolymer is predicted to stabilize the double diamond morphology.…”

Hierarchically Ordered Montmorillonite Block Copolymer Brushes

“…46,47 Initially the gyroid phase was only investigated at substantial molecular weights (100-200 kg/mol) where its stability could not be confirmed. Lodge et al recognized the slow dynamics of large chain BCP equilibrium, so to verify that the gyroid phase was not a meta-stable state they synthesized short chain BCP's (10-13 kg/mol) with very large segregation values.…”