Identification of Some New Triply Periodic Mesophases from Molten Block Copolymers.

Junhan Cho

doi:10.3390/polym11061081

Abstract

Using field-theoretic simulations based on a self-consistent field theory (SCFT) with or without finite compressibility, nanoscale mesophase formation in molten linear AB and ABC block copolymers is investigated in search of candidates for new and useful nanomaterials. At selected compositions and segregation strengths, the copolymers are shown to evolve into some new nanostructures with either unusual crystal symmetry or a peculiar morphology. There exists a holey layered morphology with Im3 symmetry, which lacks one mirror reflection compared with Im3m symmetry. Also, a peculiar cubic bicontinuous morphology, whose channels are connected with tetrapod units, is found to have Pn3m symmetry. It is shown that there is another network morphology with tripod connections, which reveals P432 symmetry. The optimized free energies of these new mesophases and their relative stability are discussed in comparison with those of double gyroids and double diamonds.

Highlights

Soft matters or complex fluids have drawn tremendous attention from condensed matter researchers because of some useful features such as complexity in their various forms or structures and flexibility in changing their physical properties through simple chemical modification [1]
It was revealed that C2mm cylinders are competing with lamellae, hexagonal P6/mm cylinders, Im3m body-centered cubic (BCC) spheres, and the mesophase of lower P23 symmetry [16]
Taking linear AB or ABC block copolymers as a model system, whose j-blocks are Nj -mers with N being the overall size of the chosen copolymers, field-theoretic simulations based on Edwards Gaussian random-walk approach are performed for our purposes

Summary

Introduction

Soft matters or complex fluids have drawn tremendous attention from condensed matter researchers because of some useful features such as complexity in their various forms or structures and flexibility in changing their physical properties through simple chemical modification [1]. The simplest molten AB diblock copolymers have exhibited 1-dimensional lamellar layers, 2-dimensional hexagonal cylinders with P6/mm, body-centered cubic (BCC) spheres with Im3m symmetry, double gyroids belonging to Ia3d space group, and an orthorhombic Fddd network morphology [9,10,11]. There is a double diamond morphology belonging to Pn3m group as a metastable one [12]. There are the core-shell-type, perforated or decorated versions of the morphologies just mentioned [9,13,14,15,17], alternating I41 32 single gyroids [9,15,18], the centered rectangular C2mm cylinders [16], and a cubic bicontinuous P23 phase [16]. The morphologies reported so far are still limited for block copolymer systems

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