Hierarchical Nanostructures of Bent-Core Molecules Blended with Poly(styrene-b-4-vinylpyridine) Block Copolymer

Abstract

We report the phase structures observed in blends of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) and a bent-core molecule 1-[4′-(3′′,4′′,5′′-tridecyloxybenzoyloxy)phenyleneoxycarbonyl]-3-[(4′-hydroxyphenyl)oxycarbonyl]benzene (BP). Hydrogen bonding between the terminal -OH group of BP and pyridine of P4VP led to the formation of P4VP(BP) n complex, which exhibited liquid crystalline (LC) order. This LC ordering, combined with microphase separation of the BCP, led to the formation of hierarchical nanostructures. The phase structures of the blend samples were investigated as a function of the concentration of BP using small-angle and wide-angle X-ray scattering and transmission electron microscopy techniques. By increasing the BP content, BCP phase morphology transformed from lamellae to cylinders. In the two cases investigated, the P4VP/BP complex formed a bilayer smectic A LC structure within the BCP domains, and these layered structures were oriented perpendicular to the BCP interface. A detailed structural and morphological study will be reported. IntroductionHierarchical nanostructures, usually spanning from the molecular scale (sub-nanometers) to hundreds of nanometers, are of great technological importance. Block copolymers (BCPs) provide one of the most straightforward templates to achieve hierarchical nanostrucutres. 1 BCP microphase separation could lead to the formation of a variety of structures such as lamellae, cylinders, gyroid, and spheres. 2 The length scale of these phase separated structures is ∼10-50 nm. Amorphous BCP (coilcoil) phase structures have been extensively investigated. 2,3 Tuning the chemical structure of one or several segments of the BCP leads to the possibility of forming a secondary structural order within the BCP domains. To this end, a few types of BCP systems have been proposed, including crystalline-amorphous (or crystalline-crystalline) BCPs 4-8 and liquid crystalline (LC) BCPs. 9-20 In the first case, polymer chains crystallize in the confined (soft or hard confinement) space that is formed by the BCP microphase separation. Structural hierarchy can be achieved due to the ordered structure formation at two different length scales as a result of BCP microphase separation (10-50 nm) and the crystalline structure formation (1-10 nm). In the second case, LC or LC polymers are used as one BCP block. LCs form ordered structures on the 1-10 nm length scale. Thus, LC BCPs represent a natural hierarchical-structure-forming system. The structural flexibility of LC also enables incorporating functionalities into BCP microdomains. A number of LC BCPs have been investigated. Depending on the LC molecular architecture, LC BCPs can be divided into side-chain LC-BCPs, 9,[12][13][14]20 main-chain LC-BCP, 15,16 and BCPs formed by mesogen-

Chemical Structures, Mesogenic Properties, and Synthesis of Liquid Crystals with Bent‐Core Structures

“…The second approach has been used to attach different amounts of bent-core units to a poly(styrene-b-4-vinylpyridine) block copolymer (PS 115 -b-P4VP 112 ). [110] On increasing the amount of bent-core units the mesophase morphology changed from lamellae to cylinders, while in both cases the P4VP/bent-core complex retained a bilayer SmA phase within the liquid crystalline domains. Copolymers bearing both hydrogen-bonded and covalently bonded units have also been reported.…”

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