Multistep hierarchical self-assembly of chiral nanopore arrays

Abstract

A series of simple hierarchical self-assembly steps achieve selforganization from the centimeter to the subnanometer-length scales in the form of square-centimeter arrays of linear nanopores, each one having a single chiral helical nanofilament of large internal surface area and interfacial interactions based on chiral crystalline molecular arrangements.aluminum oxide | liquid crystal | chirality | nanoconfinement | bent-core C ontrolled nanoscale self-assembly (SA) is one of the most important subjects in chemistry, physics, and materials science and technology. Currently, soft matter systems such as block copolymers (BCPs), biomaterials, colloids, supramolecules, and liquid crystals (LCs) are widely explored as building blocks for self-assembly because of their diverse themes of nanostructural organization (1-3). Of particular interest in this effort are nanostructures that are hierarchically SA over a broad range of length scales, because these both advance basic SA science and promise practical uses in a broad array of materials applications (4). Here we present a composite nanomaterial system based on hierarchically template-assisted self-assembly (TSA) wherein, in absence of any predisposed pattern, a series of hierarchical steps spontaneously produces, over square centimeter areas, nanopore arrays with large internal surface areas of chiral crystal interfaces.This system is based on the marriage of two robust SA scenarios: (i) the formation of films of Al 2 O 3 populated with arrays of nanometer-scale pores by the anodic oxidation of aluminum, combined with (ii) the helical crystalline nanofilament formation of the B4 phase of bent-core mesogenic molecules (4). Anodic aluminum oxide (AAO) films are one of the most widely used nanoporous media, spontaneously forming uniform cylindrical pores, 5-450 nm in diameter and many microns long, with a high areal density (∼10 9 pores/cm 2 ) and low polydispersity in size (Materials and Methods) (5-7). Such AAO pores have been used as templates for the organization of soft matter nanostructures, such as BCP lamellae, cylinders, and other structures (8-10). In these and other AAO-based self-assembled nanosystems, fabrication extends down to the mesoscopic-length scales, the interfaces produced being fluid or amorphous solid structures. Approaches for generating intrapore interfaces with the controlled atom-scale organization required for many applications, for example, the electrodeposition of crystals (11,12), generally plug the pores. We sought to explore systems that combined robust crystalline ordering with a definitive crystal morphology that would enable the fabrication by SA of clear channels with crystal interfaces running through the length of the AAO pores. The helical nanofilaments reported here represent a striking realization of this goal, promising a host of chemical and photonic applications, for example in nonlinear optics (13)(14)(15).

Physico-chemical confinement of helical nanofilaments

“…S4 and S5). 16 Our analysis of optical images also supports the hypothesis that the columnar domains were simultaneously transformed to continuous smectic layered structures upon cooling (Fig. S4, ESI †).…”

“…16 A fixed channel diameter, such as 60 nm, was used here (Fig. 16 A fixed channel diameter, such as 60 nm, was used here (Fig.…”

“…[13][14][15] Here, nanoconfinement was used to form individually controlled, isolated HNFs to minimise the complexity of HNFs, 16 a strategy that has previously been used to control the orientation of nanostructures of various types of soft matter. [13][14][15] Here, nanoconfinement was used to form individually controlled, isolated HNFs to minimise the complexity of HNFs, 16 a strategy that has previously been used to control the orientation of nanostructures of various types of soft matter.…”

Synergistic assembly of nanoparticles in smectic liquid crystals

“…31 The scattering intensity profile, I(q), gives orientation information and d-spacing on both interlayer (small-angle region) and intralayer molecular arrangement (wide-angle region). 31 The scattering intensity profile, I(q), gives orientation information and d-spacing on both interlayer (small-angle region) and intralayer molecular arrangement (wide-angle region).…”

“…31 The size of the focused beam was B70 (V) Â 450 (H) mm 2 , and the energy was 11.08 keV. 31 The size of the focused beam was B70 (V) Â 450 (H) mm 2 , and the energy was 11.08 keV.…”