Title

Directed Assembly of Anisotropic Inorganic Nanomaterials Using Self-Assembled Soft Mesophases

Date of Award

Fall 10-1-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical and Environmental Engineering (ENAS)

First Advisor

Osuji, Chineum

Abstract

Anisotropic nanomaterials have propelled new technologies and materials in diverse fields ranging from electronics and photonics to catalysis and biomedicine. While initially nanomaterials’ utilization in application focused on their unique properties which are a direct result of their confinement to the nanoscale, such as size-dependent fluorescence or bandgap, more recently, additional properties and enhanced functionality are sought after by controlling the spatial organization and orientation of nanomaterials. Such advanced functionality can be enabled by controlling the juxtaposition of nanomaterials, eliciting an array-geometry-dependent effect from multiple individual nanostructures collectively interacting with one another, as is evident in plasmonic metamaterials. Another possibility for complex functionality can be achieved by altering the orientation of anisotropic nanomaterials, achieving direction-selective properties, such as polarized emission or direction-selective conductivity in 1D nanorods or 2D nanosheets. In order to fully realize the potential in nanomaterials, as presented above, reliable methodologies are needed to achieve both spatial and orientational control of anisotropic nanomaterials. A possible handle to do so is their embedment in a soft-matter matrix. Soft materials are inexpensive, easy to modify and can be made compatible with multiple inorganic nanomaterials. Some, such as block-copolymers (BCPs), create arrays or ordered features on multiple length-scales, from just a few- to hundreds- of nanometers. Others, such as liquid crystals (LCs), are stimuli responsive and can drive the alignment and reorientation of embedded 1D nanorods or 2D sheets. This dissertation explores two main themes to achieve positional and orientational control over anisotropic nanomaterials, exemplified by two model systems: 1D ZnO nanorods and 2D MoS2 nanosheets. First, we explore BCP templated Au covered ZnO nanorod arrays, and their emerging optical properties dictated by the BCP template, and realized as a platform for surface enhanced Raman scattering (SERS) or direct plasmonic sensing. In addition, other optical effects elicited by such a platform are explored, including it being an ‘epsilon-near-zero’ (ENZ) material, or ones resulting from the BCP template being a disordered hyperuniform (DH) material. The second part of this dissertation switches gears and discusses orientation control of 2D MoS2 nanosheets in LC matrices. 2D-MoS2 was dispersed for the first time in thermotropic LCs and subsequently magnetically aligned, revealing anisotropic optical effects. This result opens up a pathway for the incorporation of 2D-MoS2 into LC-based systems and the study of MoS2’s anisotropic properties. Finally, we explore 2D-MoS2 dispersed into a lyotropic LC phase, and examines the transport properties of planarly stacked MoS2 in membrane applications. Overall, this dissertation introduces new techniques to enable positional and orientational control over anisotropic nanomaterials by embedding them in soft-matter matrices, and by doing so enables new functional properties which can be utilized in advanced applications.

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