Electronic Nanodevices from Liquid Crystals

Student thesis: Doctoral ThesisPhD

Abstract

Phytantriol is a well-known amphiphilic lipid that self-assembles into a range of mesophases, including the bicontinuous cubic phase, and has been used in cosmetics products and drug delivery [1, 2]. The phases which are stable in excess water can be exploited as a template for generating hard nano-materials.In this research, phytantriol mesophases were formed using a solvent penetration experiment, which is a dry lipid in contact with water. The formation of mesophases was confirmed by cross-polarized light microscopy (CPLM)and small-angle X-ray scattering (SAXS) techniques. SAXS measurements allowed the optically inactive phases gyroid and diamond inverse bicontinuous cubic phases QGII and QDII to be distinguished. The dynamic hydration of phytantriol mesophases as a function of time was addressed by CPLM and SAXS techniques.CPLM was exploited to track the position of boundaries between optically active and inactive phases as a function of time and temperature. Specifically, boundaries representing lyotropic transitions to and from the lamellar phase Lα (transitions: LII to Lα, and Lα to QGII ) were analysed, and their displacements evolved as √t, reflecting diffusive transport of water. This enables us to quantify the propagation of each boundary by a diffusivity constant D using a simple diffusive model [3]. The experiments were performed between 18 to 55°C. Surprisingly, the diffusivity drops at temperatures 35°C and above, and these findings are discussed. Using SAXS, the dynamic hydration was studied as a function of time at room temperature, and the lattice parameters of the QGII and QDII mesophases were obtained as a function of time.A simple method to produce oriented phases of phytantriol is demonstrated.This was achieved by two procedures: (a) a phytantriol droplet was placed between glass slides and hydrated at temperatures 25, 30 and 35°C, (b) phytantriol,that was filled in a tube, was hydrated for a long duration at room temperature.In procedure (a), the CPLM technique was used to confirm the alignment of the optically active phase, Lα, which appeared as a dark CPLM image froma top microscope. In contrast, a bright image appeared when looking at the samplefrom an angle 45º from the top microscope. The dark CPLM images indicatethe alignment of the lamellar sheet with glass slides. In procedure (b), oriented mesophases of the optically active and inactive mesophases (Lα, QGII and QDII ) were confirmed by SAXS, where diffraction spots were observed instead ofdiffraction rings, indicating oriented mesophases. The oriented phases dependedon the time of hydration, and the timescale of hydration of each phase to obtainan oriented phase varied: three days for the Lα phase, a month for the QGII phaseand three months for the QDII phase.A novel approach for fabricating electronic nanodevices was investigated.The QDII phase from phytantriol was used as a template to fabricate nanomaterials via the electrodeposition process. In the electrodeposition process, a workingelectrode is used to deposit a target material on its surface. Here, instead of oneworking electrode, two working electrodes separated by a sub-millimetre sizedgap were used, and the material was deposited across the gap. This approachproduces nanomaterials with its electrodes allowing characterisation of the nanomaterials electrically, which provides technological advantages for future devices.We started testing the approach with platinum (Pt), as it has been successfullydeposited through the phytantriol template [4]. The production of material acrossthe gap was achieved with one sample among 15 samples. The formation of thePt-nanostructure across the gap was confirmed by measuring the resistance by amultimeter, which found to be 180 Ω. In contrast, the resistance of the rest of thesamples found to be greater than ≈ 1 M Ω. SAXS measurements revealed thatthe nanostructured materials produced through the QDII phase exhibits single diamond Fd3m symmetry, which is significantly different from the double diamond(QDII ) template used with Pn3m symmetry. It has been suggested that this difference in structural symmetry indicates that the deposition occurs on one of thewater channels of the template [4]. Scanning Electron Microscopy (SEM) images of the deposited nanostructured material showed cauliflower patterns, suggestingdiffusion-limited aggregation (DLA) growth [5].
Date of Award24 Mar 2021
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorKei Takashina (Supervisor), Adam Squires (Supervisor), Frank Marken (Supervisor) & Karen Edler (Supervisor)

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