Synthesis and characterization of gold nanoparticle composites with side chain liquid crystals

Amos, Olusegun

Abstract

The properties of specifically designed nanocomposites are currently of high interest to scientists as they are different to those of materials in bulk. Of special interest are nanocomposites made up of gold nanoparticles and liquid crystalline materials. Since most applications of metal nanoparticles are based on their assemblies, controlling their self–assembly opens the potential to synergistic property combination of these composites, most actively discussed are currently those of optical metamaterials.

Here the results of the investigation of gold nanoparticle (AuNP)- and gold nanorod (AuNR)- side-chain liquid crystalline polymer chains (SCLCPs) are presented. The synthesis of these nanoystems were explored systematically. The preparation of SCLCPs, either by grafting to the NPs or by polymerisation from the preparation of an Au-NP macroinitiator were explored. The mode of polymerisation either free radical polymerisation or atom transfer radical polymerisation (ATRP) was varied.

Firstly, the AuNPs and AuNRs were synthesised and fully characterised. The sizes of AuNPs investigated were 2 nm and 3 nm while the average dimension of AuNRs investigated was 26 nm x 8 nm, with an aspect ratio of 3. These nano species were either functionalized directly with the LC thiol and/or functionalized with initiator and used as a macroinitiator in the polymerisation of different monomers.

The mesogenic compound used in the investigation was 4ˈ-undecycloxybiphenyl-4-yl 4-octyloxy-2-(pent-4-en-1-yloxy) benzoate. The alkene end of the mesogen was converted to polymerisable end group through a range of chemical reactions. The polymerisation of these polymers were investigated first by free radical polymerisation, before been polymerised using AuNP/AuNR-initiator modified to act as macroinitiators to obtain the targeted composites.

For polymer/nano composites, the optimum structural control of the composite was achieved by preassembling the inorganic nanoparticles with the organic polymer. With accurate compositional specification of the final composite, different methods were used for the synthesis which includes grafting of a polymer chain to the surface through a covalently linked monomer, or grafting polymer chains from polymerisation initiators-modified surfaces.

Based on these points, liquid crystalline polymeric composites were synthesised using both ‘grafting from’ and ‘grafting to’ methods. Disulfide functional initiator was prepared followed by methacrylate which was attached to the mesogen and polymerised. The Cu(I)Br/2,2’-bipyridine mediated atom transfer radical polymerisation of the methacrylate was first investigated and the polymer obtained fully characterised. The polymerizations of the methyacrylate mesogenic compounds were then investigated. The disulfide- containing polymers were cleaved to obtain active thiol-polymers which were coupled to the NPs to afford the composites.

The initiator-coupled AuNPs and AuNRs were used as the macroinitiator in the polymerization of the methacrylate mesogenic monomers in the ‘grafting from’ method. The mesogen, nanoparticles and the composites were analysed by TLC, 1H NMR, 13C NMR, mass spectrometry, elemental analysis and SEM while the liquid crystalline properties of the mesogens were further determined by DSC, XRD and OPM techniques. The average gold nanoparticle size/distribution was determined by GPC and TEM. The properties of polymers were determined by GPC, mass spectrometry and NMR.

Citation

Amos, O. Synthesis and characterization of gold nanoparticle composites with side chain liquid crystals. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4217823

• Thesis Type: Thesis
• Deposit Date: Apr 20, 2016
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4217823
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Oct 1, 2015