Synthesis and characterisation of tuneable, high attachment density raspberry particles

Author: Kaili Stacey

Stacey, Kaili, 2022 Synthesis and characterisation of tuneable, high attachment density raspberry particles, Flinders University, College of Science and Engineering

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The attachment of nanoparticles to each other has a wide variety of applications in areas including superhydrophobic coatings, drug delivery, synthetic opals, antifouling, and catalysis.

As the properties of nanoparticles are dictated by both their chemical composition and their size, the development of new methods to attach particles of different sizes and materials to each other is an important field of study. In particular, the use of raspberry particles in the development of superhydrophobic, catalytic, and photonic materials was of particular interest in this thesis.

This thesis focuses on the characterisation of silica nanoparticles and the development of attachment reactions to produce silica-on-silica and gold-on-silica raspberry particles.

The effect of synthesis method, cleaning method, ammonia concentration, ethanol concentration, and atmospheric oxygen on the oxidation of thiols to disulphides during MPTMS particle synthesis was studied via Raman Microscopy and Ellman’s reagent assays. These results were used to propose a mechanism for the formation of disulphides during particle synthesis. A method was also developed for the post-synthesis reduction of disulphides to thiols at the particle surface, which also confirmed the presence of disulphides on the surface of the particle.

Larger particles were synthesised from GPTMS via an emulsion method and were then used in the development of an attachment reaction of MPTMS particles to GPTMS particles to form raspberry particles. This reaction utilised the base-catalysed thiol-epoxy click reaction to form covalent bonds between the two types of particles. During the development of this reaction, the effect of particle concentration and the use of thiol-functionalised MPTMS particles vs disulphide-functionalised MPTMS particles on the final attachment density was determined. SEM and zeta potential measurements were used in the development and characterisation of the attachment reaction and the final raspberry particles.

These raspberry particles enabled a combinatorial approach to the production of multiscale superhydrophobic coatings with PDMS. The effect of particle:polymer mass ratio and small:large particle size ratio on the wettability of the final coatings was investigated through contact and sliding angle experiments, and SEM. A superhydrophobic coating with a water contact angle of 157.5o and a sliding angle of 6.8o was produced using this method.

Citrate-stabilised gold particles were synthesised via the Turkevich method. The affinity of citrate-stabilised gold for thiols, disulphides, and amines was investigated through small molecule ligand exchange reactions, attachments to functionalised flat surfaces, and attachments to thiol- and disulphide-functionalised MPTMS particles. These reactions were analysed through a combination of FTIR, UV-Vis, DLS, and SEM techniques. It was found that amines were the most suitable for attachment to citrate-gold particles.

This information was then used to develop an attachment reaction for citrate-gold particles onto a larger GPTMS silica particle core via the use of ethylene diamine as a linker. The effect of gold particle excess on the attachment density was explored via SEM analysis. This attachment reaction resulted in gold-silica raspberry particles with high attachment density.

Keywords: nanotechnology, raspberry particles, silica, thiol-click chemistry, superhydrophobic, particle synthesis, particle attachment

Subject: Nanotechnology thesis

Thesis type: Doctor of Philosophy
Completed: 2022
School: College of Science and Engineering
Supervisor: David Lewis