Silica nanoparticles grown from organofunctionalised trialkoxysilanes: Synthesis, High Density Modification Strategies and Application

Author: Daniel N Mangos

Mangos, Daniel N, 2017 Silica nanoparticles grown from organofunctionalised trialkoxysilanes: Synthesis, High Density Modification Strategies and Application, Flinders University, School of Chemical and Physical Sciences

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Owing to their thermal stability and non-toxicity, silica nanoparticles present themselves as platforms to build functionality through surface modification, for applications in medical imaging, cosmetics and for composite materials. While this concept is not novel, all too often, only low attachment density is obtained, if it is measured at all, which limits the understanding that can be obtained and in some cases, the validity of the structure-property relationships, which are obtained.

This thesis reports the straightforward synthesis, characterization, high density chemical modification and application of functionalised silica nanoparticles. The controlled growth, maturity time and condensation state have been examined for functional particles grown from (3-mercaptopropyl)trimethoxysilane (3-MPTMS), (vinyl)trimethoxysilane (VTMS), (phenyl)trimethoxysilane (PTMS) and (3-cyanopropyl)trimethoxysilane (3-CPTMS).

A simple and robust method to quantify the attachment density using ATR-FTIR was developed, using the Si-O-Si vibrational mode as an internal standard. Using a large excess of 11-bromo-1-undecene (up to 700 fold excess), up to 4.9 molecules per nm2 were able to be attached to thiol terminated particles. This value compares favourably with 4.7 thiols per nm2 calculated computationally, and 5.7 attachments per nm2 suggested by thermogravimetric analysis. The rate of this attachment reaction was also investigated, with respect to time of UV irradiation and concentration of 11-bromo-1-undecene, which provided a means to achieve the controlled attachment of multiple molecules sequentially.

Following an understanding of the critical reaction conditions for simple chemistry, the attachment of Fullerene-C60 to produce C60-f-SiNP was then then investigated. Small molecule chemistry was used to understand the chemistry of the adduct and prove covalent attachment.

Following the observation of ignition / combustion of C60-f-SiNP during a Raman spectroscopy experiment, this excitation event was recreated, and thermally tracked in a controlled environment, revealing that hollow particles can be formed by laser ablation of the C60-f-SiNP. Building upon this, a subsequent camera flash resulted in the reconstruction of the spheres into amorphous carbon sheets.

In summary, the high density attachment of a simple and more complex alkene has been demonstrated, through a free radical thiol-ene reaction on a silica nanoparticle surface. The research presented here provides multiple avenues for the applications requiring high density surface modification of particle surfaces. The natural development of this project would be to attach a high density of fluorophores or electron transport molecules on the particle surface due to the close proximity of the functional groups to one another.

Keywords: Silica, Nanoparticle, Nanotechnology, Stöber, Colloid, Surface Science, Attachment Density, ATR-FTIR, Fullerene-C60

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Chemical and Physical Sciences
Supervisor: Professor David A Lewis