Diffusion of gold nanoparticle in water and toluene

Abstract

The aim of this dissertation is to find the diffusion coefficient of gold-nanoparticles in water and toluene solvent using dynamic light scattering techniques (DLS). The application of gold nanotechnology is very diverse and improves our lives greatly, ranging from drug delivery to cancerous cell, medical diagnosing for symptoms of prostate cancer and HIV infection; pollution control and water purification dealing with global environmental issues; solar cells and gold nanoparticle catalysts etc. Besides, 'bottom up' technology is the most important aspect of nanotechnology to create new materials. Self-assembled nanoparticles serve as building blocks at a liquid-liquid interface for making new useful materials by 'bottom up' technology. However, there is a little research on the study of diffusion in different solvents and the diffusion of gold nanoparticles in the interface is not well understood. Since diffusion of gold nanoparticles is an important factor to be considering in designing gold nanoparticles based applications especially the biosensors and the catalysts in fluidic system. DLS is known as "photon correlation spectroscopy" or "quasi-elastic light scattering" for measuring temporally scattered intensity fluctuation of particles in solution undergo Brownian motion. This technique is widely adopted in measuring the size and diffusion of nanoparticles as it has several advantages such as short experiment duration and fully automated measurement. Relaxation time can be determined by the autocorrelation function fitting with Kohlrausch-Williams-Watts (KWW) function. With known relaxation time and scattering vector, the diffusion coefficient can be calculated. Diffusion coefficient is a paramount term to describe particle motion in solution. Apart from finding the diffusion coefficient, factors affecting diffusion in the range of temperature, density and viscosity of water and toluene solvent will also be discussed. Also, theories of dynamic light scattering and the method of analysing scattered intensity signals will be presented in detail.