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Date of Award
Physics and Astronomy
Soft matter is a subfield of condensed matter including polymers, colloidal dispersions, surfactants, and liquid crystals. These materials are familiar from our everyday life- glues, paints, soaps, and plastics are examples of soft materials. Many phenomena in these systems have the same underlying physical mechanics. Moreover, it has been recognized that combinations of these systems, like for example polymers and colloids, exhibit new properties which are found in each system separately. These mixed systems have a higher degree of complexity than the separate systems. In order to understand their behavior, knowledge from each subfields of soft matter has to be put together. One of these complex systems is the mixture of nanoparticles with macromolecules such as polymers, proteins, etc. Understanding the interactions in these systems is essential for solving various problems in technological and medical fields, such as developing high performance polymeric materials, chromatography, and drug delivery vehicles. The author of this dissertation investigates fundemental soft matter systems, including colloid dispersions in polymer solutions and binary mixture.
The diffusion of gold nanoparticles in semidilute and entangled solutions of polystyrene (PS) in toluene were studied using fluctuation correlation spectroscopy (FCS). In our experiments, the particle radius (R ≈ 2.5 nm) was much smaller compared to the radius of gyration of the chain but comparable to the average mesh size of the fluctuating polymer network. The diffusion coefficient (D) of the particles decreased monotonically with polymer concentration and it can be fitted with a stretched exponential function. At high concentration of the polymer, a clear subdiffusive motion of the particles was observed. The results were compared with the diffusion of free dyes, which showed normal diffusive behavior for all concentrations. In another polymer solution, Poly ethylene glycol (PEG) in water, the diffusion of the gold nanoparticles depends on the dimentionlesss length scale R/ξ, where R is the radius of the nanoparticle and ξ is the average mesh size of the fluctuating polymer network.
FCS were used to study the critical adsorption on curved surfaces by utilizing spherical nanoparticles immersed in a critical binary liquid mixture of 2,6 lutidine + water. The temperature dependence of the adsorbed film thickness and excess adsorption was determined from FCS measurements of the enlarged effective hydrodynamic radius of the particles. Our results indicated that the adsorbed film thickness is of the order of correlation length associated with concentration fluctuations. The excess adsorption per unit area increases following a power law in reduced temperature with an exponent of -1, which is the mean-field value for the bulk susceptibility exponent.
The kinetics of adsorption of gold nanoparticles in polymer solutions on silicon substrate was studied using ellipsometry by measuring the thickness of the adsorbed layer versus time. The data was fitted using exponential growth with relaxation time constants proportional to the diffusion of the gold nanoparticles in polymer solution.
Omari, Rami Ahmad Saleh, "Dynamics of nanoparticles in complex fluids." (2011). Wayne State University Dissertations. Paper 326.