Gold nanoparticles (AuNPs) have garnered considerable attention for their interesting size-dependent properties. These properties have fueled applications that span a continuum ranging from simple to sophisticated. Applications for these materials have grown more complex as syntheses for these materials have improved. For simple applications, current synthetic processes are sufficient. However, development of syntheses that generate well-defined particle sizes with specifically tailored surface functionalities is an on-going challenge for chemists. The aim of this dissertation is to improve upon current AuNP syntheses to produce sophisticated materials needed to discover new material properties, and provide efficient access to materials to develop new advanced applications. The research described in this dissertation improves upon current methods for AuNP production by using a microreactor to provide enhanced mixing and synthetic control, and small angle X-ray scattering (SAXS) as a precise, rapid, solution-based method for size distribution determination. Using four ligand-stabilized AuNP samples as reference materials, SAXS analysis was compared to traditional microscopic size determination. SAXS analysis provided similar average diameters while avoiding deposition artifacts, probing a larger number of particles, and reducing analysis time. Next, the limits of SAXS size analysis was evaluated, focusing on identifying multiple distributions in solution. Utilizing binary and ternary mixtures of well-defined AuNP reference samples, SAXS analysis was shown to be effective at identifying multiple distributions. While microscopy has limited ability to differentiate these modes, SAXS analysis is more rapid and introduces less researcher bias. Because AuNP size and ligand functionality are interdependent, accessing desired core sizes with varied functionality is challenging. To address this, a new microfluidic synthetic method was developed to produce thiolate-passivated AuNPs with targeted core sizes from 1.5 - 12 nm with tailored functionality. This ability to control size while independently varying surface functionality is unprecedented. Lastly, AuNP core formation was probed by simultaneous in situ SAXS and UV/visible spectroscopy. A coalescence mechanism for AuNP growth was observed when using Bunte salt ligands. This finding compares well to observed coalescence in other systems using weakly-passivating ligands, and supports the hypothesis that Bunte salts passivate ionically during particle growth while resulting in covalent linkages. / 2015-10-10

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2006. / Härtill 3 uppsatser.

The surface width, a global quantity that depends on time, is used to characterize the temporal evolution of growing surfaces. One of the most successful concepts for describing the property of the surface width is the famous Family-Vicsek scaling relation. We discuss an extended scaling relation that yields a complete description for various growth models. For two linear Langevin equations, namely the Edwards-Wilkinson equation and the Mullins-Herring equation, we furthermore study analytically the behavior of global quantities related to the surface width or to a quantity which is conjugated to the diffusion constant. The global quantities depend in a non-trivial way on two different times. We discuss the dynamical scaling forms of global correlation and response functions. For global functions related to the surface width, we show that the scaling behavior of the response can depend on how the system is perturbed. Different dynamic regimes, characterized by a power-law or by an exponential relaxation, are identified, and a dynamic phase diagram is constructed. We discuss global fluctuation-dissipation ratios and how to use them for the characterization of non-equilibrium growth processes. We also numerically study the same two-time quantities for the non-linear Kardar-Parisi-Zhang equation. For global functions related to the quantity which is conjugated to the diffusion constant of the linear Langevin equations, we show that the integrated response is proportional to the correlation in the linear response regime. In the aging regime, the autocorrelation and autoresponse exponents are identical and the aging exponent for the response is equal to the aging exponent for the correlation. We investigate the non-equilibrium fluctuation-dissipation theorem for non-equilibrium states based on this quantity. In the non-linear response regime a certain dissipation-fluctuation ratio approximates unity for small waiting times but approaches the ratio of perturbed and unperturbed diffusion constants for larger waiting times. / Ph. D.

Droplet growth processes in a cumulus cloud, beginning from its inception at sub-micron scale up to drizzle drop size of few hundred microns, in an average duration of about half hour, has been a topic of intense research. In particular role of turbulence in aiding droplet growth in clouds has been of immense interest. Motivated by this question, we have performed experiments in which turbulent natural convection coupled with phase change is set up inside a tall vertical insulated tube, by heating water located at tube bottom and circulating cold air at tube top. The resulting moist turbulent natural convection flow in the tube is expected to be axially homogeneous. Mixing of air masses of differing temperature and moisture content leads to condensation of water vapor into droplets, on aerosols available inside the tube. We there-fore have droplets in a turbulent flow, in which phase change is coupled to turbulence dynamics, just as in clouds. We obtain a linear mean-temperature pro le in the tube away from its ends. Because there is net flux of water vapor through the tube, there is a weak mean axial flow, but which is small compared to turbulent velocity fluctuations. We have experimented with two setups, the major difference between them being that in one setup, called AC setup, tube is open to atmosphere at its top and hence has higher aerosol concentration inside the tube, while the other setup, called RINAC setup, is closed to atmosphere and due to presence of aerosol filters has lower aerosol concentration inside the tube. Also in the latter setup, cold air temperature at tube top can be reduced to sub-zero levels. In both setups, turbulence attains a stationary state and is characterized by Rayleigh number based on temperature gradient inside the tube away from its ends, which is 107. A significant result from our experiments is that in RINAC setup, we obtain a broadened droplet size distribution at mid-height of tube which includes a few droplets of size 36 m, which in real clouds marks the beginning of rapid growth of droplets due to collisions among them by virtue of their interaction with turbulence. This shows that for broadening of droplet size distribution, high turbulence levels prevalent in clouds is not strictly necessary. Second part of our study comprises two pieces of theoretical work. First, we deal with the problem of a large collector drop settling amidst a population of smaller droplets whose spatial distribution is homogeneous in the direction of fall. This problem is relevant to the last stage of droplet growth in clouds, when the droplets have grown large enough that they interact weakly with turbulence and begin to settle under gravity. We propose a new method to solve this problem in which collision process is treated as a discrete stochastic process, and reproduce Telford's solution in which collision is treated as a homogeneous Poisson process. We then show how our method may be easily generalized to non-Poisson collision process. Second, we propose a new method to detect droplet clusters in images. This method is based on nearest neighbor relationship between droplets and does not employ arbitrary numerical criteria. Also this method has desirable invariance properties, in particular under the operation of uniform scaling of all distances and addition/deletion of empty space in an image, which therefore renders the proposed method robust. This method has advantage in dealing with highly clustered distributions, where cluster properties vary over the image and therefore average of properties computed over the entire image could be misleading.

Dans cette thèse nous proposons et nous mettons en application plusieurs modèles décrivant la croissance et la morphologie du tissu urbain. Le premier de ces modèles est issu de la percolation en gradient (correlée) déjà proposé de la littérature. Le second, inédit, fait appel à un équation différentielle stochastique. Nos modèles sont paramétrables : les paramètres que nous avons choisi d’appliquer sont naturels et tiennent compte de l’accessibilité des sites. Le résultat des simulations est conforme à la réalité du terrain. Par ailleurs, nous étudions la percolation en gradient: nous démontrons , suivant Nolin, que la frontière de cluster principal se situe dans un voisinage de la courbe critique et nous estimons ses longueurs et largeurs. Enfin, nous menons une étude du processus de croissance SLE. Nous calculons (preuve assistée par ordinateur) l’espérance des carrés des modules pour SLE2 and SLE6. Ces résultats sont liés à la conjecture de Bieberbach. / In this thesis we propose and test models that describe the growth and morphology of cities. The first of these models is used from previously developed correlated gradient percolation model. The second model is related to a stochastic differential equation and has never been proposed before. Both models are parameterizable. The parameters we chose in applications are well justified by physical observations: proximily to axes and accessibility of sites. The result is consistent with actual data. We also study the gradient percolation as a mathematical object. We prove, following Nolin’s ideas, that the front of gradient percolation cluster is localised in a neighborhood of the critical curve with width and length depending on density gradient. Finally, we also study SLE growth processes. We calculate (computer assisted demonstration) the expected value of square of moduli for SLE2 and SLE6 related to the Bieberbach conjecture.