The Brownian motion of colloidal particles in quasi-two-dimensional (q2D) confinement displays a distinct kinetic character from that in bulk. Here we experimentally report dynamic coupling motion of Brownian particles in a relatively long process (∼100 h), which displays a quasi-equilibrium state in the q2D system. In the quasi-equilibrium state, the q2D confinement results in the coupling of particle motions, which slowly damps the motion and interaction of particles until the final equilibrium state is reached. The process of approaching the equilibrium is a random relaxation of a many-body interaction system of Brownian particles. As the relaxation proceeds for ∼100 h, the system reaches the equilibrium state in which the energy gained by the particles from the stochastic collision in the whole system is counteracted by the dissipative energy resulting from the collision. The relaxation time of this stochastic q2D system is 17.7 h. The theory is developed to explain coupling motions of Brownian particles in q2D confinement.

No description available.

The synthesis of pyridinium cationic lipids, their counter-ion exchange, and the transfection of lipoplexes consisting of these lipids with firefly luciferase plasmid DNA (6.7 KDa), into lung, prostate and breast cancer cell lines was investigated. The transfection ability of these newly synthesized compounds was found to be twice as high as DOTAP/cholesterol and LipofectamineTM (two commercially available successful transfection agents). The compaction of the DNA onto silica (SiO2) nanoparticles was also investigated. For this purpose, it was necessary to study the stability and fusion studies of colloidal systems composed of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine), a zwitterionic lipid, and mixtures of DMPC with cationic DMTAP (1,2-dimyristoyl-3-trimethylammonium-propane). / Chemistry

Copper chlorophyllin (CuChl) is an antioxidant from renewable sources, which has shown as a potential active ingredient in agricultural crop sprays. The major objectives of this thesis are to understand the colloidal and interfacial behaviors of CuChl, and to develop strategies for improving its effectiveness in field applications. In this project, the following three areas are examined and analyzed. In practice, CuChl-based formulations are sprayed directly onto a plant’s foliage. As such, there is a need to understand how CuChl interacts with relevant plant surfaces. To this end, quartz crystal microbalance with dissipation (QCM-D) was used to quantify the adsorption of CuChl aqueous solutions onto four model surfaces: polystyrene, cellulose, pullulan, and silica. The results showed that cellulose adsorbed the highest amount of CuChl, followed by polystyrene and pullulan. In addition, the results also showed that the surfactants, SDS or DTAB, could alter the binding of CuChl to cellulose when used in concentrations above the critical micelle concentration. CuChl is composed of water-soluble and dispersed components, therefore it is not intrinsically rainfast, which limits its field application. To immobilize CuChl on leaves, a polymer combination of CMC (carboxymethyl cellulose) and PAE (polyamidoamine-epichlorohydrin) was designed for use as a spray adjuvant. The release behaviors of CuChl from dried spray deposits were investigated using varied polymer compositions and concentrations and compared with those of a water-soluble dye, brilliant sulfaflavine (BSF). The results indicated that a small amount of CuChl was immediately released upon exposure to water whereas BSF’s release behavior was dependent on the square root of time. The unusual behavior of CuChl was attributed to the presence of particles in the solution. These nanoparticles were coated with CMC:PAE complex, with the result of being immobilized on parafilm. Suspoemulsion is the most complex agricultural formulation that is composed of both dispersed particles and emulsion droplets. The objective of this work is to understand the relationship between the solution properties of suspoemulsions and the resulting dried deposits on hydrophobic surfaces. The results showed that the distribution of polychlorinated Cu (II) phthalocyanine (PG7) particles in dried deposits was related to the extent to which PG7 particles were adsorbed on or entrained in oil droplets. The PG7 particles that mainly ended up in the center (dome) area after drying were bound to the oil/water interface in the suspoemulsion, whereas individually dispersed particles ended up in the annulus. / Thesis / Doctor of Philosophy (PhD) / Agricultural formulations have been developed and widely applied to crops in an effort to maximize yields to keep up with the food demands of the world’s ever-growing population. However, there are still many challenges associated with the application of these formulations, such as huge losses due to spray drift, wash-off, and degradation during spraying. These issues can reduce the formulation’s overall efficacy and pose serious risks to the environment and human health. The primary objective of this thesis is to explore the agricultural application of a new environmentally-friendly active ingredient, copper chlorophyllin (CuChl). To this end, this work begins by determining CuChl’s colloidal and adsorption behaviors, with a particular focus on its binding tendencies for relevant plant surfaces. Next, a polymer combination was designed as a spray adjuvant to enhance CuChl’s rainfastness performance and CuChl’s release from dried deposits was characterized. Finally, the distribution of dispersed particles in dried suspoemulsion deposits was determined.

Controlling the size and size distribution of colloidal nanoparticles have gained extraordinary attention as their physical and chemical properties are strongly affected by size. Ligands are widely used to control the size and size distribution of nanoparticles; however, their exact roles in controlling the nanoparticle size distribution and the way they affect the nucleation and growth kinetics are poorly understood. Therefore, understanding the nucleation and growth mechanisms and developing theoretical/modeling framework will pave the way towards controlled synthesis of colloidal nanoparticles with desired sizes and polydispersity. This dissertation focuses on identifying the possible roles of ligands and size on the kinetics of nanoparticle formation and growth using in-situ characterization tools such as small-angle X-ray scattering (SAXS) and kinetic modeling. The presented work further focuses on developing kinetic models to capture the main nucleation and growth reactions and examines how ligand-metal interactions could potentially alter the rate of nucleation and growth rates, and consequently the nanoparticle size distribution. Additionally, this work highlights the importance of using multi-observables including the concentration of nanoparticles, size and/or precursor consumption, and polydispersity to differentiate between different nucleation and growth models and extract accurate information on the rates of nanoparticle nucleation and growth. Specifically, during the formation and growth of colloidal nanoparticles, complex reactions are occurring and as such nucleation and growth can take place through various reaction pathways. Therefore, sensitivity analysis was applied to effectively compare different nucleation and growth models and identify the most important reactions and obtain a reduced model (e.g. a minimalistic model) required for efficient data analysis. In the following chapters, a more sophisticated modeling approach is presented (population balance model) capable of capturing the average-properties of nanoparticle size distribution. PBM allows us to predict the growth rate of nanoparticles of different sizes, the ligand surface coverage for each individual size, and the parameters involved in altering the size distribution. Additionally, thermodynamic calculations of nanoparticle growth and ligand-metal binding as a function of size and ligand surface coverage were conducted to further shed light on the kinetics of nanoparticle formation and growth. The combination of kinetic modeling, in-situ SAXS and thermodynamic calculations can significantly advance the understanding of nucleation and growth mechanisms and guide toward controlling size and polydispersity. / Doctor of Philosophy / The synthesis of colloidal metal nanoparticles with superior control over size and size distribution, and has attracted much attention given the wide applications of these nanomaterials in the fields of catalysis, photonics, and electronics. Obtaining nanoparticles with desired sizes and polydispersity is vital for enhancing the consistency and performance for specific applications (e.g., catalytic converters for automotive emission). Ligands are often employed to prevent agglomeration and also control the nanoparticle size and size distribution. Ligands can affect the precursor reactivity and therefore the reduction/nucleation by binding with the metal precursor. Nucleation refers to the assimilation of few atoms to form initial nuclei acting as templates for nanoparticle growth. Additionally, ligands can bind with the nanoparticle surface sites and change the rate of surface growth and therefore the final nanoparticle size. Despite strong effects of ligands in the colloidal nanoparticle synthesis, their exact role in the nucleation and growth kinetics is yet to be identified. Additionally, nucleation and growth models capable of unraveling the underlying mechanisms of nucleation and growth in the presence of ligands are still lacking in the literature. Therefore, obtaining nanoparticles with desired sizes and polydispersity mostly relies on trial-and-error approach making the synthesis costly and inefficient. As such, developing models capable of predicting suitable synthesis conditions is contingent upon understanding the chemistry and mechanism involved during nanoparticles formation. Therefore, in this study, novel kinetic models were developed to capture the nucleation and growth kinetics of colloidal metal nanoparticles under different synthetic conditions (different types of solvents, different concentrations of ligand and metal). In-situ SAXS was further employed to measure the average diameter, concentration of nanoparticles, and polydispersity during the synthesis and extract the nucleation and growth rates (evolution of concentration of nanoparticles and size). First, an average-property model was developed to account for ligand-metal bindings and capture the size and concentration of nanoparticles during the synthesis. Then, a more complex modeling approach; PBM, accompanied by the thermodynamic calculations of surface growth and ligand-nanoparticle binding enthalpies was implemented to capture the size distribution. As it will be shown later, the determination of the underlying mechanisms resulted in a highly predictive kinetic model capable of predicting the synthetic conditions to obtain nanoparticles with desired sizes. The proposed methodology can serve as a powerful tool to synthesize nanoparticles with specific sizes and polydispersity.

This dissertation introduces assembly of spherical particles as a novel topography-based anti-biofouling coating. It also provides new insights on the effects of surface topography, especially local curvature, on cell–surface and cell–cell interactions during the evolution of biofilms. I investigated the adhesion, colonization, and biofilm formation of the opportunistic human pathogen Pseudomonas aeruginosa on a solid coated in close-packed spheres of polystyrene, using flat polystyrene sheets as a control. The results show that, whereas flat sheets are covered in large clusters after one day, a close-packed layer of 630–1550 nm monodisperse spheres prevents cluster formation. Moreover, the film of spheres reduces the density of P. aeruginosa adhered to the solid by 80%. Our data show that when P. aeruginosa adheres to the spheres, the distribution is not random. For 630 nm and larger particles, P. aeruginosa tends to position its body in the confined spaces between particles. After two days, 3D biofilm structures cover much of the flat polystyrene, whereas 3D biofilms rarely occur on a solid with a colloidal crystal coating of 1550 nm spheres. On 450 nm colloidal crystals, the bacterial growth was intermediate between the flat and 1550 nm spheres. The initial preference for P. aeruginosa to adhere to confined spaces is maintained on the second day, even when the cells form clusters: the cells remain in the confined spaces to form non-touching clusters. When the cells do touch, the contact is usually the pole, not the sides of the bacteria. The observations are rationalized based on the potential gains and costs associated with cell-sphere and cell-cell contacts. I concluded that the anti-biofilm property of the colloidal crystals is correlated with the ability to arrange the individual cells. I showed that a colloidal crystal coating delays P. aeruginosa cluster formation on a medical-grade stainless-steel needle. This suggests that a colloidal crystal approach to biofilm inhibition might be applicable to other materials and geometries. The results presented in appendix 1 suggest that colloidal crystals can also delay adhesion of Methicillin resistant staphylococcus aureus (MRSA) while it supports selective adhesion of this bacterium to the confined spaces. / Ph. D.

Understanding and controlling the forces between colloidal particles in solution, along with the resulting stability of a dispersion of such particles, continues to be at topic of great interest. Although most laboratory studies focus on model systems in which the number of system species is kept to a minimum, real colloidal systems can be much more complex, consisting of multiple components that can vary greatly in size, charge, shape, etc. This dissertation focused on a topic that has received very little prior study, namely synergistic effects that can arise in mixed colloidal systems in which the resulting force and stability of the system cannot be predicted using results obtained in more idealized systems consisting of fewer components. Two specific systems were studied. The first was a ternary system of particles in which micron-sized particles were in a dispersion containing both nanoparticles and submicron particles. It was shown through both computation modeling and direct force measurements that the nanoparticles can create attractive forces between the micron and submicron particles such that a halo of submicron particles is formed. This halo results in long range forces between the microparticles that cannot be predicted from measurements in systems containing only nanoparticles or only submicron particles. In addition, the forces can be large enough to alter the stability of a dispersion of these microparticles. The second system consisted of microparticles in a solution containing nanoparticles and a polyelectrolyte, specifically poly(acrylic) acid. Again, through modeling and experimentation, it was found that complexation of the nanoparticles and polyelectrolyte molecules led to depletion and structural forces between the microparticles that were substantially greater than the sum of the forces measured in systems of only nanoparticles or only polyelectrolyte. It was also found that these greater forces could lead to destabilization of a dispersion of microparticles that was stable when only nanoparticles or only polyelectrolyte was present. While these results clearly demonstrate the difficulty associated with predicting forces and stability in mixed colloidal systems, they also indicate that such systems offer new and interesting opportunities for controlling stability that clearly warrant additional study. / Ph. D.

Freeze casting is a colloidal processing technique that shows great promise for development of nanostructured materials. A ceramic nanopowder is dispersed with a polymer in water, under carefully controlled pH. The suspension is cast into a suitable mold and frozen, then de-molded and exposed to a vacuum to sublimate and remove the water. Polymer adsorption and rheology were studied to optimize and characterize a colloidal suspension of a 38 nm Al2O3 powder. The dispersant, dispersant amount, pH and solids loading were examined to determine the best conditions for freeze casting. Based on adsorption and viscosity data, optimal conditions for freeze casting were found with Poly(acrylic acid) (PAA) dispersant, at 2.00 wt% (of Al2O3), pH of 9.5, and a solids loading of 40 vol%. Carbon nanotubes (CNTs) were added to that suspension in increments of 0.14, 0.28, 0.53, 1.30 and 2.60 vol%. The viscosity increased dramatically upon addition of 1.30 vol% CNTs. The colloidal CNT-Al2O3 suspension was successfully freeze cast and the microstructure showed a very smooth fracture surface. It was determined that upon resting, the suspension undergoes a physical change which must be completed to obtain advantageous microstructure. Freeze cast Al2O3 discs with and without CNTs were measured using a concentric ring test, with strengths on the order of one MPa. The freeze cast sample was successfully debinded, but the heating profile attempted was not effective in obtaining full density. / Master of Science

This dissertation focused on the potential use of highly charged nanoparticles to stabilize dispersions of weakly charged microparticles. The experimental components of the project centered on a model colloidal system containing silica microparticles at the isoelectric point where the suspensions are unstable and prone to flocculation. The stability of the silica suspensions was studied in the presence of highly charged nanoparticles. Initial experiments used polystyrene latex with either sulfate or amidine surface groups. Effective zeta potentials were measured with nanoparticle concentrations ranging from 0.001% to 0.5% vol. Adsorption levels were determined through direct SEM imaging of the silica microparticles, showing that the nanoparticles directly adsorbed to the microparticles (amidine more than sulfate), producing relatively large effective zeta potentials. However, stability experiments showed that the latex nanoparticles did not stabilize the silica but merely provided a reduction in overall flocculation rate. It was concluded that the zeta potential was an insufficient predictor of stability as there was still sufficient patchiness on the surface to allow for the silica surfaces to aggregate. Experiments using zirconia and alumina nanoparticles did achieve effective stabilization; both types stabilized the silica suspensions for longer than the observation period of approximately 15 hours. Stability was observed at concentrations of 10^-4% to 1.0% (zirconia) and 10^-2% vol. (alumina). These particles adsorbed directly to the microparticles (confirmed via SEM) and produced increasing effective zeta potentials with increasing nanoparticle concentrations. The adsorption resulted in significant electrostatic repulsion that was determined to be effectively irreversible using colloidal probe AFM. The improved stabilizing ability was attributed to the increased van der Waals attraction between the oxide nanoparticles (compared to polystyrene). Finally, an unexpected result of the CP-AFM force measurements showed that the repulsive forces between a nanoparticle-coated particle and plate lacked the normal dependence on the radius of the probe as predicted by the Derjaguin approximation. The forces observed in nanoparticle suspensions were virtually identical for 5 µm and 30 µm probes. Based on calculations of the shear rate in the gap, it was theorized that this phenomenon may have resulted from the shearing of adsorbed particles from the surfaces, which leads to similar interaction geometries for the two probe sizes. / Ph. D.

Colloidal nanoparticles are widely used for industrial and scientific purposes in many fields, including catalysis, biosensing, drug delivery, and electrochemistry. It has been reported that most of the functional properties and performance of the nanoparticles are highly dependent on the particle size and morphology. Therefore, controlled synthesis of nanomaterials with desired size and structure is greatly beneficial to the application. This dissertation presents a systematic study on the effect of ligands on the colloidal Pd nanoparticle synthesis mechanism, kinetics, and final particle size. Specifically, the research is focused on investigating how the ligand bindings to different metal species, i.e., metal precursor and nanoparticle surface, affect the nucleation and growth pathways and rates and connecting the binding thermodynamics to the kinetics quantitatively. The first part of the work (Chapters 4 and 5) is establishing isothermal titration calorimetry (ITC) methodology for obtaining the thermodynamic values (Gibbs free energy, equilibrium constant, enthalpy and entropy) of the ligand-metal precursor binding reactions, and the simultaneous metal precursor trimer dissociation. In brief, the binding products and reactions were characterized by nuclear magnetic resonance (NMR), and an ITC model was developed to fit the unique ITC heat curve and extract the thermodynamic properties of the reactions above. Furthermore, in Chapter 6, the thermodynamic properties, especially the entropy trend changing with the ligand chain length was investigated on different metal precursors based on the established ITC methodology, showing that the entropic penalty plays a significant role in the binding equilibrium. The second part of the dissertation (Chapter 7 and 8) presents the kinetic and mechanistic study on size-tuning of the colloidal Pd nanoparticles only by changing different coordinating solvents as ligands together with the trioctylphosphine ligand. In-situ small angle X-ray scattering was applied to characterize the time evolutions of size, size distribution, and particle concentration using synthesis reactor connected to a capillary flow cell. From the real-time kinetic measurements, the nucleation and growth rates were calculated and correlated with the thermodynamics, i.e., Gibbs free energies of solvent-ligand-metal precursor reactivity and ligand-nanoparticle surface binding which were modified by the coordination of different solvents. Higher reactivity leads to faster nucleation and high nanoparticle concentration, and stronger solvent/ligand-particle coordination energy results in higher ligand capping density and slower growth. The interplay of both effects reduces the final particle size. Furthermore, because of the significance of the ligand-metal interactions, the synthesis temperature and ligand to metal precursor ratio were systematically to modify the relative binding between the ligand and precursor, and the ligand and nanoparticle, and determine the effect on the nucleation and growth rates. The results show that the relative rates of nucleation and growth is critical to the final size. A methodology for using the in-situ measurements to predict the final size by developing a kinetic model based is discussed. / Doctor of Philosophy / Metal nanoparticles dispersed in solution phase, i.e., colloidal nanoparticles, are of great scientific interests due to their unique properties different from bulk metal materials. The size, shape and other morphology features can largely affect the nanomaterial properties and functional performances. Therefore, a successful synthesis of nanoparticles with desired structures is highly beneficial to the development of their application. Ligands, which are long-chain molecules that can cap on the surface of the nanoparticles, have been known as stabilizers of the nanoparticles in the solution phase. Whereas in recent studies, it has been found that changing the ligand type and concentration in the synthesis can result in different sizes and shapes of nanomaterials, which indicates that the ligands are playing critical roles in the synthesis mechanisms to control the kinetics. To have a better understanding on the control effects of the ligands, systematic studies were conducted on the ligand interactions (bindings) between the ligand-metal compound (as the metal source and initial agent in the nanomaterial synthesis) and ligand-nanoparticle surface, of which both can be quantified by thermodynamics. Using isothermal titration calorimetry, the ligand-metal precursor binding strength was measured and found to be dependent on ligand chain length and the metal precursors, which further affects the reactivity of the metal precursor based on the results of density functional theory calculations. On the other hand, the ligand-nanoparticle surface binding strength was found to affect the capping density of the ligands on the nanoparticle surface. In order to connect the thermodynamics to the kinetics, namely the nucleation (formation of new particles) and growth (particle size increase) rates, small angle X-ray scattering (SAXS) characterization was performed in real time during the synthesis on the nanoparticles. This technique allows the capture of the size, size distribution and concentration of nanoparticles changing with time, and the nucleation and growth rates were further calculated from the SAXS data. By changing solvents with the same functions of ligands but of different coordinating abilities, a correlation between the kinetics and thermodynamics was observed. The nucleation rate increases with the metal precursor reactivity, which corresponds to stronger solvent binding to the precursor. On the other hand, the stronger ligand-nanoparticle binding slows down the growth by lowering the surface capping density. To go deeper into the ligand-metal binding and kinetics correlation, the binding properties were tuned by changing other synthesis conditions, i.e., different temperatures and ligand to metal ratios (ligand concentration), and a qualitative discussion was given on the effects of these conditions on the synthesis kinetics and final particle size.