Motion of Particles as a Probe: Dynamics and Assembly in Gel Networks/Aqueous Media

Nanoparticles are of great interest with a wide variety of potential applications due to their unexpected but interesting physical properties which are different from bulk state, enable small length scale-driven transport through complex materials, and provide the building units for well-ordered structures. Observing the motion of nanoparticles provides information about surrounding microstructures, flow dynamics, and assembly processes by virtue of fluorescence of nanoparticles. However, the proper control of surface chemistry and the fluorescence of particles are both paramount and challenging to allow particles to be used in a quantitative and robust manner. This thesis describes the use of precisely-defined particles for characterizing and building complex structures. The research exploits advantages of the particle dynamics in three distinct studies: i) the tracking of single CdSe/ZnS core/shell QDs to characterize complex structures of hydrogels, ii) the transformation of dispersed QDs in bulk phase into unique ring assemblies at the air/liquid interface, and iii) the mapping of flow dynamics within an evaporating droplet. Chapter 2 describes the diffusion dynamics of single quantum dots (QDs) within polyacrylamide (PAAm) hydrogels to characterize the structural heterogeneity of gel networks by employing the single particle tracking (SPT) technique. Due to their photo-stable and highly fluorescent emission and its small size (4- 10 nm), individual QDs can be tracked by a fluorescence microscopy as they find pathways through structurally complex gel networks. This tracking provides information about spatiotemporal dynamics. The anomalous diffusion dynamics revealed by the motion of single QDs suggests that the structural heterogeneities of PAAm gels develop with increasing cross-linker content, and the length scales discovered are in a good agreement with the correlation length scale reported in the previous light scattering studies. Chapter 3 describes the assembly of QD rings at the air/water interface by ‘2-D Pickering emulsions’. This work emanated from the unexpected observation of QD rings on the droplet of QD solutions. These rings form from QDs adsorbed to the interfacial line of surfactant islands assembled at the interface, and the QDs mark islands, appearing as rings. This island assembly was found to occur only at a specific range of surfactant concentrations due to the phase transition. Uniformly dispersed QDs in the bulk phase affording the ring patterns exclusively at the air/water interface provides insight that the thermodynamic driving force arises at the interfacial line between three phases (air/water/surfactant islands). Finally, Chapter 4 details the radial flow dynamics within an evaporating droplet with a pinned contact line is investigated. By suspending and tracking fluorescent latex beads, the flow dynamics are quantified as a function of contact angle. This phenomenon, commonly called the “coffee ring effect”, is advantageous for patterning and depositing suspended solutes on substrates. To develop evaporative assembly as a scalable process, it is particularly important to understand the effect of contact angle on radial velocity. By tracking the motion of suspended particles in a droplet, we experimentally measured the flow dynamics, specifically the height averaged radial velocity, within an evaporating droplet in the range of contact angles 5-50o. We found that our experimental results are in a good agreement with the analytical prediction by Hu and Larson. Following the analytical predictions, we modified the original equation to a simplified equation that directly links radial velocity to contact angle and evaporation rate. This study provides insight into the manipulation of evaporative assembly processes on different substrates in terms of assembly kinetics and structural dimensions

Supersymmetric M5 Brane Theories on R x CP2

We propose 4 and 12 supersymmetric Yang-Mills-Chern-Simons theories on R×CP2 obtained by twisted Zk moddings and dimensional reduction of the 6d (2,0) superconformal field theories on R×S5. These theories have a discrete coupling constant 1g2YM=k4π2 so that instantons represent the Kaluza-Klein modes correctly. We calculate the perturbative part of the SU(N) gauge group Euclidean path integral for the index function and confirm it with the known half-BPS index. The scalar and fermionic fields have the conformal dimension prescribed by the 6d theory. From the similar twisted Zk modding of the AdS7×S4 geometry, we speculate that the M region is for k≲N1/3 and the type IIA region is N1/3≲k≲N. When nonperturbative corrections are included, our theory is expected to produce the full index of the 6d (2,0) theory.1120sciescopu

Numerical Sensitivity Tests of Volatile Organic Compounds Emission to PM2.5 Formation during Heat Wave Period in 2018 in Two Southeast Korean Cities

A record-breaking severe heat wave was recorded in southeast Korea from 11 July to 15 August 2018, and the numerical sensitivity simulations of volatile organic compound (VOC) to secondarily generated particulate matter with diameter of less than 2.5 mu m (PM2.5) concentrations were studied in the Busan and Ulsan metropolitan areas in southeast Korea. A weather research and forecasting (WRF) model coupled with chemistry (WRF-Chem) was employed, and we carried out VOC emission sensitivity simulations to investigate variations in PM2.5 concentrations during the heat wave period that occurred from 11 July to 15 August 2018. In our study, when anthropogenic VOC emissions from the Comprehensive Regional Emissions Inventory for Atmospheric Transport Experiment-2015 (CREATE-2015) inventory were increased by approximately a factor of five in southeast Korea, a better agreement with observations of PM2.5 mass concentrations was simulated, implying an underestimation of anthropogenic VOC emissions over southeast Korea. The simulated secondary organic aerosol (SOA) fraction, in particular, showed greater dominance during high temperature periods such as 19-21 July, 2018, with the SOA fractions of 42.3% (in Busan) and 34.3% (in Ulsan) among a sub-total of seven inorganic and organic components. This is considerably higher than observed annual mean organic carbon (OC) fraction (28.4 +/- 4%) among seven components, indicating the enhancement of secondary organic aerosols induced by photochemical reactions during the heat wave period in both metropolitan areas. The PM2.5 to PM10 ratios were 0.69 and 0.74, on average, during the study period in the two cities. These were also significantly higher than the typical range in those cities, which was 0.5-0.6 in 2018. Our simulations implied that extremely high temperatures with no precipitation are significantly important to the secondary generation of PM2.5 with higher secondary organic aerosol fraction via photochemical reactions in southeastern Korean cities. Other possible relationships between anthropogenic VOC emissions and temperature during the heat wave episode are also discussed in this study

5-dim Superconformal Index with Enhanced En Global Symmetry

The five-dimensional N = 1 supersymmetric gauge theory with Sp(N) gauge group and SO(2N(f)) flavor symmetry describes the physics on N D4-branes with N-f D8-branes on top of a single O8 orientifold plane in Type I&apos; theory. This theory is known to be superconformal at the strong coupling limit with the enhanced global symmetry ENf+1 for N-f <= 7. In this work we calculate the superconformal index on S-1 x S-4 for the Sp(1) gauge theory by the localization method and confirm such enhancement of the global symmetry at the superconformal limit for N-f <= 5 to a few leading orders in the chemical potential. Both perturbative and (anti) instanton contributions are present in this calculation. For N-f = 6, 7 cases some issues related the pole structure of the instanton calculation could not be resolved and here we could provide only some suggestive answer for the leading contributions to the index. For the Sp(N) case, similar issues related to the pole structure appear.1151sciescopu

Cycloaddition Isomerizations of Adsorbed 1,3-Cyclohexadiene on Si(100)-2×1 Surface: First Neighbor Interactions

The initial and subsequent surface reaction mechanisms of 1,3-cyclohexadiene on the Si(100)-2×1 surface were theoretically explored, focusing on the possible first-neighbor interactions. Five different initial reaction channels leading to nine different surface products were identified, confirming previous experimental reports of inter-dimer structures. Among the nine identified products, five of these surface products are new species that have not previously been reported. Potential energy surface studies reveal that the net reaction barriers within a given channel are very small, indicating that the final product distributions within that channel are determined by thermodynamics. On the other hand, thermal isomerizations between different channels are not expected to occur easily. Therefore, the surface product distributions among the five different channels are more likely to be determined by kinetics. As a result, understanding the relationships among the available reaction channels both kinetically and thermodynamically is essential for properly interpreting the experimental results. The current study shows that the subsequent surface chemical reactions of unsaturated initial surface products are strongly coupled with the first-neighbor interactions

Comparative Study of Surface Cycloadditions of Ethylene and 2-Butene on the Si(100)-2 × 1 Surface

Multireference wave functions were used to study the ethylene and 2-butene surface reactions on Si(100) in their lowest energy singlet states. In addition to the diradical pathway, a π-complex pathway on the ethylene surface was found. The net barrier for the latter process is 4.5 kcal/mol higher than that for the former, making the π-complex pathway kinetically less accessible. Therefore, although there is a competition between the two initial channels, the diradical path is slightly favored, and rotational isomerization is possible. However, since the initial potential energy surfaces of the two channels are different, depending on experimental conditions, the branching ratio between the two channels may change. Consequently, the combined effects that would favor one channel over the other may not derive directly from the initial reaction barrier. This provides an explanation of the experimental controversy. As a result, the final distributions of surface products may depend on the experimental kinetic environment, especially when the population change due to the rotational isomerization is expected to be very small. A significantly different reaction channel is found in the 2-butene surface reaction on Si(100), in which a methyl hydrogen easily transfers to the surface yielding a new type of surface product other than the expected [2 + 2] cycloaddition product, with a comparatively small activation barrier. Consequently, the overall surface reactions of ethylene and 2-butene may be quite different. Therefore, direct comparisons between ethylene and 2-butene experimental results would be very useful