The intensity of light produced from synchrotrons enables X-ray imaging down to the micron and submicron scale. This high degree of resolution is necessary to study metals in hydrated biological samples, where trace (metal) elements are found in the lowest concentration. Water within these aqueous samples will undergo radiolysis and produce various reactive oxygen species, which degrades the quality of information gathered from the sample during X-ray imaging. Studies have shown that the best way to counter the effects of radiolysis and preserve samples in their metabolic state during X-ray imaging is to keep them cryogenically frozen. We have developed affordable cryostats and novel protocol to not only improve cryo-imaging at current third-generation synchrotrons, but also enable cryo-imaging at existing synchrotrons that have limited accessibility. This dissertation will provide a detailed description of the tasks that were accomplished to contribute to the development cryo-imaging. The first task was the fabrication of a portable cryostage. The cryostage's discreet profile and unique design successfully enabled it to be effortlessly adapted into three beamlines across two different DOE facilities and facilitate multiple imaging modalities, i.e., correlative imaging. With the next task, we explored adding an ice frame about the stage to help reduce the accumulation of frost on the surface of a frozen sample that was explored. The addition of the ice frame significantly improved the imaging of frozen samples, nearly doubling the overall image clarity in comparison to when it was absent. The final task saw the application of a cryostream, in place of a cryostage, to provide a cooled convective flux across the sample for 2D and 3D visualization for cryo X-ray imaging. / Doctor of Philosophy / Synchrotrons are light producing particle accelerators that enable X-ray imaging down to the micron and submicron scale. This high degree of resolution is necessary to study metals in hydrated biological samples, where trace elements are found in low concentrations. The X-ray beam from the synchrotron will force any water within these aqueous samples to undergo radiation induced water decomposition, i.e., radiolysis, and produce hydroxyl radicals that will degrade the quality of information gathered from the sample during X-ray imaging. Early studies have shown that the best counter to the effects of radiolysis, while also preserving samples in their metabolic state during X-ray imaging, is to keep them cryogenically frozen. We have developed affordable cryostats and novel protocols to not only improve cryo-imaging at current third-generation synchrotrons, but also enable cryo-imaging at existing synchrotrons that have limited accessibility. This dissertation will describe, in detail, three tasks that were accomplished. The first task was to the fabrication of a portable cryostage. The cryostage unique design successfully enabled it to be used within different beamlines and for multiple imaging perspectives. With the next task, an ice frame to help reduce the accumulation of frost on the surface of a frozen sample being explored. The ice frame was shown to significantly improve the imaging of frozen samples. The final task saw the application of a cryostream, a jet stream of cold nitrogen gas, to enable an alternative approach for 2D and 3D visualization for cryo X-ray imaging.

The most ubiquitous mode of frost formation on substrates is condensation frosting, where dew drops condense on a supercooled surface and subsequently freeze, and has been known since the time of Aristotle. The physics of frost incipience at a microscopic scale has, nevertheless, eluded researchers because of an unjustified ansatz regarding the primary mechanism of condensation frosting. It was widely assumed that during condensation frosting each supercooled droplet in the condensate population freezes in isolation by heterogeneous nucleation at the solid-liquid interface, quite analogous to the mechanism of icing. This assumption has very recently been invalidated with strong experimental evidence which shows that only a single droplet has to freeze by heterogeneous nucleation (typically by edge effects) in order to initiate condensation frosting in a supercooled condensate population. Once a droplet has frozen, it subsequently grows an ice bridge towards its nearest neighboring liquid droplet, freezing it in the process. Thus ensues a chain reaction of ice bridging where the newly frozen droplets grow ice bridges toward their nearest neighbor liquid droplets forming a percolating network of interconnected frozen droplets. Not always are these ice bridges successful in connecting to their adjacent liquid droplets. Sometimes the liquid droplet can completely evaporate before the ice bridges can connect, thus forming a local dry region in the vicinity of the ice bridge. In this work, we first formulate a thermodynamic framework in order to understand the localized vapor pressure gradients that emerge in mixed-mode phase-change systems and govern condensation and frost phenomena. Following this, we study droplet pair interactions between a frozen droplet and a liquid droplet to understand the physics behind the local ice bridge connections. We discuss the emergent scaling laws in ice bridging dynamics, their relative size dependencies, and growth rates. Thereafter, we show how with spatial control of interdroplet distances in a supercooled condensate and temporal control of the first freezing event, we can tune global frost propagation on a substrate and even cause a global failure of all ice bridges to create a dry zone. Subsequently, we perform a systematic study of dry zones and derive a scaling law for dry zones that collapses all of our experimental data spanning a wide parameter space. We then show that almost always the underlying mechanism behind the formation of dry zones around any hygroscopic droplet is inhibition of growth and not inhibition of nucleation. We end with a discussion and preliminary results of our proposed anti-frosting surface that uses ice itself to prevent frost. / Master of Science

Matter on earth exists mostly in three different phases of solid, liquid, and gas. With extreme amounts of energy, temperature, or pressure, a matter can be changed between the phases. Six different types of phase-change phenomena are possible: freezing (the substance changes from a liquid to a solid), melting (solid to liquid), condensation (gas to liquid), vaporization (liquid to gas), sublimation (solid to gas), and desublimation (gas to solid). Another form of phase change which will be discussed here is the wetting or dewetting transitions of a superhydrophobic surface, in which the phase residing within the surface structure switches between vapor and liquid. Phase transition phenomena frequently occur in our daily life; examples include: a ``liquid'' to ``solid'' transition when cars decrease their distance at a traffic light, solidification of liquids droplets during winter months, and the dancing of droplets on a non-sticking pan. In this dissertation we will address seven different phase-change problems occurring in nature. We unveil completely new forms of phase-change phenomena that exhibit rich physical behavior. For example, during traffic flow, drivers keep a large distance from the vehicle in front of them to ensure safe driving. When vehicles come to a stop, for example at a red light, drivers voluntarily induce a ``phase transition'' from this ``liquid phase'' to a close-packed ``solid phase''. This phase transition is motivated by the intuition that traveling as far as possible before stopping will minimize the overall travel time. However, we are going to investigate this phase-change process and show that this long standing intuition is wrong. Phase-change of solidification will be discussed for different problems. Moreover, the complex physics of oil as it wicks up sheets of frost and freezing of bubble unveil completely new forms of multiphase flows that exhibit rich physical behavior. Finally, the ``Cassie'' to ``Wenzel'' transition will be investigated for layered nano-textured surfaces. These phenomena will be modeled using thermodynamics and fluid mechanics equations. / Doctor of Philosophy / The main focus of this dissertation is on the dynamical phase change phenomena occurring in nature. First, we study the solid to liquid phase change of group of people moving from rest. We show that increasing the packing density of vehicles at a stop-and-go motion (e.g., vehicles at a traffic light) would not increase the efficiency of the flow once it is resumed. Second, we present a passive anti-frosting surfaces just by using the chemistry of ice. We show how the in-plane frost growth can be passively suppressed by patterning arrays of microscopic ice stripes across a surface. Third, we elucidate how bubbles deposited on a chilled and icy substrate freeze in different ambient conditions. We reveal the various phenomena that govern how soap bubbles freeze and produce a variety of beautiful effects. Fourth, we will study oil-ice interactions which are important for the emerging science of using oil-impregnated surfaces for anti-icing and anti-frosting applications, where oil drainage from the surface due to wicking onto ice is a pressing issue. We observe oil as it wicks up sheets of frost grown on aluminum surfaces of varying wettability: superhydrophilic, hydrophilic, hydrophobic, and superhydrophobic. Fifth, we study the effect of topography of the nanopillars on dynamics of jumping droplets. The critical diameter for jumping to occur was observed to be highly dependent on the height and diameter of the nanopillars, with droplets as small as 2 µm jumping on the surface with the tallest and most slender pillars. Sixth, we show that micrometric condensate spontaneously launches several millimeters from a wheat leaf’s surface, taking adhered pathogenic spores with it. We quantify spore liberation rates of order 10 cm⁻² hr⁻¹ during a dew cycle. Finally, inspired by duck feathers, two-tier porous superhydrophobic surfaces were fabricated to serve as synthetic mimics with a controlled surface structure. We show the effect of layers of feathers on energy barrier for the wetting transition.