The viscoelastic properties of the vitreous gel, major component in human eye, has not been investigated thoroughly so far. Despite our recent findings on the link between vitreous complications and several ocular diseases such as tractional retinal detachment, retinal tear, vitreous hemorrhage and glaucoma, there are still some unknown aspects that require more study to be done. Here, the emphasis is on characterization of the recent experimental tools invented at UCLA for analyzing rheology of the vitreous gel. We were able to present similar results in agreement with previous work. In addition to that, the relationship between the viscoelastic behavior patterns in a pair of eyes was investigated in different species. While the creep compliance behavior was different among species, we found a clear similarity pattern in creep compliance behavior within pairs in all species. This finding will significantly advance the future studies of biomechanics of vitreous gel such as more investigation on correlation between vitreous component interactions and vitreous related pathology or surgeries.

Sessile droplet evaporation is an omnipresent phenomenon both in nature and technologies such as biodiagnostics, microfabrication, inkjet printing, spray cooling, and agriculture irrigation. Evolution of single component sessile droplets has been extensively studied under various parameters. However, in real applications, sessile droplets usually consist of two or more components. It has been shown that the environmental conditions such as humidity and temperature substantially change the behavior of sessile droplets. The strong tendency of organic fluids to absorb water is an important factor in evaporation of these fluids in humid environment. The water vapor present in the surrounding adsorbs/absorbs and possibly condenses into the droplet transforming the droplet into a binary system. While the humidity of surrounding is typically an imposed condition resulting in unwanted effects for many industries, we have proposed that these undesired effects can be controlled and eliminated by tuning the temperature of the substrate. We have studied the combined effect of relative humidity of surrounding and substrate temperature on evaporation of methanol droplets. Our results demonstrated that the diffusion of water into the droplet can be limited by changing temperature of the substrate by both shortening the lifetime of droplet or increasing the temperature of the liquid-gas interface above the due point. Additionally, we have developed machine learning, classification and regression, models to analyze the behavior of droplet under different conditions. We have shown that the regime of droplet evaporation can be accurately classified by analyzing the profile of the evolution of droplet macroscopic parameters. We have also demonstrated that the humidity of surrounding can be accurately estimated by analysis of droplet profile. Furthermore, the time evolution of diameter and contact angle are estimated by the regression model. As the number of components in the droplet increases, the underlying mechanisms become more complex. The proposed approach to analyze the dynamics of sessile droplet evaporation through data-driven techniques opens up ways to better understand the complicated physics behind multi-component droplet evaporation and in general intricate interfacial fluid mechanics problems. The combined effect of surrounding humidity and substrate temperature has been experimentally studied on the behavior of ternary droplet consisting of methanol, anise oil, and water. The simultaneous optical microscopy and infrared thermography revealed different mechanisms in the droplet such as hydrothermal waves, oil microdroplet nucleation, etc. Our results showed three stages in the evolution of hydrothermal waves during droplet lifetime. The experimental procedures and results in this work introduce easy and inexpensive method to control sessile droplet behavior which are crucial for the final product resolution in numerous applications.

The vitreous humor is a clear gel with complex fluid characteristics that occupies more than two thirds of the eye globe volume. Recently vitreous structure and the connection between its characteristics and vitreoretinal diseases have drawn significant attention. However, the fluid properties of the vitreous gel and its degeneration remain poorly understood. Reported experimental studies are aggressive for the structure of the vitreous and can affect the results drastically. Hence a less invasive method can provide results with minimized alterations to the structure of the vitreous. In addition, a method that does not require dissection of the vitreous provides the opportunity for time dependent studies.

A better understanding of the complex structure and behavior of the vitreous gel and their changes during aging and various diseases such as diabetes can lead to improvements in current treatments. This knowledge can also help with the development of new therapeutic options, both surgical and pharmaceutical, for a variety of vitreoretinal conditions. Moreover, studying the connection between the macromolecular structure of the vitreous and its fluid properties can shed light on the pathobiology of vitreoretinal diseases, which may lead to the advancement of preventive care.

Rheological methods are commonly used to study the properties of complex fluids. However, it is not possible to avoid damages to the delicate structure of the vitreous gel using traditional shear rheological methods. The purpose of this study is to use a novel in situ rheological technique to measure the viscoelastic properties of the vitreous humor gel. In addition, we quantify the impact of enzyme activity on the vitreous humor structure over time to understand the caused changes in the mechanical characteristics of the vitreous. The viscoelastic behavior of vitreous gel is due to the presence of different biopolymers in its structure. In particular, fluid properties of the vitreous are directly related to the interaction of the fluid characteristics of collagen type II and hyaluronic acid networks. We studied the effects of collagenase type II on the vitreous in comparison with a control group using the in situ method. Furthermore, we analyzed the behavior of each component over time in both groups using mechanical analogies. We ran statistical analyses between the two groups to compare the changes in the collagen network characteristics over time. The results of analysis from individual components are in agreement with the results on the changes within the vitreous network in its entirety.

Condensation is a very complicated subject to fully unveil as it constitutes a complex interplay of momentum, heat and species transport and interfacial physics. Drop-wise condensation (DWC) adds more layers of complexity by introducing droplet dynamics and the two-way interaction with droplets surrounding. DWC has been shown repeatedly for about a century to possess around an order of magnitude improved heat transfer rates. Additionally, it has been shown that DWC is limited by the maximum size of droplets a surface sustains. Since this realization, promoting DWC has been greatly steered towards developing stable hydrophobic coating techniques. However, attempts have not been feasible so far especially due to the extreme conditions encountered in condensation processes. Another concern that has not been resolved adequately is the deterioration of heat and condensation rates due to the presence of non-condensable gases (NCG). This dissertation aims at understanding the process of condensation especially in the presence of NCG.

First, a numerical model of the process of vapor condensation on surfaces characterized by film-wise condensation with the presence of (NCG) is presented. State variables in both the condensate film and the diffusion layer were solved separately and the condensation interface was used to couple the two solutions. The solution of the condensate film was obtained using well-established solutions of laminar film condensation of pure vapor. In contrast to other models surveyed, this work provides a inexpensive and accurate predictions of heat and mass transfer characteristics. We validated the work against two classical condensation problems. The model was first validated against empirical correlations and experimental work, resulting in a very good agreement. We then assessed the applicability of ignoring the condensate film effect, as performed in previous models, on the condensation processes by observing the thermal resistances of both the condensate film and diffusion layer. Results indicated that for the studied cases of NCG mass fractions above 20\%, the condensate thermal resistance was at least an order of magnitude lower than that of the diffusion layer. However, the two thermal resistances seem to approach each other as NCG mass fraction becomes smaller. On another front, we observed that models that ignore the condensate film thermal resistance underestimate the interfacial temperature albeit accurately predicting the overall heat transfer rate. To simulate even lower NCG mass fractions, we validated our model to the classical analytical work of Sparrow and co-workers. Results showed an excellent agreement between the two solutions at different NCG mass fractions (0.5\%-10\%) and subcooling degrees (5$^o$F-40$^o$F). Finally, we found a good agreement between results of our model and the heat/mass transfer analogy. The heat/mass transfer analogy is a semi-empirical method therefore, is limited to the existing correlations and their uncertainties. On the other hand, our model does not use any empiricism and relies on the available solutions of laminar condensate film of pure vapor in predicting the liquid side heat transfer coefficient.

Moreover, motivated by the improvement in heat transfer by frequently disturbing the thermal boundary layer in nucleate boiling phenomenon, we attempted making the analogy to DWC. We developed an initial theoretical model to predict the transience of the diffusion boundary layer in condensation problems with NCG presence. The problem of suddenly exposing a cooled surface to a humid environment was modeled as two semi-infinite gas and solid domains in contact with the condensate film as a coupling condition. Results showed that the transient behavior of heat and condensation rates start by very high values and then decrease to steady state rates. This suggested that if the diffusion layer is frequently disturbed by droplets of heights similar to the layer's thickness, the condensation rate is expected to improve. To realize this, jet impingement of humidified air was proposed as a means of thinning the diffusion layer as well as to provide better shedding capabilities of condensate droplets.

Finally, Utilizing jet impingement technique as a means for continuous drop-wise condensation (CDC) was investigated. The technique showed an advantage of overcoming the necessity of using highly non-wetting surfaces while yet maintaining micron-sized droplets. By shifting focus from surface treatment to the force required to sweep off a droplet, we were able to utilize stagnation pressure of jet impingement to tune the shed droplet size. To demonstrate the effectiveness of this technique, we performed condensation experiments on a broad range of contact angle and contact angle hysteresis surfaces. The results showed that droplet size being shed can be tuned effectively by tuning the jet parameters namely the jet Reynolds number. Droplets as low as 20 $\mu$m in radius on a hydrophilic surface were shed with this technique surpassing the traditional gravity-assisted shedding mechanism by almost 80 folds. In terms of condensation rate improvement, we showed theoretically that CDC improves the condensation rate of pure steam, and hence heat transfer rate, by more than 300\% compared to gravity-assisted shedding DWC. Finally, our experimental observations showed that the effect of NCG, such as air in this work, is greatly alleviated by utilizing our technique. An improvement by at least six folds in mass transfer compactness factor compared to state-of-the-art dehumidification technology was possible. We illustrated the physics of droplet departure and mobility due to the stagnation flow condition by microscopically tracing a single droplet.

There are tremendous interests regarding the wettability of solid surfaces and controlling the wettability on the solid surfaces in industry, technology such as efficiency of oil recovery, micro-fluidics and nano-fluidics, drag reduction on airplane wings, efficient power plants and many other applications. To resolve such challenges, it is required to enhance the knowledge more deeply to understand the underlying physics of fluid/solid interaction at the liquid contact line that describes the dynamics of spreading.

Hence, in this research, experimental techniques have been performed to investigate parametric study about the dynamics of the liquid contact line (i.e. three-phase contact line) with consideration on molecular-kinetic theory (which concentrates on the adhesion of molecules at the vicinity of the liquid contact line) and the hydrodynamics theory (which focuses on the bulk motion of the liquid on the solid surface).

Over half a century, there have been many experimental/numerical investigations of the moving contact line in forced and spontaneous spreading. Surprisingly, there have been no experimental studies comparing these for the same solid/liquid/vapor system. In the present research such experiments have been performed on identical liquid-solid systems. It has been found out that there exists a huge distinction between experimental results obtained from spontaneous and forced spreading. For spontaneous spreading, excellent agreement has been found using the hydrodynamics theory, as expected. For forced spreading it was shown that hydrodynamic theory does not apply, but instead the molecular-kinetic theory does. This distinction between spontaneous and forced systems has never been noted before. Moreover, this research has provided a hypothesis for predicting the more appropriate model to describe the contact line dynamics for spontaneous and forced systems.

The forced spreading dynamics on low-energy surfaces (i.e. hydrophobic, ultra-hydrophobic glass surfaces, and micro-textured Teflon surfaces) has been investigated. The dynamics of spreading of several Polyethylene Glycol/Water (PEG/water) mixtures, with different weight ratios signifying the effect of the viscous force on spreading, on Teflon substrates (i.e. hydrophobic surfaces), ultra-hydrophobic sprayed glass substrates, and micro-textured Teflon plates have been investigated using Wilhelmy plate method with Tensiometer. It has been found out that spreading dynamics of the PEG/water mixtures on hydrophobic surfaces, ultra-hydrophobic glass surfaces, and micro-textured Teflon substrates are described more appropriately with molecular-kinetic theory.

The wettability of emulsions is a prominent factor with a broad impact in an extensive variety of industrial applications ranging from the petroleum to cosmetic industries. Surprisingly, there is no comprehensive study of emulsion spreading to date. In this research, the spreading of water/silicone oil emulsions on glass substrates was investigated. The time dependent variation of dynamic contact angle, base diameter, and the spreading rate of the emulsion droplets were studied. The effect of water/silicone oil weight percentage as well as the droplet size and dispersed phase bubble size were also investigated. The weight percentage of water/silicone oil emulsion and droplet size did not have a significant impact on the spreading dynamics; however the dispersed phase bubble size affected the spreading dynamics substantially. The coarsening of the dispersed phase bubbles was the key factor in the distinct spreading behavior of emulsions compared to pure liquids.

The only disadvantage of the Tensiometer is the fact of neglecting the viscous force in force measurement method applied on the plate’s surface during advancing and receding motion in the pool of highly viscous liquid. This neglect makes the Tensiometer to loose its extent of flexibility for being used for experiments with highly viscous liquids and for large liquid contact line speeds. To address this challenge, a viscous model for dynamic contact angle measurement using force-balance method with Tensiometer has been proposed.