Master of Science in Chemical Engineering, University of Toledo, 2007, Chemical Engineering

This study attempted to determine if common processing parameters cause changes in the surface tension of the polymer. Initially, several contact angle techniques were tested to determine the optimal technique to be used for the remaining experiments. From these initial tests, the Harmonic Mean method was selected to determine the surface tension of the polymers. Flat parts were injection molded from both copolymer and homopolymer resins and aged at room temperature and humidity for two months. The surface tension of these parts was measured during several intervals throughout this storage time. The surface tensions of both materials dropped slightly for the first week of storage before leveling off to 44-47dynes/cm. Varying the injection molding conditions did not seem to cause the surface tension to change drastically. Some additional materials were aged for three weeks at 40°C to accelerate the aging process; however this also did not cause a significant change in the surface tension. Films were stretched under various conditions and it was found that increasing the planar extension decreased the surface tension. To determine if this was due to polar end group concentrations on the surface, films were exposed to UV light. The surface tension was found to increase with increased UV exposure time. The end group concentrations for the exposed samples were measured and it was found that the end group concentration increased with exposure time. For times up to 96 hours, the measured end group concentrations correlated well with intrinsic viscosity measurements. Bottles were blow molded under various conditions; it was found that the bottles blown from preforms having the highest temperature had the lowest surface tension. Storage of the bottles at room temperature and humidity caused the surface tension to decrease to around 45 dynes/cm. The films that were stretched to the same level as the bottles had similar surface tensions as the bottles after storage.

Committee: Saleh Jabarin (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2024, Polymer Engineering

Reciprocating compressors are critical components for the natural gas energy infrastructure throughout the world. Proper lubrication of PTFE and PEEK based packings and piston rings (seals) in the compressor cylinder is necessary to prevent leaks of methane to the environment and allow efficient, reliable, and extended operation of the compressor. Cylinder lubrication is poorly understood and commonly cited as the reason for premature seal failures while being a major annual expense for compressor station operators. An industry priority is to reduce the amount of lubricant injected into the compressor cylinder. The lubricant is carried away by the process gas and collects in pipelines or other downstream equipment. To better understand the tribological aspects and physical phenomena of compressor cylinder lubrication, the effect of high pressure methane on the surface tension of common lubricants and sealing materials was investigated. Methane gas pressure exhibited an inverse relationship with liquid lubricant surface tension through a pendant drop test. Methane pressure also increased the contact angles of sessile drops of lubricants on the solid surfaces. Nitrogen pressure exhibited the same trends but to a lesser extent than methane. Analysis using the Owens, Wendt, Rabel and Kaelble calculation method revealed that as methane pressure increased, the surface free energy of the seal materials decreased. These results further revealed that increased gas pressure decreased the wettability of lubricants on the materials. PTFE based materials decreased much more than PEEK based materials. Spontaneous adsorption of the pressurized gases on the surface of the lubricant drops and sealing materials was determined to be the underlying cause of the reductions of surface energy. This new understanding is significant because it better explains the observed lubrication phenomena and may be able to guide the industry toward optimized lubrication, more efficient se (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor); Weinan Xu (Committee Chair); Christopher DellaCorte (Committee Member); Fardin Tayebeh Khabaz (Committee Member); Sadhan Jana (Committee Member) Subjects: Energy; Engineering; Materials Science; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2015, Biomedical Engineering

Three-dimensional (3D) cell culture technologies have gained a considerable momentum in compound screening applications to identify novel anti-cancer drugs. Increasing evidence shows substantial differences between responses of cancer cells to drug compounds in monolayer cultures (2D) traditionally used in drug discovery and in vivo during preclinical tests. 3D cell cultures more closely resemble tumors in terms of close cell-cell and cell-extracellular matrix interactions, non-uniform distribution of soluble factors, and presence of hypoxic cells. As such, they provide a relevant tumor model to elicit more realistic responses from cells treated with drugs. Screening of libraries of compounds to identify novel drugs requires high throughput 3D culture platforms that produce consistently sized cancer cell spheroids and allow convenient drug testing and analysis of cellular responses. In this study, we introduce a novel, automated technology for 3D culture of cancer cell spheroids in a high throughput format. Aqueous two-phase systems (ATPS) are used for producing spheroids with robotic tools and standard equipment. ATPS are formed by mixing appropriate mass concentrations of two biocompatible polymers such as dextran (DEX) and polyethylene glycol (PEG). A nano-liter drop of the denser aqueous DEX phase containing cancer cells is robotically dispensed into each well of a non-adherent 96-well plate containing the immersion PEG phase solution. A round drop containing cells forms at the bottom of the well while overlaid with the aqueous PEG phase. Cells remain in the DEX drop and form a spheroid, which receives nutrients from the immersion phase through diffusion into the drop. The fidelity of the ATPS spheroid culture technology depends on favorable partition of cells to the DEX drop. We investigate partition of cancer cells in ATPS and demonstrate the effect of interfacial tension between the two aqueous phases on the distribution of cells in ATPS. To facilitate (open full item for complete abstract)

Committee: Hossein Tavana (Committee Chair) Subjects: Biomedical Engineering

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

A new method is proposed to mitigate ice accretions on wind turbine blades via the creation of a microstructural gradient surface geometry that facilitates spontaneous water droplet motion along the surface. The wettability gradients are formed by laser etching 35𝜇m wide, 35𝜇m deep channels into aluminum to form a surface with a gradually increasing solid area fraction. Different design permutations are then proposed and systematically evaluated on the merits of their performance. An analytical model is also derived based on a balance of hysteresis and drag forces to predict the critical airspeed necessary for droplet movement as a function of the droplet size and surface contact angle. Experimentation has shown good agreement with the model for both the baseline and fixed-pitch channel surfaces and has also demonstrated that, in certain cases, up to 70% lower critical airspeeds are needed to initiate droplet motion on these microstructured surfaces. Finally, the effects of frozen droplets on aerodynamic performance were studied via 3D-printed airfoil prototypes. This work demonstrated that at airspeeds under <15m/s and angles of attack between 0 – 20 degrees, frozen droplets on the top surface of the airfoil can be used to strengthen the lift-to-drag ratio by up to 184

Committee: Andrew Sommers (Advisor); Medhi Zanjani (Committee Member); Edgar Caraballo (Committee Member) Subjects: Alternative Energy; Energy; Engineering; Fluid Dynamics; Mechanical Engineering

PhD, University of Cincinnati, 2020, Engineering and Applied Science: Aerospace Engineering

Surface tension force concentrates only on a thin layer near the surface or interface, it usually exists as boundary condition but not force term in momentum equation. Surface tension is a common phenomenon in many problems, such as metal casting, fuel injection systems, and droplets, etc. where surface tension force may be dominant. In simulations for such problems, surface or interface tension is unneglectable and special care is needed to reproduce surface tension effects. Even for those two-phase flows where surface tension force itself may be negligible, the accurate interface detection is still desired for proper modelling of the flow field discontinuity, such as density jump across the interface. In SPH, the most popular methods for surface tension simulating is to evaluate curvature and normal with SPH interpolation on particle cluster, surface is not explicitly constructed. The accuracy of the interpolation approaches often suffers from the nonuniform particles distribution. In mesh-based methods, it has been shown that excellent results of curvature and normal estimation are obtained from explicit surface reconstruction [23][55]. It is natural to reconstruct explicit surface from SPH particles and expect accurate surface tension effects, because the domain is discretized with particles which are moving in Lagrangian fashion in SPH. The positions of particles coincide with the interface and the domain. However, it is not easy to represent fluid surface in SPH because the connectivity (topology) between particles are not maintained. This dissertation presents a novel approach for modeling the surface tension with SPH when simulating fluids and fluid-like media where surface tension is important. The approach constructs a local Delaunay triangulation on the neighboring particles for each candidate surface particle. Both the surface particle detection and local surface reconstruction are completed with the same local Delaunay triangulation. The signific (open full item for complete abstract)

Committee: Gui-Rong Liu Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Mark Turner Sc.D. (Committee Member) Subjects: Aerospace Materials

PHD, Kent State University, 2019, College of Arts and Sciences / Department of Physics

The main goal of this research is to study the surface properties of liquid-vapor and liquid-liquid-vapor interfaces with high precision using the technique of surface light scattering spectroscopy (SLSS), which measures the power spectrum of light scattered from thermally generated capillary waves with an rms height ~1 nm. This power spectrum depends on both surface and bulk properties of the fluid, including surface tension and bulk viscosity, allowing the inference of the values of these and perhaps other parameters. In this dissertation, I focus on the surface tension and bulk viscosity associated with a liquid. Innovative optical design has increased signal and signal-to-noise ratio. This enhances measurement accuracy over the entire range of wave numbers, while enabling measurements at higher wave numbers above 1500/cm. After refining the apparatus and technique as much as possible, I apply it to a sequence of systems. (a) Simple Fluids: Standard materials including acetone, pentane, methanol and water serve to calibrate and validate the SLSS technique and experimental protocol. (b) Highly viscous fluids, relevant for capillary-driven fluid management to control propellant transfer in space flight. We explore the regime between the overdamped and underdamped cases, which have been difficult to characterize with SLSS, using well-characterized glycerol/water mixtures. (c) Mixtures: Measurements of pentane/2-methylpentane mixtures prepare for an upcoming NASA microgravity experiment to optimize the effectiveness of wickless heat pipes. (d) Thin organic films on water: coupling between upper and lower interfaces of a thin film allows the study of Casimir-Polder forces and measurement of the onset of wave mode transitions, for example, peristaltic suppression. (e) Molecularly thin films on water: thin films of a smectic liquid crystal on water have many applications, directly as biosensors, and indirectly, to develop a better understanding of alignment laye (open full item for complete abstract)

Committee: Elizabeth Mann (Advisor) Subjects: Physics

Master of Science, The Ohio State University, 2018, Food Science and Technology

The milk fat globule membrane (MFGM) plays an essential role in emulsifying milk fat. In recent decades, the behavior of MFGM polar lipids has been studied using Langmuir trough model systems, were the surface tension of lipid monolayers spread on the surface of a aqueous solution is analyzed as the surface is compressed or expanded. The problem with most Langmuir trough experiments reported in the literature that study MFGM lipid behavior is that they spread MFGM lipids on solutions that are not fully representative of milk. Pure milk naturally contains protein and lipid surfactants, which makes studying the behavior of isolated lipid monolayers spread on pure milk difficult. In this thesis, a process to produce non-surface-active (NSA) solutions from bovine skim milk and dairy-based beverages that have insignificant amounts of surfactants is described. The resulting NSA solutions from the process described here can be used to improve Langmuir trough experiments on MFGM lipids. The process to produce NSA solutions involves two steps. The first step is ultrafiltration of milk through an ultrafiltration membrane with a molecular weight cut-off of at least 10 kDa. The second step is washing the permeate obtained from ultrafiltration 4 times with water-immiscible solvents at a 10:1 permeate to solvent (v/v) ratio. Collected permeate is washed once with hexane, once with chloroform, and then twice with hexane before being filtered through activated carbon. Solvent washing removes proteins in the permeate by forming protein stabilized permeate-in-solvent emulsions that can be separated from the permeate in a separatory funnel. NSA solutions produced from skim milk had a significantly higher surface tension than pure skim milk, resulting from the loss of surfactants. There was no significant difference in the surface tension of the resulting NSA solutions when their surface was compressed, indicating a lack of adsorbed surfactants at their surface. Percent total solids we (open full item for complete abstract)

Committee: Rafael Jimenez-Flores (Advisor); Heather Allen (Committee Member); Emmanuel Hatzakis (Committee Member) Subjects: Food Science

PhD, University of Cincinnati, 2016, Engineering and Applied Science: Mechanical Engineering

The effects of surface wettability, liquid properties, and design conditions on bubble growth from orifice plates and capillary orifices submerged in liquid pools have been experimentally and computationally studied. For orifice plates submerged in water, above a certain critical contact angle, the bubble base was observed to spread away from the orifice resulting in larger bubbles at departure. By scaling the forces acting on the bubble and using a minimum energy approach, a correlation to predict the static regime equivalent bubble departure diameter was proposed using data obtained from the current experiments and existing literature. Following this, ebullience in aqueous surfactant solutions was investigated. First, bubble growth from a capillary-tube orifice submerged in pools of aqueous surfactant (SDS and CTAB) was studied. A new numerical treatment was developed to determine the surfactant transport and adsorption/desorption in the interface region. From the variation of the surfactant interfacial concentration, the spatio-temporal variation in interfacial tension is determined. Due to the resulting variation in interfacial tension, the shapes and sizes of bubbles in surfactant solution are different from those in pure liquid. The results were compared to those obtained from experiments and were found to be in excellent agreement. Experiments were then conducted for orifice plates submerged in SDS with varying concentrations. Ethanol-water binary mixtures of similar liquid-vapor interfacial tensions were also used in order to decouple the compound effect of surface tension and contact angle on bubble size. It was found that there was a critical surface tension below which spreading of the bubble base was absent even for super-hydrophobic surfaces such as Teflon. However for such surfaces, beyond the critical surface tension, there was a sharp increase in the bubble size due to surface dewetting. This increase in bubble size was not linear but more of (open full item for complete abstract)

Committee: Milind Jog Ph.D. (Committee Chair); Yuen Koh Kao Ph.D. (Committee Member); Raj Manglik Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering; Mechanics

MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering

The objective of the present work is to develop a computational model to simulate liquid droplet impact and post-impact spread-recoil dynamics on a horizontal, flat, smooth, dry surface. The governing equations of continuity and momentum are solved to simulate the transient flow. Volume of Fluid (VOF) method is applied to capture continuously deforming gas-liquid interface. Simulations are carried out for pure water and aqueous solution of Sodium Dodecyl Sulphate (SDS) droplet impact on a hydrophobic (Teflon) surface. Simulations are carried out for Weber number 20 and 80 with impact velocities of 0.7 m/s and 1.4 m/s and droplet diameters of 2 mm and 3 mm, respectively. The results show increase in maximum spreading factor with increase in Weber number. Computational results predict advancing, recoiling and bouncing behavior of water droplets on the Teflon surface which agrees with the experimental observations available in literature. Aqueous solution of Sodium Dodecyl Sulphate (SDS) at twice the Critical Micelle Concentration (2×CMC) is used and its time and space dependent surface tension behavior is modeled. It is observed that dynamic surface tension plays a primary role in the modification of droplet spread-recoil process. The simulation results for surfactant solution show larger drop spread followed by weaker recoil and no rebound from the surface. These results are validated with experimental measurements reported in the literature. Non-isothermal impact conditions are investigated to study heat transfer phenomenon during droplet impact. The solid surface is maintained at 353°K and corresponding heat flux values and overall heat transfer rates for both pure water and surfactant solution drops are calculated. The results indicate that aqueous surfactant solution improves the liquid-solid wetting area and results in higher heat transfer compared to pure water droplet.

Committee: Milind Jog Ph.D. (Committee Chair); Jude Iroh Ph.D. (Committee Member); Raj Manglik Ph.D. (Committee Member) Subjects: Mechanics

MS, University of Cincinnati, 2008, Engineering : Mechanical Engineering

Two-phase flow plays a major role in number of technologies used in fuel cells, bioreactors, phase and particle separators, thermal management systems, chemical reactors, etc. Some of these applications involve air–water two-phase flow in channels much less than 1 mm in diameter. The fundamental understanding of flow characteristics, such as flow regime, pressure drop, and heat transfer, is essential in the design and control of these devices. In this work, an experimental set-up is developed to investigate the effects of surface energy/surface wettability and geometry on characteristics of two-phase flow in horizontal microchannels at adiabatic conditions. Two-phase (air-water) slug flow is established in microchannel test sections of varying sol-gel dip coated surface wettabilities. Pressure drop measurements and flow pattern detection by high speed visualization are employed to characterize the flow. Results indicate that two-phase flow resistance is a strong function of surface wettability and it increases with static contact angle. Significant change in contact line in advancing and receding interface, and thus increase in flow resistance, is observed with increase of hydrophobicity while geometry of the channels influences the frequency of the slugs. Presence of thin liquid film, whose thickness is a strong function of wettability, is observed experimentally which clearly elucidates the pressure drop variation with surface wettability. Hence for characterizing two-phase flow in microchannels surface wettability parameters should be accounted appropriately.

Committee: Dr. Sang Young Son (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, The Ohio State University, 2012, Mechanical Engineering

The acute respiratory distress syndrome (ARDS) is a devastating lung disease. Patients with ARDS must be placed on a mechanical ventilator to survive. However, these ventilators also exacerbate the existing lung injury and as a result the mortality for ARDS is high (~25-40%). During ARDS, small pulmonary airways become occluded with fluid and mechanical ventilation of the fluid-filled lung involves the reopening of fluid-filled airways and the propagation of microbubbles over a layer of epithelial cells lining airway walls. Previous computational and experimental studies indicate that the large spatial gradients in pressure generated near the bubble tip may cause large-scale cellular deformation, rupture of the plasma membrane and cell necrosis. However, previous computational models do not account for the complex fluid-structure interactions that occur during in-vitro or in-vivo experiments. In addition, previous studies assumed rigid-wall conditions while pulmonary airways are in reality highly compliant and changes in airway wall mechanics may significantly influence the dynamics of airway reopening and cell deformation. Furthermore, the lung consists of a large network of bifurcating airways and different bifurcation patterns may influence both the hydrodynamics of airway reopening and cellular injury/deformation especially when the effect of gravity is considered. The objective of this particular thesis is to employ sophisticated computational fluid-structure interaction models to investigate how changes in the patient's biomechanical status such as airway wall compliance, fluid properties and bifurcation patterns influence the mechanics and hydrodynamics of microbubble induced cellular deformation and injury. We have developed several sophisticated computational models that can better represent the in-vivo or in-vitro conditions of compliant airway walls, fully coupled fluid-structure interactions and 3D structure of pulmonary airways with epithelial cells l (open full item for complete abstract)

Committee: Samir Ghadiali PhD (Advisor); Terrence Conlisk PhD (Committee Member); Yi Zhao PhD (Committee Member); Ronald Xu PhD (Committee Member) Subjects: Aeronomy; Biomedical Engineering; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2008, Chemical Engineering

The field of microfluidics, lab-on-a-chip technologies in particular, promises the capacity to automate sophisticated laboratory analyses into a platform that can be implemented by a user with minimal analytical experience. However, the fabrication methods traditionally employed to manufacture microfluidic devices are cost ineffective and time intensive. Consequently, current production techniques render exploiting this technology for clinical application problematic. This work describes an alternative fabrication technique to mitigate the aforementioned problems through surface tension-driven flow. Hydrophilic conduits are patterned on a variety of commodity polymeric substrates. The opposing two-dimensionally patterned devices are brought within close proximity for the fabrication of a parallel plate configured microfluidic device. The microfluidic platforms demonstrate the ability to facilitate spontaneous capillary pumping with a high degree of precision and minimal expenditure of fluid reagent. In particular, several cost-effective fabrication procedures are illustrated as well as the capacity to manipulate fluids within the platforms utilizing volumes less than 20 total microliters. Furthermore, applications are demonstrated within the devices such as enzymatic-catalysis, on-chip urinalysis (i.e. glucose and protein detection), and micromixing; demonstrating the efficacy of the platform to automate fluid transport concomitantly with reaction processes. In addition, preliminary designs and protocols are suggested in the last chapter of this work for surface tension-confined devices capable of performing enzyme-linked immunosorbent assay (ELISA) and fluorescence resonance energy transfer (FRET). Moreover, theoretical aspects of microfluidic flow are explored within this document including the physics of wetting and wetting energetics, factors influencing surface tension (and thereby the system driving force), the conservative level set method coupling two-phase (open full item for complete abstract)

Committee: Gary Wnek (Advisor) Subjects:

Master of Science, The Ohio State University, 2021, Chemistry

Some of the most common ions in the atmosphere are nitrate (NO3-) and chloride (Cl-) which play key roles in many atmospheric reactions, including ozone depletion. Additionally, they influence the iron equilibria that dictate reaction kinetics. Heterogeneous reactions are heavily influenced by the presence of ions at the air-water interface but there is still not a definitive distinction between the surface propensity of NO3- and Cl-. The impact of NO3- and Cl- on the hydrogen-bonding structure at the air-water interface has been examined using second harmonic generation (SHG) and surface tension measurements. The impact of ferric iron on the propensity of NO3- has also been examined with surface tension by comparison to sodium nitrate. The SHG electric field shows that the hydrogen-bonding structure of NaNO3 and NaCl solutions is significantly different from neat water but shows a slightly different dependence on concentration. Surface tension measurements support this change in structure by displaying significantly different concentration dependence. The introduction of iron has a large impact on the surface as shown by the increased surface tension slope as well. To confirm the presence of iron-anion dipoles, geometry optimization of ferric chloride complexes was performed to obtain dipole moments.

Committee: Heather Allen Dr. (Advisor); Anne Co Dr. (Committee Member) Subjects: Chemistry

Master of Science, The Ohio State University, 2021, Nuclear Engineering

Molecular dynamic simulations are used to calculate the thermophysical, structural and liquid-vapour interface properties of molten salts. An interaction pair potential based on Born-Mayer form with an account of polarization is used to model the systems. The potential parameters are taken from already parameters synthesized through a first-principles basis by the force-matching procedure. A benchmarking of the potential is done via the binary alkali halides. During the simulation, the thermophysical properties are calculated using either the Green-Kubo method or Einstein-type relations. The simulated results are compared with available experimental data, which showed an overall good agreement. Hence, using the same potential model, FLiBe, a common molten salt used in reactor systems, was simulated. Thermophysical properties and surface tension of pure FLiBe and FLiBe-ZrF4/ThF4 systems were obtained. Finally, to explain the release of radioactive elements into the environment through a salt mist formation, NaCl-UCl3 salt was analyzed. The surface tension indirectly affects the evaporation of molten salt. It was demonstrated that the caesium in reactor salt reduces the surface tension and thereby increasing the evaporation rate.

Committee: Dean Wang (Advisor); Marat Khafizov (Committee Member) Subjects: Nuclear Engineering

Master of Science, Miami University, 2019, Chemical, Paper and Biomedical Engineering

Light Duty Liquid (LDL) detergents are a mixture of surfactants in water, better known as dishwashing detergents, hand soap and general household products. The foamability of LDL detergent is an important metric when consumers are cleaning a surface. This study seeks to determine the effect of protein as foam booster on foamability. This study also seeks to study the location of protein in the emulsion and foam in varying LDL detergent and oil concentrations. The addition of protein acts as a foam booster to LDL detergent with olive oil in hardwater. These emulsion and foams made up of protein, LDL detergent and olive oil were separated and imaged by confocal microscopy and quantified by size exclusion high pressure liquid chromatography. Methods to remove oil from the emulsion and foam were developed for protein quantification. At low LDL detergent concentrations, the protein can be seen adsorbed to the oil-water interface. At high LDL detergent concentration, the protein is dispersed in the bulk fluid. The point at which the protein was no longer at the interface correlated well with the CMC of LDL detergent as calculated by surface tension and a pyrene assay.

Committee: Jason Berberich Dr. (Advisor); Andrew Jones Dr. (Committee Member); Justin Saul Dr. (Committee Member) Subjects: Chemical Engineering; Chemistry; Polymers

Master of Science, University of Toledo, 0, Mechanical Engineering

Superhydrophobic surfaces execute self-cleaning, anti-icing, and modifying heat transfer in many technological and industrial applications. In quest of maximizing water repellency, modification of droplet dynamics and subsequent reduction of contact time have been achieved by incorporating macrotexture on the superhydrophobic surfaces. However, the dynamics of low temperature water, and other viscous liquid droplets impacting anti-wetting surfaces with macrotextures is not well explored. In this thesis, we study the effect of viscosity on the bouncing dynamics of liquid droplets impacting macrotextured superamphiphobic surfaces using various glycerol-water mixtures as model liquids at different impacting conditions. Macrotextured surface are made by using an anti-wetting spray coating along with a tinned-copper wire as ridge on the silicon substrate. The complexity of viscous dissipation along the macrotexture and on the superamphiphobic surface is studied experimentally and then a new model is proposed for understanding when the macrotexture can induce maximum repellency of the viscous liquids on the superamphiphobic surfaces. A universal model for predicting minimum impact velocity for splitting is developed considering the droplet viscosity, velocity, volume, and other important parameters along with the surface characteristics and the macrotexture size. This enables engineering of surfaces for repelling droplets of viscous liquids such as freezing rain or inks during inkjet printing. Moreover, we studied the potentiality of superhydrophobic highly porous carbon nanotube (CNT) micropillars coated by the ultrathin, conformal, and low-surface-energy layer of poly (1H,1H,2H,2H-perfluorodecyl acrylate) (pPFDA) surfaces in condensation and freezing conditions (at high humidity). Droplet impact dynamics, condensate characteristics and freezing time delays are investigated on the CNT micropillars with various geometry along with the CNT forest and other commercially ava (open full item for complete abstract)

Committee: Hossein Sojoudi (Committee Chair); Reza Rizvi (Committee Member); Ana C. Alba Rubio (Committee Member) Subjects: Mechanical Engineering

Master of Science, Miami University, 2018, Chemical, Paper and Biomedical Engineering

Molecular force fields are not typically parameterized for properties such as surface tension at vapor-liquid equilibrium and so their performance when determining this property is difficult to predict. Grand canonical transition matrix Monte Carlo (GC-TMMC) molecular simulation is implemented in GOMC, an open source GPU-optimized Monte Carlo simulation code, which allows for a direct calculation of surface tension to compare the performance of standard Lennard-Jones and Mie n-6 potentials optimized for vapor-liquid equilibrium. While TraPPE demonstrates systematic errors in calculating this property, it significantly outperforms the Mie n-6 potential due to the latter's parameterization for saturated vapor pressure increasing the interfacial free energy relative to what TraPPE predicts.

Committee: Andrew Paluch (Advisor); Alan Ferrenberg (Committee Member); Catherine Almquist (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Chemistry

Upon wind action on the ocean surface, sea spray aerosols (SSA) are generated and released to the atmosphere. SSA are enriched in the organics and ions present in the sea surface microlayer (SSML) due to the selective transfer of these species to the aerosol phase, and can impact the climate through multiple mechanisms. Aerosols and clouds contribute the largest uncertainty in the prediction of climate change, so an understanding of SSA chemistry is of importance. The organic coatings identified on SSA contain a diverse array of surface-active molecules such as fatty acids. These coatings impact the reactivity, reflectivity, lifetime, and nucleating abilities of the aerosol particles. As these organic films impact the climate-relevant properties of SSA, an understanding of the fundamental physical chemistry phenomena of lipids and ions at these interfaces warrants investigation. In this dissertation, surface sensitive techniques were utilized to probe the structure and properties of fatty acid model systems under various pH and ion conditions. In the first part of this study, the surface-pKa values of medium-chain (C8-C10) fatty acids were quantified through the use of surface tension titration. Our simple surface tension titration technique quantified the surface-pKa of medium-chain octanoic (C8), nonanoic (C9), and decanoic (C10) fatty acids as 4.9, 5.8, and 6.4, respectively. The surface-pKa determined with surface tension differs from the bulk value obtained during a standard acid-base titration, and differences between surface- and bulk-pKa are observed starting at chain lengths of nine carbon atoms. In the titration curves of the C8 and C9 acids, surface tension minima are observed near the surface-pKa as a result of the formation of highly surface active acid-soap complexes. The direction of the titration was shown to affect the measured surface-pKa of the C9 system due to differences in Na+ concentration in the solution at pH values near the pKa. Palmi (open full item for complete abstract)

Committee: Heather Allen (Advisor) Subjects: Chemistry

Master of Science, University of Akron, 2018, Polymer Science

Knowledge of the work of adhesion and surface tension plays an important role in the design of new materials for applications such as coatings, adhesives, and lubricants. We develop an approach for obtaining work of adhesion and substrate surface tension from analysis of the equilibrium indentation data of rigid particles in contact with elastic surfaces. By comparing predictions of different models of a rigid particle in contact with a soft elastic surface we show that a crossover expression taking into account contributions of the elastic energy of the contact and surface free energy change in the contact area and outside is the best in describing the results of the coarse-grained molecular dynamics simulations. This crossover expression is applied to obtain work of adhesion and surface tension of polystyrene (PS) and poly(methyl methacrylate) (PMMA) particles on poly(dimethylsiloxane) (PDMS) substrates. This is achieved by studying the depth of indentations produced by PS and carboxyl group modified PS particles with radii Rp between 0.2 and 45.0 µm and PMMA particles with sizes between 0.58 and 52.1 µm in substrates made of super-soft, solvent-free PDMS elastomers with brush-like and linear chain network strands having the modulus from 3 to 600 kPa. Analysis of the experimental data results in the work of adhesion W=48.0±2.9 mN/m for PS/PDMS, W=268.4±27.0 mN/m for PS-COOH/PDMS and for W=56.2±2.4mN/m PMMA/PDMS. The surface tension of the PDMS substrate is found to be γs = 23.6±2.1 mN/m.

Committee: Andrey Dobrynin (Advisor); Ali Dhinojwala (Committee Member) Subjects: Materials Science; Physics; Polymers

Doctor of Philosophy, Case Western Reserve University, 2018, Biomedical Engineering

Bulk nanobubbles, also known as ultrafine bubbles (ISO/ TC281), have recently gained the interest of the research community for their potential application as ultrasound contrast agents for molecular imaging and cancer therapy. However, even with this growing interest, the very existence of nanobubbles and their use as contrast agents have been a subject of controversy for over a decade. This is due to the theoretical effect of reducing the bubble diameter to the nanoscale on both its Laplace pressure and resonance frequency leading to instability and reduced imaging quality, respectively. Despite these theoretical limitations, we have developed a stable and echogenic nanobubble formulation through incorporation of Pluronic, a nonionic triblock co-polymer surfactant, into the lipid shell of perfluorocarbon gas bubbles. To further understand the biophysical properties of these novel nanobubbles, we explored factors contributing to their echogenicity, stability, and fate after gas dissipation. Bubbles were confirmed to be in the sub-micron range and produced strong contrast at clinical ultrasound frequencies. Additionally, it was demonstrated that the incorporation of Pluronic into the lipid membrane increases the stability of nanobubbles under ultrasound by decreasing its monolayer surface tension. Due to the strong interest in the use of nanobubbles as drug delivery agents, their ultimate fate when destroyed by high-power ultrasound was investigated using cryo-EM. Lastly, as a proof of study, CA-125 and PSMA-targeted nanobubbles were developed for the detection of ovarian and prostate cancer, respectively. Results demonstrated that nanobubbles can be used to target and reach antigens expressed on cancer cells beyond the tumor vasculature. Characterization and optimization of nanobubble properties achieved the creation of novel, stabilized nanobubbles for numerous potential clinical applications.

Committee: Agata Exner Ph.D. (Advisor); Horst von Recum Ph.D. (Committee Chair); James Basilion Ph.D. (Committee Member); Dean Nakamoto M.D. (Committee Member) Subjects: Biomedical Engineering