Lubricants play an integral role in the operation of several technologies and in biology also, ranging from moving parts in machinery to the biolubrication of artificial joints. We have found that a colloidal dispersion consisting of easily synthesized highly spherical and uniform graphitic carbon particles results in a very efficient water based "green" and environmentally sustainable lubricant with very low friction coefficients and excellent surface wear protection. These particles use a rolling mechanism similar to nano --or microscale ball bearing under confinement. The effect of particle size on lubrication will be introduced and discussed. Additionally, carbon from sugars and carbohydrates, considered as "green precursors" because of their abundance in nature, have been favored for their low environmental impact and cost when compared to traditional oil based lubricants. The second part of my dissertation presents the fabrication and design of a novel bidirectional membrane device to assist child delivery in resource-limited settings. Approximately one third of pregnancies are delivered by one out of three possible operative methods: vacuum extraction, forceps operation, or caesarean section. Using these traditional devices or alternative methods, the risk of injuring to the mother and the fetus is elevated tremendously in the wake of poor training. Here, I present a polymer-based membrane, which will provide ultra-low friction thus facilitating child delivery but also have the ability to provide high friction when needed for child extraction. Specifically, the friction properties between polydimethylsiloxane (PDMS) and a borosilicate surface were studied using different lubricating media. The dynamics of the anisotropic surface morphology will be discussed and applied to this novel membranous device.

There has been significant interest in developing dry adhesives mimicking the gecko adhesive system, which offers several advantages compared to conventional pressure sensitive adhesives. Specifically, gecko adhesive pads have anisotropic adhesion properties: the adhesive pads (spatulae) stick strongly when sheared in one direction but are non-adherent when sheared in the opposite direction. This anisotropy property is attributed to the complex topography of the array of fine tilted and curved columnar structures (setae) that bear the spatulae. In this thesis, easy, scalable methods, relying on conventional and unconventional techniques are presented to incorporate tilt in the fabrication of synthetic polymer-based dry adhesives mimicking the gecko adhesive system, which provide anisotropic adhesion properties. In the first part of the study, the anisotropic adhesion and friction properties of samples with various tilt angles to test the validity of a nanoscale tape-peeling model of spatular function are measured. Consistent with the Peel Zone model, samples with lower tilt angles yielded larger adhesion forces. Contact mechanics of the synthetic array were highly anisotropic, consistent with the frictional adhesion model and gecko-like. Based on the original design, a new design of gecko-like dry adhesives was developed which showed superior tribological properties and furthermore showed anisotropic adhesive properties without the need for tilt in the structures. These adhesives can be used to reversibly suspend weights from vertical surfaces (e.g., walls) and, for the first time to our knowledge, horizontal surfaces (e.g., ceilings) by simultaneously and judiciously activating anisotropic friction and adhesion forces. Furthermore, adhesion properties between artificial gecko-inspired dry adhesives and rough substrates with varying roughness are studied. The results suggest that both adhesion and friction forces on a rough substrate depends significantly on the geometrical parameters of the substrate. The results in this study may be helpful for understanding how geckos overcome the influence of natural surface roughness. The novel designs of our dry adhesives open the way for new gecko-like adhesive surfaces and articulation mechanisms that do not rely on intensive nanofabrication. / acase@tulane.edu

The use of ethanol as an additive to gasoline fuel is becoming a common phenomenon. It helps solve the energy crisis and environmental issues that fossil fuel has brought about. However, when dissolved in motor oil, ethanol would dilute motor oil and drastically change its lubrication properties, in the same manner as gasoline dilution. Since ethanol has higher boiling point than gasoline, it takes longer time to be cooked away from the oil, causing more severe changes to motor oil properties. In this work, a new analytical method is presented to study the behaviour of ethanol/oil system. Seven motor oil formulations provided by Italian group E.n.i. are tested regarding their performance in resisting ethanol dilution. The tests are conducted in microcapillaries within which ethanol droplet dissolves in motor oil phase under 40oC or 60oC. Mathematical model is developed to study the shrinkage kinetics of ethanol droplets. And, the mass transfer coefficients of ethanol transporting to different oil formulations are obtained. Similar experiments are conducted on hexadecane and new and used Shell SAE 5W-30 motor oil to discover the difference between motor oil and pure hydrocarbon and the difference between new motor oil and used motor oil. It was found through hexadecane tests and Shell motor oil tests that hydrocarbons with shorter chain length were less capable of resisting ethanol dilution; old motor oil are slower in dissolving ethanol than new oil; and, suspected ethanol-soot complex may form in old motor oil, which might corrode engine parts. / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

"Hydrophobic hydration of non polar molecules is the principal driving force that dictates several interfacial phenomena in nature such as self assembly of surfactant molecules, fate of environmental pollutants, wetting of surfaces, solution behavior of polymers and folding of biological molecules such as proteins. However, the physics associated with hydrophobic interactions on a molecular length scale, which is central to self assembly and protein folding, is different from the macroscopic phenomena of de-mixing of oil and water or wetting of surfaces. This dissertation seeks to understand the implication of hydrophobic interactions to energy and environmental applications using different approaches. The first approach is to examine the behavior of water molecules with hydrophobic moieties at a molecular level using molecular dynamics simulations and evaluate macroscopic thermodynamic properties. The first problem addressed in this dissertation is the enclathration of gas molecules by water molecules in the presence of quaternary ammonium ions. Small polar organic molecules such as quaternary ammonium salts form crystalline inclusion compounds called semi-clathrate hydrates, where these polar molecules occupy a lattice position of the hydrogen bond network of water molecules. These crystalline structures of water are formed at ambient temperature and pressure conditions and can store as much 3%(w/w) of methane, making them potential materials for gas storage. The stability and structure of semi-clathrate hydrates of tetrabutylammonium bromide (TBAB) and methane were investigated using molecular dynamics (MD) simulations. MD simulations were done at varying conditions of temperature and pressure for methane-TBAB ratios of 0, 0.5, 1, 1.5 and 2. Thermo-mechanical properties evaluated using MD simulations were in agreement with experimental data available. Our investigation of this system shows that enclathration of methane in these semi-clathrate hydrates is thermodynamically favorable even at higher temperatures and shows signatures of hydrophobic hydration. Our estimation of free energies associated with successive inclusion of methane molecules in these cavities suggests a Langmuir-type adsorption of methane in these cages. Another problem investigated in this dissertation is the effect of chemical heterogeneity of crystalline cellulose (110) and (100) surfaces on their respective wetting behavior. Understanding the interaction of water with cellulose is important in the view of its role in consumer textiles made from cotton cellulose and potential applications of cellulose as biomaterials and as an energy source. The difference in the wetting behavior of (110) and (100) crystal surfaces is due to the asymmetry in the exposure of the hydroxyl groups by these surfaces. MD simulations were used to evaluate the contact angles of hemi-cylindrical water nanodroplets on crystalline (110) and (100) surfaces of the cellulose Iβ allomorph. While the native crystalline surfaces were completely wetted by water nanodroplets, substituting the primary hydroxyl groups with methyl and methoxy groups results in dewetting. The contact angle of a hemicylidrical water nanodroplet on the hydrophobically-modified (110) surface is greater than on the (100) surface suggesting that the (110) surface has a greater exposure of the primary hydroxyl groups. The solubility of cellulose in aliphatic N-oxides has been of particular interest because of its application in industrial processes such as Lyocell process. However, the mechanisms that dictate the dissolution of cellulose in these selective solvents are not clearly understood. Attempt is made to understand the solvation of cellulose in N-Methylmorpholine oxide (NMMO) and water from a molecular perspective. MD simulations of a model cellohexaose crystallite solvated respectively in pure water, NMMO and in an equimolar mixture suggest that while NMMO molecules preferentially cluster around the primary hydroxyl groups in cellohexaose chains, the role of water is critical in its ability to access the glycosidic oxygen. The second approach is to study the implication of introducing hydrophobicity at molecular level and experimental determination of its implication to addressing interfacial aspects of environmental remediation. Sub-micron size carbon particles derived from hydrothermal decomposition of sucrose are effective in stabilizing water-in-trichloroethylene (TCE) emulsions. Irreversible adsorption of carbon particles at the TCE-water interface resulting in the formation of a monolayer around the water droplet in the emulsion phase is identified as the key reason for emulsion stability. Cryogenic Scanning Electron Microscopy was used to clearly image the assembly of carbon particles at the TCE-water interface and the formation of bilayers at regions of droplet-droplet contact. The results from this study have broad implications to the subsurface injection of carbon submicron particles containing zerovalent iron nanoparticles to treat pools of chlorinated hydrocarbons that are sequestered in fractured bedrock. Interfacial aspects of hydrophobically modified biopolymer and its ability to enhance the stability of crude-oil droplets formed were investigated. Turbidimetric analyses show that emulsions of crude oil in saline water prepared using a combination of the biopolymer and the well-studied chemical dispersant (Corexit 9500A) remain stable for extended periods in comparison to emulsions stabilized by the dispersant alone. The hydrophobic residues attached to the polymer preferentially anchor at the oil-water interface and form a protective layer of the polymer around the droplets. The enhanced stability of the droplets is due to the polymer layer providing an increase in electrostatic and steric repulsions and thereby a large barrier to droplet coalescence. The implication of this study to current remediation methods is significant since the addition of hydrophobically modified chitosan following the application of chemical dispersant to an oil spill can potentially reduce the use of chemical dispersants. Increasing the molecular weight of the biopolymer changes the rheological properties of the oil-in-water emulsion. Emulsions stabilized by using a combination of Corexit 9500A and high molecular weight hydrophobically modified chitosan show characteristics of a weak gel. The ability of the biopolymer to tether the oil droplets in a gel-like matrix has potential applications in the immobilization of surface oil spills for enhanced removal. Carbon microspheres containing magnetite nanoparticles, synthesized using inexpensive precursors such as sucrose and iron chloride, are ferromagnetic and have affinity to the oil phase. We demonstrate that a thin layer of crude oil can be corralled and thickened by the application of nonionic surfactant. Following the application of magnetite-carbon particles, hydrophobically modified chitosan was applied to form a gel-like phase. This gel-like phase of crude oil containing magnetic carbon spheres can be removed as an aggregate using a magnet resulting in enhanced recovery of crude oil. The results from the current study point to developing potential applications for confinement, magnetic tracking and removal of surface oil. " / acase@tulane.edu

This research is focused on engineering submicron spherical carbon particles as effective carriers/supports for nanoscale zerovalent iron (NZVI) particles to address the in situ remediation of soil and groundwater chlorinated contaminants. Chlorinated hydrocarbons such as trichloroethylene (TCE) and tetrachloroethylene (PCE) form a class of dense non-aqueous phase liquid (DNAPL) toxic contaminants in soil and groundwater. The in situ injection of NZVI particles to reduce DNAPLs is a potentially simple, cost-effective, and environmentally benign technology that has become a preferred method in the remediation of these compounds. However, unsupported NZVI particles exhibit ferromagnetism leading to particle aggregation and loss in mobility through the subsurface. This work demonstrates two approaches to prepare carbon supported NZVI (iron-carbon composites) particles. The objective is to establish these iron-carbon composites as extremely useful materials for the environmental remediation of chlorinated hydrocarbons and suitable materials for the in situ injection technology. This research also demonstrates that it is possible to vary the placement of iron nanoparticles either on the external surface or within the interior of carbon microspheres using a one-step aerosol-based process. The simple process of modifying iron placement has significant potential applications in heterogeneous catalysis as both the iron and carbon are widely used catalysts and catalyst supports. Furthermore, the aerosol-based process is applied to prepare new class of supported catalytic materials such as carbon-supported palladium nanoparticles for ex situ remediation of contaminated water. The iron-carbon composites developed in this research have multiple functionalities (a) they are reactive and function effectively in reductive dehalogenation (b) they are highly adsorptive thereby bringing the chlorinated compound to the proximity of the reactive sites and also serving as adsorption materials for decontamination (c) they are of the optimal size for transport through sediments (d) they have amphiphilic chemical functionalities that help stabilize them when they reach the DNAPL target zones. Finally, the iron-carbon composite microspheres prepared through aerosol-based process can used for in situ injection technology as the process is conductive to scale-up and the materials are environmentally benign. / acase@tulane.edu

Polyethylene oxide polymers are intrinsic to oil spill dispersants used in Macondo well blowout of 2010. We believe that effective thermo-physical modeling of these materials should assist the application of lab-scale results into ocean-scales. Fully defensible molecular scale theory of such materials will be challenging. This thesis is the first step towards that challenge. Molecular dynamics simulations are useful in generating structural and phase behavior data for these versatile polymers. Microstructures of PEO polymers, hydrophobic interactions, direct numerical test of controversial Pratt-Chandler theory, concentration dependence of Flory-Huggins interaction parameter and neutron scattering experiments will be discussed. / acase@tulane.edu

With recent advancements in the synthesis and characterization of polymeric materials, scientists are able to create multi-scale novel polymers with various cases of chemical functionalities, diversified topologies, as well as cross-linking networks. Due to those remarkable achievements, there are a broad range of possible applications of smart polymers in catalysis, in environmental remediation, and especially in drug-delivery. Because of rising interest in developing therapeutic drug binding to specific treating target, polymer chemists are in particular interests in design and engineering the drug delivery materials to be not only bio-compatible, but also to be capable of self-assembly at various in-vivo physiological stimulus. Both experimental and theoretical work indicate that the thermodynamic properties relating to the hydrophobic effect play an important role in determining self-assembly process. At the same time, computational simulation and modeling are powerful instruments to contribute to microscopic thermodynamics' understanding toward self-assembly phenomenon. Along with statistical approaches, constructing empirical model based on simulation results would also help predict for further development of tailored nano-structured materials. My Research mainly focused on investigating physical and chemical characteristics of polymer materials through molecular dynamics simulation and probing the fundamental thermodynamic driving force of self-assembly behavior. We tried to surmount technological obstacles in computational chemistry and build an efficient scheme to identify the physical and chemical Feature of molecules, to reproduce underlying properties, to understand the origin of thermodynamic signatures, and to speed up current trial and error process in screening new materials. / acase@tulane.edu

To clarify the role of ab initio molecular dynamics (AIMD) simulation, this study organizes the McMillan-Mayer (MM) theorem, the potential distribution theorem, and quasi-chemical approach to provide theory for the thermodynamic effects associated with long-length scales. This multi-scale statistical mechanical (MSSM) theory implements quasi-chemical theory after utilizing the MM theorem to integrate-out the solvent degrees of freedom. The MSSM theory treats composition fluctuations which would be accessed by larger-scale calculations, and also long-ranged interactions of special interest for electrolyte solutions. The theory is applied to a primitive electrolyte solution model proposed to investigate ion pairing in the context of tetraethyammonium tetrafluoroborate in propylene carbonate. A Gaussian statistical model is shown to be an effective physical approximation for outer-shell contributions, and they are conclusive for the free energies within the quasi-chemical formulation. Gaussian statistical theory can be more effective than the Bennett numerically exact method when exhaustive sampling is not available, i.e., for finite samples. These results lead to the analysis of the asymptotical behavior of a relative information entropy and thus a new formula for the ion excess free energies. This asymptotic perspective completely avoids the computationally limiting evaluation of the outer-shell contributions. In addition, we use AIMD to obtain the charges on tetramethylammonium and tetrafluoroborate ions contacting neutral and charge carbon nanotube electrodes, and also charges tetraethyammonium and tetrafluoroborate ions in propylene carbonate solution. / acase@tulane.edu