Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / "February 2004." / Includes bibliographical references (p. 146-152). / The micron-scale manufacturing industry has grown to hundreds of billions of dollars since the advent of the transistor in 1947. Increasing demands for integration of surface mount components, greater use of portable electronic devices, and miniaturized medical diagnostic devices have given rise to the need for methods of fabricating and assembling micron-scale discrete components. Development of reliable non-contact assembly methods requires thorough understanding of electro-mechanics, surface adhesion, and gravitational forces acting on micron- scale objects. The impact of such a study will spread beyond microelectronics, and will also have broad significance in the development of micro-electromechanical systems (MEMS) for diverse applications such as biological assays, drug delivery devices, and tools for high throughput combinatorial materials development. This thesis will discuss methods for and challenges in fabrication, manipulation, and assembly of discrete micron-scale objects. The impact of these issues will be illustrated for the development of a micro-dispensing system used to manipulate microgram quantities of dry granular substances for combinatorial materials development. This method provides a model system to explore the forces on micron-scale objects, and is important in its own right as it will introduce a new range of materials that may benefit from combinatorial development. The applicability of traditional methods for computing dielectrophoretic forces on micron scale objects in the presence of spatially non-uniform electric fields will be discussed for the case of closely-spaced, interacting spheres. / (cont.) A dipole approximation model will be presented to quantitatively illustrate the limitations of existing techniques for calculating these forces, and to aid in explaining the observed motion of multiple interacting particles. / by Malinda M. Tupper. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 119-124). / Transition metal oxides comprise a fascinating class of materials displaying a variety of magnetic and electronic properties, ranging from half-metallic ferromagnets like CrO2, ferrimagnetic semiconductors like Fey's, and antiferromagnetic insulators like rocksalt-structured FeO. The accessibility of multiple electronic configurations and coordination of cations in these oxides enables the control of magnetism by external stimuli. One such stimulus is the insertion of Li+, as occurs during the discharge cycle of a lithium battery. This can lead to the change in valence and locations of the metal cations within the structure therefore a change in magnetic moment. Fey's and CrO2 are of considerable interest, primarily because they demonstrate room-temperature magnetism and high spin polarization.Previous studies focussed on use of these materials as cathodes and characterization of lithiated compounds made through solid state chemical synthesis or via chemical lithiation. In this work, changes in magnetization and structure of pulsed laser deposition (PLD)-grown Fey's (magnetite) thin films, Fe3O4 nanoparticles, and CrO2 nanoparticles have been investigated upon electrochemical lithiation. The reasonable electrical conductivity of magnetite opens the possibility of modifying the saturation magnetization by inserting Li+ ions into thin films grown on conducting substrates. A substantial decrease in M8 (up to 30%) was observed in PLD-grown thin films. Significantly larger reduction in moment (up to 75%) was observed in commercially available nanoparticles upon addition of 2 moles of Li per formula unit, along with changes in remanence and coercivity. The smaller drop in M8 observed in thin films is attributed to a kinetic effect due to high density and greater diffusion lengths in PLD-grown films. / (cont.) The electrochemical lithiation process has also been applied to needle-shaped particles of chromium dioxide and a model has been proposed to explain the observations. The effects of cycling and discharge-charge rate on these CrO2 particles have been studied. It has been shown that the process may be partially reversible for low Li contents. The effects of increasing the temperature of cycling and decreasing the length of the CrO2 particles have been explored. These changes in magnetic moment may be rendered useful in magnetomechanical or magnetoelectronic applications. / by Vikram Sivakumar. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2014. / Cataloged from PDF version of thesis. "February 2014." Page 206 blank. / Includes bibliographical references (pages 195-205). / Lithium ion batteries for large-scale applications demand a strict safety standard from a cathode material during operating cycles. Lithium manganese borate (LiMnBO₃) that crystallizes into a hexagonal or monoclinic framework is one prominent polyanionic compound to cope with such requirement since it can possess high safety and high energy density simultaneously, without trading one for the other, theoretically. However, the hexagonal phase was nothing but a disregarded composition due to its negligible Li intercalation capacity. In contrast, the monoclinic LiMnBO₃ compound exhibited much more electrochemical activity than the hexagonal polymorph. In this thesis work, the discharge capacity of 100 mAh g 1 with acceptable capacity retention was achieved by simple optimization. The different electrochemical behaviors between them were understood in relation to their structural difference as it affects the Li migration barrier, structural stability of Li-deficient states, and even particle morphology. However, although promising, monoclinic LiMnBO₃ needed further improvement in terms of the achievable capacity and cyclability. Electrochemical analysis showed that the limited capacity of LiMnBO₃ mostly originated from transport limitation, a hindered Li migration through the one-dimensional diffusion channel. It also struggled from the phase decomposition and Mn dissolution due to the instability of the delithiated state, which led to gradual capacity fading in prolonged cycles. As an effective materials design strategy to overcome such limitations, systematic substitution of transition metal elements was proposed. To increase achievable capacity, Mn was partially substituted by Fe. Also, to fortify the structural integrity, Mg replaced Mn. In order to obtain both improved capacity and cyclability, Fe and Mg are co-doping led to an optimized composition. Prepared by cold-isostatic pressing, LiMg₀.₁Mn₀.₅Fe₀.₄4BO₃ showed near theoretical capacity of 200 mAh g-¹ with much improved capacity retention. These newly established materials outperformed most of the polyanionic cathode compounds. Therefore, it can be concluded a new promising candidate as a Li storage material has been developed through this thesis research. / by Jae Chul Kim. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995. / Includes bibliographical references (p. 312-314). / by Scott E. Deering. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 246-250). / by Steve Andrew Kramer. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2000. / Includes bibliographical references (leaves 124-126). / Morphology evolution in the melting regime during compounding of immiscible polymer blends. where most of the size scale reduction occurs. is studied. Starting from an initial solid pellet mixture of two components. the progression to the final two-phase viscoelastic melt involves an intermediate stage where either one or both the components are melting or softening. Our focus is identifying and quantifying the factors that determine morphologies in the melting regime. We identify blend systems that exhibit a transformation in morphology from a minor-component continuous phase with dispersed major component domains to that with the major component being the continuous matrix phase. as a function of mixing time. This phenomenon of phase inversion during compounding is demonstrated to occur even in blends with a higher melting point minor component. A low solid modulus and a low melt viscosity are shown to favor the formation of the continuous phase by the minor component. Polycaprolactone/polyethylene. polystyrene/polyethylene. polycarbonate/ polyethylene, poly(ethylene-co-cyclohexane dimethylene terephthalate)/ polyethylene. and polybutylene/polycaprolactone blends were studied. These model blends were chosen based on the melt viscosity ratio and the relative softening temperatures of the two components. These two parameters were used to develop a two-dimensional framework for summarizing the compounding behavior of blends. For compounding runs with a small amount of the minor component (-1 Owt. % ) at a constant mixer temperature, phase inversion was observed for blend viscosity ratios less than 0.2. irrespective of the relative transition temperatures of the two components. Using a temperature ramping program resulted in the low melting component forming the continuous phase initially. Selective dissolution studies were used to quantify the amount of minor component present in the continuous phase at different mixing times. A polystyrene/polyethylene blend with a melt viscosity ratio of -0.001. was used to study the effect of batch size on the time required to form a continuous phase of the compounding of batch sizes ranging from 12g to 240g. Upon a five-fold increase in batch size the time to phase inversion increased by a factor of 3. This increase was explained by a combination of reduced heat conduction and reduced mechanical energy input to the batch. To enable studies at different batch sizes in the same mixing bowl, a novel mixing blade with modular elements was designed and constructed. This design was used for both radial and axial scaleup studies. The effect of changing the blade configuration on the time to phase inversion was explained using a specific relative stagger parameter, which is a measure of the effectiveness of stress transfer to the batch. Flow visualization using a glass window and blend sampling was used to develop a detailed description of the deformation steps leading to phase inversion in a model low viscosity ratio blend. Intermediate morphologies of flattened pellets, stacks of pellets, fibers and clusters were identified. Based on these observations a micro-structural model was developed to predict the time to phase inversion. The model incorporates a simplified flow-field approximation and calculates the strain in the major component. A strain-based criterion was proposed which in conjunction with the model yielded an explicit expression for the time to phase inversion. Model predictions of the dependence of time to phase inversion on nominal maximum-shear-rate in the mixer, volume fraction of the minor component and blend viscosity ratio were shown to be in excellent agreement with experimental results. / by Ramabhadra Ratnagiri. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Vita. / Includes bibliographical references (leaf 18). / by Jaeyong Park. / B.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Cell separation is important in medical, biological research, clinical therapy, diagnostics and many other areas. The conventional methods of cell sorting have limited applications due to sophisticated equipment settings, high costs, or time-intensive and labor-intensive processing steps. Inspired from natural cell sorting system-cell rolling, a novel microfluidic device design was proposed for point-of-care and point-of-use applications. It relies on interaction of cells with biomimetic adhesive substrates comprising multiple inclined, asymmetric bands of weak adhesive molecules. Such device design allows continuous sorting of cells without irreversible capture of cells. To realize such device, comprehensive studies of how cells settle onto the substrate, how cells capture by the substrate, the effect of substrate parameters on separation potential, and selection of adhesion molecules are needed to optimize device performance. In this thesis, first, how the cells settle and how they are captured by the receptors were studied using HL60 cells as a model leukocyte cell line and P-selectin as a model receptor. Settling distance of HL60 cells under different shear stresses inside microfluidic channels was identified from the study of convection velocity of cells at different position along the channel. The results show that settling distance increases with increasing shear stress. Cell capture was then quantified by characterizing how far settled HL60 cells travelled before they were captured by P-selectin molecules, defined as the attachment distance. Cumulative probabilities of attachment distance of cells at different shear stresses revealed that increasing shear stress results in exponential increase of the attachment distance of cells by receptor molecules. An empirical model was developed to predict capture probability by an inclined receptor band and the prediction value was verified by experimental data from a device. Second, a patterning method involving microcontact printing was developed to create biomimetic adhesive substrates comprising multiple inclined receptor bands of P-selectin molecules. The patterned substrates were then used to study how transport of HL60 cells can be controlled by the substrate parameters including pattern inclination angle with respect to shear flow direction, shear stress magnitude, and P-selectin incubation concentration. The effects of substrate parameters were quantified in terms of the edge tracking length, lateral displacement, and the rolling velocity. The edge inclination angle was identified as the strongest modulator of edge tracking length on a single band for captured cells. To study optimization of the device design, experimental data of cell settling, cell attachment, and edge tracking length were integrated into a model to predict device performance including device capture efficiency and total lateral displacement. General guidelines for microfluidic device design were established based on the results from the model: smaller band width, edge angle of 15-20°, and lower shear stress. Finally, to develop new specific receptor-ligand systems, M13 pVIII and pIll phage libraries were used for selecting peptides with affinity to CD4 proteins. Screened phage from pVIII library was immobilized on the gold surface and capture efficiency of CD4+ cells were characterized. The interaction between selectin phage and CD4+ cells were demonstrated to be CD4-dependent. Moreover, the selected phage from pIII library and the corresponding synthetic peptides were demonstrated to exhibit specificity to CD4 proteins. In summary, this thesis focuses on development of biomimetic adhesive substrates for microfluidic devices involving transient interactions between the cells and the receptor-patterned substrates. How cells flow and get captured by patterned biomimetic substrates inside the microfluidic channels, how substrates parameters affect cell rolling trajectories and device performance, and how to identify new receptor-ligand systems were discussed in this thesis. This study has led to realization of a microfluidic device for separating neutrophils from blood. This microfluidic system provides continuous sorting without irreversible capture of cells, and is believed to be an effective method that can potentially be used in many point-of-care applications. Keywords: microfluidics, cell separation, cell rolling, selectin, biopanning, M13 / by Chia-Hua Lee. / Ph. D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000. / Includes bibliographical references (leaves 176-182). / The formation of polymer nanofibers from fluid jets in· an electric field, also referred to as electrospinning, has been studied. Controlling the fiber properties requires a detailed understanding of how a millimeter-diameter fluid jet emanating from a nozzle is transformed into solid fibers that are four orders of magnitude smaller in diameter. To this end, a fiber spinner operating under a uniform electric field and providing a controlled process environment was designed. In the conventional view of electrospinning, the mechanism leading to small fiber diameters has been attributed to the splaying phenomenon, in which a single jet splits into multiple smaller jets due to radial charge repulsion. Using high-speed photography and an aqueous solution of poly(ethylene oxide) as a model fluid, it was shown that the jet does not splay but instead undergoes a rapid whipping motion. The high whipping frequency created the optical artifact of multiple jets. The whipping jet was best observed in the onset region of the instability. Further downstream, the amplitude of the instability continued to grow, and the jet trajectory became more chaotic. This was verified through photography of the entire jet and close-up observations of representative regions further downstream. Based on these findings, an alternative mechanism for the formation of polymer nanofibers is proposed. It is conjectured that the whipping instability causes stretching and bending of the jet. The large reduction in jet diameter is achieved by increasing the path length over which the fluid jet is accelerated and stretched prior to solidification or deposition on a collector. Whipping induced stretching is conjectured to be the primary mechanism causing the jet diameter reduction. To provide a concise way of displaying the stability of electrified fluid jets as a function of the electric field and the flow rate, operating diagrams were developed. These diagrams delineate regions of different jet behavior, and the stability borders for two transitions have been mapped. The first transition is from dripping to a stable jet; and represents the suppression of the Rayleigh instability. For high conductivity fluids, an additional transition from a stable to a whipping jet can be observed at higher electric fields. The experimental findings are supported by a theoretical analysis of the jet thinning and the onset of the instability. To elucidate the fundamental electrohydrodynamics, glycerol was studied as a model fluid. Based on the experimental observation that whipping occurs on a length scale much larger than the jet radius, an asymptotic approximation of the electrohydrodynamic equations has been developed by Hohman and Brenner. This theory governs both long wavelength axisymmetric and non-axisymmetric distortions of the jet, and allows the jet stability to be evaluated as a function of all relevant fluid and process parameters. Three different instabilities are predicted: the classical Rayleigh instability, an axisymmetric conducting mode, and a non-axisymmetric conducting mode. The presence of these instabilities at various locations along the jet has been verified with high-speed video and photography. The particular instability that is observed depends on the jet shape and the surface charge density. To achieve quantitative agreement between experimental and theoretical jet profiles, the jet current and the local electric field in the vicinity of the nozzle had to be taken into account. The electric currents in stable jets were found to be linear in both the electric field and the flow rate Theoretical operating diagrams were developed based on the experimental insight that the instabilities are convective. The dependence of the stability borders on both the electric field and the flow rate is correctly reproduced by the Hohman-Brenner theory. This implies that operating diagrams have the potential to be used as predictive tools to better understand and control the process. The quantitative agreement between theory and experiments suggests that the fundamental process in electrospinning involves indeed a rapidly whipping jet, which is caused by the interaction of surface charges on the jet and the applied electric field. The notion of a whipping jet has also been extended to low viscosity fluids, where the jet disintegrates into fine droplets, i.e., electrospraying. For sufficiently large jet radii, experiments have verified the theoretical prediction that the dispersal of fluid results from the growth of a non-axisymmetric conducting mode along the jet, which subsequently breaks into droplets due to the axisymmetric conducting mode. / by Y. Michael Shin. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 123-136). / The overall goal of this thesis was to exploit the versatility of the polyelectrolyte multilayer (PEM) platform to consider bacteria-substrata interactions by varying multilayer assembly and post-assembly conditions. We developed multiple PEM systems to probe the ability of substrata to resist bacteria attachment or act as contact-killing antimicrobials. In the first study, by varying the pH of assembly, we developed PEMs of identical chemical composition (polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA)) with distinct mechanical moduli (1-100 MPa). Once characterized, these PEMs showed that, under certain conditions, bacterial attachment correlated with increasing modulus. Thus, substrata stiffness was found to be an additional parameter to consider when studying bacterial attachment. The next project focused on PEMs of PAH and poly(sodium-4-styrene sulfonate) (SPS) assembled at high pH that showed a reversible swelling transition upon immersion in a low pH solution. These acid-treated PEMs presented high positive charge density and mobility, and were capable of killing bacteria on contact. SPS/PAH PEMs were used as a model system to enumerate the design parameters that should be considered to create a cationic killing surface. A third PEM system was employed to further illustrate the effects of multilayer assembly and post-assembly conditions on bacteria. Cross-linked hydrogen-bonded PAA and poly(acrylamide) (PAAm) multilayers were modified post-assembly by the adsorption of PAH at various pH values. These multilayers underwent a variety of morphological transitions depending on the pH of PAH adsorption. At mid-range pH values, the film stiffened and promoted aqueous bacterial attachment. / (cont.) At high pH values, PAH adsorbed onto the surface with many unbound uncharged amine groups. When the multilayer was exposed to physiological pH values for bacteria assays, the amine groups became protonated and participated in a cationic-killing effect. Finally, biofilm control was examined by investigating initial biofilm formation on films of various mechanical stiffness and surface charge. No differences were visible via optical microscopy. An alternative approach to biofilm control was considered whereby a dissociating multilayer region lifted-off a contaminated layer, exposing a clean, unfouled underlying surface. / by Jenny A. Lichter. / Ph.D.