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Interfacial bonding stability by in situ ellipsometry was investigated. It is found that: (1) gamma MPS is an effective primer for bonding ethylene vinyl acetate (EVA) to aluminum; (2) ellipsometry is an effective in situ technique for monitoring the stability of polymer/metal interfaces; (3) the aluminized back surface of silicon wafers contain significant amounts of silicon and may have glass like properties.
The merging of a spherical distribution of plasma jets to dynamically form a gaseous liner has been proposed for use in magnetized target fusion propulsion. In this paper, a study is made of the interfacial stability of the interaction of these jets. Specifically, the Orr-Sommerfeld equation is integrated to obtain the growth rate of a perturbation to the primary flow at the interface between the colliding jets. The analysis lead to an estimate on the tolerances on the relative flow velocities of the merging plasma jets to form a stable, imploding liner. The results show that during the merging of the jets to form a liner and before contact with the target plasma the growth of the perturbed flow at the jet interface is not likely to destabilize the liner. These data suggest that, as far as the stability of the interface between the merging jets is concerned, the formation of liner can withstand velocity variation up to 50% between the neighboring jets over the density and temperature ranges investigated.
A fusion propulsion scheme has been proposed that makes use of the merging of a spherical distribution of plasma jets to dynamically form a gaseous liner to implode a magnetized target to produce the fusion reaction. In this paper, a study is made of the interfacial stability of the interaction of these jets. Specifically, the Orr-Sommerfeld equation is integrated to obtain the growth rate of a perturbation to the primary flow at the interface between the colliding jets. The results lead to an estimate on the tolerances on the relative flow velocities of the merging plasma jets to form a stable, imploding liner. The results show that the maximum temporal growth rate of the perturbed flow at the jet interface is very small in comparison with the time to full compression of the liner. These data suggest that, as far as the stability of the interface between the merging jets is concerned, the formation of the gaseous liner can withstand velocity variation of the order of 10% between the neighboring jets over the density and temperature ranges investigated.
The stability of CoSi2/Si interfaces was examined in this study using columnar silicide structures grown on (111) Si substrates. In the first set of experiments, Co and Si were codeposited using MBE at 800 C and the resulting columnar silicide layer was capped by epitaxial Si. Deposition of Co on the surface of the Si capping layer at 800 C results in the growth of the buried silicide columns. The buried columns grow by subsurface diffusion of the deposited Co, suppressing the formation of surface islands of CoSi2. The column sidewalls appear to be less stable than the top and bottom interfaces, resulting in preferential lateral growth and ultimately in the coalescence of the columns to form a continuous buried CoSi2 layer. In the second set of experiments, annealing of a 250 nm-thick buried columnar layer at 1000 C under a 100 nm-thick Si capping layer results in the formation of a surface layer of CoSi2 with a reduction in the sizes of the CoSi2 columns. For a sample having a thicker Si capping layer the annealing leads to Ostwald ripening producing buried equiaxed columns. The high CoSi2/Si interfacial strain could provide the driving force for the observed behavior of the buried columns under high-temperature annealing.
Magnetization critical level derived for instability onset for ferromagnetic fluid having nonlinear relation with magnetic induction
The Performance Goal for NASA's Microgravity Materials Science Program reads "Use microgravity to establish and improve quantitative and predictive relationships between the structure, processing and properties of materials." The advent of the International Space Station will open up a new era in Materials Science Research including the ability to perform long term and frequent experiments in microgravity. As indicated the objective is to gain a greater understanding of issues of materials science in an environment in which the force of gravity can be effectively switched off. Thus gravity related issues of convection, buoyancy and hydrostatic forces can be reduced and the science behind the structure/processing/properties relationship can more easily be understood. The specific areas of research covered within the program are (1) the study of Nucleation and Metastable States, (2) Prediction and Control of Microstructure (including pattern formation and morphological stability), (3) Phase Separation and Interfacial Stability, (4) Transport Phenomena (including process modeling and thermophysical properties measurement), and (5) Crystal Growth, and Defect Generation and Control. All classes of materials, including metals and alloys, glasses and ceramics, polymers, electronic materials (including organic and inorganic single crystals), aerogels and nanostructures, are included in these areas. The principal experimental equipment available to the materials scientist on the International Space Station (ISS) will be the Materials Science Research Facility (MSRF). Each of these systems will be accommodated in a single ISS rack, which can operate autonomously, will accommodate telescience operations, and will provide real time data to the ground. Eventual plans call for three MSRF racks, the first of which will be shared with the European Space Agency (ESA). Under international agreements, ESA and other partners will provide some of the equipment, while NASA covers launch and integration costs. The MSRF facilities will include modular components, which can be exchanged to provide inserts specifically matched to the engineering requirements of the particular Principal Investigator. To defray costs and avoid duplication of engineering effort NASA is also pursuing the possibility of using facilities provided by international partners. By this means it is anticipated that all of the types of research outlined in the previous paragraph can be done on the ISS.
Interfacial stability at thin flexible partition between fuel and propellant flows for gas core nuclear rockets
A model problem is posed to study the influence of flow on the interfacial stability of a nearly cylindrical liquid bridge for lengths near its circumference (the Plateau-Rayleigh limit). The flow is generated by a shear stress imposed on the deformable interface. The symmetry of the imposed shear stress mimics the thermocapillary stress induced on a float-zone by a ring heater (i.e. a full zone). Principal assumptions are (1) zero gravity, (2) creeping flow, and (3) that the imposed coupling at the free surface between flow and temperature fields is the only such coupling. A numerical solution, complemented by a bifurcation analysis, shows that bridges substantially longer than the Plateau-Rayleigh limit are possible. An interaction of the first two capillary instabilities through the stress-induced flow is responsible. Time-periodic standing waves are also predicted in certain parameter ranges. Motivation comes from extra-long float-zones observed in MEPHISTO space lab experiments (June 1994).
A translucent crystal concentrates and transmits energy to a heat exchanger, which in turn heats a propellant gas, working gas of a dynamic power system, or a thermopile. Materials are the limiting issue in such a system. Central is the durability of the crystal, which must maintain the required chemical, physical/optical, and mechanical properties as it is heated and cooled. This report summarizes available data to date on the materials issues with this system. We focus on the current leading candidate materials, which are sapphire (Al2O3) for higher temperatures and silica (SiO2) for lower temperatures. We use data from thermochemical calculations; laboratory coupon tests with silica and sapphire; and system tests with sapphire. The required chemical properties include low-vapor pressure and interfacial stability with supporting structural materials. Optical properties such as transmittance and index of refraction must be maintained. Thermomechanical stability is a major challenge for a large, single-crystal ceramic and has been discussed in another report. In addition to the crystal, other materials in the proposed system include refractory metals (Nb, Ta, Mo, W, and Re), carbon (C), and high-temperature ceramic insulation. The major issue here is low levels of oxygen, which lead to volatile refractory metal oxides and rapid consumption of the refractory metal. Interfacial reactions between the ceramic crystal and refractory metal are also discussed. Finally, high-temperature ceramic insulating materials are also likely to be used in this system. Outgassing is a major issue for these materials. The products of outgassing are typically reactive with the refractory metals and must be minimized.
The ability of small peptides to organize at aqueous interfaces was examined by performing a series of large-scale, molecular dynamics computer simulations of several peptides composed of two amino acids, nonpolar leucine (L) and polar glutamine (Q). The peptides differed in size and sequence of the amino acids. Studies on dipeptides LL, LQ, QL and QQ were extended to two heptamers, LQQLLQL and LQLQLQL, designed to maximize interfacial stability of an alpha-helix and a beta-strand, respectively, by exposing polar side chains to water and nonpolar side chains to a nonpolar phase. Finally, a transition of an undecamer, composed entirely of leucine residues, from a disordered structure in water to an alpha-helix in a nonpolar phase representing the interior of the membrane was investigated. Complete folding of a peptide in solution was accomplished for the first time in computer simulations. The simulations revealed several basic principles governing the sequence-dependent organization of peptides at interfaces. Short peptides tend to accumulate at interfaces and acquire ordered structures, providing that they have a proper sequence of polar and nonpolar amino acids. The dominant factor determining the interfacial structure of peptides is the hydrophobic effect, which is manifested at aqueous interfaces as a tendency for polar and nonpolar groups of the solute to segregate into the aqueous and nonpolar phases, respectively. If peptides consist of nonpolar residue's only, they become inserted into the nonpolar phase. As demonstrated by the example of the leucine undecamer, such peptides fold into an alpha-helix as they partition into the nonpolar medium. The folding proceeds through an intermediate, called 3-10-helix, which remains in equilibrium with the alpha-helix. Once in the nonpolar environment, the peptides can readily change their orientation with respect to the interface from parallel to perpendicular, especially in response to local electric fields. The ability of nonpolar peptides to modify both the structure and orientation with respect to the interface from parallel to perpendicular, especially in response to local electric fields. The ability of nonpolar peptides to modify both the structure and orientation with changing external conditions may have provided a simple mechanism of transmitting signals from the environment to the interior of a cell.
Interfacial stability of two parallel superposed inviscid streams of fluid applied to stability of molten liquid-gas interface on ablating reentry body
The theories of diffusion-controlled dendritic crystallization will be reviewed briefly, along with recently published critical experiments on the kinetics and morphology of dendritic growth in pure substances. The influence of the gravitational body force on dendrite growth kinetics will be shown to be highly dependent on the growth orientation with respect to the gravity vector and on the level of the thermal supercooling. In fact, an abrupt transition occurs at a critical supercooling, above which diffusional transport dominates the growth process and below which convective transport dominates. Our most recent work on binary mixtures shows that dilute solute additions influence the crystallization process indirectly, by altering the interfacial stability, rather than by directly affecting the transport mode. Directions for future studies in this field will also be discussed.
The interfacial stability of rotating core-annular flows is investigated. The linear and nonlinear effects are considered for the case when the annular region is very thin. Both asymptotic and numerical methods are used to solve the flow in the core and film regions which are coupled by a difference in viscosity and density. The long-term behavior of the fluid-fluid interface is determined by deriving its nonlinear evolution in the form of a modified Kuramoto-Sivashinsky equation. We obtain a generalization of this equation to three dimensions. The flows considered are applicable to a wide array of physical problems where liquid films are used to lubricate higher or lower viscosity core fluids, for which a concentric arrangement is desired. Linearized solutions show that the effects of density and viscosity stratification are crucial to the stability of the interface. Rotation generally destabilizes non-axisymmetric disturbances to the interface, whereas the centripetal forces tend to stabilize flows in which the film contains the heavier fluid. Nonlinear affects allow finite amplitude helically travelling waves to exist when the fluids have different viscosities.
This paper is the first in a series of symposia presenting research activity in microgravity fluid mechanics. General topics addressed include two-phase flow and transport phenomena, thermo-capillary flow, and interfacial stability. Papers present mathmatical models of fluid dynamics in the microgravity environment. Applications suggested include space manufacturing and storage of liquids in low gravity.
Experiments on miscible, buoyantly unstable reaction-diffusion fronts and non-reacting displacement fronts in Hele-Shaw cells show a fingering-type instability whose wavelengths (lambda*) are consistent with an interfacial tension (sigma) at the front caused by the change in chemical composition, even though the solutions are miscible in all proportions. In conjunction with the Saffman-Taylor model, the relation sigma = K/tau, where tau is the interface thickness and K approximately equal 4 +/- 2 x 10(exp -6) dyne, enables prediction of our measured values of lambda* as well as results from prior experiments on miscible interfaces. These results indicate that even for miscible fluids, surface tension is generally a more significant factor than diffusion in interfacial stability and flow characteristics.
Improved composite solid polymer electrolytes (CSPEs) are being developed for use in lithium-ion power cells. The matrix components of these composites, like those of some prior CSPEs, are high-molecular-weight dielectric polymers [generally based on polyethylene oxide (PEO)]. The filler components of these composites are continuous, highly-Li(+)-conductive, inorganic fibers. PEO-based polymers alone would be suitable for use as solid electrolytes, were it not for the fact that their room-temperature Li(+)-ion conductivities lie in the range between 10(exp -6) and 10(exp -8) S/cm, too low for practical applications. In a prior approach to formulating a CSPE, one utilizes nonconductive nanoscale inorganic filler particles to increase the interfacial stability of the conductive phase. The filler particles also trap some electrolyte impurities. The achievable increase in conductivity is limited by the nonconductive nature of the filler particles.
Falling liquid film amine sorbent reactors have been successfully employed to scrub CO 2 aboard submarines for decades. However, applying such proven methods aboard orbiting and coast spacecraft is significantly challenged by the nearly weightless environment, where liquid sprays and films do not fall, and vapor bubbles and gases do not rise. The Capillary Sorbent (CapiSorb) Visible System (CVS) is a technology demonstration experiment performed aboard the ISS April 18 – 21, 2023. The system establishes stable steady thin liquid film flows in Contactor (absorber) and Degasser (desorber/stripper) replacing the passive role of gravity with the combined passive roles of surface tension, wetting, and system geometry. A TOX-0 fructose ersatz liquid sorbent is employed enabling ‘transparent’ experiments performed and filmed by the crew safely in the open cabin of the ISS. Completed objectives include demonstrations of stable passive ‘massively’ parallel planar thin film capillary flows across atmospheric pressure Contactor and sealed heated Degasser. The impacts of varying flow rate, flow direction, heat input, viscosity, positive and negative Degasser pressures, condensate collection and return, fluid distribution, interfacial stability, and others are reported. At least 49 diagnostics are recorded for digitization and subsequent thermal-fluids model validation by a single HD video downlink during the nearly 22 hours of operations. An overview of the flight hardware including description of the components, diagnostics, crew procedures, flight operations, and summary of accomplishments is reported in Ref. 1. Further details of the diagnostics, tests performed, and data reduction is reported in Ref. 2. This report collects both1,2 into a single report adding methods of data digitization, reduction, and archive along with analyses and discussions of technology impacts.
In this paper the stability of annular pressure-driven parallel flows of two liquids sandwiching a free cylindrical interface is considered. For small to moderate Reynolds numbers, the interface is susceptible to capillary and interfacial wave instabilities, the latter instability caused by a jump in viscosity at the interface. It is shown that favorable velocity profiles in both liquids may stabilize capillary breakup of the interface and suppress the axisymmetric interfacial wave instability. A long-wave analysis leads to the physical mechanism responsible for stabilization of capillary breakup. This physical mechanism is a generalization of that by which capillary breakup is stabilized by interfacial shear in an annular film of a single liquid. Stabilization of intermediate wavelengths is studied with a mechanical energy analysis, which leads to a description of the energetic processes at work.