The need for micropropulsion solutions for spacecraft has been steadily increasing as scientific payloads require higher accuracy maneuvers and as the use of small form-factor spacecraft such as CubeSats becomes more common. Of the technologies used for this purpose, electrospray thrusters offer performance that make them an ideal choice. Electrosprays offer high accuracy impulse bits at low power and high efficiency, and have low volume requirements. Design choice reasoning and preliminary testing results are presented for two electrospray thruster designs. The first thruster, named the Demonstration thruster, is operated in atmospheric conditions and serves as a highly visible example of the basic concepts of electrospray technology applied to micropropulsion. It features a single capillary needle emitter and the acetone propellant flow is driven actively by a syringe pump. The second thruster, named the Research thruster, is operated in the vacuum environment and is designed for modularity for its expected use in future research efforts. Propellant flow is also driven actively using a syringe pump. Initial configuration of the Research thruster is a linear array of five capillary needle emitters, though testing is conducted with only one emitter in this thesis. Tests using un-doped glycerol and sodium iodide doped glycerol (20% by weight) are conducted for the Research thruster. Both thruster designs use stainless steel 18 gauge blunt dispensing needles (0.038 in / 0.965 mm ID) as their emitters. Applied voltage to the emitter(s) relative to the grounded extractor is swept from 2100 V to 3700 V for the Demonstration thruster testing and from 4000 V to 4500 V for the Research thruster. Currents incident on a collection plate downstream of the emission plume and on the extractors of the thrusters were measured directly with a pico-ammeter. Measurements made during testing of the Demonstration thruster are inconsistent due to charge loss as propellant travels through the air, though currents as high as 5.1x10-9 A on the collection plate and 2x10-7 A on the extractor are recorded. Currents for Research thruster testing using un-doped glycerol were measured as high as 4.9x10-8 A on the collection plate and 5x10-9 A on the extractor, showing an interception rate as high as 17%. Currents using sodium iodide doped glycerol were measured as high as 7x10-7 A on the collection plate. Discussion is given for the visual qualities of cone-jet emission for all testing. Keywords:

The focus of the following research was to provide an optimized particle stabilized foam of Laponite and Pluronic L62 in water by understanding (1) the Laponite-Pluronic interactions and properties for improved performance in a particle stabilized foam and (2) the interfacial properties between air and the Laponite-Pluronic complex. These studies were conducted using both bulk and interfacial rheology, XRD, sessile droplet, TGA and UV-vis. Two novel and simple techniques, lamella break point and capillary breakup extensional rheometry, were used to both understand the Laponite Pluronic L62 interaction and determine a different mechanism for foaming properties. Bulk rheological properties identified an optimal Laponite concentration of 2% with Pluronic L62 ranging from 2.5% and 6.5%, due to the ease of flow for the dispersion. The Pluronic L62 was observed to enhance the Laponite bulk rheological properties in solution. Additionally TGA showed a similar trend in thermal resistance to water with both addition of Laponite and Pluronic L62. XRD demonstrated that 0.25% Pluronic intercalated into Laponite from dried 2% Laponite films. XRD demonstrated that the Laponite matrix was saturated at 1% Pluronic L62. UV-vis demonstrated that a monolayer of Pluronic L62 is observed up to 0.65% Pluronic L62 onto Laponite. Interfacial rheology showed that Laponite enhances Pluronic L62 at the air-liquid interface by improving the storage modulus as low at 0.65% Pluronic L62 with 2% Laponite. The lamella breakpoint of Laponite with Pluronic films indicate strong film interaction due to higher increases in mass. Extensional rheology indicates that 2.5% to 6.5% Pluronic with 2% Laponite show the most filament resistance to stretching.

No description available.

<p>Here presents the studies of polymerization kinetics and crosslinking efficiency of nm-resolution striped phases on surface, which depends on lengths of alkyl segments and headgroup chemistry. While fluorescence readouts offer the overall efficiencies of polymerization and crosslinking transfer, SPM measurements reveal molecular details accounting for reactivity differences. Additionally, this research also demonstrates the utilization of primary amines striped phases on soft materials, achieving post-functionalization and specific  adsorption of nanocrystals, highlighting the versatile applications of this nm-scale chemistry boundary.</p>

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19240号 / 工博第4075号 / 新制||工||1628(附属図書館) / 32239 / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 山本 量一, 教授 宮原 稔, 教授 松坂 修二 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Colloid thrusters, and electrospray thrusters as a whole, have been around since the 1960s. When they were first developed, the high efficiency and fine thrust control was overshadowed by the high power requirement for such a low thrust that the system provides. This caused the technology to be put on hold for aerospace applications. Now, as small satellites are becoming more prevalent, there has been a resurgence in interest in electrospray thruster technology. The recent advancements in tech- nology allow electrospray thrusters to use significantly less power and occupy less volume than their predecessors. As electrospray technology continues to advance, these thrusters are meeting the demands of small satellite propulsion. As such, in an effort to keep the spacecraft propulsion curriculum current with today’s technology, a colloid thruster is designed, built, tested, and implemented as a laboratory activity at California Polytechnic State University, San Luis Obispo. Electrospray thrusters work by placing a voltage on an ionic liquid and extracting either beads of propellant or ions to generate thrust. By definition, colloid thrusters are a specific class of electrospray thrusters that use solvents, such as glycerol or formamide, to emit droplets or, in special cases, ions to generate thrust. To keep with the University’s “Learn by Doing” pedagogical philosophy, the thruster for this activity is designed to have a tactile and experiential impact on the students. The final design is a scaled up configuration of an existing electrospray design so that the students can easily see each component with the naked eye and can be correlated to a real world thruster that they might see in industry. As a laboratory experiment, the thruster needs to be able to utilize current equip- ment in the Space Environments and Testing Laboratory. One of the Student Vacuum Chambers (SVC) is utilized as well as two 1 kV power supplies and a 100V power supply. An indirect method of measuring performance metrics needs to be developed as there are no thrust balances sensitive enough in the lab designated for undergrad- uate use. As such, the students will be using the mass of the propellant, the time of operation, and knowledge of the propellant’s properties to estimate the performance of the thruster. To prove success of the thruster, a performance profile of the thruster is produced using an indirect method of measurement as well as visual observations of the thruster moving propellant byway of the electrospray theory. The tests show thrusts produced between 96-311 μN with an Isp ranging from 1270-1684 seconds. The visual evidence demonstrates propellant being collected as well as the operation of the thruster under the electrospray theory. The visual evidence also sheds light on which emission mode the thruster is operating at as well as a self-correcting failure mode that was occurring. The thruster is implemented as a lab for Cal Poly’s AERO 402 Spacecraft Propulsion Lab in Fall 2018, and it receives positive feedback from the students through an anonymous survey. While the colloid thruster demonstrates success in meeting performance and pedagog- ical goals, future work should be continued to improve the thruster. Further design and manufacturing work can be undertaken to improve the efficiency and decrease failure due to propellant impingement. Additionally, the procurement of power sup- plies capable of applying higher voltages can provide a greater range of operation which can enable a more dynamic student discovery of electrospray thrusters.

<p dir="ltr">There is a plethora of applications that require chemical patterning on the molecular scale. While the surface science community has made tremendous progress in achieving this level of control on hard, crystalline interfaces, significant challenges are associated with extending this progress to less “perfect” systems such as soft, amorphous interfaces. Applications ranging from soft robotics and wearable electronics to regenerative medicine often utilize polymeric materials such as polydimethylsiloxane (PDMS) and hydrogels. These materials have advantageous properties, including biocompatibility and mechanical tunability. Biological applications, for example, often require the display of functional groups with precise spatial resolution. Cellular behavior is dictated by biochemical and biophysical cues in the extracellular matrix; therefore, substrate properties, including stiffness and ligand density, must be independently tunable. Soft, polymeric materials are highly heterogenous with pore sizes ranging from 10 nm to 1 µm and hence, particularly difficult to pattern below the length scale of substrate heterogeneity. Furthermore, deconvolving mechanical properties such as elastic modulus from the density of surface-active functional groups is especially challenging, with softer materials typically corresponding is lower ligand densities. Additionally, many traditional surface science characterization and patterning methods are incompatible with soft interfaces (e.g. amorphous surface structure, low mechanical strength, hydrated environment). Recently, we have reported a method capable of achieving high-resolution chemical patterning of PDMS and hydrogels. Long studied within the scanning probe community, amphiphiles with long alkyl chains self-assemble into lying down stripe phases on highly ordered pyrolytic graphite (HOPG), generating 1-nm-wide stripes of functional headgroups between 5-nmwide stripes of exposed alkyl chains. Stripe phases of functional diacetylenes (DA) are photopolymerized, producing a polydiacetylene backbone that tethers together adjacent molecules, generating a PDA film on HOPG (sPDA). We have shown that PDA films on HOPG can be transferred to PDMS as well as polyacrylamide hydrogels. When PDMS is cured in contact with sPDAs, the PDA backbones can act as a site for hydrosilylation, the same reaction responsible for PDMS curing, covalently linking sPDAs to the PDMS mesh. Careful exfoliation reveals nm-scale functional patterns on the surface layer of PDMS. 10 Here, we examine the impact of PDMS structural components on the efficiency of interfacial reactions between sPDAs and the PDMS network. We also illustrate the impact of PDAfunctionalized PDMS on the adhesion and spreading behavior of C2C12 murine myoblasts.</p>

<p>An improved understanding of colloid transport in fractured media is required to assess the potential for microorganisms to contaminate groundwater, to develop groundwater management/protection plans, to design remedial action strategies based on the application of microorganisms, and to quantify colloid-facilitated transport of many organic and inorganic contaminants. Although colloid transport has been investigated to an extent in porous media environments, this field is still in its infancy in fractured media environments.</p> <p>Colloid transport in fractured media involves a host of complex and interacting processes, including (among others): advection, hydrodynamic dispersion, attachment and detachment, straining, size/ charge exclusion, and gravitational settling. These processes are, in turn, influenced by the physicochemical properties of fractured media, the geochemical properties of groundwater, hydrodynamics, and the colloid properties. This research program focused on investigating the effects of aperture field variability, specific discharge, and ionic strength on colloid transport in saturated, variable-aperture, single fractures. An extensive literature review was first conducted, and a combination of physical model experiments and numerical simulations were then employed to achieve this goal.</p> <p> Three transparent fracture replicas were fabricated, and the light transmission method was employed to obtain a direct measurement of each of the three aperture fields. A systematic series of hydraulic and tracer tests was conducted on each of the three experimental fractures, and the cubic law, mass balance and frictional loss apertures were calculated. Additionally, the experimental breakthrough curves were fit to the one-dimensional advection-dispersion equation. The results clearly demonstrate that the mass balance aperture is the only appropriate 'equivalent aperture' for describing transport in a single variable-aperture fracture, and that the mass balance aperture is an excellent approximation ofthe arithmetic mean aperture.</p> <p>A 3^3 factorial experimental design was then implemented to numerically investigate the interactive effect of the arithmetic mean (μb), standard deviation (σb), and anisotropic ratio (AR=λ^b x/ λ^b,y where λ^b x and λ^b y is the correlation length of the aperture field along x- and y- direction respectively) of single fracture apertures on dispersion regimes (specifically Taylor dispersion and geometric dispersion) and dispersivity. The simulation results show that: (1) for a fixed hydraulic gradient: (a) the dominant dispersion regime is controlled by μb, and to a lesser degree, σb, and (b) geometric dispersion becomes more dominant as the coefficient of variation (CoV = σb/μb) increases; (2) for a fixed mean aperture, the dispersivity and the spread in dispersivity for varying ARs increase with the CoV; and (3) the AR has a significant effect on dispersivity only when the CoV is large (>0.2).</p> <p> Numerical simulations investigating colloid and solute transport in single parallel-plate fractures, conducted using the Random Walk Particle Tracking (RWPT) method, demonstrated that: 1) There exists a threshold value, δo , of the aspect ratio, δ (δ= 2rc/b, where rc and b represent the colloid radius and fracture aperture respectively), where the average transport velocities of colloids and solutes are similar. When δ> δo , the Taylor Aris assumption is satisfied, and tp (tp = tc/ts, where tc and ts represent colloid and solute retention times respectively) decreases as δ increases, as is well documented in the hydrodynamic chromatography literature. However, when δ < δo , the Taylor-Aris assumption is violated, and tp increases as δ increases. This has never been documented before, and it helps to explain some seemingly contradictory work in the literature. 2) The Taylor dispersion coefficient and its extension by James and Chrysikopoulos (2003) will overestimate the colloid dispersion coefficient significantly when the Taylor-Aris assumption is violated. Additionally, these simulations demonstrated that tp and DL,coll/DL,solute (where DL,coll and DL,solute represent the dispersion coefficients of colloids and solutes respectively) decrease with increasing CoV, and that the anisotropy ratio, AR, only plays a minor role on these two ratios compared to the CoV. These observations have never been documented before to the knowledge of these authors, and have important implications towards the interpretation of colloid transport in both porous and fractured media.</p> <p> A combination of physical experiments, numerical simulations and visualization techniques was employed to investigate the impact of aperture variability, specific discharge, and ionic strength on colloid transport processes. The mean colloid transport velocity and colloid dispersion coefficient were obtained by fitting the analytical solution of the one-dimensional advection-dispersion equation (ADE) to the measured breakthrough curves. Two significant observations were made from the colloid transport experiment images: (1) colloids migrate along preferential pathways, and bypass some aperture regions; and (2) the colloid plume is irregular in shape, and becomes more irregular with increasing specific discharge, indicating non-Fickian transport. It is therefore postulated that the dispersivity cannot be completely determined by the aperture field characteristics alone; it is also a function of specific discharge. The colloid recovery in all fractures was found to increase with increasing specific discharge. For each specific discharge, it was found that the colloid recoveries in F2 and F3 were similar, and were always larger than the recovery in F1. This is consistent with the fact that the arithmetic mean apertures of F2 and F3 were similar (μb,F2= 1.57 mm, /μb,F3= 1.75 mm), and larger than that of F1 (μb,F1 = 0.88 mm). This suggests that it is the transport step (the step in which the colloids are transported from the bulk fluid to the vicinity of the fracture wall), and not the attachment step, that plays the dominant role in the colloid sorption process. It was also found that the mean transport velocity and dispersion coefficient of colloids are larger than those of solutes in F3 (CoV = 0.29), but similar to those of solutes in F1 (CoV = 0.78) and F2 (CoV = 0.71). This confirms the numerical simulation results from this work indicating that tp and DL,coll/DL,solute decrease with increasing CoV. These findings have significant implications on the interpretation of colloid transport data.</p> / Thesis / Doctor of Philosophy (PhD)

No description available.

No description available.