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Browsing by Author "Sarles, Stephen Andrew"

Now showing 1 - 3 of 3
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    Active Rigidization of Carbon Fiber Reinforced Composites via Internal Resistive Heating
    Sarles, Stephen Andrew (Virginia Tech, 2006-02-20)
    The use of inflatable, rigidizable structures in solar arrays and other space structures has the potential to drastically reduce the weight, volume, and cost of placing payloads into orbit. Inflatable components consist of ultra-lightweight, flexible materials that enable compact packaging prior to launch. These structures are then transformed from their initially flexible state to one that offers permanent shape-holding and structural integrity through a tailored rigidization process. Inflatable spacecraft must be impervious to the environmental conditions in space--such as ionizing radiation, UV and particle radiation, atomic oxygen, and impacts from space debris and meteoroids. They must also exhibit stable operation over a useful storage and mission life. Methods for causing rigidization in inflatable spacecraft include both passive and active techniques. Passive techniques rely on an uncontrolled, unprovoked reaction between the rigidizable materials in the structure and the surrounding space environment. The benefits of a passive system are offset by their inherent lack of control, which can lead to long curing times and weak spots due to uneven curing. This work presents internal resistive heating as an alternative approach for inducing matrix consolidation and curing of thermoset-coated carbon fiber tows. The ability to dictate this physical transformation through temperature-controlled resistive heating highlights the responsive nature of thermoset polymer composites and demonstrates the advantages of active rigidization. Feedback temperature control is implemented so as to provide a reliable, robust heating method for prescribing material-specific curing profiles. Resistive heating curing schedules developed from previous thermal analysis on two resins, U-Nyte Set 201A and 201B, are prescribed for samples of carbon fiber tow coated with each resin. The rigidization success of each curing profile is then evaluated with respect to both the increase in mechanical stiffness and the cure completion. These experiments indicate that rigidizing the coated fiber tow results in a composite material that is 20 times stronger in bending than prior to curing. The stiffening process requires roughly 1W-hr of energy with 5W peak power over the course of a 24-minute curing schedule. Curing temperature, curing time, and heating rate are also individually varied to determine their effect on rigidization as well as develop methods for reducing curing time and energy. The rigidization of an inflatable structure culminates this work and demonstrates the ability to achieve real strengthening through temperature-controlled internal resistive heating.
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    Physical Encapsulation of Interface Bilayers
    Sarles, Stephen Andrew (Virginia Tech, 2010-04-08)
    This dissertation presents the development of a new form of biomolecular material system which features interface lipid bilayers capable of hosting a wide variety of natural and engineered proteins. This research builds on the droplet interface bilayer (DIB) platform which first demonstrated that, through self-assembly, lipid-encased water droplets submersed in oil can be physically connected to form a liquid-supported lipid bilayer at the droplet interface. Key advantages of the DIB method over previous bilayer formation techniques include the lack of a supporting substrate which simplifies bilayer formation and the ability to connect many droplets to form `cell-inspired' networks which can provide a collective utility based on the compositions and arrangement of the droplets. The research present herein specifically seeks to overcome three limitations of the original droplet interface bilayer: limited portability due to lack of droplet support, the use of externally supported electrodes to electrically probe the network, and the requirement that in order to form DIB networks, aqueous volumes must be individually dispensed and arranged. The approach presented in this document is to provide increased interactions between the contained liquid phases and a supporting substrate in order to achieve both increased usability through refined methods of packaging and in situ interface formation which eliminates the need to create individual droplets. Physical encapsulation is defined as the the use of a solid substrate to contain both liquid phases such that the aqueous volumes are physically supported on one length scale (10-1000µm) while not inhibiting the self-assembly of phospholipids at the oil/water interface occurring on a much smaller length scale (1-10nm). Physically-encapsulated droplet interface bilayers are achieved by connecting lipid-encased droplets within a substrate that tightly confines the positions of neighboring droplets. A term called the packing factor is introduced to quantify the ratio of the aqueous volumes per the total compartment volume. Physically-encapsulated droplet interface bilayers formed in high packing factor substrate (30%) that also features integrated electrodes demonstrate all of the properties that unencapsulated DIBs exhibit (electrical resistances greater than 1GΩ, failure potentials between |200-300|mV, and the ability to host transmembrane proteins) but these confined assemblies can be moved, shaken, and even completely inverted. Additionally, a structured experiment to quantify the durability of interface bilayers shows that encapsulated and unencapsulated droplet interface bilayers can both survive 3-7g of lateral acceleration prior to bilayer failure, but have different modes of failure. Encapsulated DIBs tend to rupture, while unencapsulated DIBs completely separate. Physical encapsulation is also shown to permit the in situ formation of durable interface bilayers when the substrate is made from a flexible material. The importance of this approach stems from the fact that, by using the substrate to locally partition a single aqueous volume into multiple volumes, there is no need to arrange individual droplets. This method of bilayer formation is termed the regulated attachment method (RAM), since the separation and subsequent reattachment of the aqueous volumes is regulated by the opening and closing of an aperture within the flexible substrate. In this dissertation, a mechanical force is used to directly modulate the aperture dimension for controlling both the initial formation and final size of the interface. With the demonstrated advantages of portability and controlled attachment offered by physical encapsulation, encapsulated lipid bilayers are formed within a completely sealed flexible substrate. A key aspect of this final work is to demonstrate that both the organic and aqueous phases can be stabilized internally, creating a complete material system that features tailorable interface bilayers.
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    Using Lipid Bilayers in an Artificial Axon System
    Vanderwerker, Zachary Thomas (Virginia Tech, 2013-12-08)
    Since the rise of multicellular organisms, nature has created a wide range of solutions for life on Earth. This diverse set of solutions presents a broad design space for a number of bio-inspired technologies in many different fields. Of particular interest for this work is the computational and processing power of neurons in the brain. Neuronal networks for transmitting and processing signals have advantages to their electronic counterparts in terms of power efficiency and the ability to handle component failure. In this thesis, an artificial axon system using droplet on hydrogel bilayers (DHBs) in conjunction with alamethicin channels was developed to show properties of action potential signal propagation that occur in myelinated nerve cells. The research demonstrates that the artificial axon system is capable of modifying signals that travel perpendicular to a lipid bilayer interface due to the voltage-gating properties of alamethicin within the connected bilayer. The system was used to show a signal boosting behavior similar to what occurs in the nodes of Ranvier of a myelinated axon. In addition, the artificial axon system was used to show that alamethicin channels within a lipid bilayer behave similarly to slow-acting potassium channels in a real axon in that they follow a sigmoid activation curve in response to a step potential change.