Browsing by Author "Bartlett, Michael D."

Now showing 1 - 9 of 9
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    All-graphene-based open fluidics for pumpless, small-scale fluid transport via laser-controlled wettability patterning
    Hall, Lucas S.; Hwang, Dohgyu; Chen, Bolin; Van Belle, Bryan; Johnson, Zachary T.; Hondred, John A.; Gomes, Carmen L.; Bartlett, Michael D.; Claussen, Jonathan C. (2021-01)
    Open microfluidics have emerged as a low-cost, pumpless alternative strategy to conventional microfluidics for delivery of fluid for a wide variety of applications including rapid biochemical analysis and medical diagnosis. However, creating openmicrofluidics by tuning the wettability of surfaces typically requires sophisticated cleanroom processes that are unamenable to scalable manufacturing. Herein, we present a simple approach to develop open microfluidic platforms by manipulating the surface wettability of spin-coated graphene ink films on flexible polyethylene terephthalate via laser-controlled patterning. Wedge-shaped hydrophilic tracks surrounded by super-hydrophobic walls are created within the graphene films by scribing micron-sized grooves into the graphene with a CO2 laser. This scribing process is used to make superhydrophobic walls (water contact angle B1608) that delineate hydrophilic tracks (created through an oxygen plasma pretreatment) on the graphene for fluid transport. These allgraphene open microfluidic tracks are capable of transporting liquid droplets with a velocity of 20 mm s(-1) on a level surface and uphill at elevation angles of 78 as well as transporting fluid in bifurcating cross and tree branches. The all-graphene open microfluidic manufacturing technique is rapid and amenable to scalable manufacturing, and consequently offers an alternative pumpless strategy to conventional microfluidics and creates possibilities for diverse applications in fluid transport.
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    Characterization of the Integration of Additively Manufactured All-Aromatic Polyimide and Conductive Direct-Write Silver Inks
    Oja, Thomas Edward (Virginia Tech, 2020-12-07)
    Hybridizing additive manufacturing (AM) structures and direct write (DW) deposition of conductive traces enables the design and physical creation of integrated, complex, and conformal electronics such as embedded electronics and complex routing on a fully AM structure. Although this hybridization has a promising outlook, there are several key AM substrate-related limitations that limit the final performance of these hybridized AM-DW electronic parts. These limitations include low-temperature processability (leading to high trace resistivity) and poor surface finish (leading to electronic shorts and disconnections). Recently discovered ultraviolet-assisted direct ink write (UV-DIW) all-aromatic polyimide (PI) provides an opportunity to address these previous shortcomings previously due to its high-temperature stability (450C) and superior surface finish (relative to other AM processes). The primary goal of this thesis is to characterize the integration of this UV-DIW PI with DW-printed conductive inks as a means for obtaining high-performance hybrid AM-DW electronics. This goal has been achieved through an investigation into the increased temperature stability of AM PI on the conductivity and adhesion of DW extrusion and aerosol jet (AJ) silver inks, determining the dielectric constant and dissipation factor of processed UV-DIW PI, and determining the achievable microwave application performance of UV-DIW PI. These performance measurements are compared to commercially-available PI film and relative to existing AM substrates, such as ULTEM 1010. The temperature stability of UV-DIW PI enabled higher-temperature post-processing for the printed silver traces, which decreased DIW trace resistivity from 14.94±0.55 times the value of bulk silver at 160 °C to 2.16±0.028 times the resistivity of bulk silver at 375 °C, and AJ silver trace resistivity from 5.27±0.013 times the resistivity of bulk silver at 200 °C to 1.95±0.15 times the resistivity of bulk silver at 350 °C. The adhesion of these traces was not negatively affected by higher processing temperatures, and the traces performed similarly on UV-DIW PI and commercial PI. Furthermore, at similar thicknesses, UV-DIW PI was found to have a similar dielectric constant and dissipation factor to commercial Dupont Kapton PI film from 1 kHz to 1 MHz, indicating its ability to perform highly as a dielectric electronics substrate. Finally, the decrease in resistivity was able to decrease the gap in microwave stripline transmission line performance when compared with ULTEM 1010 processed at 200°C, with peak 10 GHz S21 loss differences decreasing from 2.46 dB to 1.32 dB after increasing the UV-DIW processing temperature from 200 °C to 400°C.
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    Enabling New Material and Process Capabilities for Ultraviolet-Assisted Direct Ink Write Additive Manufacturing via Exploration of Material Rheology and Reactivity
    Rau, Daniel Andrew (Virginia Tech, 2022-05-24)
    Ultraviolet-Assisted Direct Ink Write (UV-DIW) is a material extrusion additive manufacturing (AM) technology in which a viscous ink, often at room temperature, is selectively extruded through a translating nozzle to selectively deposit material. The extruded ink is solidified via UV irradiation (photocuring) and three-dimensional parts are created by repeating the process in a layer-by-layer fashion. UV-DIW is an attractive AM technology due to its ability to (1) extrude highly viscous inks (i.e. >10,000 Pa·s if ink exhibits shearthinning behavior) (2) the promise of leveraging the broad photopolymer material library and chemistries established for other AM technologies capable of processing photopolymers and (3) the promise of processing a wide range of inks, which enables the fabrication of metal, ceramic, polymer, bio-based, and multi-material parts. Currently, the technology faces a few shortcomings including (1) limited material selection for UV-DIW due to requirement for inks to be photocurable and limited mechanical properties of photocurable materials (2) lack of feature resolution and topological complexity of printed parts and (3) lack of material screening models providing robust definition of the material requirements (e.g., viscosity, cure time, strength) for successful UV-DIW printing. To address these shortcomings, the goal of this work is to gain a fundamental understanding of the rheological and reactive properties required for successful Ultraviolet-Assisted Direct Ink Write (UV-DIW). The first approach to answering the fundamental research question is establishing the existing rheology experiments used to characterize DIW inks and the relationships between rheology and printability. An in-depth literature review of the techniques and relationships was compiled to better understand ink requirements for successful printing (Chapter 2). This broad survey is not limited to only UV-DIW, but includes all variations of DIW. The first part of the review provides a summary of the rheological experiments that have been used to characterize a wide variety of DIW inks. The second part of this review focuses on the connections between rheology and printability. This survey helps identify the required rheological properties for successful printing that is then used throughout the rest of this work. Additionally, this review identifies shortcomings in current work and proposes areas for future work. From this exhaustive literature review, a systematic roadmap was developed that investigators can follow to quickly characterize the printability of new inks, independent of that ink's specific attributes (Chapter 3). The roadmap simplifies the trends identified in literature into a brief and intuitive guide to the rheology experiments relevant to DIW printing and the relationship between those experiment and printing results. The roadmap was demonstrated by evaluating the printability of two inks: (1) a silicone ink with both yield-stress and reactive curing behavior and (2) urethane acrylate inks with photocuring behavior. Experimental printing studies were used to support the conclusions on printability made in the roadmap. The second main approach focuses on the development of three novel UV-DIW inks to address the current limited material selection for UV-DIW and help better understand the rheological and reactive properties required for successful printing. For the three novel UVDIW inks, the iterative process of ink synthesis, analysis of ink rheology, and printability evaluation was detailed. Data from the development process contributed to gaining a fundamental understanding of how rheology and reactivity affect printability. The three inks each had novel rheological properties that impacted their printing behavior: (1) photocuring (2) yield-stress behavior + photocuring and (3) photocuring + thermal curing. Additionally, each ink had unique properties that expands material selection for UV-DIW including (1) an all-aromatic polyimide possessing a storage modulus above 1 GP a up to 400 °C (Chapter 4), (2) a styrene butadiene rubber (SBR) nanocomposite with elongation at break exceeding 300 % (Chapter 5), and (3) a dual-cure ink enabling the printing of inks containing over 60 vol% highly opaque solids (Chapter 6). The third approach details the development of two UV-DIW process models to better understand the process physics of the UV-DIW process and give insight to the properties of a successful ink. The first process model uses data from photorheology experiments to model how a photocurable ink spreads upon deposition from the nozzle, accounting for transient UV curing behavior (Chapter 7). This model allows for the rapid evaluation of an ink's behavior during the solidification sub-function of UV-DIW solely based on its rheology, without the time-consuming process of trial-and-error printing or complex computer simulations. The second process model combines modeling with a novel experimental method that uses a UV photorheometer to accurately characterize the relationship between cure depth and UV exposure for a wide range of photopolymers (Chapter 8). This model helps understand an inks photocuring behavior and ensure a sufficient cure depth is produced to adhere to the previous layer in UV-DIW printing. Lastly, two UV-DIW process modifications are introduced to address research gaps of printing high resolution features and limited material selection. A hybrid DIW + Vat Photopolymerization system is presented to improve the feature size and topographical complexities of parts, while still retaining UV-DIW's ability to print with very high viscosity photoresins (Chapter 9). A high temperature Heated-DIW system is presented to heat inks to over 300 °C and ultimately enable printing of poly(phenylene sulfide) aerogels (Chapter 10). In enabling the DIW of poly(phenylene sulfide) aerogels, the production of ultra-lightweight thermally insulating components for applications in harsh environments is enabled. With the use of additive manufacturing, hierarchical porosity on the macroscale is enabled in addition to the meso-scale porosity inherent to the aerogels.
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    Heterogeneous Distribution and Corresponding Mechanical Significance of The Mineral Phase in Fish Scales
    Tan, Yiming (Virginia Tech, 2023-03-15)
    Fish scales can be considered as a laminated composite based on collagen fibrils arranged in a cross-plywood structure. This collagen-based composite is often partially mineralized (primarily hydroxyapatite) in the scale exterior in order to resist penetration and hence to enhance protection. Together with the overlapping assembly, the fish scales offer an excellent model system for developing fiber composite materials and flexible armor systems. The primary objective of this thesis is to characterize the distribution of the mineral phase within individual scale and to investigate the corresponding mechanical consequences of the scale as a whole and its different fields through experimental and computational approaches. In this thesis, we chose the scales from the black drum (Pogonias cromis) fish as a model system. First of all, the exterior surface morphology of individual scales was systematically studied, from which several distinct structural regions are identified, including focus field (central), lateral field (dorsal and ventral), rostral field (anterior), and caudal field (posterior). In the focus field, the classic two-layer design, i.e., mineralized exterior layer and collagen-based interior layer, was observed, and nanoindentation results revealed that the high mineral exterior layer results in a much higher hardness (800 vs 450 MPa). Moreover, macroscopic tensile tests indicate that the mechanical removal of mineralized layer did not lead to reduction in strength values, whereas acid-treated demineralized scales showed reduced mechanical properties. Finally, we identified a previously unreported mineral distribution pattern in the rostral field, in which the mineral phase is segregated into long strips along the anterior-posterior direction (width, ~300 μm). In addition, towards the interior of the scale, it appears that the mineral deposition is highly correlated with the collagen orientation, resulting a unique mineralized-unmineralized collagen-based composite structure. We built finite element models to compare this unique structure to two other mineral phases in different fields at the individual scale. This unique structure demonstrates a larger deformation displacement when load was applied, indicating that it provides further flexibility in anterior end of an individual scale. The mineralized phases and structures of various fields within a single scale provide different mechanical characteristics and properties. The structural and mechanical analysis of the various regions of the fish scale can further investigate the flexibility and protective capacity of the individual scale.
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    A Kirigami Approach for Controlling Properties of Adhesives and Composites
    Hwang, Dohgyu (Virginia Tech, 2022-02-25)
    Controlling the layout of elasticity in materials provides new opportunities for generating various functionalities such as shape-morphing capability, large stretchability, and elastic softening for aeronautics, drug delivery, soft robotics, and stretchable electronics applications. Recently, techniques building upon kirigami principles, the Japanese art of paper cutting, have been considered an effective strategy to control stiffness and deformation of materials by systemically integrating cut patterns into inextensible sheets. The performance of kirigami-inspired materials relies primarily on geometric features defined by cut patterns rather than chemistry of constituents, which can enable high compatibility with diverse material sets across a wide range of length scales. However, kirigami has been relatively unexplored to control adhesion and current challenges such as the intrinsic trade-off between high deformability and load-bearing capacity limits applications that require large shape change and structural strength. This thesis demonstrates that the kirigami approach is a powerful tool to control interfacial properties of adhesive films, and that composite approaches in kirigami-inspired material can overcome the deformation-strength trade-off. The kirigami principle is applied to adhesives to control adhesion through arrays of linear cut patterns (Chapter 2). The spatial layout of elasticity in the kirigami-inspired adhesive enhances adhesion over homogeneous adhesive systems and generates anisotropic adhesion. The utility of the proposed adhesive design criteria is further extended to complex non-linear cut patterns (Chapter 3). These non-linear patterns significantly enhance adhesion relative to linear patterns in adhesives and unpatterned films, while also enabling easy release and spatial control of adhesion across a sheet. The enhancement enabled by cut geometry remains effective in diverse adhesives, on various surfaces, and in wet and dry conditions. The adhesion dependence on cut geometry is further investigated to understand how arrays of sub-patterns adjacent to primary non-linear patterns affect adhesion performance (Chapter 4). Kirigami composites are also developed to overcome the trade-off between large deformability and load-bearing capacity (Chapter 5). A composite architecture is developed consisting of low melting point metal alloys incorporated into patterned elastomeric layers. This composite approach shows the ability to rapidly morph into complex, load-bearing shapes, while achieving reversibility and self-healing capability through phase change driven by embedded heaters. The utility of the multi-functional composite is demonstrated through a multimodal morphing drone which transforms from a ground to air vehicle and an underwater morphing machine which can be reversibly deployed to collect cargo. This thesis is then summarized by discussing key findings, contributions, and future perspectives (Chapter 6).
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    Octopus-inspired adhesive skins for intelligent and rapidly switchable underwater adhesion
    Frey, Sean T.; Tahidul Haque, A.B.M.; Tutika, Ravi; Krotz, Elizabeth V.; Lee, Chanhong; Haverkamp, Cole B.; Markvicka, Eric J.; Bartlett, Michael D. (American Association for the Advancement of Science, 2022-07-13)
    The octopus couples controllable adhesives with intricately embedded sensing, processing, and control to manipulate underwater objects. Current synthetic adhesive–based manipulators are typically manually operated without sensing or control and can be slow to activate and release adhesion, which limits system-level manipulation. Here, we couple switchable, octopus-inspired adhesives with embedded sensing, processing, and control for robust underwater manipulation. Adhesion strength is switched over 450× from the ON to OFF state in <50 ms over many cycles with an actively controlled membrane. Systematic design of adhesive geometry enables adherence to nonideal surfaces with low preload and independent control of adhesive strength and adhesive toughness for strong and reliable attachment and easy release. Our bio-inspired nervous system detects objects and autonomously triggers the switchable adhesives. This is implemented into a wearable glove where an array of adhesives and sensors creates a biomimetic adhesive skin to manipulate diverse underwater objects.
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    Octopus-Inspired Adhesives with Switchable Attachment to Challenging Underwater Surfaces
    Lee, Chanhong; Via, Austin C.; Heredia, Aldo; Adjei, Daniel A.; Bartlett, Michael D. (Wiley-VCH, 2024-10-09)
    Adhesives that excel in wet or underwater environments are critical for applications ranging from healthcare and underwater robotics to infrastructure repair. However, achieving strong attachment and controlled release on difficult substrates, such as those that are curved, rough, or located in diverse fluid environments, remains a major challenge. Here, an octopus-inspired adhesive with strong attachment and rapid release in challenging underwater environments is presented. Inspired by the octopus’s infundibulum structure, a compliant, curved stalk, and an active deformable membrane for multi-surface adhesion are utilized. The stalk’s curved shape enhances conformal contact on large-scale curvatures and increases contact stress for adaptability to small-scale roughness. These synergistic mechanisms improve contact across multiple length scales, resulting in switching ratios of over 1000 within ≈30 ms with consistent attachment strength of over 60 kPa on diverse surfaces and conditions. These adhesives are demonstrated through the robust attachment and precise manipulation of rough underwater objects.
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    Select figures from Peel Tests for Quantifying Adhesion and Toughness: A Review
    Bartlett, Michael D.; Case, Scott W.; Kinloch, Anthony J.; Dillard, David A. (2023-02)
    Images licensed CC BY-SA and scheduled to appear in the journal Progress in Materials Science.
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    Self-healing liquid metal composite for reconfigurable and recyclable soft electronics
    Tutika, Ravi; Tahidul Haque, A.B.M.; Bartlett, Michael D. (Springer Nature, 2021)
    Soft electronics and robotics are in increasing demand for diverse applications. However, soft devices typically lack rigid enclosures which can increase their susceptibility to damage and lead to failure and premature disposal. This creates a need for soft and stretchable functional materials with resilient and regenerative properties. Here we show a liquid metal-elastomerplasticizer composite for soft electronics with robust circuitry that is self-healing, reconfigurable, and ultimately recyclable. This is achieved through an embossing technique for ondemand formation of conductive liquid metal networks which can be reprocessed to rewire or completely recycle the soft electronic composite. These skin-like electronics stretch to 1200% strain with minimal change in electrical resistance, sustain numerous damage events under load without losing electrical conductivity, and are recycled to generate new devices at the end of life. These soft composites with adaptive liquid metal microstructures can find broad use for soft electronics and robotics with improved lifetime and recyclability.