Browsing by Author "Yap, Te Faye"

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    A predictive model of the temperature-dependent inactivation of coronaviruses
    (AIP, 2020) Yap, Te Faye; Liu, Zhen; Shveda, Rachel A.; Preston, Daniel J.
    The COVID-19 pandemic has stressed healthcare systems and supply lines, forcing medical doctors to risk infection by decontaminating and reusing single-use personal protective equipment. The uncertain future of the pandemic is compounded by limited data on the ability of the responsible virus, SARS-CoV-2, to survive across various climates, preventing epidemiologists from accurately modeling its spread. However, a detailed thermodynamic analysis of experimental data on the inactivation of SARS-CoV-2 and related coronaviruses can enable a fundamental understanding of their thermal degradation that will help model the COVID-19 pandemic and mitigate future outbreaks. This work introduces a thermodynamic model that synthesizes existing data into an analytical framework built on first principles, including the rate law for a first-order reaction and the Arrhenius equation, to accurately predict the temperature-dependent inactivation of coronaviruses. The model provides much-needed thermal decontamination guidelines for personal protective equipment, including masks. For example, at 70 °C, a 3-log (99.9%) reduction in virus concentration can be achieved, on average, in 3 min (under the same conditions, a more conservative decontamination time of 39 min represents the upper limit of a 95% interval) and can be performed in most home ovens without reducing the efficacy of typical N95 masks as shown in recent experimental reports. This model will also allow for epidemiologists to incorporate the lifetime of SARS-CoV-2 as a continuous function of environmental temperature into models forecasting the spread of the pandemic across different climates and seasons.
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    A wearable textile-based pneumatic energy harvesting system for assistive robotics
    (AAAS, 2022) Shveda, Rachel A.; Rajappan, Anoop; Yap, Te Faye; Liu, Zhen; Bell, Marquise D.; Jumet, Barclay; Sanchez, Vanessa; Preston, Daniel J.
    Wearable assistive, rehabilitative, and augmentative devices currently require bulky power supplies, often making these tools more of a burden than an asset. This work introduces a soft, low-profile, textile-based pneumatic energy harvesting system that extracts power directly from the foot strike of a user during walking. Energy is harvested with a textile pump integrated into the insole of the user’s shoe and stored in a wearable textile bladder to operate pneumatic actuators on demand, with system performance optimized based on a mechano-fluidic model. The system recovered a maximum average power of nearly 3 W with over 20% conversion efficiency—outperforming electromagnetic, piezoelectric, and triboelectric alternatives—and was used to power a wearable arm-lift device that assists shoulder motion and a supernumerary robotic arm, demonstrating its capability as a lightweight, low-cost, and comfortable solution to support adults with upper body functional limitations in activities of daily living.
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    Teflon AF–Coated Nanotextured Aluminum Surfaces for Jumping Droplet Thermal Rectification
    (Wiley, 2024) Shimokusu, Trevor J.; Nathani, Alia; Liu, Zhen; Yap, Te Faye; Preston, Daniel J.; Wehmeyer, Geoff
    Jumping droplet thermal diodes (JDTDs) are promising candidates to achieve thermal rectification for next-generation thermal control. However, most prior demonstrations of JDTDs have relied on monolayer-coated copper-based superhydrophobic (SHPB) surfaces, while lower-cost aluminum JDTDs with more durable thin polymeric coatings have not been explored. In this work, a JDTD is constructed that employs SHPB aluminum surfaces coated with protective thin films of Teflon AF (amorphous fluoropolymer) 1601. Measurements for different heating orientations, gap heights (H), and fill ratios (ϕ) show that a maximum thermal rectification ratio of 7 can be achieved for H = 2.4 mm and ϕ = 10%. A thermal circuit is demonstrated that uses the JDTD to rectify time-periodic temperature profiles, achieving thermal circuit effectiveness values up to 30% of the ideal-diode limit. Coupon-level durability tests and device-level cycling show that dip coated Teflon AF enables stable operation of Al JDTDs over >20 cycles, improving on the performance of a monolayer-coated surface that fails after 5 cycles. The findings of this work signify that Teflon AF coated Al SHPB surfaces can be used for thermal rectification and motivate future research into Al JDTDs for advanced thermal management applications.
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    Thermally accelerated curing of platinum-catalyzed elastomers
    (Elsevier, 2024) Yap, Te Faye; Rajappan, Anoop; Bell, Marquise D.; Rasheed, Rawand M.; Decker, Colter J.; Preston, Daniel J.
    Silicone elastomers exhibit extraordinary compliance, positioning them as a material of choice for soft robots and devices. To accelerate curing times of platinum-catalyzed silicone elastomers, researchers have employed elevated temperatures; however, knowledge of the requisite duration for curing at a given temperature has remained limited to specific elastomers and has relied primarily on empirical trends. This work presents an analytical model based on an Arrhenius framework coupled with data from thermo-rheological experiments to provide guidelines for suitable curing conditions for commercially available addition-cured platinum-catalyzed silicone elastomers. The curing reaction exhibits self-similarity upon normalizing to a dimensionless reaction coordinate, allowing quantification of the extent of curing under arbitrary time-varying thermal conditions. Mechanical testing revealed no significant changes in properties or performance as a result of thermally accelerated curing. With this framework, higher throughput of elastomeric components can be achieved, and the design space for elastomer-based manufacturing can be developed beyond conventional casting.
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    Understanding and Leveraging the Temperature-Dependent Curing of Silicone Elastomers
    (2024-08-28) Yap, Te Faye; Preston, Daniel J
    Silicone elastomers offer a wide range of mechanical properties, and their inherent compliance renders them suitable for use in applications including medical devices, shock absorbers, water-repellant surfaces, and cookware. Moreover, in the past decade, silicone elastomers have facilitated significant progress in the field of soft robotics. However, knowledge of the curing duration at a given temperature for thermally polymerizable elastomers often relies on empirical trends, and furthermore, the curing parameters—typically determined through trial and error—are limited to specific geometries and elastomers. Additionally, over-curing elastomeric parts at elevated temperatures consumes excess energy and contributes to device failure due to subsequent weak adhesion between components. The lack of understanding of the curing behavior limits the accessible design space of elastomers. Building on a framework introduced in my prior research quantifying the inactivation reaction of viruses, in this thesis, I present a modeling framework based on thermo-rheological experiments and the Arrhenius equation to provide a new understanding of the temperature-dependent curing of platinum catalyzed elastomers. The experimental results reveal that the curing behavior exhibits self-similarity upon normalizing with the gelation time, and the reaction is characterized by a dimensionless reaction coordinate that represents the extent of curing. Next, I leverage this understanding of the curing kinetics to study the adhesion between elastomer layers only as a function of the extent of curing, which accounts for both duration and temperature, and demonstrate the utility of the reaction coordinate to pinpoint failure regimes. Adhesion between elastomeric components represents a longstanding problem in the field of soft robotics and soft lithography. New insight into improving adhesion will enable new fabrication methodologies. Finally, I investigate the effects of curing silicone elastomers at temperatures beyond room temperature on the mechanical properties. The corresponding experimental results highlight the feasibility of using temperature to control the speed of curing while maintaining the desired mechanical behavior. Overall, my thesis aims to understand and leverage the curing behavior of elastomers as a function of time and temperature, informed by reaction kinetics, to broaden elastomer processing beyond traditional casting, and expand the accessible design space for the manufacturing of elastomeric devices.