In the printing of electronic materials for electronic textiles (e-textiles), reliability and durability of devices are of critical importance. A unique capability of a direct-write (DW) printing process is introduced that takes advantage of ink penetration in fiber bulks, owed in part to the capillary action phenomena of conductive inks on the textile. As a result of the penetration, the durability of the printed patterns improved in deformability and washability. To understand this phenomenon, the ink-to-substrate interaction of the Ag-based conductive ink on thermoplastic polyurethane (TPU) films, polyethylene terephthalate (PET) nonwoven textiles, and nylon-PET nonwoven (Evolon®) textiles are studied. Substrate properties such as surface roughness and porosity show a significant impact on the flow properties of the ink. The penetration of the conductive ink into the fiber bulk created a unique fiber-ink composite structure that is structurally more stable under mechanical deformation. Due to the high porosity and penetration to the cross-sectional direction, the patterns on the PET nonwoven textiles showed less ink spreading on the surface and higher resistance compared to a densely structured Evolon® textiles. The printed patterns were demonstrated as wearable textile heaters and showed reliable performance during mechanical deformation, wash, and cyclic heating tests. Finally, a printed heater wrap was demonstrated on the human body to explain a use case scenario for the DW process for wearable electronics.

The objective of this study is to understand light emission characteristics of fracto-mechanoluminescent (FML) europium tetrakis(dibenzoylmethide)-triethylammonium (EuD4TEA) crystals under high strain-rate compressive loading. As a sensing material that can play a pivotal role for the self-powered impact sensor technology, it is important to understand transformative light emission characteristics of the FML EuD4TEA crystals under high strain-rate compressive loading. First, EuD4TEA crystals were synthesized and embedded into polydimethylsiloxane (PDMS) elastomer to fabricate EuD4TEA-PDMS composite test specimens. Second, the prepared EuD4TEA-PDMS composites were tested using the modified Kolsky bar setup equipped with a high-speed camera. Third, FML light emission was captured to yield 12 bit grayscale video footage, which was processed to quantify the FML light emission. Finally, quantitative parameters were generated by taking into account pixel values and population of pixels of the 12 bit grayscale images to represent FML light intensity. The FML light intensity was correlated with high strain-rate compressive strain and strain rate to understand the FML light emission characteristics under high strain-rate compressive loading that can result from impact occurrences.

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Liquid coiling occurs as a viscous fluid flows into a stagnant reservoir causing a localized accumulation of settling material, which coils into a stack as it accumulates. These coiling flows are broadly characterized into three primary coiling regimes of viscous, gravitational, or inertial coiling, based on the velocity of the falling fluid, the height of the fall, the radius of the fluid rope, the stack height, and the fluid properties including viscosity. A computer-controlled flow delivery apparatus was developed here to produce precisely controlled flow conditions to study steady and transitional coiling regimes with independently varied parameters. Data were recorded using high-speed digital video cameras and a purpose-built digital image processing routine to extract rope and stack dimensions as well as time-resolved coiling frequency. The precision of the setup and data analysis methods allowed a detailed study of the transition between gravitational and inertial flow regimes. The results show a smooth transition between the regimes, with no evidence of the inertial-gravitational regime. Unsteady coiling was able to be momentarily produced by applying a perturbation to the system, but the unstable regime quickly decayed to either the base inertial or gravitational regime.