FEP Encapsulated Crack-Based Sensor for Measurement in Moisture-Laden Environment

Abstract

Among many flexible mechanosensors, a crack-based sensor inspired by a spider’s slit organ has received considerable attention due to its great sensitivity compared to previous strain sensors. The sensor’s limitation, however, lies on its vulnerability to stress concentration and the metal layers’ delamination. To address this issue of vulnerability, we used fluorinated ethylene propylene (FEP) as an encapsulation layer on both sides of the sensor. The excellent waterproof and chemical resistance capability of FEP may effectively protect the sensor from damage in water and chemicals while improving the durability against friction.

Ultrasensitive Anti-Interference Voice Recognition by Bio-Inspired Skin-Attachable Self-Cleaning Acoustic Sensors

“…It is worth knowing that the direct contact with human skin tends to introduce water-based contaminants such as sweat to the device, which results in performance degradation or even functional failure. Although encapsulation can protect the device, an additional protective layer on the sensing film will severely degrade the sensing performance in terms of sensitivity and detection bandwidth. , As a consequence, the intrinsic waterproof and self-cleaning functions are essential for wearable sensors to retain the sensing performance. The electromechanical properties of the sensor were characterized by monitoring the relative resistance variation (Δ R / R 0 , where Δ R = R – R 0 , and R 0 and R are the initial resistance and the resistance under strain, respectively) at a bias voltage of 1 V when bending the device to different strains (ε = h /2 r , where h is the sum thickness of the patterned film and the underneath substrate, and r is the bending radius) using a motorized translation stage (Figure S10).…”

Surface Wettability for Skin‐Interfaced Sensors and Devices

“…[25] The 50 µm thick FEP with an even low water vapor permeability of 2.04 g/m 2 /day ensures the high underwater performance for the crack-based strain sensor (i.e., >93% or 72% of initial sensitivity on the 6th or 18th day). [122] However, the hydrophobic polymeric encapsulation with relatively high adhesion (compared to superhydrophobic surfaces) to the water droplets may retain them on the surface for increased risk of water penetration. [123] To achieve superhydrophobicity for the surface, the micro-/nanostructure has been introduced to reduce the contact area and increase the contact angle.…”

“…As the superhydrophobic encapsulation inevitably changes the mechanical and thermal properties of the wearable sensor to affect its sensitivity, [121,122,127,128] it is highly desirable to explore the intrinsically superhydrophobic sensors. [75,85,117,129] For example, the composite of stretchable thermoplastic elastomer (TPE) and conductive multi-walled carbon nanotubes (MWCNTs) treated with ethanol provides the resulting strain sensor with enhanced mechanical stability and robust superhydrophobicity (Figure 3f).…”

“…As the most commonly used hydrophobic encapsulation layer, PDMS can encapsulate flexible optoelectronics systems that consist of photodetectors and proximity sensors on the fingertip to exhibit invariant performance in saline solution for 3 h or 1000 cycles of immersion (Figure 3b). [ 28 ] However, the insufficient hermeticity of PDMS to water vapor (e.g., ≈ 708.1 g/m 2 /day even with a thickness of 92 µm) [ 120 ] has led to the use of polymeric materials with lower permeability, including PI, [ 121 ] fluorinated ethylene propylene (FEP), [ 122 ] and SIS. [ 25 ] For example, the 125 µm thick SIS layer has a water vapor permeability of 37 g/m 2 /day, which provides a much lower water mass change (<20% for 4 h) in soft microfluidic devices than that with PDMS (100% within 3 h) at 37 °C for precise biomarkers analysis.…”

Crack-Assisted Charge Injection into Solvent-Free Liquid Organic Semiconductors via Local Electric Field Enhancement

“…The Ag films on the polymer substrates were mechanically gripped and stretched up to fixed ratios, resulting in the formation of the cracks with reproducible patterns [39,40]. Although this simple cracking method can be easily performed to fabricate a large number of edges on metal surfaces without any lithographic processes, heavily cracked metal electrodes normally give a rise to high electrical resistance resulting in performance degradation [41][42][43]. To avoid increases in electrical resistance originating from the structural deformations, the cracked Ag films were transferred and welded onto other intact Ag films to complete the electrode structures, and then the charge injection properties were investigated using a typical non-volatile liquid organic semiconducting material, (9-2-ethylhexyl)carbazole (EHCz) [1,[5][6][7][8]10,[12][13][14].…”