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Hanif, Adeela,Trung, Tran Quang,Siddiqui, Saqib,Toi, Phan Tan,Lee, Nae-Eung American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.32
<P>Human skin is highly stretchable at low strain but becomes self-limiting when deformed at large strain due to stiffening caused by alignment of a network of stiff collagen nanofibers inside the tissue beneath the epidermis. To imitate this mechanical behavior and the sensory function of human skin, we fabricated a skin-like substrate with highly stretchable, transparent, tough, ultrathin, mechanosensory, and self-limiting properties by incorporating piezoelectric crystalline poly((vinylidene fluoride)-<I>co</I>-trifluoroethylene) (P(VDF-TrFE)) nanofibers with a high modulus into the low modulus matrix of elastomeric poly(dimethylsiloxane). Randomly distributed P(VDF-TrFE) nanofibers in the elastomer matrix conferred a self-limiting property to the skin-like substrate so that it can easily stretch at low strain but swiftly counteract rupturing in response to stretching. The stretchability, toughness, and Young’s modulus of the ultrathin (∼62 μm) skin-like substrate with high optical transparency could be tuned by controlling the loading of nanofibers. Moreover, the ultrathin skin-like substrate with a stretchable temperature sensor fabricated on it demonstrated the ability to accommodate bodily motion-induced strain in the sensor while maintaining its mechanosensory and thermosensory functionalities.</P> [FIG OMISSION]</BR>
Choi, Young-In,Hwang, Byeong-Ung,Meeseepong, Montri,Hanif, Adeela,Ramasundaram, Subramaniyan,Trung, Tran Quang,Lee, Nae-Eung The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.9
<P>Creating stretchable and transparent conductive electrodes for stretchable and transparent electronics is very challenging due to difficulties in obtaining adequate optical and mechanical properties simultaneously. Here, we designed a stretchable and transparent nanofiber-networked electrode (STNNE) based on a networked structure of electrospun stretchable nanofibers made from a mixture of polyurethane (PU)/reduced graphene oxide (rGO)/silver nanoparticles (AgNPs). The STNNE showed a sheet resistance as small as 210 Ω sq<SUP>−1</SUP> at an optical transparency of ∼83%. In addition, the STNNE has up to 40% mechanical stretchability and relatively high electrical stability (<I>i.e.</I>, a resistance change of 83% at 40% stretching). The good electrical conductance, mechanical stretchability, and electrical stability under static/dynamic stretching or after cyclic stretching are attributed to the high dispersion of AgNPs in the nanofibers, which creates more electrically conductive pathways and forms fused junctions at the intersections between nanofibers during electrospinning. As a demonstration, an STNNE with a simple selective-patterning process was employed to fabricate a stretchable capacitive touch sensor with a stretchable and transparent dielectric (PU) on a polydimethylsiloxane substrate. The signal output of the touch sensor upon touching under stretched conditions was nearly unchanged. This STNNE has great potential in stretchable and transparent electronics.</P>
Minh Triet, Nguyen,Thai Duy, Le,Hwang, Byeong-Ung,Hanif, Adeela,Siddiqui, Saqib,Park, Kyung-Ho,Cho, Chu-Young,Lee, Nae-Eung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.36
<P>A Schottky diode based on a heterojunction of three-dimensional (3D) nanohybrid materials, formed by hybridizing reduced graphene oxide (RGO) with epitaxial vertical zinc oxide nanorods (ZnO NRs) and Al0.27GaN0.73(similar to 25 nm)/GaN is presented as a new class of high-performance chemical sensors. The RGO nanosheet layer coated on the ZnO NRs enables the formation of a direct Schottky contact with the AlGaN layer. The sensing results of the Schottky diode with respect to NO2, SO2, and HCHO gases exhibit high sensitivity (0.88-1.88 ppm(-1)), fast response (similar to 2 min), and good reproducibility down concentration levels at room temperature. The sensing mechanism of the Schottky diode can be explained by modulation of the reverse saturation current due to the change in thermionic emission carrier transport caused by ultrasensitive changes in the Schottky barrier of a van der Waals heterostructure between RGO and AlGaN layers upon interaction with gas molecules. Advances in the design of a Schottky diode gas sensor based on the heterojunction of high-mobility two-dimensional electron gas channel and highly responsive 3D-engineered sensing nanomaterials have potential not only for the enhancement of sensitivity and selectivity but also for improving operation capability at room temperature.</P>
Bae, Chan Wool,Toi, Phan Tan,Kim, Bo Yeong,Lee, Won Il,Lee, Han Byeol,Hanif, Adeela,Lee, Eung Hyuk,Lee, Nae-Eung American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.16
<P>Biosensor systems for wearable continuous monitoring are desired to be developed into conformal patch platforms. However, developing such patches is very challenging owing to the difficulty of imparting materials and components with both high stretchability and high performance. Herein, we report a fully stretchable microfluidics-integrated glucose sensor patch comprised of an omnidirectionally stretchable nanoporous gold (NPG) electrochemical biosensor and a stretchable passive microfluidic device. A highly electrocatalytic NPG electrode was formed on a stress-absorbing 3D micropatterned polydimethylsiloxane (PDMS) substrate to confer mechanical stretchability, high sensitivity, and durability in non-enzymatic glucose detection. A thin, stretchable, and tough microfluidic device was made by embedding stretchable cotton fabric as a capillary into a thin polyurethane nanofiber-reinforced PDMS channel, enabling collection and passive, accurate delivery of sweat from skin to the electrode surface, with excellent replacement capability. The integrated glucose sensor patch demonstrated excellent ability to continuously and accurately monitor the sweat glucose level.</P> [FIG OMISSION]</BR>