A transparent stretchable (TS) gated sensor array with high optical transparency, conformality, and high stretchability of up to 70% is demonstrated. The TS-gated sensor array has high responsivity to temperature changes in objects and human skin. This unprecedented TS-gated sensor array, as well as the integrated platform of the TS-gated sensor with a transparent and stretchable strain sensor, show great potential for application to wearable skin electronics for recognition of human activity.

The role of organically modified silicate (OMS), Lucentite STN on the formation of β‐crystalline phase of poly(vinylidene fluoride) (PVDF) is investigated in the present study. The OMS was solution blended with PVDF and cast on glass slide to form PVDF‐OMS nanocomposites. Solution cast samples were subjected to various thermal treatments including annealing (AC‐AN), melt‐quenching followed by annealing (MQ‐AN), and melt‐slow cooling (MSC). Fourier‐transform infrared spectroscopy (FT‐IR), wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the crystalline structure of thermally treated samples. As a special effort, the combination of in situ thermal FT‐IR, WAXD, and DSC studies was utilized to clearly assess the thermal properties. FT‐IR and WAXD results of MQ‐AN samples revealed the presence of β‐phase of PVDF. Ion‐dipole interaction between the exfoliated clay nanolayers and PVDF was considered as a main factor for the formation of β‐phase. Melt‐crystallization temperature and subsequent melting point were enhanced by the addition of OMS. Solid β‐ to γ‐crystal phase transition was observed from in situ FT‐IR and WAXD curves when the representative MQ‐AN sample was subjected to thermal scanning. Upon heating, β‐phase was found to disappear through transformation to the thermodynamically stable γ‐phase rather than melting directly. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2173–2187, 2008

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To realize the potential applications of stretchable sensors in the field of wearable health monitoring, it is essential to develop a stable sensing device with robust electrical and mechanical properties in the present of varying external conditions. Herein, we demonstrate a stretchable temperature sensor with the elimination of strain-induced interference via geometric engineering of the free-standing stretchable fibers (FSSFs) of reduced graphene oxide/ polyurethane composite. The FSSFs were formed in serpentine structures and enabled the implementation of a strain-insensitive stretchable temperature sensor. On the basis of the controlled reduction time of graphene oxide, we can modulate the response and thermal index of the device. These results are attributed to the variation in the density of oxygen-containing functional groups in the FSSFs, which affect the hopping charge transport and thermal generation of excess carriers. The FSSF temperature sensor yields increased responsivity (0.8%/°C), stretchability (90%), sensing resolution (0.1 °C), and stability in response to applied stretching (±0.37 °C for strains ranging from 0 to 50%). When the sensor is sewn onto a stretchable bandage and attached to the human body, it can detect the temperature changes of the human skin during different body motions in a continuous and stable manner.

Nanoscale thin films of PVDF containing the β‐crystalline phase were directly prepared by heat‐controlled spin coating without the influence of external stimuli either in the form of additives or post‐treatments. Sample preparation was carried out at different temperatures, ranging from 10 to 70 °C. At elevated temperatures (40, 50, 60 and 70 °C), PVDF was crystallized into the β‐phase, while at near‐ambient conditions (20 and 30 °C) it was crystallized into the α‐phase. Some samples exhibited a phase‐segregated morphology, with varying particle sizes depending on the preparation temperature. The ferroelectric nature of a typical sample, prepared at 40 °C, was visualized by piezoresponse imaging studies.magnified image

3438www.MaterialsViews.com wileyonlinelibrary.com mechanically fl exible, light-weight, inexpensive, and easily attached to a substrate will play an important role in detecting human body temperature and in monitoring perishable food, electronic skins, and in other environmental monitoring applications. [ 3,11,15,18 ] The optical transparency of the fl exible temperature sensor may enable its easy integration into human-friendly, fl exible and transparent electronics. Several types of fl exible temperature sensors such as thermocouples [ 19 ] and resistive temperature detectors [ 15 ] have been developed. Recently, a resistive fl exible Ni composite-based temperature sensor developed by Bao et al. [ 18 ] showed a small dynamic range (25 to 40 °C). Rogers et al. [ 15 ] introduced a class of stretchable temperature sensors based on the temperature coeffi cient resistance (TCR) using serpentine gold and a PIN diode using Si nanoribbons transferred onto microperforated elastomers, which can monitor precise and continuous thermal characterization of human skin. These temperature sensors are not optically transparent because conventional opaque inorganic sensing materials and electrodes were used. Therefore, the development of a fl exible temperature sensor with high responsivity, transparency, ease of integration, large dynamic range, and stability in an ambient environment is an alternative, suitable approach for realizing the stable monitoring of temperature in many fl exible and transparent electronic systems.Graphene (Gr) has exceptional electrical and mechanical properties and has shown interesting stimuli-responsive properties to light, [20][21][22] heat, [ 23,24 ] and strain. [ 12,25,26 ] In addition, graphene and reduced graphene oxide (R-GO) are also known as multi-functional materials with transparency, fl exibility, and stretchability. [27][28][29][30][31][32][33][34] Based on those features, Gr or R-GO is a promising candidate as a physically responsive material for sensing devices. There have been recent reports regarding different types of physically responsive FETs (physi-FETs) for sensing applications based on Gr and R-GO. These include, for example, photodetectors based on mechanically exfoliated Gr and Gr nanoribbons, [ 20,21 ] phototransistors from band gap-tuneable R-GO, [ 35 ] thermal sensors based on a networked R-GO, [ 24 ] and strain sensors based on Gr and R-GO. [ 12,25 ] Although these physical sensing devices make possible new fi elds of applications in electronics, the many processing steps required, such A new class of temperature-sensing materials is demonstrated along with their integration into transparent and fl exible fi eld-effect transistor (FET) temperature sensors with high thermal responsivity, stability, and reproducibility. The novelty of this particular type of temperature sensor is the incorporation of an R-GO/P(VDF-TrFE) nanocomposite channel as a sensing layer that is highly responsive to temperature, and is optically transparent and mechanically fl exible. Furthermore, the...

Ultra‐thin films of poly(vinylidene fluoride) (PVDF) and its organically modified silicate (OMS) nanocomposites were prepared by heat‐controlled spin coating and characterized using FTIR‐GIRAS, AFM, DC‐EFM, and P–E measurements. Incorporation of OMS, Lucentite STN into the PVDF matrix favored the preferential formation of β‐phase in nanoscale thin films, irrespective of preparation temperature. The PVDF–OMS nanocomposite films have a little higher degree of orientation of molecular chains along the ITO substrate surface than that of the neat PVDF film. This gave the PVDF–OMS nanocomposite higher remanent polarization and better contrast in a DC‐EFM phase image. Unlike the thick PVDF–OMS nanocomposites films showing only α‐crystalline phase after quenching and slow cooling from the melt, the nanoscale thin PVDF–OMS films showed a mixture of β‐ and γ‐crystalline phases without any trace of α‐crystalline phase.

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