Because a wearable device comprised of a flexible film should be comfortable to wear over the skin, several reports have focused on the film thickness to prepare ultrathin films that are a few micrometers or nanometers thick. [26,27] Thinning a film to this scale should realize a film capable of covering the skin asperity conformally, resulting in a good comfort while wearing and a relatively strong adhesion on skin without glue. However, ultrathin films can be difficult to handle and attach to skin. Additionally, assembling other components such as a signal processing circuit and battery without sacrificing the advantage of thickness remains challenging. Thus, many reports still employ both ultrathin film flexible devices and relatively thick films (several hundred micrometers). [1,[4][5][6][7]9,12,16,18,19,22,28] However, the effect of film thickness on sensing has yet to be discussed, although a systematical study is important to realize precise health data recordings. In addition to the wearability and film thickness depedences, biocompatibility of the sensor and film materials is another important parameter to consider for the practical application as a wearable device.In this study, we explore the dependence of the temperature change, which is measured by a printed temperature sensor fabricated on polyethylene terephthalate (PET), on thickness. A thick film was selected due to handling ease and ability to integrate other components in the future. However, some sensors such as an ECG sensor must attach onto skin with good adhesion without sacrificing conductivity, and a relatively thick flexible film itself cannot attach to skin without an adhesion layer. To create good adhesion between an ECG sensor and skin without losing conductivity, a high adhesive conductive polymer onto skin is also developed. Although gel-based electrodes are often used in medical applications, gel-based electrodes are unsuited for long-time measurements due to skin irritation. [15] Thus, we developed a gel-less sticky electrode using biocompatible materials by characterizing the adhesion, impedance between skin and the ECG sensor, and repeatability for use. Finally, as a proofof-concept demonstration, simultaneous efficient skin temperature and ECG signal recordings were conducted using a conductive polymer with an optimized film thickness. Figure 1a describes an integrated device image with a temperature sensor, an ECG sensor, an equivalent circuit between Wearable, flexible healthcare devices, which can monitor health data to predict and diagnose disease in advance, benefit society. Toward this future, various flexible and stretchable sensors as well as other components are demonstrated by arranging materials, structures, and processes. Although there are many sensor demonstrations, the fundamental characteristics such as the dependence of a temperature sensor on film thickness and the impact of adhesive for an electrocardiogram (ECG) sensor are yet to be explored in detail. In this study, the effect of film thickness for skin te...

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Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD-organic hybrid materials. Three peripherally functionalised GQDs having a third-generation dendritic wedge (GQD-2), long alkyl chains (GQD-3) and a polyhedral oligomeric silsesquioxane group (GQD-4) were prepared by the Cu(I) -catalysed Huisgen cycloaddition reaction of GQD-1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD-1-4 and on the five-membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO-LUMO bandgaps of GQD-1-4 were estimated to be approximately 2 eV, and their low-lying LUMO levels (<-3.9 eV) were lower than that of phenyl-C61 -butyric acid methyl ester, an n-type organic semiconductor. The solubility of GQD-1-4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD-2, both GQD-3 and GQD-4 emitted white light upon excitation at 360 nm. Size-exclusion chromatography demonstrated that white-light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.

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A soluble precursor of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) is developed for high-performance printed organic thin-film transistors (OTFTs). The DNTT precursor enables excellent thin-film formation and can induce specific phase separations when blended with inert polymers. The DNTT OTFTs processed from the precursor/polymer blend exhibit field-effect mobilities of up to 1.1 cm(2) V(-1) s(-1) and excellent durability against air exposure and thermal stress.

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Low-frequency dielectric properties were measured for study of the transport properties of impurity ions in nematic liquid crystal (NLC: 4-cyano-4'-pentyl biphenyl) cells with and without polyimide alignment layers. It was found that the dielectric behavior of the NLC cells without polyimide alignment layers is due to the electrode polarization. The diffusion constant and the concentration of the impurity ions are determined from the dielectric behavior. The NLC cells with polyimide alignment layers exhibit interface polarization between the polyimide alignment layers and the NLC slab. The ion concentration is estimated from the frequency at the dielectric loss peak of the interface polarization. The ion concentration is much higher in the NLC cells with polyimide alignment layers than in the cells without polyimide alignment layers, indicating that a considerable amount of impurity ions are dissolved from the polyimide layers. The temporal variations of the dielectric properties of the NLC cells with and without polyimide alignment layers after the cell preparation were also measured.