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Graphical abstract Highlights • A superior QCM humidity sensor with GQDs-CS sensitive film was fabricated. • It was proved that the introduction of GQDs into CS enhanced the mechanical stiffness of the CS film. • The prepared QCM sensor exhibits excellent humidity sensing properties and high Q-factor. Abstract A quartz crystal microbalance (QCM) humidity sensor based on graphene quantum dots-chitosan (GQDs-CS) sensitive film has been successfully fabricated in this work. The composite ratio of sensitive material and the coating quality of the sensitive film were optimized. The morphological and chemical properties of GQDs-CS composites were inspected via scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier Transform infrared spectroscopy (FT-IR). The results manifest that prepared QCM sensor exhibits high response sensitivity (a frequency shift of −3291 Hz at 95% RH), short response/recovery time (36 s/3 s), tiny humidity hysteresis (˜1.6% RH), and excellent reproducibility, reversibility and long-term stability. Additionally, the electroacoustic parameters of the QCM sensors were also investigated by means of the impedance analysis method. Based on dynamic and static analysis of the sensor, it is speculated that the introduction of GQDs into CS enhanced the mechanical stiffness of the CS film, which could effectively improve the performance of QCM sensor. [ABSTRACT FROM AUTHOR]

Composites fabricated by mesoporous silica loading hydrophilic elements have been widely investigated as humidity sensitive materials. The physical mixing process for loading hydrophilic elements is difficult to guarantee the uniformity and structural stability of the composites. Furthermore, the poor dispersibility of the silica skeleton restricts its solution processability. Herein, solution processible organic-inorganic hybrid materials were synthesized via a thiol-ene click reaction between sulfhydryl functionalized microporous silica nanoparticles (MSNs) and hydrophilic alkenyl monomer. The optimal hybrid material could disperse in water stably with a concentration of 50 mg/mL owing to the small particle size (about 105 nm) and the hydrophilic characteristic. Humidity sensors were fabricated by solution process and the humidity sensing properties were investigated. The sensor exhibits high sensitivity (about three orders impedance modulus change), small hysteresis (∼2% RH) and rapid response (the response and recovery time are 5 and 40 s, respectively) in the humidity range of 11%–95% RH. [ABSTRACT FROM AUTHOR]

A novel organic-inorganic hybrid material with the core-shell framework was prepared by modifying the poly(vinylsulfonic acid, sodium salt) (PSS) on vinyl functionalized silica nanoparticles (VSNs) via the free radical polymerization. SNs with different contents of PSS were prepared and the structures were carefully characterized. The hybrid material could enhance the durability of PSS under high humidity environment. Meanwhile, the SNs skeleton provides interstitial channels in the PSS@SNs films, which are available for water molecules transport. The PSS coated SNs (PSS@SNs) films were formed by drop-coating and their sensing properties were investigated. The impedance of the optimal humidity sensor changed more than four orders of magnitude over the relative humidity range of 33–95%, with good linearity under semi-logarithm scale (R 2 = 0.950) and a small humidity hysteresis of 2% RH. The obtained sensor also showed rapid response to humidity change (the response and recovery time were 2 and 65 s, respectively). Finally, the resultant sensor was explored for respiratory rate monitoring. [ABSTRACT FROM AUTHOR]

A physical mixing is usually needed in order to load lithium chloride (LiCl) in a matrix. A method of in situ loading LiCl in the cross-linked polymer framework by click reaction is demonstrated in this work. Pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) and divinylbenzene (DVB) were taken as the monomers to construct stable cross-linked polymer matrix, while different contents of LiCl were introduced in the polymerization process for preparing humidity sensitive composites. The cross-linked composites with uniform distribution of LiCl were obtained. Humidity sensors based on the composites were fabricated and their sensing properties were systematically investigated. The optimum mass ratio of LiCl was determined to be 8 wt%, the corresponding sensor owns a variation of impedance modulus beyond two orders of magnitudes from 11% to 95% relative humidity (RH), a maximum humidity hysteresis of ∼1.5% RH, and a short response and recovery time of 3.5 and 63 s, respectively. The humidity sensing mechanism of the obtained sensor was explored by the complex impedance spectroscopy and the equivalent circuit. [ABSTRACT FROM AUTHOR]

Mesoporous silicas loading hydrophilic materials composites were widely used in humidity sensors during the last decade. However, the physical mixing process used for loading the hydrophilic materials in the channel of mesoporous silicas is hard to guarantee their uniform dispersion, and there is no strong force to bind the host and guest materials together. To solve above problems, novel vinyl functionalized mesoporous silicas (SBA-15-vinyl) were chemically modified with hydrophilic sodium p -styrenesulfonate (SSS) with free radical polymerization. The chemical and porous structures of the obtained hybrid materials (SBA-15-PSSx) were characterized by fourier transform infrared spectroscopy (FT-IR), elemental analyses (EA), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and N 2 adsorption-desorption. The humidity sensing properties of the sensors based on SBA-15-vinyl and SBA-15-PSS indicate the introduction of PSS could effectively enhance the sensing properties of SBA-15-vinyl. The impedance of the optimized sensor changed by more than three orders of magnitude over the relative humidity (RH) range of 11%–95%, with rapid response to RH change. [ABSTRACT FROM AUTHOR]

Water-resistance and defined structure are important characteristics for the polymers used in humidity sensors. Here, cross-linked organic-inorganic hybrid polymers based on mercaptopropyl polyhedral oligomeric silsesquioxane (MPOSS), 1,4-divinylbenzene (DVB) and methacrylatoethyl trimethyl ammonium chloride (DMC) with defined structures have been synthesized via click chemistry. The structures of the resultant polymers were characterized by Fourier transform infrared spectra (FT-IR). Humidity sensors based on the cross-linked polymers were fabricated and their humidity sensing properties were systematically investigated. The impedance modules of the optimized sensor change about three orders of magnitude over the relative humidity range from 11% to 95%. The obtained sensor also shows small humidity hysteresis and rapid response to humidity change. [ABSTRACT FROM AUTHOR]

Mesoporous silica based composites are widely used for humidity sensors. But a physical mixing is needed to load humidity sensitive materials in the mesoporous silica materials, so the uniform dispersion of humidity active materials could not be guaranteed. A chemically modification method has been used to ensure the uniform dispersion and stable structure of the humidity active units in this work. Novel organic-inorganic hybrid materials have been prepared via modifying the sulfhydryl functionalized mesoporous silica SBA-15 (SBA-15-propyl-SH) with hydrophilic unit methacrylatoethyl trimethyl ammonium chloride (DMC) via a thiol-ene click reaction. Mesoporous silica skeletons could ensure the stability at high humidities and hydrophilic groups modified on the skeletons behave as humidity sensitive parts. The content of DMC on the silica could be tuned by the feed ratios. The obtained hybrid materials keep the mesoporous characteristics of silica, which is beneficial for the transport of water molecules in adsorption and desorption processes. The humidity sensing properties of the sensors based on SBA-15-propyl-SH and SBA-15-propyl-S-DMCx were investigated in details. The impedance modulus of the optimized sensor changes by more than three orders of magnitude over the relative humidity (RH) range of 11% to 95%, with prompt response to RH change (11 s and 60 s for adsorption and desorption processes, respectively). [ABSTRACT FROM AUTHOR]

Abstract: P-SBA-15 and A-SBA-15 and LiCl-A-SBA-15 (X) were prepared and characterized by IR and XRD. These different characteristic results suggest that these materials have the similar mesoporous structure. The dopant of LiCl improves the pure A-SBA-15 sorption ability to moisture. A resistive-type humidity sensor is fabricated on a ceramic substrate with Ag-Pd interdigital electrodes. The testing results on humidity sensing properties show that the material with 15wt.% LiCl as a dopant has the best sensing properties to humidity. The discussion on the sensing principle suggests that the protons are the domination carrier in a low humidity range and ions in a high humidity range. The complex impedance plots support this discussion result. [Copyright &y& Elsevier]

Abstract: A novel porous polymer was synthesized by Friedel-Crafts alkylation polymerization, and the structure and characteristic of the polymer was determined by Fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained polymer was used to prepare humidity sensitive composites by loading LiCl. Compared with the pure polymer, LiCl-loaded composites showed improved humidity sensing properties and the 4wt% LiCl/polymer sensor showed the best sensing properties. The impedance of the optimum sensor changed near four orders of magnitude over the whole humidity range, with a good linearity, little hysteresis, good stability and short response and recovery times (2 and 7s, respectively). The complex impedance plots were used to research conductive mechanism. [Copyright &y& Elsevier]

Abstract: An ordered mesoporous In2O3 material with crystalline walls has been synthesized through the nanocasting method. It was investigated as an impedance-type humidity sensor for the detection of water vapor. A nanostructured In2O3 matrix has been obtained by the hard template route from the KIT-6 silica template. The crystalline In2O3 belonged to the Ia3d space group, and its structure was characterized by X-ray diffraction (XRD), N2 adsorption–adsorption, and transmission electron microscopy (TEM). The sensor based on mesoporous In2O3 showed excellent performance in terms of humidity changes and favorable stability. Through the analysis of its semiconductor characteristics, Kelvin equation, and complex impedance, we found that the 3D mesoporous structure contributes greatly to the improvement of humidity-sensitive properties. A possible mechanism was established to explain the excellent performance of the mesoporous In2O3-made humidity-sensing device. The evaluation of its electrical characterization and the establishment of its sensing mechanism shows that mesoporous In2O3 is a good candidate for developing humidity sensors. It has potential applications in the chemical-sensing field. [Copyright &y& Elsevier]

Abstract: A fast, simple and reliable humidity sensor based on ion-doped SnO2 nanofibers has been developed by screen-printing on ceramic substrates with Ag–Pd interdigital electrodes in this research. The optimized results show that the impedance of the sensor decreases by more than five orders of magnitude with increasing relative humidity (RH) from 11% to 95%, the response and recovery time of the sensor are about 5 and 6s, respectively. Compared to the previous electrical conductivity-based SnO2 humidity sensors, the proposed sensor exhibits higher humidity sensitivity, more rapid response and recovery, smaller hysteresis, and better linearity and stability. [Copyright &y& Elsevier]

Abstract: This paper reports the study of humidity sensitive properties of pure and K+-doped LaCo0.3Fe0.7O3 thick film sensors. The humidity sensitive thick films were prepared by screen printing on ceramic substrates with interdigitated electrodes. It was found that pure LaCo0.3Fe0.7O3 showed sensitivity only in the relative humidity (RH) above 54%. The addition of alkali ion K+ was beneficial for improving the humidity sensitive properties of the sample. The best results were obtained for 2wt.% K2CO3-doped sample, which exhibited excellent linearity in the whole humidity range of 11–95%. A resistance variation of about four orders of magnitude, narrow hysteresis loop, and rapid response were obtained. The effects of dopant content on humidity sensitivity were also discussed. [Copyright &y& Elsevier]

Low humidity detection has been a great challenge in the field of humidity sensing. In recent years, polyelectrolytes have been proven to be promising materials for highly sensitive humidity sensors. In this work, cross-linked poly(ionic liquid)s (PILs) were prepared for low humidity detection. The strong hydrophilicity of PILs contributes to humidity sensing while the cross-linked structure guarantees the stability of the sensing film. The optimized sensor shows high response (48.0) in 5–35% RH, with short response/recovery time (1 s/10 s) and a small humidity hysteresis (0.2% RH). The possible sensing mechanism of the sensors was discussed. • Cross-linked poly(ionic liquid)s were used as low humidity sensitive materials. • The optimized sensor shows high response in 5–35% RH. • The optimized sensor has short recovery time and small humidity hysteresis. • The introduction of glycerol could reduce the impedance of the sensor. [ABSTRACT FROM AUTHOR]

Highlights • A novel MCM-41/PPy (Polypyrrole) based humidity sensor was prepared. • An in-situ way of loading PPy into the channels of MCM-41 framework was used for quantity control. • The MCM-41/PPy (90) sensor shows a high sensitivity and wider humidity sensing range than MCM-41sensor or PPy sensor. • A proper mechanism about dielectric constant change was discussed to explain the sensing phenomenon. Abstract Inorganic zeolites, such as MCM (Mesoporous Crystalline Material), are widely used as skeleton to load humidity sensitive materials for constructing high-performance humidity sensor. In this work, an in-situ preparation method was developed to prepare MCM-41/polypyrrole (PPy) humidity sensors, by inducing the polymerization of pyrrole vapor inside MCM-41 film that was coated on the ceramics substrate with carbon interdigital electrodes. MCM-41/PPy sensors with different polymerization times were fabricated, and their capacitance humidity sensing properties demonstrate much better performance than individual MCM-41 sensor or PPy sensor, with high sensitivity and a wide humidity sensing range. The sensing properties of MCM-41/PPy sensors were further optimized by controlling the polymerization time. In addition, a humidity sensing mechanism explanation is discussed at the end of this paper. [ABSTRACT FROM AUTHOR]

The stability of sensitive materials is of great importance to humidity sensors. A novel method is used to synthesize cross-linked polymers by a free radical polymerization while introducing the pyridine salt unit with a click reaction by a one-pot reaction. The obtained polymers were used for humidity sensors and the humidity sensitive properties were researched systematically. By introducing polar units to the side chain of the polymer, the humidity sensitive properties were improved greatly. The optimum sensor shows good sensing properties during the whole relative humidity range. In addition, the polymer sensor shows very quick response to humidity, with a response time of 6 s and a recovery time of 17 s. This method is also applicable for developing other functional materials. [ABSTRACT FROM AUTHOR]

A nanoporous organic polymer based on triphenylamine was synthesized, and the structure and morphology of the resultant polytriphenylamine (PTPA) were described by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N 2 adsorption/desorption analysis. PTPA was acted as the host to load the guest Fe(NO 3 ) 3 for preparing humidity sensitive composites. Compared with pure PTPA sensor, Fe(NO 3 ) 3 /PTPA sensors showed improved humidity sensitive properties, especially the 20 wt% Fe(NO 3 ) 3 /PTPA sensor. The impedance of the 20 wt% Fe(NO 3 ) 3 /PTPA sensor changed four orders of magnitude over the whole humidity range, with a good linearity, litter hysteresis, rapid response and good long-time stability. The complex impedance plots and direct current (DC) reverse polarity method were used to research the mechanism of the optimized sensor. [ABSTRACT FROM AUTHOR]

Defined structure and water-resistance are two important requirements for polymeric humidity sensors. Most of polymer electrolytes applied in humidity sensors do not bear both features at the same time. Herein, a novel method was used to develop stable humidity sensitive polymer electrolytes with defined structures. Nanoporous polymers based on 1,4-divinylbenzene (DVB) and methacrylatoethyl trimethyl ammonium chloride (DMC) were synthesized by free radical polymerization with a solvothermal route. The cross-linked structure could afford good stability of the polymers even at high humidity levels. The impedance module of the optimized sensor changed more than three orders of magnitude over the whole humidity range, with little humidity hysteresis and rapid response. [ABSTRACT FROM AUTHOR]

Self-supported polymer films were fabricated by the thiol-ene click cross-linking reaction in this work. The cross-linked frameworks were used to guarantee the stability the films. The hydrophilic monomer with different contents were introduced into the self-supported thick films and uniformly dispersed in the polymer frameworks. The interdigitated electrodes were screen printed with silver paste on the self-supported films to obtain humidity sensors. Herein, the self-supported film acts as both the sensor substrate and the humidity-sensing material. The humidity sensing performances of the obtained sensors were systematically researched. By optimizing the ratio of hydrophilic monomer in the polymer films, the sensitivities of the sensors were enhanced from 1.58 to 103.75 (in the humidity from 11% RH to 95% RH), the response under low RH environment was significantly improved with good linearity. The response/recovery times of the sensor within the humidity range are measured to be 12.5 s and hundreds of seconds. The prepared flexible sensors possess certain mechanical properties, and exhibit good stability under bending and long-term tests up to 60 days. The applications of the as-prepared sensor in the detection of non-contact human skin humidity, human respiration and relative humidity of green plant were explored. The sensor shows excellent sensing performance in various applications and indicates the potential application in wearable and multifunctional devices. [Display omitted] • Self-supported polymer films were fabricated by the thiol-ene click cross-linking reaction. • Flexible and stable humidity sensors were fabricated by screen printing electrodes on the self-supported films. • The roles of the self-supported film are the substrate of the sensor, as both the humidity-sensing material. • The humidity sensing properties and the multifunctional applications of the obtained sensors were systematically researched. [ABSTRACT FROM AUTHOR]

Low humidity detection has always been a challenge in the field of humidity detection. Humidity sensors base on ionic liquid modified metal organic frameworks (MOFs) derived polymer films were prepared in this work. The ionic liquid ligand was uniformly introduced in the frameworks of UIO-66 to enhance the hydrophilicity of sensing materials, the caused defects sites are beneficial for adsorption and desorption, and the MOFs based functional films were easily obtained by in situ photoinduced thiol-ene click reaction. The obtained humidity sensor exhibits a linear response in low relative humidity (RH) range (5% RH - 30% RH) with a tiny humidity hysteresis (~0.2% RH) and short response time to humidity change (response/recovery time is 0.6 s/1.7 s, respectively). ● Humidity sensors based on ionic liquid modified UIO-66 derived polyelectrolyte films were prepared. ● The sensors were prepared facilely in situ on the electrodes by thiol-ene click polymerization in batches. ● The sensor presents linear response under low humidity (5% RH - 30% RH) with a small hysteresis and fast response speed. ● The introduction of ILs and the resulting defect sites are the reasons for effective low humidity detection. [ABSTRACT FROM AUTHOR]

Abstract: Nanoporous polymer based on divinylbenzene was synthesized by radical polymerization with a solvothermal route. The nanoporous characteristic of the resultant polymer poly(divinylbenzene) (PDVB) was determined by a series of characterizations. The hydrophobic porous polymer was used as the host to prepare composited humidity sensitive materials. Different levels of LiCl were loaded into the nanoporous polymer and their humidity sensing properties were researched. Humidity sensitivities of the composites were greatly improved by LiCl loading compared with pure PDVB. The sensor based on 5wt% LiCl/PDVB showed the best sensing properties to relative humidity (RH). The impedance of the optimum sensor changed three orders of magnitude over the whole humidity range, with a good linearity and rapid response. The mechanism by the complex impedance plots suggests the protons are the domination carrier in low humidities and ions (Li+ and Cl−) in a high humidity range. The results demonstrate nanoporous polymers are a new kind of promising materials for humidity sensors. [Copyright &y& Elsevier]

Abstract: Mesoporous LaFeO3 with high surface area and pore volume was prepared through a nanocasting route by using mesoporous silica SBA-15 as a hard template. The structure and chemical composition of the sample were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry (ICP-MS). The humidity sensing properties of the mesoporous LaFeO3 were investigated. Impedance greatly changes by more than five orders magnitude (1.7×106 to 4.5kΩ) when the relative humidity varies from 11% to 98% at 10Hz, and it also exhibits the satisfactory response time, hysteresis and stability. The sensor utilizing mesoporous LaFeO3 via nanocasting method displays superior humidity performance compared to that using bulk LaFeO3 via sol–gel technique. Such sensing behavior of the mesoporous LaFeO3 can be attributed to the high surface area (83.2m2/g) and porosity, which lead to highly effective interaction between the water molecules and the surface active sites. A possible mechanism is discussed to explain the excellent performance of the humidity sensing device using the mesoporous LaFeO3. [Copyright &y& Elsevier]

Abstract: SBA-15, SBA-16 and crystal like-SBA-16 were synthesized by a simple chemical method, and the copolymer template was removed by calcination or microwave digestion (MWD) method. They were investigated as humidity sensing materials at room temperature within the relative humidity range of 11–95%RH. It was found that after MWD treatment, the humidity sensitive property of mesoporous silica have been greatly improved, and the impedance of MWD-crystal like SBA-16 changed by more than three orders of magnitude over the whole humidity range. Further testing proved that it is a promising humidity sensing material and can be widely used. A possible mechanism was also proposed to explain the correlation between material and property. [Copyright &y& Elsevier]

Abstract: Mesoporous ZnO–SiO2 composites with various Si/Zn molar ratios were synthesized through a simple one-pot sol–gel method and their humidity sensing properties were also examined. Compared with pure SBA-15, ZnO–SiO2 composite shows improved humidity sensing properties and the introducing level of ZnO has a great influence on the humid sensitivity of ZnO–SiO2 composites. The results exhibited that the sample with Si/Zn=1 showed better humidity sensing properties than others within the range of 11–95% relative humidity (RH). Its impedance changed by more than four orders of magnitude over the whole humidity range. The response and recovery time were about 50s and 100s, respectively. High sensitivity and low hysteresis were also observed. A possible mechanism was suggested to explain the humidity sensitive properties. [ABSTRACT FROM AUTHOR]

Abstract: MgO-SBA-15 has been successfully developed as a kind of humidity-sensitive material. The structure of MgO-SBA-15 materials was characterized by XRD, IR spectroscopy, N2 adsorption–desorption, TEM and XPS. The study proved that the MgO did not destroy the mesoporous structure of SBA-15 via the characteristic results of XRD and N2 adsorption–desorption. Researchers built the thick film humidity sensors on the Al2O3 ceramic substrate with two Ag–Pd interdigital electrodes with five fingers. The sensor shows excellent humidity sensitivity from 11% to 95%RH, and it has very good response and recovery property. The response time is about 10s and the recovery time is about 20s. We found that the mesoporous structure of the sensing materials contributed to the humidity sensitivity. We discussed a possible mechanism based on the humidity sensor produced by MgO-SBA-15. [Copyright &y& Elsevier]

Abstract: A simple chemical method was employed to form Fe2+ doped polypyrrole (PPY) by the introduction of hydrated ferric chloride (FeCl3·6H2O) during the polymerization of pyrrole, where FeCl3·6H2O played a role of oxidant for the polymerization and the in situ forming reduced product (FeCl2·2H2O) was well doped in PPY. The resultant Fe2+ doped PPY species were characterized by using various techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electronic microscope (FE-SEM). Humidity-sensitive properties of the samples were also examined. The Fe2+ doped PPY exhibited a fast response to humidity change (about 20s), in which great changes of more than three orders (nearly four) of magnitude in impedance was observed when relative humidity was varied over the whole range. The improved properties may be related to the presence of the hydrophilic Fe2+, and a possible mechanism was also provided. [Copyright &y& Elsevier]

Abstract: K2CO3-SBA-15 with different K2CO3 content was prepared by thermal dispersion. The structures of resultant powders were characterized by XRD, N2 adsorption and IR. The humidity sensing properties of the powders were also investigated. Compared with pure SBA-15, K2CO3-SBA-15 shows improved humidity sensing properties and the introducing level of K2CO3 has a great influence on the humid sensitivity of K2CO3-SBA-15 composites. The optimal mixing ratio was K2CO3-SBA-15 (0.8g/g), which exhibited excellent linearity in the whole range of 11–95%RH, a resistance variation of about five orders of magnitude, and a rapid response time and recovery time about 15 and 50s, respectively. The mechanism of the humidity sensitive properties was also discussed. [Copyright &y& Elsevier]

[Display omitted] • Humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC) modified cellulose paper via a facile solution method were fabricated. • The paper is used for the purpose of the humidity sensing material and the sensor substrate. • The as-fabricated paper-based humidity sensor is provided with outstanding humidity sensing properties and good stability. • The humidity sensor was applied to multifunctional applications including human breath rate, non-contact switch and skin humidity. It is of great significance to exploit a simple, cost-effective and environmentally friendly preparation method of multifunctional humidity sensors. However, most humidity sensors need complex manufacturing processes, high cost and narrow usage range. Herein, humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC) modified cellulose paper via a facile solution method were fabricated, among which the paper is used for the purpose of the humidity sensing material and the sensor substrate. The sensitivity of the obtained sensor was improved by the modification of EPTAC, the response time was decreased to 25 s, which is equivalent to the first-rate paper-based humidity sensors. In addition, the paper-based humidity sensor is provided with well flexibility and biocompatibility, and it exhibits multifunctional applications in respiratory monitoring, non-contact switch and skin humidity monitoring. The low cost and facile preparation technique in this work could provide a useful strategy for developing multifunctional humidity sensor. [ABSTRACT FROM AUTHOR]

Abstract: The highly ordered TiO2 thin films are prepared by anodic oxidation and calcined at 300, 400, 500 and 600°C, respectively. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are employed to analyze the structure and the morphology of the TiO2 films. We design a novel sensor to investigate the humidity sensing behaviours of the samples. The samples calcined at 600°C show high sensitivity with nearly two orders change in the resistance and short response and recovery time (<190s) during the relative humidity variation from 11 to 95%. [Copyright &y& Elsevier]

• The porous ionogel humidity sensitive material was successfully fabricated with the aid of PAA as the template and humidity sensing component. • The humidity sensor based on the porous ionogel shows rapid response (1.2/0.6 s) to humidity change. • Various molecular weights PAA were applied to investigate PAA's function in pore construction and humidity sensing. • The ultrafast-response humidity sensor can accurately record the human breath in real time, which is benefit for respiration data calculation. Electronic devices that can accurately record and monitor human respiration in real-time are of great interest for researchers. Ultrafast-response ionogel humidity sensors that can follow the human respiration were realized by an in-situ vinyl-thiol click reaction in this work. Polyacrylic acid (PAA) was utilized both as the template to construct porous films and for preparing humidity sensing component. The obtained optimal sensor owns a rapid response to humidity change (response and recovery time is 1.2 s and 0.6 s, respectively) and a small humidity hysteresis (∼2.2% RH). The water adsorption capability and sensing mechanism were investigated systematically. The ionogel humidity sensor with good stability and repeatability was applied in breath monitoring, which has a great potential application in diagnostic breath analysis. [ABSTRACT FROM AUTHOR]