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Although it is well known that photocatalytic titanium dioxide nanoparticles effectively decompose atmospheric nitrogen oxides (NOx), the long-term effects of the photocatalytic oxidation on the cementitious substrate have not been well explored. In this study, cement paste samples containing titanium dioxide nanoparticles were exposed to multiple cycles of nitrogen dioxide gas and ultraviolet radiation, along with wetting and drying, to simulate the effects of field exposure. The photocatalytic efficiency was monitored at each cycle and the surface of the samples was examined visually, chemically and mechanically between the cycles. The results indicate that the nitrogen dioxide oxidation efficiency decreased with cycling, possibly due to carbonation of the paste or loss of titanium dioxide particles. The pits found from the scanning electron microscopy images indicate there has been deterioration on the sample surfaces. Observations of surface deterioration imply possible acid attack, leaching and/or loss of titanium dioxide, suggesting that particularly the surfaces of cement-based materials can be negatively affected by photocatalysis.

Biomimetic piezoelectric mobile acoustic sensor is fabricated for exceptional accuracy of AI-based biometric authentication., Flexible resonant acoustic sensors have attracted substantial attention as an essential component for intuitive human-machine interaction (HMI) in the future voice user interface (VUI). Several researches have been reported by mimicking the basilar membrane but still have dimensional drawback due to limitation of controlling a multifrequency band and broadening resonant spectrum for full-cover phonetic frequencies. Here, highly sensitive piezoelectric mobile acoustic sensor (PMAS) is demonstrated by exploiting an ultrathin membrane for biomimetic frequency band control. Simulation results prove that resonant bandwidth of a piezoelectric film can be broadened by adopting a lead-zirconate-titanate (PZT) membrane on the ultrathin polymer to cover the entire voice spectrum. Machine learning–based biometric authentication is demonstrated by the integrated acoustic sensor module with an algorithm processor and customized Android app. Last, exceptional error rate reduction in speaker identification is achieved by a PMAS module with a small amount of training data, compared to a conventional microelectromechanical system microphone.

We developed a novel concept of a highly efficient, transparent, and flexible triboelectric nanogenerator (TF-TENG) based on a metallic nanowire-embedded conducting polymer as a contact electrode. In contrast to metals that are highly tribopositive but opaque and less flexible, a conducting polymer, poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS), is transparent, flexible, and shows moderately high tribonegativity which is capable of accepting the electrons from the counter surface in the TF-TENG during contact. The silver nanowire layer placed beneath the conducting polymer layer results in the increase of the conductivity and the surface roughness as well. The output voltage was about 160 V. The output current (> 50 µA) was at least five times larger than any of existing TF-TENGs and a substantially high value of the instantaneous power density (> 1.5 mW/cm2) was obtained. Using such TF-TENG, a self-powered system for instantaneous touch visualization was demonstrated using a liquid crystal device. Our TF-TENG, built on a stretchable substrate, exhibits high transparency and excellent output performance on an arbitrary surface like a human skin or a fabric so that it enables to devise a variety of power sources for flexible and transparent electronics.

In this study, the influence of pore structure on the extent of calcium nitrate salt crystallization damage on mortar samples was examined. The pore volume and structure was altered by varying water-to-binder ratio and by adding nanoparticles. The results show that calcium nitrate salt exposure induces cracking in mortar samples and that more damage was observed at higher water-to-binder ratio and higher rate of nanoparticle use. It is proposed that the refined pore structure induced by nanoparticle use can result higher salt crystallizing pressure. Thus, cementitious structures that are expected to be exposed to salt crystallization should be designed to meet strength needs by lowering water-to-binder ratio

The accurate measurement of effective absorption capacity is crucial for highly absorptive materials when they are used within cement-based materials. In this study, a method for examining effective absorption capacity using isothermal calorimetry is reviewed and investigated in detail to accommodate different circumstances. Specifically, the effect of different pore structures and water-to-cement ratios in determining effective absorption capacity is experimentally examined using activated carbon fibre and powdered activated carbon. The results suggest that the method may be suitable for porous materials with micropores but not suitable for those with mesopores. Also, the results indicate that the effective absorption capacity value can change with the water-to-cement ratio used. These findings can be used to find the effective absorption capacity of highly absorptive materials more accurately using the isothermal calorimetry method.

A microarray of conducting polymer electrodes with high resolution and high pattern-fidelity is developed on a stretchable substrate through the directed wetting localization (DWL) by the differential hydrophobicity. The large difference in the surface energy between the wetting and dewetting regions serves as the major determinant of the pattern resolution and the pattern-fidelity, yielding the full surface coverage in the stretchable electrode array (SEA) with 30 μm in width. The electrical characteristics of the SEA are well preserved under different types of elastic deformations. All-solution-processed polymer light-emitting diodes (except for the cathode) based on our patterned stretchable electrodes show no appreciable degradation of the performance under stretching. The DWL provides a simple and effective way of building up diverse stretchable electrical and optoelectronic devices in advanced wearable and bio-integrated electronics.

We developed a low-cost flexible pressure sensor based on an elastomer film with uniformly distributed micro-pores as a dielectric layer. The dispersion of the micro-pores in the elastomer film results from the phase separation between a prepolymer material and deionized water to the elastomer, followed by the subsequent evaporation of the solvent within the polymer matrix after polymerization. Owing to the enhanced deformability by the pore structures, the relatively high sensitivity of 1.18 kPa−1 in the low pressure (

After a piezoelectric inkjet printhead jets the first droplet, the actuating membrane still vibrates, creating residual vibrations in the ink channel, which can degrade the inkjet printhead performance. For suppressing these vibrations, an optimized actuating voltage waveform with two pulses must be obtained, of which the first pulse is used for jetting and the second pulse is used to suppress the residual vibrations. In this study, the pressure history within the ink channel of a recirculating piezoelectric inkjet printhead was first acquired using lumped element modeling. Then, for suppressing residual vibrations, a bipolar voltage waveform was optimized via analysis of the tuning time (tt ), dwell time (td2), rising time (tr2), falling time (tf2), and voltage amplitude of the second pulse. Two voltage waveforms, Waveform 01 and Waveform 02, were optimized thereafter. In Waveform 01, tt=2 μs, td2=2 μs, and tr2 and tf2=1 μs were finalized as the optimal parameters, in the case of another waveform, the optimal parameters of td2, tr2, and tf2 were found to be 4, 1, and 1 μs, respectively. The optimal voltage amplitude of the second pulse was found to be 1/3 the amplitude of the first pulse. On the basis of our analysis, the tuning time in Waveform 01 is the most sensitive parameter, and the performance yielded is even poorer than that yielded by standard waveform, if not optimized. Therefore, the other waveform is recommended for the suppression of residual vibrations.

A new concept of intensity-tunable structural coloration is proposed on the basis of a helical photonic crystal (HPC). The HPCs are constructed from a mixture of chiral reactive mesogens by spin-coating, followed by the photo-polymerization. A liquid crystal (LC) layer, being homogeneously aligned, is prepared on the HPCs to serve as a tunable waveplate. The electrical modulation of the phase retardation through the LC layer directly leads to the intensity-tunable Bragg reflection from the HPCs upon the incidence of the polarized light. The bandwidths of the structural colors are found to be well preserved regardless of the applied voltage. A prototype of a full color reflective-type display, incorporated with three primary color units, is demonstrated. Our concept of decoupling two mutually independent functions, the intensity modulation by the tunable waveplate and the color reflection by the HPCs provides a simple and powerful way of producing a full color reflective-type display which possesses high color purity, high optical efficiency, the cycling durability, and the design flexibility.

Colloidal microwires are constructed using anisotropic assembling templates with periodically wrinkled patterns of a liquid crystalline polymer (LCP). The wrinkled LCP patterns with the period of a...

Demonstrated herein is a liquid-crystal-(LC)-based lenticular lens array with a polarization-dependent focusing effect, fabricated through a simple imprinting process. The input polarization dependence of the proposed LC lenticular lens array arises mainly from the index matching scheme between the polymer lenticular lens and the LC on it. For the input polarization perpendicular to the LC director, the focal length of the lenticular lens is about 3.1 mm. The focusing and non-focusing properties depending on the input polarization are useful for realizing autostereoscopic 2D/3D convertible displays combined with polarization selection elements.

Photocatalytic cement has been receiving attention due to its high oxidation power that reduces nitrogen oxide, thus contributing to a clean atmospheric environment. However, there has not yet been a thorough investigation on the effect of photocatalytic reactions on the durability of cementitious material, the parent material. In this study, photocatalytic cement samples were exposed to nitric oxide gas and UV along with cycles of wetting and drying to simulate environmental conditions. The surface of samples was characterized mechanically, chemically, and visually during the cycling. The results indicate that that the photocatalytic efficiency decreased with continued NO oxidation. The pits found from SEM indicated that chemical deterioration, such as acid attack or leaching, did occur. However, this was not confirmed by X-ray diffraction. The hardness was not affected, probably due to the formation of CSH as evidenced by the XRD pattern. In conclusion, it was found that photocatalysis could alter cementitious materials both chemically and mechanically, which could further affect long-term durability.

The photocatalytic oxidation and binding capacity of cement containing titanium dioxide nanoparticles under nitric oxide and nitrogen dioxide gas exposures were examined experimentally both in the presence and absence of ultraviolet (UV) light, to examine independently the contributions of photocatalysis and potential additional mechanisms for binding of nitrogen oxides (NOx) inherent in cement-based materials. The overall, photocatalytic efficiency was similar for both gas exposures, with faster initial rates of initial NO binding for higher water-to-cement ratio pastes, due to higher surface area. In the absence of UV light, greater binding of NO2 gas was found compared to NO gas, perhaps due to the greater polarity of the NO2 molecule, although further examination of this phenomenon is warranted. Overall, these experiments show not only the fact that cementitious materials can be tailored to decrease NOx levels through photocatalysis but also the fact that Portland cements possess the inherent ability to bind NOx, and in particular NO2.

The effect of titanium dioxide (TiO2) nanoparticles on early age and long-term properties of cement-based materials is examined experimentally through isothermal calorimetry, chemical shrinkage, setting time, compressive strength and surface microhardness, where part of the cement is replaced with TiO2. Early age hydration is accelerated by TiO2 nanoparticles which also increase degrees of hydration of Portland cement, as evidenced by isothermal calorimetry and chemical shrinkage results. With increasing amounts of TiO2, setting time is reduced, despite decreasing cement content, due to TiO2 replacement, again showing accelerated hydration. Comparing TiO2–cement composites from two different TiO2 manufacturers, results suggest that size of nanoparticles and dispersability are critical in the rate of hydration, with smaller size agglomerates, but not necessarily smaller size particles, producing a greater effect. Compressive strength increases with higher TiO2 nanoparticle replacement at lower water-to-solids ratio (w/s = 0·40) and strength is not compromised by up to 10% TiO2 replacement at higher w/s = 0·60. However, microhardness of the composite decreases with higher TiO2 amount. Broadly, these results indicate that mineral addition as cement replacement can be optimised in terms of dosage and dispersability to achieve lower cement fractions without compromising strength, but that the potential for reductions in hardness should be considered.

The use of nano-sized particles in cementitious materials introduces a myriad of potential innovations from new functionality to enhanced mechanical performance, but such materials can be energy-intensive to manufacture. With increasing emphasis on sustainable development, it is important to investigate and understand benefits and costs of using nanomaterials compared to relatively less energy-intensive microparticles. The current research investigates the effect of chemically inert nano and microparticles (i.e., titanium dioxide (TiO 2 ) and calcium carbonate (limestone)) on early age properties and behavior of cement-based materials. Results indicate that the early age hydration rates, shrinkage, and pore structure of cement-based materials can be modified and optimized by tailoring the size of fillers. Life cycle analysis indicates that photocatalytic reactivity of TiO 2 could offset initial higher environmental impacts. Thus, optimally sized nanoparticles could revolutionize the construction industry by allowing tailoring of structure and properties of cement-based composites, with environmental sustainability preserved through the selection of lower embodied-energy particles.

A simply modified biosensor based on protein A-modified distributed Bragg reflectors (DBR) porous silicon (PSi) chip for the detection of human immunoglobin G (IgG) are developed. The fabrication, optical characterization, and surface derivatization of DBR PSi are investigated. The sensor system studied consist of multi-layer of porous silicon modified with protein-A. The sensor is operated by the measurement of the reflection peak in the white light reflection spectrum. Molecular binding is detected as a shift in wavelength of reflection peaks.

Photoluminescence properties and surface morphologies of porous silicon were investigated by controlling of etching times and applied current densities. FE-SEM image of porous silicon surface indicated that the porous silicon prepared at currents below 200mA/cm^2 exhibited very stable and even surface. However the porous silicon prepared at currents above 300mA/cm^2 displayed the cracked surface of porous silicon. This cracked surface was collapsed to give cracked domains at currents over 500mA/cm^2. Photoluminescence of porous silicon was investigated by controlling of etching times and applied current densities in the range from 50 to 900s and from 50 to 800mA/cm^2, respectively. Photoluminescence intensity of porous silicon increased gradually during etching process, reached maximum, and then decreased as the etching time increased. Porous silicon showed the best photoluminescence efficiency was prepared at currents of 200mA/cm^2 and etching time of 300s.

The effect of chemically inert nanoparticles of anatase titanium dioxide (TiO2) on hydration rate of belite (β-C2S) was studied using isothermal calorimetry. The TiO2 was added to β-C2S paste at 0%, 5%, and 10% by mass. The results indicate that the addition of TiO2 nanoparticles shorten the induction period and accelerate hydration beyond 3 days, showing rate peaks at 40 days of age. The cumulative heat data suggests that TiO2-containing C2S pastes increase in degree of hydration at 90 days by 47% compared to neat C2S pastes. These results suggest that addition of inert nanoparticles could potentially promote earlier strength gain of C2S in cement, ameliorating a perceived deficiency in cement compositions which could contribute to sustainability in terms of lower CO2 emissions and lower energy use compared to traditional chemistries.

The effect of nanoanatase titanium dioxide (TiO2) powder on early-age hydration kinetics of tricalcium silicate (C3S) was investigated. Isothermal calorimetry was performed on C3S pastes with 0%, 5%, 10%, and 15% of TiO2 addition by weight, and two mathematical models—the Avrami (or JMAK) model and the boundary nucleation model (BN model)—were fitted to the data. For all of the mixes, the addition of TiO2 increased the peak reaction rate, and increased the degree of hydration at 12 and 24 h. The rate of hydration of 10% and 15% TiO2 pastes were accelerated, while the 5% TiO2 paste was delayed, lengthening the induction period as compared with the control paste. The model fits demonstrate that the BN model captures the kinetics of the reaction better, particularly in the deceleration period, than the Avrami model. This is related to the ratio of rate parameters (kB/kG) of the BN model, that the increasing ratio gives a more unsymmetrical shape of a rate curve. The increase in kB/kG with TiO2 addition at 5%, 10%, and 15% suggests that hydration product is formed on or near the surfaces of TiO2 particles, as well as on the C3S surface. These results demonstrate that the addition of TiO2 nanoparticles accelerates the early hydration by providing additional nucleation sites, forming the foundation for future optimization of photocatalytic and other nanoparticle-containing cements.

The performance and properties of cement-based materials can potentially be altered by the addition of nano-sized inclusions. In this study, the effect of chemically nonreactive anatase TiO2 nanoparticles on early-age hydration of cement was investigated. First, the effects of different percentage addition rates of TiO2 to portland cement on early-age behavior were examined through isothermal calorimetry and measurements of chemical shrinkage. On the basis of accelerations in hydration observed in TiO2 portland cements, additional experiments were performed with tricalcium silicate (C3S), the main strength-giving mineral component of portland cement, to determine whether the influence of TiO2 could be adequately described by a kinetic model that relies on boundary nucleation theory. Comparison of the experimental results and the modeling showed that (a) an increase in addition rates of TiO2 accelerates the rate of cement hydration and (b) the heterogeneous nucleation effect rather than the dilution effect was dominant. The result of the boundary nucleation model reinforces the concept of the heterogeneous nucleation effect and demonstrates that the surface area provided by nano-TiO2 particles increases the rate of hydration reaction. This research forms the foundation for future studies aimed at optimizing photocatalytic and other nanoparticle-containing cements.

While there is an increasing interest in using photocatalytic cement-based materials, a lack of an appropriate standard procedure for testing the photocatalytic activity and efficiency of such materials makes comparisons among materials and data from different sources challenging. Current standard test methods are not appropriate for assessing photocatalytic nitrogen oxide conversion by cementitious materials because the standards do not consider surface properties of cementitious materials, nor are the test conditions appropriate for evaluation of cementitious materials. Therefore, the main objective is to propose a standard procedure for assessing the photocatalytic activity of cement mixtures with TiO₂ additives and to define a parameter-the photocatalytic efficiency factor (PEF)-that could be used to compare the photocatalytic activity of different TiO₂ cement mixtures, even for extended exposure conditions. The use of PEF is demonstrated, and values of PEF ranging from 8.40 to 51.55 µmol·h⁻¹·m⁻² (0.78 to 4.79 µmol·h⁻¹·ft⁻²) was observed for mixtures with TiO₂ up to 15% replacement.

The effect of nano-scale non-reactive anatase titanium dioxide (TiO2) on early age hydration of cement was experimentally studied. Isothermal calorimetry was performed on cement pastes with two different particle sizes of TiO2 at replacement levels of 5, 7.5 and 10%. The addition of TiO2 to cement increased the heat of hydration and accelerated the rate of reaction at early stages of hydration. This increase was found to be proportional to the percentage addition and the fineness of TiO2. These results demonstrate that the addition of non-reactive nano-scale fillers could affect the rate of cement hydration by heterogeneous nucleation.

We described the effect of the ultraviolet ozone (UVO) treatment of a polydimethylsiloxane (PDMS) stamp on the fidelity of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) patterns produced from a TIPS-PEN/polymer blend by selective contact evaporation (SCE). During the SCE process, the TIPS-PEN in contact with the nanoporous PDMS was absorbed into the PDMS stamp, leaving out the TIPS-PEN patterns, complementary to the PDMS patterns, in the non-contact regions. For the case of the untreated, hydrophobic PDMS surface, the TIPS-PEN patterns developed initially were shrunken and eventually disappeared after 24 h due to the steady absorption of the TIPS-PEN in time. In contrast, for the UVO-treated case, the TIPS-PEN patterns were found to maintain the initial shapes over the period of 24 h since the absorption of the TIPS-PEN was limited by the hydrophilic nature of the UVO-treated PDMS. The modified PDMS surface by the UVO for 30 min yielded the highest fidelity of the TIPS-PEN patterns in both height and width. The patterned TIPS-PEN layer by the SCE was implemented into an organic field-effect transistor to demonstrate the viability of the SCE combined with the UVO treatment for solution-processed organic electronic devices.

We demonstrate an all-optically switchable ferroelectric liquid crystal (FLC) grating constructed in an alternating binary configuration with different optical properties from domain to domain. A dye-doped FLC is uniformly aligned in one type of domains whereas it is infiltrated into the photo-polymerized networks of reactive mesogens in the other. Compared to conventional nematic LC cases, our FLC grating allows more efficient all-optical modulation and faster diffraction switching between the 0th and the 1st orders in subsecond since the optical response associated with the dye molecules in the layered state is less hindered than in the orientationally ordered state. Our dye-doped FLC grating with periodically infiltrated structures will be useful for designing a new class of all-optically switching systems. (C) 2015 Optical Society of America