Xun Yu

Silver nanowire-based transparent, flexible, and conductive thin film

The fabrication of transparent, conductive, and uniform silver nanowire films using the scalable rod-coating technique is described in this study. Properties of the transparent conductive thin films are investigated, as well as the approaches to improve the performance of transparent silver nanowire electrodes. It is found that silver nanowires are oxidized during the coating process. Incubation in hydrogen chloride (HCl) vapor can eliminate oxidized surface, and consequently, reduce largely the resistivity of silver nanowire thin films. After HCl treatment, 175 Ω/sq and approximately 75% transmittance are achieved. The sheet resistivity drops remarkably with the rise of the film thickness or with the decrease of transparency. The thin film electrodes also demonstrated excellent flexible stability, showing < 2% resistance change after over 100 bending cycles.

A carbon nanotube/cement composite with piezoresistive properties

This paper studies the piezoresistive property of the CNT/cement composite to explore its feasibility as an embedded stress sensor for civil structures such as roadways, levees and bridges. The experimental results show that the electrical resistance of the CNT/cement composite changes with the compressive stress level, indicating the potential of using the CNT/cement composite as a stress sensor for civil structures. The piezoresistive responses of the composite with different fabrication methods and CNT doping levels were also studied. It is found that dispersion-assistant surfactants could block the contacts among carbon nanotubes, thus impairing the piezoresistive response of the composite, while a higher CNT doping level could improve the sensitivity of the composite stress response.

Multifunctional and Smart Carbon Nanotube Reinforced Cement-Based Materials

Nanotechnology has changed and will continue to change our vision, expectations and abilities to control the material world. These developments will definitely affect the field of construction and construction materials. Carbon nanotubes (CNTs) are considered to be one of the most beneficial nano-reinforcement materials. The combination of high aspect ratio, small size, low density, and unique physical and chemical properties make them perfect candidates as reinforcements in multifunctional and smart cement-based materials. Here, we review recent progress and advances of CNTs reinforced cement-based materials, with attention to their fabrication methods, mechanical properties, electrical and piezoresistive properties, thermal conductive and damping properties, and potential structural applications. Future challenges for the development and deployment of multifunctional and smart CNTs reinforced cement-based materials and structures are also discussed.

Effects of CNT concentration level and water/cement ratio on the piezoresistivity of CNT/cement composites

Carbon nanotube (CNT)/cement composites with different concentration levels of multi-walled CNT (MWNT) and water/cement ratios are fabricated. By comparing the responses of electrical resistance of these CNT/cement composites to compressive stress, the effects of MWNT concentration level and water/cement ratio on the piezoresistive sensitivity of composites are investigated. Experimental results indicate that the piezoresistive sensitivities of CNT/cement composites with 0.05, 0.1, and 1u2009wt% of MWNT first increase and then decrease with the increase of CNT concentration levels. Water/cement ratio is another factor that affects the composite properties, the electrical resistance of CNT/cement composite with 0.6 water/cement ratio is more sensitive to compressive stress than that of composite with 0.45 water/cement ratio. The piezoresistive sensitivity is heavily dependent on the conductive network in the composites, which in turn is influenced by the CNT concentration level and water/cement ratio.

Fabrication of Piezoresistive CNT/CNF Cementitious Composites with Superplasticizer as Dispersant

AbstractDispersion of carbon nanotubes (CNTs)/carbon nanofibers (CNFs) in cement matrixes is one of the key problems for fabricating piezoresistive CNT/CNF cementitious composites. The use of existing dispersants such as sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (NaDDBS), and methylcellulose to disperse CNTs/CNFs has negative effects on the hydration of cement and will cause decreases in the mechanical properties of cementitious composites. In this study, a superplasticizer, a commonly used component in cementitious composites, is found to be capable of effectively dispersing CNTs and CNFs in a cement matrix. This eliminates the need for additional dispersants for fabricating piezoresistive CNT/CNF cementitious composites and avoids the impairment of composite properties by additional dispersants. The dispersion of CNTs/CNFs in cement matrix is evaluated by observing the dispersion of CNTs/CNFs in the superplasticizer aqueous solution, examining the morphology of composites, and analyz...

Effects of the content level and particle size of nickel powder on the piezoresistivity of cement-based composites/sensors

To explore the effects of the content level and particle size of spiky spherical nickel powder on electrical conductivity and piezoresistivity, three types of spiky spherical nickel powder with different particle sizes (3–7 µm, 2.6–3.3 µm and 2.2–2.8 µm) were dispersed into the cement–matrix to fabricate the nickel powder filled cement-based composites/sensors. Experimental results indicate that a high content level and a small practical size are beneficial for the improvement of electrically conductivity. The piezoresistive sensitivities of composites/sensors with 20, 24 and 22 vol% of nickel powder increase orderly when nickel powder particle size is in the range of 3–7 µm. The piezoresistive sensitivities of composites/sensors with different particle sizes of nickel powder decrease with an increase of nickel powder particle sizes at 24 vol% of nickel powder content level. The piezoresistive sensitivity is highly dependent on the conductive network in the composites, which is dominated by the content level and the particle size of the spiky spherical nickel powder.

Experimental study on the contribution of the quantum tunneling effect to the improvement of the conductivity and piezoresistivity of a nickel powder-filled cement-based composite

The voltage?current characteristics of a nickel powder (NP)-filled cement-based composite (NPCC) and the variation of electrical resistivity of NPCC under compression are studied by using a four-pole method based on embedded loop electrodes. The generation of conductivity and piezoresistivity in NPCC is investigated by examining the morphology of NPCC by SEM and studying the variation of distance between NP particles under compression. Experimental results indicate that the electrical conductivity of NPCC is ohmic when the voltage is below 3.5?V. Although NP particles are dispersed in the cement matrix and they do not form a connected conductive network, NPCC has a low electrical resistivity of 2.29 ? 103??cm without loading. A decrease of 0.042% in the fractional change in volume of NPCC under compression causes the tunneling distance to decrease 0.60?1.42?nm and the fractional change in electrical resistivity to reach 62.61%. It is therefore concluded that the improvement of conductivity and piezoresistivity of NPCC is due to the quantum tunneling effect.

Adhesion, proliferation and differentiation of pluripotent stem cells on multi-walled carbon nanotubes

This article studies the adhesion, growth and differentiation of stem cells on carbon nanotube matrices. Glass coverslips were coated with multi-walled carbon nanotube (MWNT) thin films using layer-by-layer self-assembling techniques. Pluripotent P19 mouse embryonal carcinoma stem cells were seeded onto uncoated or MWNT-coated glass coverslips and either maintained in an undifferentiated state or induced to differentiate by the addition of retinoic acid. The authors found that cell adhesion was increased on the MWNT-coated glass surfaces, and that the expression patterns of some differentiation markers were altered in cells grown on MWNTs. The results suggest that MWNTs will be useful in directing pluripotent stem cell differentiation for tissue engineering purposes.

Pulse wave sensor for non-intrusive driver's drowsiness detection

This research proposes a PVDF film pulse wave sensor for use in drivers drowsiness detection. The sensor non-intrusively measures heart pulse wave from drivers palm and an adaptive filter is employed to cancel the measurement noise aroused by the changing of gripping force. Experimental results show clear pulse wave signals can be obtained. Two-hour driving simulation is performed for drowsiness detection tests. The low frequency to high frequency (LF/HF ratio) is calculated from power spectrum density (PSD) of subjects heart rate time series. The LF/HF ratio shows decreasing trends as subjects go from awake to drowsy.

Active Control of Sound Transmission Through Windows With Carbon Nanotube-Based Transparent Actuators

This paper explores the development of active sound transmission control systems for windows that can achieve a significant reduction in window noise transmission. Two major challenges need to be addressed in order to make the development of such noise blocking windows feasible. These are the need for a distributed actuation system that is optically transparent and the unavailability of a real-time reference signal that can be used by the active control system to provide advance information on the noise affecting the window. To address the first challenge, a transparent thin-film actuator (speaker) is first developed for the control system, which consists of a piezoelectric poly (vinylidene fluoride) (PVDF) thin film coated with compliant carbon nanotube-based transparent conductors on both sides. The developed thin-film speaker shows excellent acoustic response over a broadband frequency range, and has the advantages of being flexible, transparent, thin, and lightweight. To address the second challenge of providing a time-advanced reference signal from a moving noise source, a small microphone array distributed on the outside wall of the home is used. New noise source identification algorithms are employed, by which an appropriate microphone from the array can be chosen to provide a reference signal. Experimental results show that over 12 dB reduction in sound transmission is achieved globally in the case of broadband sound, which demonstrates the effectiveness of the control system in blocking sound transmission.