Predictable and adjustable broadband gold nanorods for photothermal effects and foldable performances.

Colloidal gold nanorods (GNRs) have demonstrated their potential to absorb light within specific wavelength bands and induce photothermal effects. However, the unpredictability and lack of adjustability in the broadband spectrum formed by the self-assembly of gold nanospheres or the coupling of various sizes of GNRs have posed significant challenges. To address this, we have developed broadband GNRs (BGNRs) with a predictable and adjustable extinction band in the visible and near-infrared regions. The BGNRs were synthesized by simply mixing GNRs with different aspect ratios, allowing for control over the bandwidths and positions of the extinction bands. Subsequently, the BGNRs were coated with silica and underwent surface modification. The resulting BGNRs@SiO2were then mixed with either polydimethylsiloxane (PDMS) or polyvinylidene fluoride (PVDF) to create BGNRs@SiO2/PDMS (or PVDF) films. The BGNRs@SiO2/PDMS and BGNRs@SiO2/PVDF films both exhibit excellent photothermal performance properties. Additionally, the light absorption intensity of the BGNRs@SiO2/PVDF film linearly increases upon folding, leading to significantly enhanced photothermal performance after folding. This work demonstrates that plasmonic colloidal GNRs, without the need for coupling, can yield predictable and adjustable extinction bands. This finding holds great promise for future development and practical applications, particularly in the transfer of these properties to films.

Ultrasound Measurement of Skeletal Muscle Contractile Parameters Using Flexible and Wearable Single-Element Ultrasonic Sensor.

Skeletal muscle is considered as a near-constant volume system, and the contractions of the muscle are related to the changes in tissue thickness. Assessment of the skeletal muscle contractile parameters such as maximum contraction thickness ( T h ), contraction time ( T c ), contraction velocity ( V c ), sustain time ( T s ), and half-relaxation ( T r ) provides valuable information for various medical applications. This paper presents a single-element wearable ultrasonic sensor (WUS) and a method to measure the skeletal muscle contractile parameters in A-mode ultrasonic data acquisition. The developed WUS was made of double-layer polyvinylidene fluoride (PVDF) piezoelectric polymer films with a simple and low-cost fabrication process. A flexible, lightweight, thin, and small size WUS would provide a secure attachment to the skin surface without affecting the muscle contraction dynamics of interest. The developed WUS was employed to monitor the contractions of gastrocnemius (GC) muscle of a human subject. The GC muscle contractions were evoked by the electrical muscle stimulation (EMS) at varying EMS frequencies from 2 Hz up to 30 Hz. The tissue thickness changes due to the muscle contractions were measured by utilizing a time-of-flight method in the ultrasonic through-transmission mode. The developed WUS demonstrated the capability to monitor the tissue thickness changes during the unfused and fused tetanic contractions. The tetanic progression level was quantitatively assessed using the parameter of the fusion index (FI) obtained. In addition, the contractile parameters ( T h , T c , V c , T s , and T r ) were successfully extracted from the measured tissue thickness changes. In addition, the unfused and fused tetanus frequencies were estimated from the obtained FI-EMS frequency curve. The WUS and ultrasonic method proposed in this study could be a valuable tool for inexpensive, non-invasive, and continuous monitoring of the skeletal muscle contractile properties.

A Flow Velocity Measurement Method Based on a PVDF Piezoelectric Sensor.

To measure the flow velocity of a fluid without affecting its motion state, a method was proposed based on a polyvinylidene fluoride (PVDF) piezoelectric film sensor. A self-made PVDF piezoelectric sensor placed parallel with the flow direction was used to measure the flow velocity. First, the piezoelectric characteristics of PVDF were obtained theoretically. Next, the relationship between flow velocity and sound pressure was verified numerically. Finally, the relationship between flow velocity and the electrical output of the PVDF piezoelectric film was obtained experimentally. In conclusion, the proposed method was shown to be reliable and effective.

Sound Power Estimation for Beam and Plate Structures Using Polyvinylidene Fluoride Films as Sensors.

The theory for calculation and/or measurement of sound power based on the classical velocity-based radiation mode (V-mode) approach is well established for planar structures. However, the current V-mode theory is limited in scope in that it can only be applied to conventional motion sensors (i.e., accelerometers). In this study, in order to estimate the sound power of vibrating beam and plate structure by using polyvinylidene fluoride (PVDF) films as sensors, a PVDF-based radiation mode (C-mode) approach concept is introduced to determine the sound power radiation from the output signals of PVDF films of the vibrating structure. The proposed method is a hybrid of vibration measurement and numerical calculation of C-modes. The proposed C-mode approach has the following advantages: (1) compared to conventional motion sensors, the PVDF films are lightweight, flexible, and low-cost; (2) there is no need for special measuring environments, since the proposed method does not require the measurement of sound fields; (3) In low frequency range (typically with dimensionless frequency kl < 4), the radiation efficiencies of the C-modes fall off very rapidly with increasing mode order, furthermore, the shapes of the C-modes remain almost unchanged, which means that the computation load can be significantly reduced due to the fact only the first few dominant C-modes are involved in the low frequency range. Numerical simulations and experimental investigations were carried out to verify the accuracy and efficiency of the proposed method.

Development of a Microforce Sensor and Its Array Platform for Robotic Cell Microinjection Force Measurement.

Robot-assisted cell microinjection, which is precise and can enable a high throughput, is attracting interest from researchers. Conventional probe-type cell microforce sensors have some real-time injection force measurement limitations, which prevent their integration in a cell microinjection robot. In this paper, a novel supported-beam based cell micro-force sensor with a piezoelectric polyvinylidine fluoride film used as the sensing element is described, which was designed to solve the real-time force-sensing problem during a robotic microinjection manipulation, and theoretical mechanical and electrical models of the sensor function are derived. Furthermore, an array based cell-holding device with a trapezoidal microstructure is micro-fabricated, which serves to improve the force sensing speed and cell manipulation rates. Tests confirmed that the sensor showed good repeatability and a linearity of 1.82%. Finally, robot-assisted zebrafish embryo microinjection experiments were conducted. These results demonstrated the effectiveness of the sensor working with the robotic cell manipulation system. Moreover, the sensing structure, theoretical model, and fabrication method established in this study are not scale dependent. Smaller cells, e.g., mouse oocytes, could also be manipulated with this approach.

Energy Storage via Polyvinylidene Fluoride Dielectric on the Counterelectrode of Dye-Sensitized Solar Cells.

To study the fundamental energy storage mechanism of photovoltaically self-charging cells (PSCs) without involving light-responsive semiconductor materials such as Si powder and ZnO nanowires, we fabricate a two-electrode PSC with the dual functions of photocurrent output and energy storage by introducing a PVDF film dielectric on the counterelectrode of a dye-sensitized solar cell. A layer of ultrathin Au film used as a quasi-electrode establishes a shared interface for the I-/I3- redox reaction and for the contact between the electrolyte and the dielectric for the energy storage, and prohibits recombination during the discharging period because of its discontinuity. PSCs with a 10-nm-thick PVDF provide a steady photocurrent output and achieve a light-to-electricity conversion efficiency (η) of 3.38%, and simultaneously offer energy storage with a charge density of 1.67 C g-1. Using this quasi-electrode design, optimized energy storage structures may be used in PSCs for high energy storage density.

Multiresponsive 3D Structured PVDF Cube Switches for Security Systems Using Piezoelectric Anisotropy.

Advancements in flexible electronics using piezoelectric materials have paved the way for numerous applications. In this study, we suggest a three-dimensional (3D) structured poly(vinylidene fluoride) (PVDF) film cube switch to maximize piezoelectric anisotropy and flexibility. Unlike piezoelectric material-based flexible electronics, PVDF cube switches have a simple design and easy fabrication process. Each side of the cube switch demonstrates independent voltage signals with pressing displacements and corresponding directions. With cutting angle variations and planar figure designs, derived cube switches respond with various combinations of voltage waveforms. PVDF switches can endure more than 1000 cycles of 70% vertical strain in terms of both electrical responses and mechanical operations. As an application, we establish a security system with multiresponsibility of a cube switch. This security system can protect users from potential threats owing to its multiresponsibility and user-dependent operability.

Investigation of the transient behavior of a cantilever beam using PVDF sensors.

In this paper, a PVDF film sensor was used to measure the transient responses of a cantilever beam subjected to an impact loading. The measurement capability of a PVDF sensor is affected by the area of the PVDF film sensor and the signal conditioner (charge amplifier). The influences of these effects on the experimental measurements were investigated. The transient responses for the dynamic strain of the beam were measured simultaneously by the PVDF sensor and a conventional strain gauge. The resonant frequencies of the beam were determined by applying the Fast Fourier Transform on transient results in the time domain of the PVDF sensor and the strain gauge. The experimentally measured resonant frequencies from the PVDF sensor and the strain gauge were compared with those predicted from theoretical and FEM numerical calculations. Based on the comparison of the results measured for these two sensors, the PVDF film sensor proved capable of measuring transient responses for dynamic strain, and its sensitivity is better than that of the strain gauge. Furthermore, almost all the resonant frequencies can be obtained from the results of transient responses for PVDF film.

A visual bi-layer indicator based on roselle anthocyanins with high hydrophobic property for monitoring griskin freshness.

This study designed a new type indicator with hydrophobic Polyvinylidene Fluoride (PVDF) film as a moisture prevent-layer. And the sensor layer was provided based on polyvinyl alcohol/Sodium alginate (PS) and Roselle anthocyanins (RAs). Physical properties, microstructure, and color stability of the bi-layer indicator have been investigated. The Water contact angle (WCA) of PS/RAs/ PVDF film (PSRF) was 108.85°, which can be considered as an excellent hydrophobic surface. The lowest Water Vapor Permeability (WVP) value of PSRF exhibited a good barrier property for moisture. Therefore, PSRF film was used to monitor the griskin freshness. The Total volatile basic nitrogen (TVB-N) level was increased to 18.02 mg/100 g at 72 h, and the color of the indicator presented visible color changes. The acquired results revealed a good correlation between TVB-N, pH and color change of the indicator. The research indicated that PSRF indicator has increasing potential application on food intelligent packaging.

Shielding Effectiveness Study of Barium Hexaferrite-Incorporated, ß-Phase-Improved Poly(vinylidene fluoride) Composite Film: A Metamaterial Useful for the Reduction of Electromagnetic Pollution.

The present work reports the high electromagnetic interference (EMI) shielding effectiveness of ∼-93.5 dB at 8.63 GHz and -97.6 dB at 8.61 GHz in the X- and Ku-bands for 10 and 20 wt % of barium hexaferrite (BaH) nanoparticle-loaded poly(vinylidene fluoride) (PVDF)-based composite films with a thickness of ∼0.210 and 0.260 mm, respectively. BaH-PVDF composite films with a layer structure have been considered in the present report in order to establish an excellent EMI shielding material for the suppression of electromagnetic pollution, with good control on flexibility, surface area, and thickness. Structural and morphological measurements reveal that the polar ß-phase crystallization of the BaH-PVDF composite films has been enhanced in comparison to the pure PVDF film, and these measurements also reveal the influence of BaH nanoparticles on structural alteration from nonpolar α-phase to the polar/electroactive ß-phase of the PVDF matrix. The resultant BaH-PVDF composite films produce multiple interfaces between magnetic BaH nanoparticles and ß-phase-enriched electroactive PVDF, which plays the most significant role for the enhancement of the EMI shielding effectiveness (SE) in the microwave/GHz frequency range. This high value of the EMI SE with >99.999999999% attenuation has not been found so far in the PVDF-based composite materials by anyone else. This particular feature of BaH-PVDF composite materials suggests that the BaH-PVDF composite films can be considered as the most useful ones for the fabrication of lightweight, flexible, and thickness-controlled EMI shielding materials for the reduction of pollution created by the electromagnetic waves in the microwave/GHz frequency region.

Ultra-Sensitive Strain Sensor Based on Flexible Poly(vinylidene fluoride) Piezoelectric Film.

A flexible 4 × 4 sensor array with 16 micro-scale capacitive units has been demonstrated based on flexible piezoelectric poly(vinylidene fluoride) (PVDF) film. The piezoelectricity and surface morphology of the PVDF were examined by optical imaging and piezoresponse force microscopy (PFM). The PFM shows phase contrast, indicating clear interface between the PVDF and electrode. The electro-mechanical properties show that the sensor exhibits excellent output response and an ultra-high signal-to-noise ratio. The output voltage and the applied pressure possess linear relationship with a slope of 12 mV/kPa. The hold-and-release output characteristics recover in less than 2.5 µs, demonstrating outstanding electro-mechanical response. Additionally, signal interference between the adjacent arrays has been investigated via theoretical simulation. The results show the interference reduces with decreasing pressure at a rate of 0.028 mV/kPa, highly scalable with electrode size and becoming insignificant for pressure level under 178 kPa.

Glucose Sensing Using Capacitive Biosensor Based on Polyvinylidene Fluoride Thin Film.

A polyvinylidene fluoride (PVDF) film-based capacitive biosensor was developed for glucose sensing. This device consists of a PVDF film sandwiched between two electrodes. A capacitive biosensor measures the dielectric properties of the dielectric layers at the interface between the electrolyte and the electrode. A glucose oxidase (GOx) enzyme was immobilized onto the electrode to oxidize glucose. In practice, the biochemical reaction of glucose with the GOx enzyme generates free electron carriers. Consequently, the potential difference between the electrodes is increased, resulting in a measurable voltage output of the biosensor. The device was tested for various glucose concentrations in the range of 0.013 to 5.85 M, and various GOx enzyme concentrations between 4882.8 and 2.5 million units/L. We found that the sensor output increased with increasing glucose concentration up to 5.85 M. These results indicate that the PVDF film-based capacitive biosensors can be properly applied to glucose sensing and provide opportunities for the low-cost fabrication of glucose-based biosensors based on PVDF materials.