Development Of Flexible Materials Research Articles

Underwater Adhesion and Anti‐Swelling Hydrogels

AbstractWearable devices, biomaterials, and tissue engineering have all gained from the development of flexible materials. Hydrogels are made up of the polymer matrix in an amount of water and are now being explored extensively. Ascribed to their high hydrophilicity, conventional hydrogels are difficult to deal with high humidity, being easily swell and even decompose. The utilization of hydrogel underwater is influenced by two key factors: the hydrogel absorbs water and swells easily to depress the mechanical characteristics, and the hydration layer at the contact interface also prevents the hydrogel from making close contact with the target surface, preventing conformal and accurate smart perception. So far, many researchers have proposed satisfying improvements for underwater applications from these two perspectives. This review first summarizes the general mechanisms of underwater adhesion hydrogels. Then, various anti‐swelling strategies of the reported hydrogel are described. Finally, the existing challenges and prospects of underwater adhesion and anti‐swelling hydrogels are provided.

Trends on Carbon Nanotube-Based Flexible and Wearable Sensors via Electrochemical and Mechanical Stimuli: A Review

Flexible and wearable sensors increasingly draw attention owing to their advantages of providing lightweight, portable, wearable, or implantable capabilities. Along with the development of flexible materials toward wearable devices, flexible sensors operating via electrochemical and mechanical stimuli demonstrate promise to fulfill potential healthcare and robotics applications, including artificial muscles, health monitoring, human motion detection, soft robotic skin, and human–machine interfaces. This review focuses on carbon nanotube (CNT)-based flexible sensors to detect diverse chemical species and mechanical forces. Often, combined with polymers to imbue flexibility, CNT-based flexible sensors enable specific and stable detections of mechanical deformations and electrochemical analytes while withstanding various mechanical loads, including stretching, bending, and twisting.

Eu3+-Doped Electrospun Polyvinylidene Fluoride-Hexafluoropropylene/Graphene Oxide Multilayer Composite Nanofiber for the Fabrication of Flexible Pressure Sensors.

The development of flexible materials with higher piezoelectric properties and electrostrictive response is of great significance in many applications such as wearable functional devices, flexible sensors, and actuators. In this study, we report an efficient fabrication strategy to construct a highly sensitive (0.72 kPa–1), red light-emitting flexible pressure sensor using electrospun Eu3+-doped polyvinylidene fluoride–hexafluoropropylene/graphene oxide composite nanofibers using a layer-by-layer technology. The high β-phase concentration (96.3%) was achieved from the Eu3+-doped P(VDF-HFP)/GO nanofibers, leading to a high piezoelectricity of the composite nanofibers. We observed that a pressure sensor is enabled to generate an output voltage of 4.5 V. Furthermore, Eu3+-doped P(VDF-HFP)/GO composite nanofiber-based pressure sensors can also be used as an actuator as it has a good electrostrictive effect. At the same time, the nanofiber membrane has excellent ferroelectric properties and good fluorescence properties. These results indicate that this material has great application potential in the fields of photoluminescent fabrics, flexible sensors, soft actuators, and energy storage devices.

Wearable biosensors for human fatigue diagnosis: A review.

Fatigue causes deleterious effects to physical and mental health of human being and may cause loss of lives. Therefore, the adverse effects of fatigue on individuals and the society are massive. With the ever-increasing frequency of overtraining among modern military and sports personnel, timely, portable and accurate fatigue diagnosis is essential to avoid fatigue-induced accidents. However, traditional detection methods require complex sample preparation and blood sampling processes, which cannot meet the timeliness and portability of fatigue diagnosis. With the development of flexible materials and biosensing technology, wearable biosensors have attracted increased attention to the researchers. Wearable biosensors collect biomarkers from noninvasive biofluids, such as sweat, saliva, and tears, followed by biosensing with the help of biosensing modules continuously and quantitatively. The detection signal can then be transmitted through wireless communication modules that constitute a method for real-time understanding of abnormality. Recent developments of wearable biosensors are focused on miniaturized wearable electrochemistry and optical biosensors for metabolites detection, of which, few have exhibited satisfactory results in medical diagnosis. However, detection performance limits the wide-range applicability of wearable fatigue diagnosis. In this article, the application of wearable biosensors in fatigue diagnosis has been discussed. In fact, exploration of the composition of different biofluids and their potential toward fatigue diagnosis have been discussed here for the very first time. Moreover, discussions regarding the current bottlenecks in wearable fatigue biosensors and the latest advancements in biochemical reaction and data communication modules have been incorporated herein. Finally, the main challenges and opportunities were discussed for wearable fatigue diagnosis in the future.

Properties and Configurations of B-N Co-Doped ZnO Nanorods Fabricated on ITO/PET Substrate

Based on flexible materials, optoelectronic devices with optoelectronic technology as the core and flexible electronic devices as the platform are facing new challenges in their applications, including material requirements based on functional electronic devices such as lightness, thinness, and impact resistance. However, there is still a big gap between the current preparation technology of flexible materials and practical applications. At present, the main factors restricting the more commercial development of flexible materials include preparation conditions and performance. In this work, B-N co-doped ZnO nanorod arrays (NRAs) were successfully synthesized on the polyethylene terephthalate (PET) substrate coated with indium tin oxide (ITO) by the hydrothermal method. Based on the density functional theory, the effect of B-N co-doping on the electronic structure of ZnO was calculated; the incorporation of B and N led to an increase in the lattice constant of ZnO. The B-N co-doped ZnO has obvious rectification characteristics with the positive conduction voltage of 2 V in the I–V curve.

Flexible dielectric ZnO‐doped reduced graphene oxide bionanocomposites from solution blending for potential application in bio‐related devices

AbstractBiocompatible materials with high dielectric constant and low dielectric loss have applications in bio‐related electronic devices. Development of flexible materials with those properties is still a challenge. In this work, electrospun membranes and films are prepared from poly(vinyl alcohol) (PVA) and chitosan (CS) solutions, incorporated with a reduced graphene oxide‐zinc oxide composite (rGO‐ZnO). Blending CS with flexible PVA favors electrospinnability and mechanical properties. ZnO contributes to hinder agglomeration of conductive rGO sheets. The structural, mechanical, dielectric and electrical properties of the hybrid materials are investigated. Infrared spectroscopy reveals interaction between the filler and the polymeric components. For mats and films, the increase in rGO‐ZnO content leads to lower crystallinity. The Young's modulus and stress at break values increase with increasing rGO‐ZnO content. High dielectric constants (ε' = 132 to ε' = 166, at 103 Hz), associated with low dielectric loss factor (tan δ = 0.02), are determined for the PVA/CS/rGO‐ZnO films.

Advances in Textile-Based Flexible Temperature Sensors

In recent years, smart clothing, as a hot spot in the current research field, is booming, but mainly because it requires a strong interdisciplinarity, most still adopt the method of attaching sensitive components, and it cannot be called smart clothing in the true sense. This paper introduces the application and development of flexible materials in the development of smart temperature-sensitive clothing from two perspectives: fiber and non-fiber materials, and pointed out the use of fiber characteristics instead of sensitive components as a future research direction to achieve smart clothing monitoring.

Plasma-Induced Bubble Microjet Metallization of Elastomer.

As the development of flexible materials and advanced materials progresses, innovative wiring methods for these materials are attracting attention. In this study, we investigated a new wiring technology using plasma-induced microbubbles for elastomer without any surface treatment. Our technology includes three main points. (1) Unlike electroless plating and other conventional methods, it does not require complicated pre-surface treatment processes before wiring. (2) A wiring resolution of 500 micro meter can be reached quickly and economically. (3) Robust metallic adhesion on a wide range of materials can be successfully carried out with precise positioning. Here, by applying our method, we adhered nickel nanoparticles to a latex rubber substrate and demonstrated the electrical conductivity of the created line. The result suggests that our method has potential as an innovative wiring technology to precisely, robustly, and simply fabricate an electric circuit without any complicated procedures or pre-treatment. Our method can contribute to microfabrication technologies.

Influence of melt spinning parameters on electrical conductivity of carbon fillers filled polyamide 12 composites

Nowadays, the market is flooded by smart textiles due to the major advances made in the development of flexible materials. Electrical conductivity is one of the most important properties, which can be assured by the introduction of metallic filaments in the yarns. However, such introductions of metallic filaments can cause a decrease of the characteristics of textile (flexibility, durability). Thus, a lot of studies focus on the development of electrical conductivity that does not decrease the characteristics of textile. An alternative to develop conductive polymer composites (CPC), is conductive fillers which can be integrated into the polymer. The current technic a bulk functionalization of the polymer during melt spinning allowing a thermoplastic yarn to become electrically conductive. In this study, the electrical conductivity of carbon black (CB) fillers filled multifilaments based on polyamide 12 (PA12) was optimized. The CPC were prepared in two steps: the first step was the incorporation of the fillers in PA12 by twin screw extrusion, and the second step was the melt spinning to obtain multifilament yarns. After extrusion, the blend has an electrical conductivity of 101 S/m. However, after the melt spinning of this blend, the electrical conductivity dropped sharply to 10-6 S/m. Several experimental parameters during the melt spinning can modify the structure filaments and impact on their electrical conductivity, which could explain this loss of electrical conductivity. Drawing out of rod during extrusion, as well as different melt spinning parameters, such as volumetric pump output and speed variation of the drawing rolls, were identified as key factors that not only influence the electrical conductivity but also the mechanical properties of the yarn. A low drawing ratio combined with a low pump output can increase the electrical conductivity. With the same value of volumetric pump output and the same supply roll speed, if the drawing roll speed increases from 225 rpm (rpm) to 450 rpm, the electrical conductivity decreases by a factor of 10, respectively 7.10-5 S/m and 7.10-6 S/m. Observations by transmission electron microscopy (TEM) of the two CBs inside PA12 give insight the dispersion of nanofillers, which effects on the CB physical network and its subsequent electrical conductivity. At the scale of the yarn, twisting can increase the contact path between the monofilaments and increase (from 10-6 S/m to 10-5 S/m) the global conductivity until a plateau for the multifilament. Thus, the key factors explaining this loss of electrical conductivity between the rod and the multifilament were identified. However, these parameters also effect the mechanical characteristic of the materials too.

Tracing hail stone impact on external thermal insulation composite systems (ETICS) – An evaluation of standard admission impact tests by means of high-speed-camera recordings

Hail impact damage on External Thermal Insulation Systems (ETICS) is increasingly recognized by insurance companies owing to increased storm occurrence frequency and storm intensity. To develop hail resistant ETICS for houses and better understand existing admission tests, high-speed-camera recordings of ice ball impacts at an angle of 45° and steel ball impacts at angles of 90° and 45° were used to characterize the impact process and to derivate the damaging mechanisms of impacts on facades.Recorded surface deformation is characterized by high indentation depth of the impactor and high flexural bending causing high surface parallel strain. Analyses of the impact process allowed the identification of the mechanisms and timing of fracture formation in different regions.Additionally, differences in the impact process of the European steel ball impact test (90°, ETAG 004) and the Swiss ice ball impact test (45°, VKF P. No 8) are discussed in detail. Caused by the difference in impact angle, the 45° ice ball impacts lead to lower indentation depth and consequently to lower tensile strain and damage. However, surface parallel movement of the impactor caused the formation of an elongated damage pattern in the 45° impacts. To avoid the observed brittle failure behavior, the development of flexible materials with the ability to elastically accommodate impact strains is favorable to reduce hail stone impact damage.