Improved response time of flexible microelectromechanical sensors employing eco-friendly nanomaterials

Fan, Shicheng; Li, Dan; Meng, Lingju; Zheng, Wei; Elias, Anastasia L.; Wang, Xihua

doi:10.1039/c7nr05218a

Cited by 14 publications

(12 citation statements)

References 27 publications

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“…The results show that KCl-templated 10:1 PDMS gave the best sensing performance with regards to a large linearity range over a broad pressure, exhibiting a sensitivity of 14.1 kPa –1 (up to 3.5 kPa) and good stability. These results are on par with current known pressure sensors. − The pores offer a larger range of resistance change under applied pressure but render the materials to be soft; therefore, varying the curing agent to PDMS was first proposed for the aim of shortening the response time. The 5:1 (elastomer:curing agent) gave the shortest response time (47 ms).…”

Section: Discussionmentioning

confidence: 56%

“…These results agree well with the DMA data, showing the addition of more curing agent could improve the response time of the sensor. This simple method is advantageous compared to adding fillers to the PDMS to enhance the response time of the sensors …”

Section: Resultsmentioning

confidence: 99%

“…In addition, the mechanical properties of both porous and nonporous PDMS materials were investigated by a tensile tester and dynamic mechanical analysis (DMA). To further improve the response time, the stiffness of the PDMS was tuned by varying the ratio of PDMS base to curing agent . The sensing mechanism and output performance of the devices were characterized by compressing devices while measuring their electrical characteristics.…”

Section: Introductionmentioning

confidence: 99%

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Porous Polydimethylsiloxane–Silver Nanowire Devices for Wearable Pressure Sensors

Shi

Chung

et al. 2019

ACS Appl. Nano Mater.

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We demonstrate a simple, nonlithographic method for fabricating piezoresistive pressure sensors with a broad range of working pressures and low detection limit. Our wearable pressure sensor is fabricated by using two metallized, porous polymer layers which undergo a change in resistance as a function of pressure. This sensor has a sandwich structure composed of top and bottom sheets of porous polydimethylsiloxane (PDMS) fabricated by using a simple templating method. The inner face of each of these layers is coated with a layer of conductive silver nanowires (AgNWs). The AgNW layers are initially in light contact, and the device undergoes a change in resistance when pressure is applied perpendicular to the plane of the sheets. In these devices, the size of the pores is an important determinant of the device sensitivity and range. Powder templates of KCl, NaCl, and sugar are used to create different sized pores (60–90, 200–275, and 400–550 μm, respectively) in the elastomeric PDMS layers, which in turn affects the mechanical deformability of the devices. The sensors fabricated with KCl porous layers (which had the smallest pores) demonstrate the best performance, with a sensitivity of 14.1 kPa–1 (up to 3.5 kPa), 4.8 kPa–1 (up to 10 kPa), and 1.84 kPa–1 (up to 40 kPa) and good stability over 1000 loading and unloading cycles. Pressure sensors are also fabricated by decreasing the ratio of PDMS base to curing agent from the standard 10:1 formulation, which increases the stiffness of the viscoelastic PDMS layer and thus shortens the response time. The stiffest formulation (5:1 (base:curing agent)) sample gives the shortest response time of ∼47 ms. Wearable electronic applications of these devices, including pulse measurement, facial movements, and sound tracking, are demonstrated in this work.

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Section: Discussionmentioning

confidence: 56%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Porous Polydimethylsiloxane–Silver Nanowire Devices for Wearable Pressure Sensors

Shi

Chung

et al. 2019

ACS Appl. Nano Mater.

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“…In this work, YAG phosphor was chosen due to its superior thermal stability and brightness and though other phosphors can be chosen based on requirements it is important to make sure about its thermal stability as, otherwise, the luminescence of phosphor and quality of light from white LED will decrease. [41] PDMS type and mixing technique can also change the optical properties [42,43] and even though the mechanical properties of CNCs and PDMS mixture have already been studied which did not show significant degradation, [44] further investigation is needed, first, to understand the effect of PDMS on the light quality of white LED and, second, to find out the change in optical properties of such film over time. Going forward, this study provides an excellent platform for future efforts to investigate the potential of CNCs for application in solid-state lighting.…”

Section: Discussionmentioning

confidence: 99%

Improving the Light Quality of White Light‐Emitting Diodes Using Cellulose Nanocrystal‐Filled Phosphors

Chowdhury

Wang

2021

Advanced Photonics Research

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Light‐emitting diode (LED) lighting delivers better performance and reliability, and substantially lowers the total cost of ownership compared with conventional lighting. The most common white LED is generally produced using a blue LED chip and phosphor combination to generate white light. This type of phosphor‐converted white LED can be a great alternative to the more expensive 3 chip RGB (red, green, blue) LED. Herein, cellulose nanocrystals, a wood‐derived biopolymer, are used with phosphor to improve the uniformity of correlated color temperature (CCT) and luminous flux from the white LED. These nanocrystals can scatter light strongly and for an optimized concentration of nanocrystals, it is found to increase the luminous flux of the white LED by over 30% compared with the reference sample without any nanocrystal. The CCT uniformity is also improved from 173.45 K for the reference sample to 59 K for the optimized sample. The chromaticity coordinates are also studied and found to be shifting toward lower correlated color temperatures with increasing cellulose concentrations. Combining these results with low cost, wide availability, and environmental impact, cellulose nanocrystals can play an important role in the future generation of white LEDs.

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“…Such piezoresistive devices are required to enable conformal coverage on soft surfaces and display the strain information by sensing external stimuli . Many key factors should be considered to develop a high‐performance strain sensor, including the sensitivity, stretchability, response time, and stability . Composite structure that combines the electrical conductivity of the micro/nanomaterials and mechanical flexibility of the elastic polymer has been a very popular choice for fabricating a flexible piezoresistive device, which possesses a satisfactory sensitivity and stretchability simultaneously .…”

Section: Introductionmentioning

confidence: 99%

Piezoresistive Sensors Based on rGO 3D Microarchitecture: Coupled Properties Tuning in Local/Integral Deformation

Zhang

et al. 2018

Adv Elect Materials

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device, [7] which possesses a satisfactory sensitivity and stretchability simultaneously. [8] However, the polymer precursor infiltration process should be well controlled to preserve the surface roughness of the conductive network, [9] which is the key to achieving high sensor response. [10] And the polymer fully filled bulk structure provides little free space for deformation of the conductive network, making it difficult to form or rupture the filler-filler contacts with a small deformation variation. Such undesirable composite morphology may result in the poor sensor sensitivity.On the basis of previous research, the sensitivity of this conductive elastomer composite can be improved by optimizing the electrical property or mechanical property. For simplification, the electrical property refers to the electrical conductivity, usually using the resistance of the composite. The mechanical property is defined as static mechanical elasticity, which refers to the quality that the composite is able to stretch and return to its original shape. On the one hand, it is a common strategy to increase the device sensitivity by decreasing the conductivity of the composite. [11] On the other hand, increasing the ratio of conductive filler ratio (exceeds the percolation threshold) perhaps improves the overall mechanical elasticity of the strain sensor, thus increasing the sensitivity and stretchability. [12] Obviously, these two properties are normally interdependent in composite materials, because they can be influenced by the conductive filler ratio simultaneously. For example, when one tries to decrease the conductivity of the composite by decreasing the ratio of the conductive micro/nanomaterials, the relative increasing of polymer must lead to the decreasing of mechanical elasticity, which turned out harmful to the device sensitivity and working region (the maximum strain of the composite that electronic signal can be measured steadily and repeatedly). Due to such coupled tuning effect of the electrical and mechanical properties, we have not found the ideal state of equilibrium between the high sensitivity and wide working region (satisfactory strain limit). A general composite structure based on a simple process and low cost is urgently required, which can be used to rigorously investigate the coupled properties tuning of electrical and mechanical properties for different application potential.Here, we demonstrate a collaborative 3D microarchitecture based on conductive reduced graphene oxide (rGO) foams and insulated fibrous framework, which can realize the coupled properties tuning by varying the rGO weight fraction. At the An ideal flexible piezoresistive sensor should possess high sensitivity as well as wide sensing range, and provide a stable and excellent response under different deformation, such as local and integral strain. However, these properties are difficult to achieve simultaneously with conventional all-polymer-filled composite, as tuning of one material component always causes the unpredictable change o...

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Improved response time of flexible microelectromechanical sensors employing eco-friendly nanomaterials

Cited by 14 publications

References 27 publications

Porous Polydimethylsiloxane–Silver Nanowire Devices for Wearable Pressure Sensors

Porous Polydimethylsiloxane–Silver Nanowire Devices for Wearable Pressure Sensors

Improving the Light Quality of White Light‐Emitting Diodes Using Cellulose Nanocrystal‐Filled Phosphors

Piezoresistive Sensors Based on rGO 3D Microarchitecture: Coupled Properties Tuning in Local/Integral Deformation

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