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13 pages, 3636 KiB

Open AccessArticle

Fabrication and Investigation of Deformable Rubber–Carbon Nanotube–Glue Gel-Based Impedimetric and Capacitive Tactile Sensors for Pressure and Displacement Measurements

by Khasan S. Karimov, Muhammad Tariq Saeed Chani, Tahseen Kamal, Syed Zameer Abbas, Naved Azum and Abdullah Mohamed Asiri

Gels 2024, 10(1), 76; https://doi.org/10.3390/gels10010076 - 20 Jan 2024

Viewed by 804

Abstract

Carbon nanotube–glue composite gel-based surface-type elastic sensors with a cylindrical shape deformable (flexible) metallic body were fabricated for tactile pressure and compressive displacement sensing. The fabrication of the sensors was performed using the rubbing-in technique. The effect of the pressure and the compressive [...] Read more.

Carbon nanotube–glue composite gel-based surface-type elastic sensors with a cylindrical shape deformable (flexible) metallic body were fabricated for tactile pressure and compressive displacement sensing. The fabrication of the sensors was performed using the rubbing-in technique. The effect of the pressure and the compressive displacement on the capacitance and the impedance of the sensors were investigated at various frequencies (in the range of 1 kHz to 200 kHz). It was found that under the effect of pressure from 0 to 9 g/cm², the capacitance increased by 1.86 and 1.78 times, while the impedance decreased by 1.84 and 1.71 times at the frequencies of 1 kHz to 200 kHz, respectively. The effect of displacement on the impedance and the capacitance of the device was also investigated at various frequencies from 1 kHz to 200 kHz. The results showed that under the effect of compressive displacement up to 25 µm, the impedance of the sensors decreased on average by 1.19 times, while the capacitance increased by 1.09 times, accordingly. The frequency response of the displacement sensor showed that it matched with the low-pass filter. The obtained results are explained based on changes in the shape and geometrical parameters of the cylindrical-shaped conductive body. These results have also been explained on the basis of the distance between the conductive plates of the capacitive sensors during compression, which takes place under the effect of applied pressure or displacement. Moreover, the design of the sensors is simple and easy to fabricate, and their use is also earthy. The fabricated sensors have great potential for commercialization. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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13 pages, 3795 KiB

Open AccessArticle

Orange Dye and Silicone Glue Composite Gel-Based Optimized Impedimetric and Capacitive Surface-Type Proximity Sensors

by Khasan S. Karimov, Muhammad Tariq Saeed Chani, Noshin Fatima, Abdullah M. Asiri and Mohammed M. Rahman

Gels 2023, 9(9), 721; https://doi.org/10.3390/gels9090721 - 05 Sep 2023

Viewed by 752

Abstract

Optimized surface-type impedimetric and capacitive proximity sensors have been fabricated on paper substrates by using rubbing-in technology. The orange dye (OD) and silicone glue (SG) composite-gel films were deposited on the zig-zag gap between two aluminum electrodes fixed on a paper (dielectric) substrate. [...] Read more.

Optimized surface-type impedimetric and capacitive proximity sensors have been fabricated on paper substrates by using rubbing-in technology. The orange dye (OD) and silicone glue (SG) composite-gel films were deposited on the zig-zag gap between two aluminum electrodes fixed on a paper (dielectric) substrate. The effect of proximity of various objects (receivers) on the impedance and the capacitance of the sensors was investigated. These objects were semi-cylindrical aluminum (metallic) foil, a cylindrical plastic tube filled with water, a kopeck-shaped plastic tube filled with carbon nanotubes and a human finger. The mechanism of sensing was based on the change in impedance and/or the capacitance of the sensors with variation of proximity between the surfaces of the sensor and the object. On decreasing proximity, the impedance of the sensors increased while the capacitance decreased. The impedimetric proximity sensitivities of CNT, water, metal-based receivers and the finger were up to 60 × 10³ Ω/mm, 35 × 10³ Ω/mm, 44 × 10³ Ω/mm and 6.2 × 10³ Ω/mm, respectively, while their capacitive sensitivities were −19.0 × 10⁻² pF/mm, −16.0 × 10⁻² pF/mm, −16.4 × 10⁻² pF/mm and −1.8 × 10⁻² pF/mm. If needed for practical application, the sensors can be built in to the Wheatstone bridge, which can also increase the sensitivity of the measurement. Moreover, the sensor’s materials are low cost, while the fabrication technique is easy and ecologically friendly. The sensor can also be used for demonstrative purposes in school and college laboratories. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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17 pages, 5168 KiB

Open AccessArticle

Modulating the Configurations of “Gel-Type” Soft Silicone Rubber for Electro-Mechanical Energy Generation Behavior in Wearable Electronics

by Vineet Kumar, Md. Najib Alam, Manesh A. Yewale and Sang-Shin Park

Gels 2023, 9(9), 686; https://doi.org/10.3390/gels9090686 - 25 Aug 2023

Cited by 2 | Viewed by 933

Abstract

Electro-mechanical configurations can be piezo-electric transducers, triboelectric generators, electromagnetic induction, or hybrid systems. Our present study aims at developing energy generation through the piezoelectric principle. Gel-type soft SR with Shore A hardness below 30 was used as a versatile material for an elastomeric [...] Read more.

Electro-mechanical configurations can be piezo-electric transducers, triboelectric generators, electromagnetic induction, or hybrid systems. Our present study aims at developing energy generation through the piezoelectric principle. Gel-type soft SR with Shore A hardness below 30 was used as a versatile material for an elastomeric substrate. Also, multi-wall carbon nanotube (MWCNT), and diatomaceous earth (DE) were used as reinforcing fillers. This “gel-type” soft SR has crosslinking polymer networks with silicone encapsulated within its structure. Mechanical properties such as modulus or stretchability are of utmost importance for such devices based on “gel-type” soft. From the experiments, some of the mechanical aspect’s values are summarized. For example, the stretchability was 99% (control) and changes to 127% (3 phr, MWCNT), 76% (20 phr DE), and 103% (20 phr hybrid). From electro-mechanical tests, the output voltage was 0.21 mV (control) and changed to 0.26 mV (3 phr, MWCNT), 0.19 mV (20 phr DE), and 0.29 mV (20 phr hybrid). Moreover, from real-time biomechanical human motion tests in “gel-type” soft-based composites, a relationship among output voltage from machine to human motions was established. Overall, these configurations make them promising against traditional portable devices such as batteries for small power applications such as mobile phones. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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13 pages, 3951 KiB

Open AccessArticle

Dual Network Hydrogel with High Mechanical Properties, Electrical Conductivity, Water Retention and Frost Resistance, Suitable for Wearable Strain Sensors

by Chen Miao, Penghui Li, Jiangdong Yu, Xuewen Xu, Fang Zhang and Guolin Tong

Gels 2023, 9(3), 224; https://doi.org/10.3390/gels9030224 - 14 Mar 2023

Cited by 2 | Viewed by 1784

Abstract

With the progress of science and technology, intelligent wearable devices have become more and more popular in our daily life. Hydrogels are widely used in flexible sensors due to their good tensile and electrical conductivity. However, traditional water-based hydrogels are limited by shortcomings [...] Read more.

With the progress of science and technology, intelligent wearable devices have become more and more popular in our daily life. Hydrogels are widely used in flexible sensors due to their good tensile and electrical conductivity. However, traditional water-based hydrogels are limited by shortcomings of water retention and frost resistance if they are used as the application materials of flexible sensors. In this study, the composite hydrogels formed by polyacrylamide (PAM) and TEMPO-Oxidized Cellulose Nanofibers (TOCNs) are immersed in LiCl/CaCl₂/GI solvent to form double network (DN) hydrogel with better mechanical properties. The method of solvent replacement give the hydrogel good water retention and frost resistance, and the weight retention rate of the hydrogel was 80.5% after 15 days. The organic hydrogels still have good electrical and mechanical properties after 10 months, and can work normally at −20 °C, and has excellent transparency. The organic hydrogel show satisfactory sensitivity to tensile deformation, which has great potential in the field of strain sensors. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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11 pages, 4249 KiB

Open AccessArticle

Conductive and Adhesive Granular Alginate Hydrogels for On-Tissue Writable Bioelectronics

by Sumin Kim, Heewon Choi, Donghee Son and Mikyung Shin

Gels 2023, 9(2), 167; https://doi.org/10.3390/gels9020167 - 19 Feb 2023

Cited by 7 | Viewed by 2634

Abstract

Conductive hydrogels are promising materials in bioelectronics that ensure a tissue-like soft modulus and re-enact the electrophysiological function of damaged tissues. However, recent approaches to fabricating conductive hydrogels have proved difficult: fixing of the conductive hydrogels on the target tissues hydrogels requires the [...] Read more.

Conductive hydrogels are promising materials in bioelectronics that ensure a tissue-like soft modulus and re-enact the electrophysiological function of damaged tissues. However, recent approaches to fabricating conductive hydrogels have proved difficult: fixing of the conductive hydrogels on the target tissues hydrogels requires the aids from other medical glues because of their weak tissue-adhesiveness. In this study, an intrinsically conductive and tissue-adhesive granular hydrogel consisting of a PEDOT:PSS conducting polymer and an adhesive catechol-conjugated alginate polymer was fabricated via an electrohydrodynamic spraying method. Because alginate-based polymers can be crosslinked by calcium ions, alginate-catechol polymers mixed with PEDOT:PSS granular hydrogels (ACP) were easily fabricated. The fabricated ACP exhibited not only adhesive and shear-thinning properties but also conductivity similar to that of muscle tissue. Additionally, the granular structure makes the hydrogel injectable through a syringe, enabling on-tissue printing. This multifunctional granular hydrogel can be applied to soft and flexible electronics to connect humans and machines. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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15 pages, 6367 KiB

Open AccessArticle

A Novel Poly(vinyl alcohol)–tetraethylorthosilicate Hybrid Gel Electrolyte for Lead Storage Battery

by Bipin S. Chikkatti, Ashok M. Sajjan, Prakash B. Kalahal, Nagaraj R. Banapurmath, T. M. Yunus Khan, Shaik Dawood Abdul Khadar, Shaik Mohamed Shamsudeen and A. B. Raju

Gels 2022, 8(12), 791; https://doi.org/10.3390/gels8120791 - 02 Dec 2022

Cited by 7 | Viewed by 3176

Abstract

The gel electrolyte significantly influences gel valve-regulated lead acid battery performance. To address this, the paper describes the preparation of novel polymer gel electrolytes using poly (vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) for valve-regulated lead–acid batteries. FTIR technique is used to confirm the [...] Read more.

The gel electrolyte significantly influences gel valve-regulated lead acid battery performance. To address this, the paper describes the preparation of novel polymer gel electrolytes using poly (vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) for valve-regulated lead–acid batteries. FTIR technique is used to confirm the chemical reaction between PVA and TEOS. Electrochemical analyses such as cyclic voltammetry and electrochemical impedance spectroscopy were applied to optimize the concentration of PVA-TEOS polymer gel electrolyte. The optimum concentration of polymer gel electrolyte was determined as 20 wt% of TEOS in PVA (PE-1) with higher anodic peak and lower Rs and Rct values. The Galvanostatic charge–discharge tests were performed on the optimized gel system prototype battery. The highest capacity of 6.86 × 10⁻⁵ Ah at a current density of 0.2 mA cm⁻² was achieved with an excellent capacity retention ratio of 85.7% over 500 cycles. The exceptional cycle performance and high capacity make PVA-TEOS gel electrolyte a promising candidate for practical battery application. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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10 pages, 12361 KiB

Open AccessArticle

PEDOT Composite with Ionic Liquid and Its Application to Deformable Electrochemical Transistors

by Sangkyu Lee, Jaepyo Jang, Sungjun Lee, Daekwang Jung, Mikyung Shin and Donghee Son

Gels 2022, 8(9), 534; https://doi.org/10.3390/gels8090534 - 25 Aug 2022

Cited by 4 | Viewed by 2510

Abstract

Organic electrochemical transistors (OECTs) have become popular due to their advantages of a lower operating voltage and higher transconductance compared with conventional silicon transistors. However, current OECT platform-based skin-inspired electronics applications are limited due to the lack of stretchability in poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). [...] Read more.

Organic electrochemical transistors (OECTs) have become popular due to their advantages of a lower operating voltage and higher transconductance compared with conventional silicon transistors. However, current OECT platform-based skin-inspired electronics applications are limited due to the lack of stretchability in poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). Some meaningful structural design strategies to resolve this limitation, including rendering OECT to make it more stretchable, have been reported. However, these strategies require complicated fabrication processes and face challenges due to the low areal density of active devices because wavy interconnect parts account for a large area. Nevertheless, there have been only a few reports of fully deformable OECT having skin-like mechanical properties and deformability. In this study, we fabricated stretchable and conductivity-enhanced channel materials using a spray-coating method after a composite solution preparation by blending PEDOT:PSS with several ionic liquids. Among these, the PEDOT composite prepared using 1-butyl-3-methylimidazolium octyl sulfate exhibited a better maximum transconductance value (~0.3 mS) than the other ion composites. When this material was used for our deformable OECT platform using stretchable Au nanomembrane electrodes on an elastomer substrate and an encapsulation layer, our d-ECT showed a barely degraded resistance value between the source and drain during 1000 cycles of a 30% repeated strain. We expect that our d-ECT device will serve as a step toward the development of more precise and accurate biomedical healthcare monitoring systems. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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Review

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22 pages, 4065 KiB

Open AccessReview

Recent Progress in Self-Healable Hydrogel-Based Electroluminescent Devices: A Comprehensive Review

by Melkie Getnet Tadesse and Jörn Felix Lübben

Gels 2023, 9(3), 250; https://doi.org/10.3390/gels9030250 - 21 Mar 2023

Cited by 7 | Viewed by 1711

Abstract

Flexible electronics have gained significant research attention in recent years due to their potential applications as smart and functional materials. Typically, electroluminescence devices produced by hydrogel-based materials are among the most notable flexible electronics. With their excellent flexibility and their remarkable electrical, adaptable [...] Read more.

Flexible electronics have gained significant research attention in recent years due to their potential applications as smart and functional materials. Typically, electroluminescence devices produced by hydrogel-based materials are among the most notable flexible electronics. With their excellent flexibility and their remarkable electrical, adaptable mechanical and self-healing properties, functional hydrogels offer a wealth of insights and opportunities for the fabrication of electroluminescent devices that can be easily integrated into wearable electronics for various applications. Various strategies have been developed and adapted to obtain functional hydrogels, and at the same time, high-performance electroluminescent devices have been fabricated based on these functional hydrogels. This review provides a comprehensive overview of various functional hydrogels that have been used for the development of electroluminescent devices. It also highlights some challenges and future research prospects for hydrogel-based electroluminescent devices. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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20 pages, 2237 KiB

Open AccessReview

Review on Hydrogel-Based Flexible Supercapacitors for Wearable Applications

by Melkie Getnet Tadesse and Jörn Felix Lübben

Gels 2023, 9(2), 106; https://doi.org/10.3390/gels9020106 - 26 Jan 2023

Cited by 10 | Viewed by 3628

Abstract

Smart hydrogels with high electrical conductivity, which can be a real source of power while also collecting and storing the diverse sources of energy with ultrahigh stretchability, strong self-healability, low-temperature tolerance, and excellent mechanical properties, are great value for tailored wearable cloths. Considerable [...] Read more.

Smart hydrogels with high electrical conductivity, which can be a real source of power while also collecting and storing the diverse sources of energy with ultrahigh stretchability, strong self-healability, low-temperature tolerance, and excellent mechanical properties, are great value for tailored wearable cloths. Considerable effort has been dedicated in both scientific and technological developments of electroconductive hydrogels for supercapacitor applications in the past few decades. The key to realize those functionalities depends on the processing of hydrogels with desirable electrochemical properties. The various hydrogel materials with such properties are now emerging and investigated by various scholars. The last decade has witnessed the development of high-performance supercapacitors using hydrogels. Here, in this review, the current status of different hydrogels for the production of flexible supercapacitors has been discussed. The electrochemical properties such as capacitance, energy density and cycling ability has been given attention. Diverse hydrogels, with their composites such as carbon-based hydrogels, cellulose-based hydrogels, conductive-polymer-based hydrogels and other hydrogels with excellent electromechanical properties are summarized. One could argue that hydrogels have played a central, starring role for the assembly of flexible supercapacitors for energy storage applications. This work stresses the importance of producing flexible supercapacitors for wearable clothing applications and the current challenges of hydrogel-based supercapacitors. The results of the review depicted that hydrogels are the next materials for the production of the flexible supercapacitor in a more sustainable way. Full article

(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)

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