- Nano Express
- Open Access
Facile Fabrication of Multi-hierarchical Porous Polyaniline Composite as Pressure Sensor and Gas Sensor with Adjustable Sensitivity
© The Author(s). 2017
- Received: 17 May 2017
- Accepted: 24 July 2017
- Published: 1 August 2017
A multi-hierarchical porous polyaniline (PANI) composite which could be used in good performance pressure sensor and adjustable sensitivity gas sensor has been fabricated by a facile in situ polymerization. Commercial grade sponge was utilized as a template scaffold to deposit PANI via in situ polymerization. With abundant interconnected pores throughout the whole structure, the sponge provided sufficient surface for the growth of PANI nanobranches. The flexible porous structure helped the composite to show high performance in pressure detection with fast response and favorable recoverability and gas detection with adjustable sensitivity. The sensing mechanism of the PANI/sponge-based flexible sensor has also been discussed. The results indicate that this work provides a feasible approach to fabricate efficient sensors with advantages of low cost, facile preparation, and easy signal collection.
- Facile fabrication
- Low cost
- PANI composite
- Flexible pressure sensor
- Adjustable sensitivity gas sensor
Nowadays, varieties of sensors, including pressure sensor [1, 2], strain sensor [3, 4], gas sensor [5–7], temperature sensor [8, 9], and displacement sensor , have been extensively explored. Particularly, with the popularity of artificial intelligence technology, low-cost flexible sensors are highly desirable for the fabrication of portable, wearable, and foldable devices. However, it is usually expensive and complicated to design flexible sensors with elaborate structures [11, 12]. Thus, an efficient and low-cost approach is highly required to fulfill flexible and portable sensors.
Sponge, as a three-dimensional (3D) ubiquitous material, has aroused extensive concerns due to its unique performance, such as high elasticity, high specific surface area, low density, and low-cost manufacturing. Therefore, conductive sponges are considered as excellent materials to assemble sensors and devices, such as graphene-polyurethane sponge as pressure sensor , superhydrophobic polyaniline (PANI) sponge as oil absorbent , and graphene platelets/PANI sponge  as supercapacitors. Herein, besides carbon series semiconductor materials, conducting polymer is often used as functional element of devices due to their good electrical conductivity, physical robustness, and large surface area [3, 16, 17]. As one of conducting polymers, for the aim of fabricating flexible and low-cost sensors, PANI has already been used as sensing material in various application fields, such as supercapacitors [18, 19], sensors [3, 20], electrodes [21, 22], microwave absorption , and electromagnetic shielding . In general, there are two main methods to prepare PANI composites: doping and in situ polymerization [3, 25–27]. Normally, in situ polymerization provides more feasible preparation and remarkable effectiveness.
Generally, for pressure sensors, according to the sensing mechanisms, there mainly exist piezoelectric sensors [28, 29], capacitive sensors , transistor sensors [2, 31], and piezoresistive sensors [13, 32, 33]. Piezoresistive sensor, as a typical pressure sensor, which transduces pressure to resistance signal, has been widely used due to outstanding advantages, such as simple principle, convenient signal collection, low cost, and simple preparation [13, 28, 32, 33]. Additionally, for gas sensor, the alkali gas sensing mechanism of PANI can be attributed to the conducting mechanism . As we know, the charge carriers of PANI are polarons, and the conjugated molecule chain in PANI will become more conductive after the doping of proton. When the alkaline gas molecules are absorbed by the nanostructured PANI, this will result in a decrease of the charge carriers and increase of the electrical resistance of PANI.
In this study, we used in situ polymerization method to prepare multi-hierarchical porous PANI/sponge composite for piezoresistive sensor and adjustable sensitivity gas sensor. As a porous scaffold, the sponge provided sufficient surface for the growth of nanostructured PANI. The sensor with abundant pores and PANI nanostructures showed excellent performances in pressure sensitivity with fast response to diverse pressure and release. The mechanism of piezoresistive sensing could be attributed to the resistance change by the contact variation of the conductive porous structure. Besides, based on the conducting mechanism of PANI and the piezoresistive sensing mechanism mentioned above, the potential application of the composite for adjustable sensitivity gas sensor has also been investigated. The results indicate that this work provides an effective and low-cost approach to fabricate porous conductive composite and device.
Ammonium persulfate (APS, M w = 228.20), 5-sulfosalicylic acid (SSA, M w = 254.22), and ammonia solution were supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai China). The aniline (M w = 93.13) was purchased from Chemical Reagent (Tianjin China). The sponge was commercial grade polyurethane sponge (Brand: Domaxe, China).
Preparation of PANI/Sponge Composite
The sponge and PANI/sponge composite were characterized by a scanning electron microscope (SEM, JEOL, JSM-7500F) and a Micro-Roman spectroscopy system (Renishaw inVia Plus, 50 mW DPSS laser at 532 nm). The electrical properties were measured by a Keithley 6487 high-resistance meter system.
Morphological and Structural Properties
Pressure Sensitivity Test
To demonstrate pressure sensitivity, the resistance variation of the PANI/sponge composite with pressure applied on surface was explored. The composite with 3D size of 2 × 2 × 2 cm3 was sandwiched by two copper electrodes (as shown in Fig. 2), and the electricity was recorded with the applying of pressure on the two electrodes.
Application in Finger Bending-Release Detection
Application in Adjustable Sensitivity Gas Sensor
In conclusion, we report a facile method via in situ polymerization to prepare PANI/sponge composite which could be used in good performance pressure sensor and adjustable sensitivity gas sensor. The flexible interconnected porous structure helped the composite to show good sensitivity and recoverability to pressure. Besides, the flexible sensor based on PANI/sponge showed good performance in finger bending detection and NH3 detection with adjustable sensitivity. This work may provide a feasible approach to fabricate efficient portable and wearable devices with the advantages of low cost, facile preparation, and easy signal collection.
This work was supported by the National Natural Science Foundation of China (51673103 and 51373082), the Taishan Scholars Program of Shandong Province, China (ts20120528), the Key Research and Development Plan of Shandong Province, China (2016GGX102011), and the Postdoctoral Scientific Research Foundation of Qingdao.
YZL developed the concept and designed the experiments. XXH, JTL, XSJ, LT and JIZ performed the experiments. YZL, XXH, JTL, JUZ, XXW and XN contributed to the data analysis. All authors wrote and revised the paper. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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