An official website of the United States government
To improve their electrical conductivity for various applications, semiconducting polymer films are often chemically doped to increase their equilibrium charge carrier density. Recently, a novel doping method involving anion exchange has provided control over the identity of the counterions that reside in such films, leading to increased stability under ambient conditions. In this work, however, we show that by ion-exchanging 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane-doped poly(3-hexylthiophene-2,5-diyl) films with hygroscopic salts like bis(trifluoromethane)sulfonimide lithium or LiPF6, the doped film's electrical conductivity drops significantly when exposed to ambient humidity. The change in electrical conductivity depends directly on the degree of hygroscopicity of the counterion and can be over 50% with relatively modest changes in relative humidity (RH), and up to a factor of four between ambient and completely dry conditions. The film's humidity response is entirely reversible when adsorbed water is removed, potentially allowing the doped semiconducting polymer films to function as humidity sensors. Hall effect measurements show that the cause of the drop in conductivity with increasing RH is due to a decrease in carrier mobility and not due to de-doping. Our results emphasize that it is important to control the sample environment when making electrical measurements on anion-exchange doped semiconducting polymer films.
more »
« less
Humidity sensors based on molecular rectifiers
Ambient humidity plays a key role in the health and well-being of us and our surroundings, making it necessary to carefully monitor and control it. To achieve this goal, several types of instruments based on various materials and operating principles have been developed. Reducing the production costs for such systems without affecting their sensitivity and reliability would allow for broader use and greater efficiency. Organic materials are prime candidates for incorporation in humidity sensors given their extraordinary chemical diversity, low cost, and ease of processing. Here, we designed, assembled and tested humidity sensors based on molecular rectifiers that can electrically transduce the changes in the ambient humidity to offer accurate quantitative information in the range of 0 to 70% relative humidity. Their operation relies on the changes occurring in the electric field experienced by the molecular layer upon absorption of the polar water molecules, resulting in modifications in the height and shape of the tunneling barrier. The response is reversible and reproducible upon multiple cycles and, coupled with the simplicity of the device architecture and manufacturing, makes these nanoscale sensors attractive for incorporation in various applications.
more »
« less
- PAR ID:
- 10391687
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 15
- Issue:
- 1
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 171 to 176
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The friction and wear behavior of materials are not intrinsic properties, but extrinsic properties; in other words, they can drastically vary depending on test and environmental conditions. In ambient air, humidity is one such extrinsic parameter. This paper reviews the effects of humidity on macro- and nano-scale friction and wear of various types of materials. The materials included in this review are graphite and graphene, diamond-like carbon (DLC) films, ultrananocrystalline diamond (UNCD), transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), boric acid, silicon, silicon oxide, silicates, advanced ceramics, and metals. Details of underlying mechanisms governing friction and wear behaviors vary depending on materials and humidity; nonetheless, a comparison of various material cases revealed an overarching trend. Tribochemical reactions between the tribo-materials and the adsorbed water molecules play significant roles; such reactions can occur at defect sites in the case of two-dimensionally layered materials and carbon-based materials, or even on low energy surfaces in the case of metals and oxide materials. It is extremely important to consider the effects of adsorbed water layer thickness and structure for a full understanding of tribological properties of materials in ambient air.more » « less
-
Abstract Auxetic materials showing a negative Poisson’s ratio can offer unusual sensing capabilities due to drastic percolation changes. This study presents the capacitive response of wet-fractured carbon nanotube paper composites in exposure to humidity. A strained composite strip is fractured to produce numerous cantilevers consisting of cellulose fibers coated with carbon nanotubes. During stretching, the thin composite buckles in the out-of-plane direction, which causes auxetic behavior to generate the radially structured electrodes. The crossbar junctions forming among the fractured electrodes significantly increase capacitance and its response to humidity as a function of sensor widths. The molecular junctions switch electric characteristics between predominantly resistive- and capacitive elements. The resulting capacitive response is characterized for humidity sensing without the need for an additional absorption medium. The normalized capacitance change (ΔC/C 0 ) exhibits a sensitivity of 0.225 within the range of 40 ∼ 80% relative humidity. The novel auxetic behavior of a water-printed paper-based nanocomposite paves the way for inexpensive humidity and sweat sensors.more » « less
-
Monitoring humidity and temperature is critical for many applications, including enhancing food production in greenhouses and open farms. This demands for environmentally friendly, cost-effective, and biocompatible sensors. Paper-based sensors meet these requirements as they are cost-effective, eco-friendly, and adaptable to varying agricultural conditions due to their affordability, biodegradability, and flexibility. This research developed printed capacitance-based humidity and resistance-based temperature sensors using a dry additive nanomanufacturing technique on four distinct types of commercially available uncoated paper substrates. Based on the principles of a capacitor and resistor, humidity and temperature sensors were fabricated by printing silver interdigitated electrodes on papers with varying solubility and thicknesses to measure the humidity absorption capability and the printed silver electrode’s response to temperature change. The sensors successfully detected the changes in relative humidity levels from 20 to 90% and temperature variations from 25 to 50 °C. The humidity and temperature sensors developed in this study have strong implications for use in smart agricultural applications, food supply, food storage, and preservation. Since these sensors are affordable, biodegradable, and environmentally friendly, they can be intended for one- or two-time applications and safely disposed of after use.more » « less
-
null (Ed.)Due to their ability to move without sliding relative to their environment, soft growing robots are attractive for deploying distributed sensor networks in confined spaces. Sensing of the state of such robots would add to their capabilities as human-safe, adaptable manipulators. However, incorporation of distributed sensors onto soft growing robots is challenging because it requires an interface between stiff and soft materials, and the sensor network needs to undergo significant strain. In this work, we present a method for adding sensors to soft growing robots that uses flexible printed circuit boards with self-contained units of microcontrollers and sensors encased in a laminate armor that protects them from unsafe curvatures. We demonstrate the ability of this system to relay directional temperature and humidity information in hard-to-access spaces. We also demonstrate and characterize a method for sensing the growing robot shape using inertial measurement units deployed along its length, and develop a mathematical model to predict its accuracy. This work advances the capabilities of soft growing robots, as well as the field of soft robot sensing.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2NR04498F
