Triboresistive Touch Sensing: Grid‐Free Touch‐Point Recognition Based on Monolayered Ionic Power Generators

Abstract

been applied more closely to the human body. Owing to the soft and curved nature of human skin, the systems need to be flexible, robust, and transparent to ensure operational reliabilities and to provide comforts. [3,4] However, it has been challenging to ensure these desirable properties due to the complicated structures of conventional touch-sensing systems, which contain a network of individual electrodes and stacked multilayers. [4,5,8,10,12] More importantly, sensing systems inevitably rely on external power sources, which potentially sacrifice flexibility, add weight, and decrease the lifetime of the sensing systems. [4,5,8,[12][13][14] To address the issues originated from the use of external power sources, systems that rely on energy-harvesting technologies have been highlighted as an alternative to conventional touch-sensing systems. [3,[15][16][17] Recently, triboelectric nanogenerators (TENGs), which convert mechanical touch to electrical energy, have been developed to provide a platform for touch-sensing capability that does not rely on additional power sources. [16][17][18][19][20] The self-powered touch-sensing capability of TENGs can be realized with a couple of materials, i.e., a dielectric layer attached to a conducting layer, based on the combined effects of contact electrification and electrostatic induction. [3,17,18,21] To ensure that triboelectric touch sensors are skin-mountable, researchers have worked to make the components stretchable and transparent. Soft materials such as poly(dimethylsiloxane) (PDMS) and ionically conductive gels are suitable for use in skin-mountable triboelectric touch sensors thanks to their high transparency, stretchability, resilience, and easily tunable mechanical properties. [17,[22][23][24][25] Nonetheless, the development of triboelectric touch position sensors with reliable stretchability and transparency remains challenging due to the complicated structures of the sensors, which contain multiple stacked layers and arrays of individual electrodes. [16,17,19,21,26,27] Unfortunately, the stacking process deteriorates the outstanding mechanical/optical properties of the soft materials in TENGs since the sensors require an additional conducting layer of a material such as metal, ceramic, carbon materials, etc. [16,[28][29][30] The inclusion of transparent and stretchable materials like gels also results in easy delamination and blurring at the bonding interfaces. [17,19,31] Relying on a complex array of individual electrodes and corresponding wires Recent growing pursuit of skin-mountable devices has been impeded by the complicated structures of most sensing systems, containing electrode grids, stacked multilayers, and even external power sources. Here, a type of touch sensing, termed "triboresistive touch sensing", is introduced for gridless touch recognition based on monolayered ionic power generators. A homogeneous monolayer, i.e., ionic poly(dimethylsiloxane) (PDMS), generates electricity based on the electric field generated by touch. Voltages generated at ...

Plasticized PVC‐Gel Single Layer‐Based Stretchable Triboelectric Nanogenerator for Harvesting Mechanical Energy and Tactile Sensing

“…First, we found a distance-sensitive output voltage of the S-TENG because the electric displacement field depends on the contact position's distance and the relatively high electric resistance of the PVC-gel. [45] As shown in Figure 5d, the output voltage, as a function of the distance between the touch point and electrode, is inversely proportional to the distance. The open-circuit voltage based on the distances of the S-TENG can be expressed as…”

“…First, we found a distance‐sensitive output voltage of the S‐TENG because the electric displacement field depends on the contact position's distance and the relatively high electric resistance of the PVC‐gel. [ 45 ] As shown in Figure 5d , the output voltage, as a function of the distance between the touch point and electrode, is inversely proportional to the distance. The open‐circuit voltage based on the distances of the S‐TENG can be expressed as where h is the gap distance, a n is the distance of the contact point on the PVC‐gel to the electrode “ n ”, S is the active area, and k is the Coulomb force constant, which are expressed in detail in Figure S17 and Note S6 (Supporting Information).…”

Materials development in stretchable iontronics

“…Recently, Sun et al reported a triboresistive touch sensor based on the ionic PDMS. 91 The ionic PDMS in that study was composed of hydrophilic PDMS and hydrophobic IL through H-bonding and van der Waals interactions (Fig. 9e).…”

“…To combine polymers with ILs, it is important to find appropriate interactions between the functional groups of polymers and ILs, as these interactions determine their compatibility. The polymers can be roughly classified as polymer-based type 52,74–88 and monomer-based type, 89–109 and the ILs are composed of diverse pairs of the cationic and the anionic units (Fig. 7a and b).…”

Structure and Diffusion of Ionic PDMS Melts

“…It is used in biomedicine [ 3 , 4 ], microfluidics [ 5 , 6 , 7 ], MEMS [ 8 ], triboelectricity [ 9 ] and piezoelectrics [ 10 ]. Motivation to explore the structure and dynamics of ionic PDMS [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] or other melts [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], is very high since ionic interactions inherit polymers with a functionality that leads to a high performance and applications as gas-separating membranes [ 15 ], water purification membranes [ 13 , 14 , 16 ], energy storage devices [ 39 , 40 ] as well as in sensing [ 22 , 23 ], actuation [ 21 ], fuel cells [ 41 ], and others [ 18 , 19 , 24 , 42 ].…”