Abstract:

Objective Touch-sensing devices are the most promising technology for human-computer interaction. However, current touch-sensing devices still suffer from poor bending resistance and low comfort due to the use thin films or silicone as substrate. Herein, this work proposes a novel strategy to breakthrough above bottleneck. PLA nonwoven materials with skin-friendly is used as substrate and combined with intrinsically flexible ionic hydrogels to develop a touch-sensing electronic textile with wearable comfort and resistance to deformation interference.

Method The touch-sensing electronic textile is a typical sandwich structure, where the ionic hydrogel is encapsulated by the upper and lower polylactic acid nonwoven layers. The ionic hydrogel is polymerized by acrylamide and lithium chloride under a thermal environment. It is noteworthy that the upper PLA nonwoven layer possesses conductive properties, which is a result of the uniform deposition of graphene nanosheet layers on the PLA fiber surface using the core-absorption deposition effect. The touch-sensing electronic textile has precise touch localization capability, which stems from the construction of a uniform low-voltage AC electric field on the surface of the touch-sensing electronic textile. When the human body touches the surface of the electronic fabric, a coupling capacitance is formed, which trigger the flow of current from the electrodes to the touch point. Owing to the surface capacitive sensing mechanism and the selected intrinsically flexible material, the touch-sensing electronic textile is resistant to bending and comfortable to wear.

Results The results show that the touch-sensing electronic textile can recognize the locations of touch points, and an example test was designed for illustration. Five points were selected at equal intervals on the fabric named 1#—5#, respectively. When the points 1#—5# were touched on, the touch current monitored by the A1 ammeter showed a decreasing tendency (from 8.08 μA to 7.61 μA), while the A2 touch current demonstrated an increasing trend (from 7.68 μA to 8.05 μA). It is noteworthy that the touch currents monitored by the two ammeters at the midpoint are approximately equal in magnitude at 7.85 μA and 7.84 μA, respectively (Fig. 3). Response speed is a crucial parameter to wearable interaction devices. As excepted, the touch-sensing electronic textile demonstrated an excellent response speed. In particular, the touch-sensing electronic textile showed response time of about 25 ms. Besides, the touch-sensing electronic textile has brilliant release time of about 31 ms. This result illustrates that the touch-sensing electronic textile has great advantages in the wearable field (Fig. 4). At the same time, the touch-sensing electronic fabric showed stable touch performance. Three different sliding velocities (40, 100 and 200 mm/s) were selected to observe the change law of touch current. The results revealed that the maximum fluctuation of touch current at the same slip speed was only 5 % (Fig. 5). In addition, the touch sensing electronic fabric illustrated bending resistance. The touch-sensing electronic textile was subjected to 0, 50, 150, 300 and 500 bending cycles, respectively. The midpoint of the touch-sensing electronic textile was selected as the touch point to monitor its current changes. The touch current at the midpoint was 7.86 μA, when no bending deformation was applied. Then the touch currents at the midpoint were 7.97, 7.96, 7.95 and 7.98 μA when different cycles of bending deformation were applied sequentially. The above results suggested that the touch-sensing electronic textile had anti-deformation characteristics (Fig. 6). Further, thermal and humid comfort is an important characteristic of wearable devices and a key index to evaluate the microenvironment of the wearable interface. After the touch-sensing electronic textile was attached to the arm for a period of time, the skin surface morphology was observed (Fig. 7). After wearing the touch sensing electronic fabric for 48 h, the surface temperature of the covered skin does not change significantly, which proves that the nonwoven material-based touch sensing electronic fabric has excellent thermal and wet comfort.

Conclusion The touch-sensing electronic-textile can accuracy locate and recognize the touching points, attributing to the surface capacitive touch-sensing mechanism. Meanwhile, the touch-sensing electronic-textile exhibits excellent response speed (< 25 ms), mechanical stability and anti-interference properties. In addition, the touch-sensing electronic-textile exhibits excellent wearing comfort by virtue of the polyactic acid nonwoven substrate material. As a proof-of-concept, the touching controllers have been fabricated to achieve real-time game control function. Based on this, this work opens a new path for flexible touch sensing devices and has great potential in the field of wearable interaction.

Key words: ionic hydrogel, graphene, conductive nonwoven fabric, flexible electronic textile, touch-sensing