# Underwater Highly Pressure-Sensitive Fabric Based on Electric-Induced Alignment of Graphene
## 3 Results and Discussion  
Figure 1a shows the fabrication process of the superhydrophobic conductive fabric. The preparation of the fabrics involves three steps: the dipping-coating process of graphene/PDMS precursor, the drying directional curing in the electric field, and the radio frequency capacitively coupled Ar plasma (RF-CCP) treatment. As shown in Figure 1b, in the graphene dispersion, a layer of graphene nanosheets adhered firmly and uniformly to the surface. Compared with the modified sample, the surface of the original knitted sample is relatively smooth. Under Ar plasma exposure, ions penetrated the polymer, initiating the self-diffusion of polymer chains and subsequent cross-linking (Figure 1c). The bombardment produced broken bonds and small molecules and formed active sites on the polyester surface. In addition, in the cavity, repolymerization and cross-linking reactions occur between the polyester fabric and PDMS and some small molecules, after which a three-dimensional network interpenetrating structure is formed on the polyester surface. This may be due to the partial activation of -Si-CH\({}_{3}\) as -Si-CH\({}_{2}\)- under high-energy plasma and subsequent polymerization into -Si-CH\({}_{2}\)-CH\({}_{2}\)-Si- [20; 21; 22; 23]. The plasma discharge time has an effect on the hydrophobicity of the fabric. A discharge time of 20 s predicted the best hydrophobic performance (Figure S3). Rough surfaces and long alkyl chains are formed under the action of plasma. Due to the formation of these structures, the stability of the coating is enhanced and a hydrophobic effect is achieved. On one hand, the hydrophobicity of the coating protects it from liquid erosion during underwater sensing and increases its stability and durability. On the other hand, the formed coating has a certain encapsulation effect on graphene and reduces graphene shedding during service. An electric field is applied to graphite nanosheets on PDMS substrates induce directional alignment of nanosheets. To clarify the effect of the electric field on the sensitivity of the fabric sensor, the response and recovery time of the sensor are measured when pressure is applied and removed from the sensor. As shown in Table 1, the preparation methods and materials used in our research and reported work are summarized, as well as the response performance of the obtained devices. We used a simple impregnation method combined with an electric field to obtain a device with short response and recovery times. As shown in Figure 2a, when 50 kPa pressure (the weight is a cylinder with a base radius of 0.5 cm and a height of 3 cm.) is placed on the sensor surface, the response and recovery times of the fabric sensor without the electric field are both 200 ms (Figure 2a(i)). In contrast, in Figure 2a(ii), after the electric field is applied, the response and recovery times of the fabric sensor are reduced to 100 ms. This phenomenon is explained by the scanning electron microscopy of the coating section (Figure 2b). To better observe the cross-sectional morphology of the coating, it was fixed on the PET film. The action of the electric field makes graphene sheets deflected along the direction of the electric field. This arrangement enables the lap of graphene sheets. PDMS can be used as a spatial support material to form a more three-dimensional spatial structure. The additional structural deformation can produce a faster response when external forces are applied. Therefore, response time and recovery time are reduced. However, the graphene nanosheets are not twisted completely parallel to the electric field, which may be due to the joint influence of the viscosity of macromolecules and the force between graphene nanosheets, and the movement of graphene nanosheets is greatly hindered by space. Therefore, the graphene nanosheets tend to move in one direction as a whole. Figure 2c shows a schematic diagram of the electric field-induced preparation of directionally aligned graphene subjected to forces.