Stretchable color-changing fiber to help technological innovation in smart wearable materials

Smart stretchable fiber devices have grown rapidly in the last 15 years, not only because of their good device design, but also because of their unique one-dimensional structure that is easy to integrate with fabrics and is expected to be widely used in smart wearable devices . . However, it is still a challenge to prepare a color-controllable, responsive, stretchable color-changing fiber by a simple method.

[Introduction]

Recently, the AFMG group led by Professor Wang Hongzhi of Donghua University used double-layered core-spun yarns (DCYs) as a stretchable elastic matrix, and sequentially prepared chemically reduced graphene (RGO)-TiO2 conductive by simple dip coating method. Layer, PDMS protective layer and thermochromic ink layer (Figure 1). This multi-layered design ensures fiber elongation and discoloration stability under deformation conditions such as bending, twisting and stretching. (Journal of Materials Chemistry C, 2017, DOI: 10.1039/C7TC02471A)

[Graphic introduction]

Figure 1. Schematic diagram of the structure of the stretchable electrochromic fiber (a), cross-section SEM (b) and preparation flow chart (c). Ruler: 300 μm

The electrical conductivity of the fiber conductive layer reaches 0.02 Ω·m, and the color stretching and discoloration can be realized by the formulation and selection of the thermochromic ink. Fibers can change between two colors (black to green) or three colors (red to blue to white, etc.) under two different color changing mechanisms. For the stretching/release transition mechanism (Fig. 2), at a constant current, as the degree of stretching increases, the fiber resistance increases, and the Joule heat generation heat increases, causing the color to change intelligently according to temperature, that is, visual sensing.

Figure 2. (ab) Digital photo of the stretchable electrochromic fiber during stretching at a current density of 142 mA/cm and an infrared thermal imaging photograph; (c) Stretchable electrochromic fiber in a different The reflectance spectrum under tension; (d) the relationship between the surface temperature of the electrochromic fiber and the corresponding relative reflectance (505 nm) and the degree of stretching at a current density of 142 mA/cm; (e) at 142 mA/ The relationship between the relative reflectivity (505 nm) of the electrochromic fiber during the stretching/recovering cycle and the different degree of stretching at the current density of cm; (f) the reflectance spectrum of the electrochromic fiber at different current densities; g) In-situ response curve of the current switch of the electrochromic fiber from black to green at a current density of 284 mA/cm.

For the current conversion mechanism, the prepared fiber can directly achieve color change at a large current (Fig. 3).

This type of stretchable electrochromic fiber can be combined with traditional knitting or weaving processes to provide a new and very effective solution for the functionalization of the fiber and the development of the wearable field.