Self-Reporting Joule Heating Modulated Stiffness of Polymeric Nanocomposites for Shape Reconfiguration

Abstract

Shape reconfigurable devices, e.g., foldable phones, have emerged with the development of flexible electronics. But their rigid frames limit the feasible shapes for the devices. To achieve freely changeable shapes yet keep the rigidity of devices for user-friendly operations, stiffness-tunable materials are desired, especially under electrical control. However, current such systems are multilayer with at least a heater layer and a structural layer, leading to complex fabrication, high cost, and loss of reprocessability. Herein, we fabricate covalent adaptable networks–carbon nanotubes (CAN-CNT) composites to realize Joule heating controlled stiffness. The nanocomposites function as stiffness-tunable matrices, electric heaters, and softening sensors all by themselves. The self-reporting of softening is used to regulate the power control, and the sensing mechanism is investigated by simulating the CNT–polymer chain interactions at the nanoscale during the softening process. The nanocomposites not only have adjustable mechanical and thermodynamic properties but also are easy to fabricate at low cost and exhibit reprocessability and recyclability benefiting from the dynamic exchange reactions of CANs. Shape and stiffness control of flexible display systems are demonstrated with the nanocomposites as framing material, where freely reconfigurable shapes are realized to achieve convenient operation, wearing, or storage, fully exploiting their flexible potential.

Rigidity‐Tunable Materials for Soft Engineering Systems

“…Such electronics have been reported to offer properties that combine user convenience in a rigid state and can change shape when soft. [135][136][137][138] Here, a polyurethan (PU) and CNTs composite demonstrated a high degree of shape reconfiguration, making it suited for display applications. [135] This composite can alter its stiffness from 1 GPa to 100 MPa through Joule heating, allowing for various deformations-such as bending, twisting, waving, and folding -without compromising its electronic functionality in its soft and flexible state.…”

“…[135][136][137][138] Here, a polyurethan (PU) and CNTs composite demonstrated a high degree of shape reconfiguration, making it suited for display applications. [135] This composite can alter its stiffness from 1 GPa to 100 MPa through Joule heating, allowing for various deformations-such as bending, twisting, waving, and folding -without compromising its electronic functionality in its soft and flexible state. These freely reconfigurable electronics could potentially be used in wearable devices that conform to and securely adhere to the skin without frame, enhancing user comfort.…”

PVDF Hybrid Nanocomposites with Graphene and Carbon Nanotubes and Their Thermoresistive and Joule Heating Properties

“…The coefficient could serve as an evaluation of the sensitivity of the resistivity to temperature. TCR = (ρ − ρ0)/ρ0 × (T − T0), (7) where ρ is the maximum resistivity at 100 • C, ρ0 is the resistivity at 30 • C, T0 is 30 • C, and T is the maximum temperature at 100 • C. The calculated TCR is given in Figure 8. In general, the obtained values are very small, confirming the low sensitivity of the resistivity to temperature in the studied region.…”

“…In the last few years, there has been a growing interest in the study of the thermoresistive effect (the change in electrical resistance due to a temperature change) and the Joule heating (resistive heating produced by the flow of electric current) of polymeric nanocomposites. These thermoresistive properties have attracted scientific attention due to their potential applications in electronics, energy harvesting, and sensor applications [ 5 , 6 , 7 , 8 ]. Thermoresistive polymer-based materials need conductive particles to evaluate the change in resistivity of the material.…”