Precise Dynamic Control of the Mechanical and Self‐Healing Properties of an Electrolytic Cell with Soluble Porous Anode

Abstract

The performance of engineering products is inherently dependent on the properties of its constituent materials. Because these properties are mostly fixed for each material, the range of requirements that the engineering product can satisfy is consequently very narrow. The environment that these engineering parts operate in, however, can be very dynamic, requiring quick and substantial property modifications for optimal performance. For instance, to effectively attenuate acoustic noise, [1-3] impact, [4-7] or seismic waves, [8,9] materials with stiffnesses and strengths that can be temporally varied are needed. Similarly, tumor cell migration rates can be controlled in real time by hydrogels with variable stiffness. [10,11] Having materials with dynamic mechanical properties would also allow for the reconciliation of soft robotics, which has the advantages of dexterity and interacting safely with delicate bodies, [12-15] with conventional hard robotics, which is needed to bear and transmit large loads, [12,16] within a single machine. Moreover, having a versatile product that can meet a wide range of requirements eliminates the need for multiple specialized parts with dedicated functions, such as functionally graded materials, [4,17] thus reducing energy and material wastage, leading to a positive ecological impact. One of the easiest methods to induce changes in mechanical properties is to spatially compact a given structure. A biological body does this with muscular contractions, for instance, in a human tongue and elephant trunk, [12] whereas structural foams can be infused with magnetic particles, either in the struts [2] or in the pores, [6] so that the material will stiffen in the presence of a magnetic field. However, a constant energy input is required to maintain this property change and the accompanying alteration in volume may be undesirable, especially if the material is part of an assembly with tight tolerances. An alternative method that has been explored involves heating/cooling a material to induce a phase change. [18,19] For a low-melting-point alloy (e.g., Field's metal), this change in phase is between a solid and liquid, which can lead to a modulus variation over four orders of magnitude. [19] In the case of shape memory polymers (SMPs), the phase change occurs when they are heated above their glass transition temperature, and two to three orders of magnitude change in flexural rigidity of these beams have been demonstrated. [20,21] Although the change in stiffness can be very large using these techniques, the property variation is essentially binary because it is difficult to control and maintain the relative amounts of stiff and soft material at the melting point or glass transition temperature. Furthermore, the temperature change involved may not be ideal for applications involving sensitive environments (e.g., biomedical settings). It has also been shown recently that the application of an electrochemical potential to a nanoporous gold foam can cause the adsorption of a submonolayer of oxyg...