Wearables that sense our moves, hearth beats, or sugar levels, implants that adapt to soft body tissues, artificial skins that help to bring haptic feeling to prostheses, or soft robots that can reshape and adapt to the environment are just some examples of challenges that technology is addressing. For that, new materials must be developed. Classical electronic components are stiff. Today, two main alternatives are used to overcome this problem: liquid metals and composites.
Liquid metals are good conductors and able to adapt easily and fast during mechanical deformation retaining their electrical properties. However, their use is limited to Gallium and some of its alloys and their properties cannot be easily tuned, for example to create sensors. These aspects limit their use.
Composites combine an elastomer as matrix and conductive particles as fillers. Both electrical conductivity and mechanical elasticity are more limited than in the case of liquid metals. As the particles are embedded in a solid elastomer, they are limited in the degree of freedom to rearrange under mechanical deformation. However, by design, composites can be fabricated with tuned properties depending on the application.
Here, we propose a new concept: “ELECTROFLUID”, that conducts electrons while flowing. We mix conductive particles (carbon- and metal-based) in solvents with different polarity and viscosity to create a conductive fluid/paste. Similar to a classical composite but in this case, the matrix remains liquid. The number of particles is sufficient, so they are in contact forming a 3D network that ensures connectivity, and thus electrical conductivity. The contacts between the particles are transient, so they can move in the liquid and rearrange under mechanical deformation preserving the electrical conductivity of the material.
We study the particle-particle and particle-solvent interactions attending to the nature of interfaces (e.g. shape of the particles, surface-volume ratio, or surface chemistry). This helps us to understand the 3D network formation of the solid in the liquid. The structure of the network dominates both the conductivity and the viscosity of the material. We tune the properties of the Electrofluids by adjusting its components. The objective is to create electrical conductors with tunable mechanoelectrical properties and integrate them into devices. The specific aims of the project are: (i) to design highly concentrated suspensions that form transient percolating networks, (ii) to use this knowledge and synthesize fluids with tunable electrical conductivity at low viscosity, (iii) to demonstrate that Electrofluids can be curtailed for targeted applications.
