Researcher: Dr Eleonora D´Elia

Supervisor: Professor Eduardo Saiz

Sponsor: DARPA

            Smart materials have captivated the world of science and technologies for decades. The idea that a man-made material could sense the environment and respond to external stimuli such as light, temperature, or damage in an autonomous and programmed way is fascinating and, at the same time, closer than anticipated.

             In this work we describe an approach for the fabrication of adaptive composite materials able to self-repair autonomously, sense mechanical stimuli such as pressure or flexion self-monitor their structural integrity and change their shape in response to external stimuli. These smart materials are based on the controlled integration of microscopic electrically conductive networks within polymeric matrices having self-healing or shape-memory capabilities. To realize this concept, we have taken advantage of the 2D nature of graphene combined with new processing techniques to design minimally-invasive networks able to provide a platform for inducing electrical stimuli in the composites. Superlight electrically conductive carbon-based networks with microscopic porosity obtained by freeze-casting, have been infiltrated with a second polymeric phase. The networks are tailored to provide controlled and localized joule heating at relatively low voltages in order to stimulate the desired response in the polymeric matrix (healing or shaping). The resulting materials have graphene contents below 0.5 wt. %. Their mechanical response (strength and toughness) is evaluated and related to their microstructure.

             Their healing ability is quantified in terms of recovery of these mechanical properties after damage. In parallel, their shape changing and mechanical sensing capabilities in response to electrical currents are also tested. Preliminary results on shape-memory compositions show strengths up to 60 MPa and complete shape recovery through joule heating in 10 seconds. Furthermore, the composites are able to record, through a conductivity change, the initiation and progression of a crack, providing damage monitoring capabilities.

             The work brings together the fields of construction, materials science, robotics, energy and bioengineering in an innovative way, opening new paths for the design of smart actuators and adaptive composites.

Fig Living materialsFigure 1. Joule heating effect in a shape-memory conductive sample showing the sample curling up and grabbing a weight due to current being passed through it.