Self-Healing Materials
Self-healing materials are a class of smart materials that have the structurally incorporated ability to repair damage caused by mechanical usage over time. The inspiration comes from biological systems, which have the ability to heal after being wounded. Initiation of cracks and other types of damage on a microscopic level has been shown to change thermal, electrical, and acoustical properties, and eventually lead to whole scale failure of the material. Usually, cracks are mended by hand, which is difficult because cracks are often hard to detect. A material (polymers, ceramics, etc.) that can intrinsically correct damage caused by normal usage could lower production costs of a number of different industrial processes through longer part lifetime, reduction of inefficiency over time caused by degradation, as well as prevent costs incurred by material failure. For a material to be defined as self-healing, it is necessary that the healing process occurs without human intervention. (Wikipedia, Self-Healing Materials, 3/27/2011)
Recent Journal Articles
Self-Healing Fibre Reinforced Composites via a Bioinspired Vasculature
(3624–3633) Advanced Functional Materials 21 #19 (2011)
Norris et al of the University of Bristol, United Kingdom, demonstrated the first steps towards self-healing composites that exploit a design philosophy inspired by the damage tolerance and self-repair functions of bone. Cracking in either fibre reinforced polymers (FRP) or bone, if left unattended, can grow under subsequent cyclic stresses eventually leading to catastrophic failure of the structure. On detection of cracks, an FRP component must be repaired or completely replaced, whereas bone utilises a series of complex processes to repair such damage. Under normal circumstances, these processes allow the skeleton to continually perform over the lifespan of the organism, a highly desirable aspiration for engineering materials. A simple vasculature design incorporated into a FRP via a “lost wax” process was found to facilitate a self-healing function which resulted in an outstanding recovery (≥96%) in post-impact compression strength. The process involved infusion of a healing resin through the vascule channels. Resin egress from the backface damage, ultrasonic C-scan testing, and microscopic evaluation all provide evidence that sufficient vascule–damage connectivity exists to confer a reliable and efficient self-healing function. (RDC 9/26/2011)
Azide/Alkyne-“Click”-Reactions of Encapsulated Reagents: Toward Self-Healing Materials
(419–425)Macromolecular Rapid Communications 32 #5 (2011)
Gragert, Schunack and Binder of Martin-Luther-University, Germany, encapsulated a liquid, azido-telechelic three-arm star poly(isobutylene) (Mn=3900 g/mol) as well as trivalent alkynes into micron-sized capsules and embedded into a polymer-matrix (high-molecular weight poly(isobutylene), (Mn=250 000 g/mol). Using (CuIBr(PPh3)3) as catalyst for the azide/alkyne-“click”-reaction, crosslinking of the two components at 40C is observed within 380 min and as fast as 10min at 80 C. Significant recovery of the tensile storage modulus was observed in a material containing 10wt.-% and accordingly 5wt % capsules including the reactive components within 5 d at room temperature, thus proving a new concept for materials with self-healing properties. (RDC 2/24/2011)