Designing Sensory and Adaptive Composite Materials

Newly developed computational approaches aid in the design of composites that exhibit remarkable abilities to both sense external cues and adapt to these cues in controllable, ‘programmable’ ways.

Air Force Research Laboratory, Arlington, Virginia

Biological systems have developed structural motifs that allow these systems to resist mechanical deformation. On the molecular scale, biological catch bonds play a vital role in this functionality since these bonds effectively become stronger under deformation. Inserted into hybrid materials, biomimetic catch bonds could lead to composites that exhibit improved mechanical properties in response to an applied force.

Computer simulations were used to investigate the mechanical properties of a network of polymer-grafted nanoparticles (PGNs) that are interlinked by labile “catch” bonds. In contrast to conventional “slip” bonds, the lifetime of catch bonds can potentially increase with the application of force (i.e., the rate of rupture can decrease). Subjecting the PGN networks to a tensile deformation (Figure 1), it was found that the networks encompassing catch bonds exhibit greater ductility and toughness than the networks interconnected by slip bonds. Moreover, when the applied tensile force is released, the catch bond networks exhibit lower hysteresis and faster relaxation of residual strain than the slip bond networks. The effects of the catch bonds on the mechanical behavior are attributed to transitions between two conformational states, which differ in their sensitivity to force. These findings provide guidelines for creating nanocomposite networks that are highly resistant to mechanical deformation and show rapid strain recovery.