Biological materials exhibit hierarchical structuring involving sacrificial bonds, which allows them to be adapted and optimized when under deformation through a mechanism that involves the scattering of molecular-scale energy to produce extraordinary performance. This has inspired the development of strategies meant for strengthening and toughening polymeric materials such as the incorporating of high-functionality cross-linkers into polymeric networks to achieve hydrogels of high extensibility and strengths.
The incorporation of multiple mechanisms of energy dissipation into polymer matrices is believed to be a promising method towards polymers of high performance. This overcomes the limitations of hydrogel systems in materials with high-functionality cross-linkers which only have a single energy dissipation mechanism.
The production of rubber has incorporated various nanofillers to improve on the mechanical performance of the rubber matrix. However, this has been limited by difficulties in processing, increased filler loading, and complex regulation of the interface. To overcome this, a sacrificial bond strategy has been previously implemented in order to achieve diene-rubbers of high performance, but even then, it only involved one mechanism of energy dissipation.
South China University of Technology researchers led by Professor Baochun Guo incorporated amine-passivated carbon nanodots in the biomimetic design of robust diene-rubber as high functionality cross-linkers to produce several sacrificial units that have multiple mechanisms of energy dissipation. Their wok is now published in Macromolecules.
From the assessment of the structure of the synthesized carbon nanodots, the authors observed that they display a quasi-spherical geometry as well as successive lattice fringes. Further analysis proved that primary amide and amine functional groups exist on the synthesized carbon nanodot surface. Investigation on the swelling behavior of the carbon nanodots in the grafted polyisoprene rubber compound in the presence of toluene, verified the existence of cross-linked covalent network. With this regard, the carbon nanodots can be said to be chemical and physical high-functionality cross-linkers which allows multiple sacrificial units to be introduced into the grafted polyisoprene skeleton. It was seen that the grafted polyisoprene samples containing carbon nanodots showed increased stress relation rate as compared with those without.
From the rheological measurements, it was evident that carbon nanodots have a profound effect on the storage and loss modulus. The carbon nanodots were able to integrate toughness, intact stretchabilty, and strength in rubbers and at a lower filler content as compared with other fillers. The study also deduced that the mechanical performance of the grafted polyisoprene carbon nanodot composites could be facilely tuned by regulating the sulphur content and carbon nanodot content. This creative method is contrary to traditional technologies to achieve rubber reinforcement, such as highly filling or simply including sacrificial bonds. Most impressively, the work provides a fundamental understanding of the coupling effects between different mechanisms in toughening rubber, and thus rational guidance for the design of advanced elastomers.
Siwu Wu, Min Qiu, Zhenghai Tang, Jie Liu, and Baochun Guo. Carbon Nanodots as High-Functionality Cross-Linkers for Bioinspired Engineering of Multiple Sacrificial Units toward Strong Yet Tough Elastomers. Macromolecules 2017, 50, 3244-3253.Go To MacroMolecules