Knotted synthetic polymer or carbon nanotube microfibres with enhanced toughness, up to 1400 J/g

In the past 50 years, a number of synthetic polymer microfibres, such as para-aramid or ultra-highmolecular- weight polyethylene, have been developed, exhibiting remarkable strength. However, their toughness is considerably smaller than that of some natural fibres such as spider silk, thus limiting their performance in applications ranging from surgical devices to vehicle parts. Here, we implement a recently proposed strategy, using micro-knots as frictional energy dissipators, to achieve record toughness values of up to 1400 J/g in synthetic microfibres, while maintaining their strength virtually unchanged. The same strategy is also applied to carbon nanotube microfibres, exploiting their superior ideal mechanical strength compared to any other existing fibre at the nanoscale, and toughness improvements of more than an order of magnitude are observed.We also show how knotted nanotube fibre configurations can be optimized for maximum toughness by modifying fibre diameter and twist angle, and how frictional and wear levels can be tuned by varying tightening and number of coils in the microknots. The results demonstrate the potential to design and produce fibres and textiles with unprecedented simultaneous strength and toughness for a variety of technological applications.