发布日期:2021/2/2 15:57:15
Two-dimensional (2D) covalent organic frameworks (COFs) are
promising polymeric crystalline nanomaterials with broad applica
tions. However, the understanding of their mechanical properties
and fracture mechanisms remains elusive. Here, we report a quanti
tative in situ tensile study of ultrathin COFTAPB-DHTA fifilms. The frac
ture strength was measured to be 0.75 G 0.34 GPa, and the tensile
modulus was measured to be 10.38 G 3.42 GPa, with a nominal den
sity of 0.393 g/cc, thus having specifific strength equivalent to Kevlar
(2 GPa$cc/g), and specifific modulus comparable with titanium alloys
(23 GPa$cc/g). In addition, the fracture toughness was measured to
be 0.55 G 0.09 MPaOm, and it was found that the crack propagation
could be insensitive to the pre-crack when the size of pre-crack is
below a critical value, leading to intriguing flflaw insensitivity in
such ultrathin nanomaterials. This work provides in-depth insights
into the fracture properties of 2D COF fifilms and lays a foundation
for their future applications.

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