posted on 2016-07-27, 00:00authored byZenghui Yang, Qihua Wang, Tingmei Wang
Conventional
thermoset shape memory polymers can maintain a stable permanent shape,
but the intrinsically chemical cross-linking leads to shape that cannot
be altered. In this paper, we prepared shape memory graphene-vitrimer
composites whose shape can be randomly changed via dynamic covalent
transesterification reaction. Consecutive shape memory cycles indicate
stable shape memory with undetected strain shift and constant shape
fixity and recovery values (Rf > 99%, Rr > 98%). Quantitative characterization of
shape reconfiguration by dynamic mechanical thermal analysis (DMA)
shows prime reconfigurable behavior with shape retention ratio of
100%. Thus, the arbitrary 2D or 3D newly permanent shape can be easily
obtained from a simple plain sample by facile thermal treatment at
200 °C above transesterification temperature (Tv). Besides, it is found that graphene-vitrimers show
a ductile fracture in tensile test with a large breaking strain and
classical yield phenomenon because of the well-dispersed graphene
sheets in the vitrimer that endow effective stress transfer. As the
graphene loading increases from 0% to 1%, the yield strength and breaking
stain increase from 12.0 MPa and 6% to 22.9 MPa and 44%, respectively.
In addition, graphene also serves as energy convertor to convert near-infrared
(NIR) irradiation into thermal energy to induce a helix shape sample
that is recovered totally within 80 s sequent NIR irradiation. These
dual-triggered and reconfigurable shape memory graphene-vitrimers
are expected to significantly simplify processing of complex shape
and broaden the applications of shape memory polymers.