Elastomers inevitably suffer scratches and damage during
the application;
thus, the design and fabrication of self-healing elastomers with covalent
adaptive networks is a meaningful strategy to extend the service life
of materials. In this study, a facile two-step approach was proposed
to synthesize self-healing elastomers based on the dynamic oxime–carbamate
bonds. Hydroxyl-terminated polybutadiene was first reacted with isophorone
diisocyanate to synthesize the prepolymer with isocyanate groups terminated,
followed by further reaction with dimethylglyoxime as a chain extender
to obtain self-healing elastomers. Specially, all-atom molecular dynamics
simulations were used to construct the same model as the experiments.
Together with the experimental characterization of FTIR and 1H NMR, all-atom molecular dynamics simulations can further verify
the formation of hydrogen bonds and dynamic oxime–carbamate
bonds. By fixing the ratio of hydroxyl to isocyanate constant, we
found that the mechanical strength increased with the increase of
hard segment content. At the same time, the loss factor decreased
in the glass transition region and at room temperature. Finally, the
self-healing behavior of the elastomer was verified at a certain temperature.
The corresponding mechanism is explained by means of molecular dynamics
simulations, where dynamic oxime–carbamate bonds play more
important roles than hydrogen bonds. The combined simulation and experimental
studies provided a reasonable approach for the subsequent self-healing
system.
The dispersion and diffusion mechanism of nanofillers
in polymer
nanocomposites (PNCs) are crucial for understanding the properties
of PNCs, which is of great significance for the design of novel materials.
Herein, we investigate the dispersion and diffusion behavior of two
geometries of nanofillers, namely, spherical nanoparticles (SNPs)
and nanorods (NRs), in bottlebrush polymers by utilizing coarse-grained
molecular dynamics simulations. With the increase of the interaction
strength between the nanofiller and polymer (εnp),
both the SNPs and NRs experience a typical “aggregated phase–dispersed
phase–bridged phase” state transition in the bottlebrush
polymer matrix. We evaluate the validity of the Stokes–Einstein
(SE) equation for predicting the diffusion coefficient of nanofillers
in bottlebrush polymers. The results demonstrate that the SE predictions
are slightly larger than the simulated values for small SNP sizes
because the local viscosity that is felt by small SNPs in the densely
grafted bottlebrush polymer does not differ much from the macroscopic
viscosity. The relative size of the length of the NRs (L) and the radius of gyration (R
g) of
the bottlebrush polymer play a key role in the diffusion of NRs. In
addition, we characterize the anisotropic diffusion of NRs to analyze
their translational and rotational diffusion. The motion of NRs in
the direction perpendicular to the end-to-end vector is more hindered,
indicating that there is a strong coupling between the rotation of
NRs and the motion of the polymer. The NR motion shows stronger anisotropic
diffusion at short time scales because of the steric effects generated
by side chains of the bottlebrush polymer. In general, our results
provide a fundamental understanding of the dispersion of nanofillers
and the microscopic mechanism of nanofiller diffusion in bottlebrush
polymers.
Bio-based polyester elastomers have been widely concerned by researchers in recent years because of their wide sources of monomers and environmentally friendly characteristics. However, compared with traditional petroleum-based elastomers, the...
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