Silicone elastomers
(SRs) are of great scientific and technological
importance due to their resistance to low temperatures. However, the
glass transition temperature (T
g) of existing
SRs is not low enough to satisfy its utilization in the extremely
low-temperature environment. Meanwhile, crystallization often occurs
at the low-temperature, making it difficult for SRs to maintain their
original properties in the extremely low-temperature environment.
Here, by combining molecular dynamics (MD) simulation and experiment,
a novel low-temperature resistance and crystalline-free SR (Epoxidized-Methyl-Ethyl-Vinyl
Silicone Elastomer, also referred to E-MEVQ) is fabricated by random
copolymerization of three different siloxane repeat units (dimethyl-siloxane,
diethyl-siloxane and methyl-epoxy-siloxane). We showed that the T
g of E-MEVQ computed from MD simulations using
three different methods (specific volume, nonbond potential energy
and conformational transition versus temperature) agrees well with
that of the as-synthesized E-MEVQ determined by Differential Scanning
Calorimetry. The T
g is approximately −130
°C, much lower than that of Polydimethylsiloxane (PDMS), and
the E-MEVQ is in the amorphous state without any crystallization.
This novel silicone elastomer is expected to be widely applied in
the field of smart devices, sensors, and medical equipment under extreme
situations. Our work also provides a promising framework for designing
and fabricating high-performance elastomeric polymer materials via
simulation and experiment.
The control of the self-assembly of the nanocrystals into ordered
structures has been extensively investigated, but fewer efforts have
been devoted to studying one-component polymer-grafted nanoparticles
(OPNPs). Herein, through coarse-grained molecular dynamics simulation,
we design a novel nanoparticle (NP) grafted with polymer chains, focusing
on its self-assembled structures. First, we examine the effects of
length and density of grafted polymer chains by calculating the radial
distribution function between NPs, as well as through direct visualization.
We observe a monotonic change of the arranged morphology of grafted-NPs
as a function of the density of grafted polymer chains, which indicates
that the increase of the grafting density contributes to the order
of the morphology. Meanwhile, we find that much longer grafted polymer
chains worsen the regularity of the morphology. Then, we probe the
influence of the stiffness of grafted polymer chains (denoted by K ranging from 0 to 500) on the order of grafted-NPs, finding
that the order of the structure exhibits a nonmonotonic behavior as
a function of K at moderate grafting density. For
high grafting density, the order of the morphology is initially enhanced
and becomes saturated as a function of K. For the
effect of K on the stress–strain behavior,
the system with the lowest order demonstrates the most remarkable
reinforced mechanical behavior for both low and high grafting density.
Last, we establish the phase diagram by varying the stiffness and
density of the grafted polymer chains, which contains the amorphous,
ordered, and superlattice structures, respectively. In general, our
simulated results provide guidelines to tailor the self-assembly of
the OPNPs by taking advantage of the length, density, and stiffness
of grafted polymer chains.
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