4 research outputs found
Self-Assembled Morphologies of Polystyrene-<i>block</i>-poly(ethylene oxide)/1-Ethyl-3-methylimidazolium Thiocyanate Membranes by Mesoscopic Dynamics Simulation
The stability of gas separation membranes cast from diblock
copolymer/ionic
liquid (IL) blends depends on the resulting self-assembled morphologies
of the cast films. Therefore, controlling the copolymer/IL morphology
by tuning parameters such as IL loading and copolymer block size ratio
is essential to prevent the membrane from leaching out the IL at high
transmembrane pressures. In the present study, we used the dynamic
mean-field density functional method to investigate the self-assembly
of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers in 1-ethyl-3-methylimidazolium thiocyanate
([EMIM][SCN]) at different PS:PEO block size ratios and IL loadings
(10–90 vol %) at room temperature (298 K). The IL was observed
to be either confined by the hydrophilic PEO phase (designated as
IL-PEO) due to strong IL-PEO interactions or yield a separate partially
or fully encapsulated microphase (IL-Micro). The copolymer morphologies
observed herein were lamellar (L), cylindrical (C), body-centered
cubic (BCC), and spherical micelle (S). The dominant copolymer/IL
morphology on the ternary phase diagram was L/IL-PEO, which formed
at medium loadings of the three components (40 vol % < PS <
80 vol %, PEO < 90 vol %, and IL < 50 vol %). The IL-Micro morphologies
appeared as transition phases to the IL-PEO phases, typically at low
IL loadings and PS:PEO block size ratios. We also investigated the
morphology evolution of select copolymer/IL compositions. Overall,
the G, L, and C copolymer morphologies were observed at low to medium
IL loadings, while the BCC and S copolymer morphologies appeared at
higher IL loadings. The potential applications of these self-assembled
morphologies could be further explored by investigating the role of
electrostatic interactions and varying the types and loadings of ILs,
as well as the type of the diblock copolymers, to discover new membrane
systems with unique properties for gas separations
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Applying molecular dynamics simulation to take the fracture fingerprint of polycrystalline SiC nanosheets
Graphene-like nanosheets are the key elements of advanced materials and systems. The mechanical behavior of the structurally perfect 2D nanostructures is well documented, but that of polycrystalline ones is less understood. Herein, we applied molecular dynamics simulation (MDS) to take the fracture fingerprint of polycrystalline SiC nanosheets (PSiCNS), where monocrystalline SiC nanosheets (MSiCNS) was the reference nanosheet. The mechanical responses of defect-free and defective MSiCNS and PSiCNS having regular cracks and circular-shaped notches were captured as a function of temperature (100–1200 K), such that elevated temperatures were unconditionally deteriorative to the properties. Moreover, larger cracks and notches more severely decreased the strength of PSiCNS, e.g. Young's modulus dropped to ca. 41% by the crack enlargement. The temperature rise similarly deteriorated the failure stress and Young's modulus of PSiCNS. However, the stress intensity factor increased by the enlargement of the crack length but decreased against temperature. We believe that the findings of the present study can shed some light on designing mechanically stable nanostructures for on-demand working conditions. © 2021 Elsevier B.V.24 month embargo; available online 19 August 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]