Fully hydrated hybrid membranes based on a polyelectrolyte mixed with an ionic liquid possess gas permeation properties of significant interest for CO2 capture applications.
Block copolymers have been extensively studied due to their ability to spontaneously self-organize into a wide variety of morphologies that are valuable in energy-, medical-, and conservation-related (nano)technologies. While the phase behavior of bicomponent diblock and triblock copolymers is conventionally governed by temperature and individual block masses, it is demonstrated here that their phase behavior can alternatively be controlled through the use of blocks with random monomer sequencing. Block random copolymers (BRCs), i.e., diblock copolymers wherein one or both blocks are a random copolymer comprised of A and B repeat units, have been synthesized, and their phase behavior, expressed in terms of the order-disorder transition (ODT), has been investigated. The results establish that, depending on the block composition contrast and molecular weight, BRCs can microphase-separate. We also report that large variation in incompatibility can be generated at relatively constant molecular weight and temperature with these new soft materials. This sequence-controlled synthetic strategy is extended to thermoplastic elastomeric triblock copolymers differing in chemistry and possessing a random-copolymer midblock.
Strong physical gels derived from
thermoplastic elastomeric ABA
triblock copolymers solvated with a midblock-selective oil continue
to find use in increasingly diverse applications requiring highly
elastic and mechanically robust soft materials with tunable properties.
In this study, we first investigate the morphological characteristics
of thermoplastic elastomer gels (TPEGs) derived from a homologous
series of linear A(BA)
n
multiblock copolymers
composed of styrene and hydrogenated isoprene repeat units and possessing
comparable molecular weight but varying in the number of B-blocks:
1 (triblock), 2 (pentablock), and 3 (heptablock). Small-angle X-ray
scattering performed at ambient temperature confirms that (i) increasing
hydrogenation reduces the microdomain periodicity of the neat copolymers
and (ii) increasing the oil concentration of the TPEGs tends to swell
the nanostructure (increasing the periodicity), but concurrently decreases
the size of the styrenic micelles, to different extents depending
on the molecular architecture. Complementary dissipative particle
dynamics simulations reveal the level to which midblock bridging,
which is primarily responsible for the elasticity in this class of
materials, is influenced by both oil concentration and molecular architecture.
Since constrained topological complexity increases with increasing
block number, we introduce a midblock conformation index that facilitates
systematic classification of the different topologies involved in
nearest-micelle bridge formation. Those possessing at least one bridged
and one looped midblock with no dangling ends are found to be the
most predominant topologies in the pentablock and heptablock networks.
Conventional insect repellent treatments for fibers, fabrics, and garments suffer from limited durability to repeated laundering and, depending on the insecticide, potential irritation, or toxicity. In this work, electrospinning was employed to control the composition of hierarchically structured functional microscale to nanoscale fibers for tunable insect repellent release by physically incorporating picaridin into nylon-6,6 nanofibers. The size and morphology of nylon fibers were unaffected by picaridin incorporation, even at loading concentrations up to 50 wt%. Picaridin release kinetics were largely dependent on loading concentration and temperature, as picaridin-nylon intermolecular interactions were minimal affording diffusion based release. Coaxial nanofibers, in which the sheath component has potential to protect additives in the core for more durable fabrics and act as a diffusion barrier for extended release applications, were also developed and demonstrated altered release kinetics compared to monofilament analogues, indicating the capability to further tune release behavior.
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