De Novo Ion-Exchange Membranes Based on Nanofibers

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de novo ion-exchangers. In particular, the combination of large surface areas and ionizable groups in the IEX-NFs improves their performance through indices such as extremely rapid ion-exchange kinetics and high ion-exchange capacities. In reality, the membranes based on ion-exchange NFs exhibit superior properties such as high catalytic efficiency, high ion-exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of IEX-NFs (i.e., their unique size-dependent properties), scalable production methods, and the recent advancements in their applications in catalysis, separation/adsorption processes, and fuel cells, as well as the future perspectives and endeavors of NF-based IEMs.

Stretching Wormlike Chains in Narrow Tubes of Arbitrary Cross-Sections

We considered the stretching of semiflexible polymer chains confined in narrow tubes with arbitrary cross-sections. Based on the wormlike chain model and technique of normal mode decomposition in statistical physics, we derived a compact analytical expression on the force-confinement-extension relation of the chains. This single formula was generalized to be valid for tube confinements with arbitrary cross-sections. In addition, we extended the generalized bead-rod model for Brownian dynamics simulations of confined polymer chains subjected to force stretching, so that the confinement effects to the chains applied by the tubes with arbitrary cross-sections can be quantitatively taken into account through numerical simulations. Extensive simulation examples on the wormlike chains confined in tubes of various shapes quantitatively justified the theoretically derived generalized formula on the force-confinement-extension relation of the chains.

Diffusive dynamics of polymer chains in an array of nanoposts

The diffusion of the head, side, and middle segments in confined polymer chains displays different dynamics in different directions.

Diffusion of Confined Polymer Chains

Simple lattice model of polymer systems was developed and studied using the Monte Carlo method. The model chains were star-branched with f = 3 arms and rings. The number of polymer segments in a chain was varied up to 800. The chains were built on a simple cubic lattice with the excluded volume interactions only (the athermal system). The polymers were confined between two parallel impenetrable walls with a set of irregular obstacles what can be treated as porous media. A Metropolis-like sampling algorithm employing local changes of chain conformation was used. The dynamic properties of the model system were studied. The differences in the mobility of chains with different internal architectures were shown and discussed. The possible mechanisms of motions were presented.