Coarse-grained molecular dynamics simulations using explicit solvent models were performed to understand Nafion ionomer morphology in 1-propanol (NPA)/water solutions under various conditions (ionomer concentration, NPA/water fraction, and salt addition). The self-assembly behavior of ionomers into a cylindrical aggregate with a diameter of ∼2−3 nm was observed. At low ionomer concentration (≤5.0 wt %), the ionomer aggregate becomes smaller in size and thinner with increasing NPA fractions. At high ionomer concentration (7.5 wt %), the size of aggregates in a longitudinal direction increases significantly at high NPA fractions, suggesting that excess addition of NPA does not necessarily contribute to the dispersivity of ionomers, particularly at high ionomer concentration. These nonmonotonic behaviors of ionomer aggregation are controlled by the electrostatic repulsion among the sulfonate groups, which is determined by the balance among the dielectric constants of solvents, the distribution of hydronium ions, and the surface density of sulfonate groups. Upon the addition of salts, the size of aggregates increases significantly, and the formation of a larger disk-shaped aggregate and a secondary aggregate of multiple bundles for low and high NPA contents, respectively, was found.

The self-assembly of Nafion ionomer in a mixture of 1-propanol (NPA) and water was investigated using coarsegrained molecular dynamics simulations. Ionomer formation into cylindrical bundle-like aggregates is observed when the ionomer chain size is sufficiently large. The size of ionomer bundles decreases (the diameter decreased from~2.5 to~1.9 nm) with increasing NPA content, which indicates that the ionomers tend to be more dispersed at higher NPA content. The results of simulations are in good quantitative agreement with the stable size of an ionomer bundle estimated from our free energy calculations as well as the available experimental data. Furthermore, in contrast to the polarizable NPA model, the standard nonpolarizable NPA model shows the opposite trend that the ionomer size increases with increasing NPA content because of a higher localization of hydronium ions at the bundle surface, revealing that the polarization effect plays a significant role in determining the aggregation behaviors. The present study provides insight into the control of ionomer self-assembly toward obtaining targeted structures for specific purposes.

Coarse-grained molecular dynamics simulations were performed to understand the evolution of ionomer morphologies in solutions during solvent evaporation. To reproduce experimental fabrication conditions, the simulation conditions, such as evaporation and sedimentation rate, were determined based on a dimensionless parameter, the Péclet number, providing a direct link between simulation results and experimental findings. The effects of ionomer loading and substrate wettability on the morphologies of ionomer thin films after drying were investigated extensively, which exhibit similar trends reported in experiments. At low ionomer loading, a discontinuous patchy film with a minimum thickness of ≈3 nm was formed on the hydrophobic substrate, whereas a high-coverage continuous film of ≈2 nm thickness was found on the hydrophilic substrate. At high ionomer loading, regardless of the substrate wettability, a lamellar-like morphology with multiple water-rich layers was observed, although the stability of the layer structures and the ionomer surface roughness differ between the substrate types because the substrate wettability strongly affects the adsorption behaviors of ionomers and water as the first layer in the interfacial region. Our findings of a decrease in the degree of phase segregation with increasing thickness suggest an eventual collapse of the lamellar structure at a certain thickness within a few tens of nanometers or even thinner.

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An ideal carrier that delivers small interfering RNA (siRNA) should be designed based on two criteria: high gene transfection efficiency and low cytotoxicity. In this work, arginine was used to modify polyvinylamine (PVAm) to form a novel PVAm derivative (PVAm‐Arg) for siRNA delivery and the derivative was characterized using Fourier transform infrared spectroscopy. PVAm‐Arg/siRNA complexes were formed by the self‐assembly method. The zeta potential and size of the complexes were measured using electrophoretic light scattering and dynamic light scattering, respectively. The siRNA binding capacity of PVAm‐Arg was assessed using gel retardation assay. The results showed that PVAm‐Arg derivatives can bind siRNA effectively and form complexes with sizes of about 72 ± 2 nm. What is more, the ability of PVAm‐Arg to condense siRNA was better than that of PVAm. Cytotoxicity assay with RSC96 cells also showed that PVAm‐Arg had lower cytotoxicity compared with PVAm. In in vitro cellular uptake assay, PVAm‐Arg showed good transfection efficiency. Therefore, we concluded that PVAm‐Arg would be a promising candidate as a gene delivery vector. © 2022 Society of Industrial Chemistry.