Humidity-Induced Self-Assembled Nanostructures via Ion Aggregation in Ionic Linear Polysiloxanes

Polysiloxanes exhibit practical properties not observed in carbon or carbon-oxygen backbone polymers. Linear ionic polysiloxanes containing an amine hydrochloric salt exhibit a humidity-induced self-assembly (HiSA) behavior. HiSA leads to nanoscale structuring by the uptake of absorbed water around the ionic aggregates of the polymer, promoting the hydrophilic-hydrophobic phase separation of the polymer. The resulting polymer forms a self-assembled lamellar nanostructure with a period of ca. 1.6 nm. Herein, we investigate the factors affecting the HiSA behavior. Introducing a dimethylsiloxane unit into the ionic polysiloxane achieves a more ordered lamellar structure and improves the nanostructure stability at higher humidities. The flexibility of the polysiloxane backbone, formation of ionic aggregates, and hydrophilic-hydrophobic phase separation affect the HiSA behavior. This nanoscale assembly can be characterized as a lyotropic liquid crystal formed with the assistance of ion aggregation instead of the hydrophobic effect in aqueous systems of ordinary surfactants.

Automated summary

Polysiloxanes exhibit unique properties and can self-assemble into nanoscale structures in the presence of humidity-induced self-assembly (HiSA) behavior. The flexibility of the polysiloxane backbone, formation of ion aggregates, and hydrophilic-hydrophobic phase separation play important roles in the HiSA behavior.