Synthesis and Aggregation Behavior of Trisiloxane Ionic Liquids in Aqueous Solution

Trisiloxane ionic liquids with polyether groups (Si₃pyCl-EO₃) were synthesized via thiol-ene reaction between 1-methyl-1-[bis(vinyldimethylsiloxy)methyl]silylpropylpyrrolidinium chloride (Vi-Si₃pyCl) and tri(ethylene glycol) methyl ether thiol. The aggregation behavior of the trisiloxane ionic liquids, Si₃pyCl-EO₃ and Vi-Si₃pyCl, in aqueous solution was investigated using surface tension, electrical conductivity, dynamic light scattering, and transmission electron microscopy. The structures of trisiloxane ionic liquids can obviously influence their aggregation behavior. Vi-Si₃pyCl has excellent surface activity (22.3 mN m⁻¹). However, Si₃pyCl-EO₃ can only reduce the surface tension of water to 33.5 mN m⁻¹. In comparison with Vi-Si₃PyCl, Si₃PyCl-EO₃ has a bulkier hydrophobic group and a higher Α_min value (127.8 Ų) caused by the introduction of the tri(ethylene glycol) methyl ether groups by thiol-ene reaction. The micellization of Vi-Si₃PyCl is entropy driven, while the aggregation process of Si₃PyCl-EO₃ in aqueous solution is enthalpy driven.