Self-assembly and diffusion of block copolymer templates in SBA-15 nanochannels

Molecular dynamics of triblock copolymers under confinement by the nanochannels of SBA-15 was investigated using pulsed field gradient (PFG) NMR spectroscopy with high-intensity field gradient pulses. The mesoporous material SBA-15 was synthesized using the surfactant Pluronic P123 (EO(20)-PO(70)-EO(20)). The diffusion of P123 in mixtures with water was studied both in bulk and under the condition of confinement by the mesoporous channels of SBA-15. As a result, at room temperature the diffusion of P123 in SBA-15 is more than a factor three smaller than that of the same polymer in the bulk mixture with water. A pronounced atypical temperature dependence of the measured diffusivities was observed both in the confined and in the bulk systems. This atypical temperature dependence was attributed to the transition from the aggregated state to the molecular solution and gave an evidence for a qualitative similarity of the supermolecular organization of the Pluronic/water mixtures under confinements and in the bulk. Confinements were shown to produce significant effects on diffusion properties of Pluronic molecules. The diffusivity of self-associates forming up at room temperature was considerably diminished in comparison to the bulk systems. In contrast, at low temperatures diffusion of the individually dissolved molecules was comparably fast, but subjected to anisotropy induced by channels.