¹⁴N: A Sensitive NMR Probe for the Study of Surfactant–Oxide Interfaces

We explored the sensitivity of the ¹⁴N quadrupolar interaction toward the characterization of surfactant–oxide interfaces. For the first time, experimental ¹⁴N NMR spectra are recorded, modeled, and compared for three different mesostructured silica (hexagonal p6mm, cubic Ia3d, and lamellar) templated by hexadecyltrimethylammonium cations (CTA⁺). Broad distributions in quadrupolar coupling constant C_Q are obtained showing differences between phases. In parallel, quantum chemical calculations using the Born–Oppenheimer molecular dynamics in combination with DFT have been successfully undertaken in a time scale of 25–32 ps to better understand the experimental results. From the two simulated models (CTA⁺ alone vs CTA⁺ in interaction with a D4R^– silicate oligomer), we evidenced the relative effect of fast conformational variations and of intermolecular interactions on the time-averaged ¹⁴N quadrupolar parameters. ¹⁴N relaxation and ¹³C CSA NMR data are also briefly presented and discussed. Our approach opens new directions for studying a wide range of mesostructured materials.