Dynamics and Disorder in Surfactant-Templated Silicate Layers Studied by Solid-State NMR Dephasing Times and Correlated Line Shapes

Surfactant-templated layered silicates are shown to possess complex compositional, structural, and dynamic features that manifest rich and interrelated order and disorder at molecular length scales. Temperature-dependent 1D and 2D solid-state 29 Si NMR measurements reveal a chemical-exchange process involving the surfactant headgroups that is concomitant with reversible broadening of 29 Si NMR line shapes under magic-angle-spinning (MAS) conditions at temperatures in the range 205−330 K. Specifically, the temperature-dependent changes in the 29 Si transverse dephasing times T 2 ′ can be quantitatively accounted for by 2-fold reorientational dynamics of the surfactant headgroups. Variable-temperature analyses demonstrate that the temperature-dependent 29 Si shifts, peak broadening, and 2D 29 Si{ 29 Si} correlation NMR line shapes are directly related to the freezing of the surfactant headgroup dynamics, which results in local structural disorder within the silicate framework.