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 Si-29 NMR measurements reveal a chemical-exchange process involving the surfactant headgroups that is concomitant with reversible broadening of Si-29 NMR line shapes under magic-angle-spinning (MAS) conditions at temperatures in the range 205-330 K. Specifically, the temperature-dependent changes in the Si-29 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 Si-29 shifts, peak broadening, and 2D Si-29{Si-29} 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.