Monitoring solvent dynamics and ion associations in the formation of cubic octamer polyanion in tetramethylammonium silicate solutions

NMR methods were utilized to monitor the in situ structural and dynamic changes of various species in highly alkaline tetramethylammonium (TMA) silicate solutions. Quantitative 29 Si NMR, 1 H, 2 H, and 17 O relaxation NMR, and 1 H and 29 Si diffusion NMR of silicates, TMA, H 2 O and D 2 O demonstrate that the growth of the cubic octamer Q 3 8 is accompanied by reduced water mobility and increasing TMA coordination number per Q 3 8 , which reaches an equilibrium value of 4.5 at 15 °C. Temperature-dependent measurements further reveal that the increased control over speciation by TMA at lower temperatures results from the more stable ion associations via slower solvent motions. Solvent dynamics and ion associations were monitored during the formation of cubic octamer polysilicate using multiple NMR methods.