Molecular speciation and mesoscale clustering in formaldehyde-methanol-water solutions in the presence of sodium...

Nanoporous organic gels can be synthesized from aqueous solutions of formaldehyde and resorcinol in the presence of basic electrolytes such as sodium carbonate. It is well known that formaldehyde is present in the form of methylene glycols or methoxy-glycols in aqueous and methanolic solutions, but influence of pH or electrolytes on speciation in these solutions has not been previously studied. Here we investigated effects of sodium carbonate on the speciation and colloidal scale clustering in formaldehyde-methanol-water solutions in the absence of resorcinol. We used (13)C NMR spectroscopy to quantitatively characterize molecular speciation in solutions and to estimate corresponding equilibrium constants for glycol dimerization and methoxylation. We found that species distribution is essentially independent of carbonate concentration for pH values between 3.4 (no carbonate) and 10.6. This was also consistent with ATR IR measurements of the same solutions. However, NMR spin-spin relaxation time measurements showed an unexpected behavior for glycols and especially for diglycol (but not for methanol), with relaxation times strongly decreasing with increasing carbonate concentration, indicating differences in local molecular environment of glycols. We further used dynamic light scattering to confirm the presence of mesoscale clustering in formaldehyde-methanol-water (for both H2O and D2O) solutions in the presence of sodium carbonate. We propose that the observed phenomena are due to glycol-rich cluster mesospecies in equilibrium bulk solution, together forming a thermodynamically stable mesostructured liquid phase.