Conformational Behavior of Dodecyldiamine inside the Confined Space of Montmorillonites

We have investigated the change of the intercalated amount and conformational behavior of dodecyldiamine (C12H28N2, di-C12amine) inside the confined space of the montmorillonite (MMT) intergallery at different pHs of the intercalation solution (H2O/ethanol/Na+-MMT/di-C12amine), and these results were compared with those of dodecylmonoamine (C12H27N, mono-C12amine). The mono-C12amine with one end-functional amine (−NH2) has a constant intercalated amount independent of the pH of the intercalation solution, confirming the tail conformation in the MMT intergallery. On the other hand, the intercalated amount of di-C12amines remains quite low at low pH due to the long-range Coulombic repulsion among protonated amines. The di-C12amines dominantly take the bridge conformation inside the MMT intergallery up to pH 9.5 and adopt a fraction of the tail conformation at pH 11.5, which is verified by Fourier transform infrared spectra with an abrupt frequency shift of the CH2 stretching band and the emergence of a new NH2 scissoring band at 1598 cm-1 related to unanchored free amines. The d-spacing and the square of the half-width at half-maximum of the MMT based on X-ray diffraction measurements are also constant up to pH 9.5, while these two variables are suddenly increased at pH 11.5. The bridge conformation of di-C12amines in the confined space of the MMT intergallery prevents poly(ethylene oxide) chains from intercalation into the MMT intergallery, called the gluing effect.This work was financially supported by the National Research Laboratory Program (Grant M1-0104-00-0191) and funded in part by the Ministry of Education through the Brain Korea 21 Programs at Seoul National University. The X-ray experiments performed at Pohang Light Source were supported by the Ministry of Science and Technology of Korea (MOST) and POSCO