Molecular dynamics of n-dodecylammonium chloride studied by nuclear magnetic resonance

The relation between molecular dynamics and phase properties of the bilayer ed compound C12H25NH3Cl is studied by differential scanning calorimetry, pr oton second moment, and spin-lattice relaxation Limes. In the low-temperatu re Phase I of the compound methyl and ammonium groups execute a classical t hreefold reorientation, while the alkylammonium chains are rigid on the nuc lear magnetic resonance time scale. In the intermediate-temperature phase d elta a trans-gauche isomerization of the alkyl chains is observed. In the h igh-temperature phase alpha the reorientation of the whole chains about the ir long axes, which are parallel to the normal to the ionic layer is eviden ced. In the meta-stable epsilon phase the dynamics involves classical rotat ion of methyl and ammonium groups and CH2 groups motion of the trans-gauche isomerization type.