Molecular dynamics of n-dodecylammonium chloride in aqueous solutions investigated by 2{sup left}H NMR and 1{sup left}H NMR relaxometry

摘要

Molecular dynamics in n-dodecylammonium chloride/water solutions for concentrations of 34 and 45 wt% was studied by 2{sup left}H NMR and by 1{sup left}H NMR dispersion of spin-lattice relaxation in the 2kHz-90 MHz frequency range. The system exhibits a number of lyotropic liquid crystalline phases, which differ in symmetry and involve motions characterized by a wide frequency scale. The analysis of 2{sup left}H NMR lineshapes of selectively deuterated DDAC1 molecules gave us an evidence for local trans-gauche conformational changes in the chains, whereas the dispersion of spin-lattice relaxation times T{sub}1 explored by fast field cycling method revealed fast local motions, translational diffusion and collective molecular dynamics of the chains. In particular, we have found that the order director fluctuation mechanism in smectic and nematic phases dominates spin-lattice relaxation below 1 MHz and that local motions and translational diffusion are responsible for the spin-lattice relaxation in the higher Larmor frequency range.