In Pfg-nmr Self-diffusion Coefficient Of The Application

Two of interest issues were investigated by employing pulsed field gradient NMR (PFG-NMR) technique. One was related to the weak interaction between a-cyclodextrin and fatty acids, and the other was concerned with the poly(ethylene oxide) (PEO) coil tangling under extremely dilute solution. The main results include:1. PFG-NMR techniques were used to study the interaction between a-cyclodextrin and three kinds of fatty acids under critical sedimentation concentration. With increasing of the a-oyclodextrin content, the diffusion coefficients (Z)s) of the fatty acids were found to decrease continuously; Ds for the longer alkyl chains fatty acids tended to decrease more quickly. The measured diffusion coefficient data were used to calculate the equilibrium constants of the complex. It was concluded that fatty acids keep a 1:1 ratio with the a-cyclodextrin in the complex and the hydrophobic interaction is predominant among various interactions between a-cyclodextrin and fatty acids. 2D ROESY ( Rotating Frame Overhauser Effect Spectroscopy ) experiment also supported the above conclusion.2. A series of low molecule weight PEOs were studied by PFG-NMR in extremely dilute region. It was found that the diffusion coefficients of PEO decreased with increasing concentration above a certain concentration and that kept constant below the certain one. The critical concentration was so-called dynamic contact concentration (Cs) put forward by Qian. The experiment results indicated the polymer coil dispersed in solution with single chain model below Cs and colliding probability with each other is nearly zero. The influence of molecule weight and end group was also studied. Cs decreased with increasing molecule weight and didn't relate to end methyl group.