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The Transport Properties of Small Molecules: the Effects of their Shape and Environment

Antigoni Messaritaki

Antigoni Messaritaki (previous student, left the group in 2003)

An investigation on the transport properties of small organic molecules, using Pulsed Field Gradient NMR, complimented by Rheology and densitometry. The study was focused on the effect of the structural conformation and the intermolecular interactions of the molecules on their transport properties.

The effect of molecular size and molecular architecture on the diffusion coefficients of small organic molecules such as alkanes, alcohols and diols, was investigated. The self-diffusion coefficients of these molecules were found to decrease with increasing molecular weight. The effect of the molecule architecture on the transport properties of the alkanes was clearly demonstrated by studying the diffusion process of a number of alkane structural isomers. Molecules with a linear configuration diffused faster than those isomers with branched and cyclic configurations. Investigations on the transport properties of alcohols and diols revealed a significant dependence on the size of the molecules as well as on intermolecular interactions.

The mixing process of binary alkane mixtures was also studied using diffusion measurements. The measured average diffusion coefficients depend on the concentration of the mixture but the dependence is not linear. The average diffusion constants are affected by the difference in molecular size of the components. The self-diffusion coefficient of each component depends on the mixture concentration in a non-linear way.

A number of physical properties such as diffusion, viscosity and density of glycol ether/water mixtures were also investigated. The mixing process was found to be very complicated and strongly dependent on a number of parameters such as molecular size, concentration and intermolecular interactions.

This project is funded by the University of Bristol and BP.