Quasielastic neutron scattering study of water in agarose gels
Trantham, Eugene Clark
Rorschach, Harold E.
Master of Arts
The differential cross section for the scattering of thermal neutrons from a solid or liquid contains information about the thermal motion of the nuclei. Measurement of the line shape in liquids for small energy transfer can be interpreted in terms of the mechanism of the diffusive motion and is refered to as the Quasielastic Neutron Scattering (QNS) technique. QNS has been used in this investigation to study the effect of macromolecules on the physical properties of water. A pilot study on the aqueous agarose gel system which made use of a triple axis spectrometer at the Oak Ridge National Laboratory has been completed. Studies have been conducted on the scattering intensity vs. energy transfer as a function of gel concentration and momentum transfer. The concentration dependence was studied by preparing gels of 4%, 9%, 15%, and 2% agarose by weight in H2O. The momentum transfer was studied for values of the scattered wave vector in the range .7A^-1 to 1.9A^-1. The contribution of the agarose to the scattering was determined by measuring the quasielastic spectrum of a 2% agarose in D2O gel. This allowed the scattering contribution of the water to be separated from that of the agarose. These data were analysed using the "bound-free" model for the distribution of correlation times in water. In this model, one fraction is assumed to be identical to pure water and the remaining fraction is assumed to be tightly bound to the agarose macromolecules. This analysis gave an estimate for the "bound" fraction in the 2% HgO gel of 21% +/- 4%. This result is in good agreement with previous nuclear magnetic resonance studies of the diffusion coefficient in agarose gels.