Neutron Diffraction Studies of Structure in Aqueous Solutions of Urea and Tetramethylammonium Chloride and in Methanol

Abstract

Abstract Neutron diffraction measurements on aqueous 2-14 molal urea solutions have been made using nitrogen isotope substitution on the urea and hydrogen isotope substitution on the water. In addition, the hydration region of the tetramethylammonium ion in 2.0 m urea solution has been investigated by nitrogen isotope substitution on the TMA at 0.5 m and 2.0 m concentration of TMAC1. The N-water correlation functions are very similar across the concentration range, and the H-H correlation function in concentrated urea solution is little changed from that of pure water. In the TM AC1 solutions the hydration peak is unchanged by the addition of 2.0 m urea. Thus urea appears to fit into the water network without causing significant perturbation of the average water structure or of the hydration region of another solute. In addition to the study of urea we have also made preliminary measurements to test the feasibility of carbon isotope substitution in liquid methanol.