Structure and Dynamics of Magnetic Nanoparticle Assemblies

Deep Inelastic Neutron Scattering (DINS) from Hydrogen (or other light nuclei) can be used to measure momentum distributions. The availability of sources of high energy neutrons and improvements in data fitting methods[1,2] enable us to measure the anharmonic details of the momentum distribution, and in some cases, the Born-Oppenheimer potential of the particle. Quasi-one-dimensional water encapsulated inside single-walled open-ended carbon nanotubes SWNT, here referred to as nanotube-water, was studied by neutron scattering at different temperatures. [3] The system is regarded as a model system for the study of the transport of water in biological pores. The earlier results revealed an anomalously soft dynamics characterized by pliable hydrogen bonds and large-amplitude motions of the hydrogen. We have used DINS to examine the momentum distribution of the protons in nanotube water. We find that the protons are delocalized to such a degree at low temperatures (4K) as to qualitatively change the nature of the hydrogen bonds, to the extent that we appear to be seeing a new phase of water, while at higher temperatures (268K) the bonds resemble that of bulk water but are much more strongly anharmonic.[4