The experimental and calculated density of states and UCN loss coefficients of perfluoropolyether oils at low temperatures

We report the inelastic neutron scattering (INS) measurements of the density of vibrational states G(omega) of two perfluoropolyether (PFPE) oils which differ by chemical composition, molecular weight and solidification temperatures. Interpretation of vibrational bands observed in the energy transfer range 0.5-200meV is based on the density functional theory (DFT) ab initio modeling of structure and dynamics of molecular clusters of investigated PFPE. These polymers have turned out promising for the storage of ultra-cold neutrons (UCN) in closed volumes covered with PFPE film. From inferred G(omega) we calculate the expected UCN loss coefficients and compare them with the existing experimental data. (c) 2007 Elsevier B.V. All rights reserved.