Dynamics studied by Quasielastic Neutron Scattering (QENS)
Margarita Kruteva
Abstract
Abstract Quasielastic neutron scattering (QENS) allows measurement of the molecular displacements in time and space, from pico- to tens of nanoseconds and from Ångstroms to nanometers, respectively. The method probes dynamics from fast vibrational modes down to slow diffusive motion. Every scattering experiment leads to a dynamic structure factor $$S\left( {\vec Q,\omega } \right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>S</mml:mi> <mml:mfenced> <mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>→</mml:mo> </mml:mover> <mml:mo>,</mml:mo> <mml:mi>ω</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> </mml:math> or its spatial and temporal Fourier transform (van Hove correlation function $$G\left( {\vec r,t} \right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>G</mml:mi> <mml:mfenced> <mml:mrow> <mml:mover> <mml:mi>r</mml:mi> <mml:mo>→</mml:mo> </mml:mover> <mml:mo>,</mml:mo> <mml:mi>t</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> </mml:math> ). This shows exactly where the atoms are and how they move. In this manuscript the basics of the QENS method are presented and a few examples highlighting the potentials of QENS are given: (i) diffusion of liquids and gases in nano- and mesoporous materials; (ii) hydrogen dynamics in a high temperature polymer electrolyte fuel cell (HT-PEFC) and (iii) influence of the surface interactions on polymer dynamics in nanopores.