Time-resolved nuclear spin-dependent small-angle neutron scattering from polarised proton domains in deuterated solutions

Abstract.: We have investigated the process of dynamic proton polarisation by means of time-resolved polarised small-angle neutron scattering (SANS) on frozen solutions of EHBA-CrV molecules in glycerol-water mixtures as a function of the concentration of EHBA-CrV and for different degrees of deuteration of the solvent. In the EHBA-CrV complex, the spins of the 20 protons which surround the paramagnetic CrV can be oriented using the method of dynamic nuclear polarisation (DNP), thereby offering the possibility to create locally a nuclear spin-dependent contrast for SANS. The time constants which describe the build-up of polarisation around the paramagnetic centre and the subsequent diffusion of polarisation in the solvent were determined by analysing the temporal evolution of the nuclear polarisation, which in turn was obtained by fitting a core-shell model to the time-dependent SANS curves. The results on the spin dynamics obtained using the scattering function of a core-shell could be independently confirmed by evaluating the integrated SANS intensity. A thermodynamic one-centre model is presented which is able to reproduce the observed dependence of the proton polarisation times on the proton concentration of the solven

Neutron scattering from polarised proton domains

International audienceWe report on time-resolved small-angle polarised neutron scattering from domains of polarised protons created by dynamic nuclear polarisation in frozen deuterated glycerol–water solutions containing a small amount of paramagnetic centres. In order to observe the rapid build-up of the polarisation of the protons around the paramagnetic ions and to separate it from the much slower polarisation change of the protons in the solvent, we have developed techniques that include stroboscopic SANS and NMR synchronised to cyclic microwave irradiation

Neutron scattering from polarised proton domains

Time-dependent small-angle polarised neutron scattering from domains of polarised protons has been observed at the onset of dynamic nuclear polarisation in a frozen solution of 98% deuterated glycerol-water at 1\un{K} containing a small concentration of paramagnetic centres (EHBA-\chem{Cr^V}). Simultaneous NMR measurements show that the observed scattering arises from protons around the \chem{Cr^V}-ions which are polarised to $\sim 10$% in a few seconds, much faster than the protons in the bulk

An experimental approach to the dynamics of nuclear polarisation

In the past 3 years a series of experiments have shed new light on the mechanism of dynamic nuclear polarisation (DNP). Time-resolved polarised small-angle neutron scattering and nuclear magnetic resonance have been used simultaneously to study the nuclear polarisation build-up around paramagnetic centres during DNP. This approach, which aims at visualising the nuclear polarisation process on a microscopic scale, shall be exemplified and the experimental techniques used described in some detail

Time-resolved nuclear spin-dependent small-angle neutron scattering from polarised proton domains in deuterated solutions

We have investigated the process of dynamic proton polarisation by means of time-resolved polarised small-angle neutron scattering (SANS) on frozen solutions of EHBA-Cr V molecules in glycerol-water mixtures as a function of the concentration of EHBA-Cr V and for different degrees of deuteration of the solvent. In the EHBA-Cr V complex, the spins of the 20 protons which surround the paramagnetic Cr V can be oriented using the method of dynamic nuclear polarisation (DNP), thereby offering the possibility to create locally a nuclear spin-dependent contrast for SANS. The time constants which describe the build-up of polarisation around the paramagnetic centre and the subsequent diffusion of polarisation in the solvent were determined by analysing the temporal evolution of the nuclear polarisation, which in turn was obtained by fitting a core-shell model to the time-dependent SANS curves. The results on the spin dynamics obtained using the scattering function of a core-shell could be independently confirmed by evaluating the integrated SANS intensity. A thermodynamic one-centre model is presented which is able to reproduce the observed dependence of the proton polarisation times on the proton concentration of the solvent. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006