Page 89 - ILL Annual Report 2019

MODERNISATION PROGRAMMES AND TECHNICAL DEVELOPMENTS
86-87
The final design, shown in figure 1, allows the control
of relative humidity of up to 99.9 % with an accuracy of ±0.05 % RH. The lower part of the humidity chamber, which is fixed to the D16 sample table, contains the water bath and several access ports for evacuating the chamber, reading sensors and heating the base of the goniometer. The water is poured in a gold-plated copper bath decoupled thermally from the sample space. The upper part controls the sample temperature and is removable to provide quick access to the sample.
In order to quantify the absolute precision of the humidity chamber, we measured the d-spacing of a lipid standard DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine)
and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) on the neutron diffractometers D16 (ILL) and V1 (HZB),
at various temperatures and relative humidities. The final test consisted of measuring the d-spacing at the highest possible relative humidity. We tuned the chamber to
100 % RH and stored the cell apart for one day until we remeasured the d-spacing on D16. We fitted a d-spacing
Figure 2
The d-spacings of DMPC measured by neutron diffraction at 30 °C from 27.5 % to 99.9 % relative humidity. The open markers correspond to the gel phase Lβ, the filled ones to the fluid phase Lα.
of 57.1 Å, which corresponds to a relative humidity
of 99.9 % according to [3]. The d-spacings of DMPC measured from 27.5 % to 99.9 % RH are presented in figure 2 and follow the phase diagram published in [4].
Three identical chambers are available at the ILL on D16 allowing samples to be measured after short or long off- line equilibration times, thereby saving precious neutron beamtime. Sample alignment can be performed off-line thanks to a dedicated optical bench equipped with a laser. The equilibration of samples can be started anytime during or before an experiment, with no need to access the instrument area or the neutron beam.
Acknowledgements
The authors thank the technical staff at Helmholtz-Zentrum Berlin, and the DFG for financial support. This project received funding from the European Union’s 7th Framework Programme for research, technological development and demonstration under the NMI3-II Grant number 283883.
Figure 3
The D16 instrument.
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