Page 88 - ILL Annual Report 2019

TECHNICAL AND COMPUTING DEVELOPMENTS
Bruno Démé. French and German
Institut Laue Langevin, Grenoble, France
‘I am a scientist in the Large Scale Structures (LSS) group and I’m responsible for the D16 instrument.
I’m interested in model and biological membranes, with a focus on membrane interactions in oriented lipid multilayers.’
Ultimate humidity chambers for neutron diffraction
High-resolution diffractometer with variable vertical focusing D16 instrument
The characteristics and behaviours of biological or soft-matter samples investigated in neutron scattering experiments are strongly coupled to the temperature and relative humidity of the surroundings. Accurate observation and control of these parameters is crucial to the success of such experiments, as is control of thermodynamical parameters such as the osmotic pressure of samples
in equilibrium with humid air. We, along with colleagues from Helmholtz-Zentrum Berlin (HZB), have therefore designed a precision humidity chamber for neutron diffraction that allows a 20 mm x 60 mm2 sample to be maintained at temperatures ranging from ambient to 80 °C in a relative humidity of between 20 % to 100 %.
Figure 1
CAD design of the humidity chamber. The temperature of the water bath is controlled by a thermostated bath connected to the base
of the chamber. The sample, mounted on a goniometer insulated from the water bath, is thermalised with a second thermostated bath connected to the top of the chamber.
AUTHORS
B. Demé, O. Aguettaz, S. Baudoin, N. Belkhier, E. Bourgeat-Lami, J. Gonthier and E. Lelièvre-Berna (ILL)
ARTICLE FROM
J. Neutron Res. (2019)—doi: 10.3233/JNR-190109
REFERENCES
[1] A. Carotenuto and M. Dell’Isola, Int. J. Thermophys. 17 (1996) 1423 [2] M. Kanduc et al., Nat. Commun. 8 (2017) 1
[3] N. Kucerka et al., Biophys. J. 88 (2005) 2626
[4] G.S. Smith et al., Phys. Rev. Lett. 60 (1988) 813
Biological systems are generally warm and moist, if not directly in contact with liquid water. We can get insights into their behaviour in situ only by creating experimental conditions that closely match their natural conditions. In recent years, efforts have been made to produce humidity chambers using techniques such as saturated salt solutions [1], saturated/dry gas flow and partial vapour pressure through temperature regulation of a water reservoir [2]. However, because of the unreliability of humidity sensors and the presence of thermal gradients resulting in undesired condensation, these systems have been restrictive or finicky. In particular, it has been difficult to achieve relative humidities above 95 %, this near-saturation regime being of special interest to the field of biological sciences.
We therefore decided to create relative humidity using a water reservoir (H2O, D2O, or a mix of both) regulated
at a temperature deduced from Antoine’s equation. The sample space and the water reservoir are decoupled from the experimental environment by a double-wall geometry allowing the sample space to be vacuum-insulated.
The dimensions were optimised in an iterative process to determine the geometry, resulting in the most stable, thermal gradient-free design. Each step in this iterative design process was scrutinised using finite element simulations of thermal equilibrium and convection.
ANNUAL REPORT 2019
Connections to thermostated bath controlling sample temperature
Fluid circulation (sample, top loop) Vacuum vessel thinned at beam height Guiding post for easy opening/closing Fluid circulation (sample, bottom loop) H2O or D2O gilded copper bath
Connection to thermostated bath controlling water bath
Inner and outer chambers are tightly attached and removed altogether when changing sample
Vacuum flange hosting the connector of thermometers placed on the fluid loops
Sample deposited on Silicon wafer Channel connecting top and bottom loops
Goniometer mounted on Cu base providing leak tight feedthroughs for wiring sensors
Insulating post hosting wiring (PEEK) Gliding seal for easy access to sample
Pumping flange (+ 2 connectors wired to sensors and heaters, no visible here)
Chamber base fixed to sample table