Preliminary Report on Measurements of Dynamic Contributions to Coherent Neutron Scattering

TL;DR

This study investigates whether standing waves in phospholipid membranes produce detectable signals in coherent neutron scattering, using temperature variation to distinguish dynamic modes from artifacts.

Contribution

It provides experimental evidence linking standing wave modes to specific neutron scattering signals in membrane systems, confirming their dynamic nature.

Findings

Standing wave signals vary with temperature as predicted.

Reappearance of signals upon reheating confirms their dynamic origin.

Temperature-dependent peak shifts support the eigenmode hypothesis.

Abstract

During this experiment we were testing the hypothesis that standing waves in a phospholipid membrane stack indeed lead to a detectable signal in coherent grazing-incidence small-angle neutron scattering, GISANS. These modes were identified earlier in a previous experiment using grazing-incidence neutron spin-echo spectroscopy, GINSES, (Jaksch, S., Frielinghaus, H. et al. (2017). Nanoscale rheology at solid-complex fluid interfaces. Scientific Reports, 7(1), 4417.). In order to identify those modes and prove conclusively that they were indeed a dynamic mode of the membrane and not a measurement artifact we were following a predetermined protocol: Starting at a physiological temperature (35$^\circ$C), where the modes were previously identified in GINSES, we lowered the temperature of the sample. Dynamic modes as an eigenmode of the lamellar system would under those conditions at least shift the position of any occurring peaks. Possibly below a phase transition temperature (approximately 25$^\circ$C for such a layered system) the peaks due to coherent scattering from a standing wave would vanish altogether, as the standing wave cannot be sustained by thermal excitation at that temperature. Upon reheating, any scattering contribution that is purely due to scattering from a standing wave would reappear. All experiments were performed on the MARIA instrument at MLZ.