Understanding near-surface polymer dynamics by a combination of grazing-incidence neutron scattering and virtual experiments

Abstract

Neutron spin-echo spectroscopy is a unique experimental method for the investigation of polymer dynamics. The combination of neutron spin-echo spectroscopy with grazing-incidence geometry (GINSES) opens the possibility to probe the dynamics of soft-matter materials in the vicinity of the solid substrate in the time range up to 100 ns. However, the usage of the GINSES technique has some peculiarities and, due to the novelty of the method and complexity of the scattering geometry, difficulties in further data analysis occur. The current work discusses how virtual experiments within the distorted-wave Born approximation using the BornAgain software can improve GINSES data treatment and aid the understanding of polymer dynamics in the vicinity of the solid surface. With two examples, poly(N-isopropyl acrylamide) brushes and poly(ethylene glycol) microgels on Si surfaces, the simulation as well as the application of the simulation to the GINSES data analysis are presented. The approach allowed a deeper insight to be gained of the background effect and scattering contribution of different layers.

Grazing Incidence Small-Angle Neutron Scattering: Background Determination and Optimization for Soft Matter Samples

“…This has been shown here for GISANS of microgel particles at the solid interface, and also helped in understanding background contributions for GINSES experiments (see Ref. [24]).…”

“…In this work, we used the software BornAgain [25] to mimic a GISANS experiment as close as possible with its 2D detector image for a given incident angle. The sample, in this case microgel particles adsorbed at the silicon interface, was modelled as core-shell truncated spheres with pre-knowledge from neutron reflectometry and AFM measure-ments [24]. The scattering signal was then obtained on small-angle neutron scattering instruments in grazing incidence geometry.…”

“…In the first part of this paper, we present an example where GISANS experiments together with simulations help to understand the scattering signal and background contributions on the side of reflection and transmission of the GISANS cell. Since scattering under grazing incidence is treated within the distorted wave Born approximation (DWBA) [23], simulations were performed with BornAgain being a modern and easy-to-use open-source software package suitable for simulating GISANS scattering (and also the equivalent x-ray scattering GISAXS) within the DWBA [24,25]. In the second part, we propose a simple version of sample cell for GISANS experiment aiming decrease the background scattering from the cell parts.…”

MembraneDyn: simulating the dynamics of supported membrane stacks on the nanosecond timescale

“…9(a) and 9(b) are identical; the data have not been fitted. Such issues may be solved by optimization of the experimental methods as well as through the use of virtual GISANS experiments (for polymers at interfaces, see, for example, Kyrey et al, 2021) in which these contributions can be simulated.…”