Integrating simultaneous interfacial shear rheology with neutron reflectometry for structural and dynamic analysis of fluid interfacial systems.

Abstract

The study of the structure and mechanical properties of complex fluid interfaces has attracted growing interest in recent decades due to its fundamental relevance to biological systems, drug development and industrial applications. A central challenge in this field is establishing a direct link between the macroscopic mechanical response of an interface and its underlying molecular-scale structural evolution. To address this, we present an integrated experimental approach that combines interfacial rheology with neutron reflectometry, enabling simultaneous measurement of dynamical and structural properties on the same sample. This strategy eliminates the uncertainties inherent in comparing separately prepared samples and, more importantly, provides direct mechanistic insight into phenomena such as film formation, phase transitions and kinetic processes. We validated the methodology using Langmuir monolayers of the saturated phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine at the air/water interface. The measurements were performed using a newly developed sample environment for the FIGARO horizontal neutron reflectometer at the Institut Laue-Langevin, which integrates a double wall-ring interfacial shear rheometer compatible with commercial rotational rheometers. This innovative setup paves the way for broad application to complex interfacial systems (including polymers, biomembranes and multi-layer films), where coupled structural-mechanical insight is critical.