Y. Shang
Oak Ridge National Laboratory,
United States
Keywords: neutron scattering, small-angle
Summary:
The Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) are among the most powerful and versatile instruments for neutron science globally. A key technique employed at these facilities is Small Angle Neutron Scattering (SANS), which is essential for probing the nanoscale structure of materials across a range from several nanometers up to tens or even hundreds of nanometers. This capability makes SANS a critical tool for research in fields such as biomedical materials, polymers, and micelles. Numerical modeling has emerged as an invaluable asset in neutron science, providing insights that are often challenging to achieve experimentally. However, several significant obstacles remain. First, modeling systems on the scale of hundreds of nanometers is challenging due to computational constraints and the complex nature of SANS samples. Second, the heterogeneous components and intricate interactions within these systems further complicate the simulation process. To address these challenges, we have integrated numerical simulations with SANS data, employing several innovative approaches to refine both modeling and experimentation. One such approach utilizes the implicit solvent model, enabling efficient simulation of large-scale systems by simplifying the treatment of solvent molecules, thereby reducing computational overhead. This method has significantly decreased computation time for large, dilute solution systems. Additionally, we have applied Density Functional Theory (DFT) to study the temperature-dependent properties of functional groups, offering crucial insights that complement experimental data. Bulk polymer systems present unique challenges in both simulation and neutron scattering experiments. In numerical simulations, the slow diffusion of entangled polymer chains makes it difficult to observe structural evolution within a feasible computation time. We employed coarse-graining techniques to enhance chain mobility in models and utilized a semi-quantitative method to validate the simulation results. On the experimental side, the use of deuterated mineral oil as a solid solvent has provided valuable insights into the behavior of complex bulk polymer systems, allowing us to observe structural features such as crystallization and entanglement of polymer chains. These experimental findings were then compared with numerical simulations, leading to a more comprehensive understanding of material properties. These approaches not only overcome the inherent challenges in numerical modeling for SANS but also underscore the synergistic relationship between experimental neutron scattering and computational methods. This synergy paves the way for more accurate and insightful analyses in material science.