Deformation Behaviors of Soft Matter Revealed by Neutron Scattering

Contact: Wei-Ren Chen (ORNL) chenw@ornl.gov


A direct mathematical connection between
the gyration tensor of an orienting deforming
object and its anisotropic scattering spectra
is recently developed by us.

Soft materials are indispensable building blocks in a wide variety of advanced materials. While it owes its name to its soft mechanical properties, the microscopic mechanisms controlling its flow and deformation have remained poorly understood to date. The imposed external deformation on a soft material drives its microstructure away from the equilibrium state and leads to complicated viscoelastic responses. A lucid fundamental understanding of the deformation behavior of soft matter at the molecular level is crucial for the prediction and manufacture of new materials. 

It has been recognized that the combination of rheology and neutron scattering offers a powerful experimental tool for probing the microstructural changes of flowing soft matter. However, despite decades of extensive studies, the full power of neutron scattering is yet to be unearthed. The current methodology mainly provides qualitative characterizations. The harder question of how to extract the micromechanical characteristics from the SANS spectra to address the macroscopic deformation behavior has not been answered unambiguously. Little attention has been paid to its origin at the particle level, because it was believed that the individual motions were so random that their details would be irrelevant to the physics of rheology. Recently our study synergistically combining neutron scattering, simulation and statistical mechanics has demonstrated the possibility of extracting the micromechanical characteristics featuring these localized plastic flows, such as stress and strain between the neighboring particles, from the scattering signature of deforming materials.    

Based on our success in connecting the microstructural distortion to the macroscopic mechanical properties of soft materials in their steady states, we are extending our structural study to a dynamical regime to investigate the transient phenomena such as shear-induced spinodal decomposition, homogenization and critical phenomenon which are scientifically interesting and commonly encountered in many important transport processes.  

Collaborations

ORNL; University of Tennessee, Knoxville; Institut Laue-Langevin; MIT; Louisiana State University; Eindhoven University of Technology; Argonne National Laboratory; University of Florence; European Synchrotron Radiation Facility; NIST