Characterization of microscopic deformation through two-point spatial correlation function

TL;DR

This paper introduces a phenomenological method to characterize microscopic deformation in fluids using anisotropic pair distribution functions, applicable in small-angle scattering and molecular dynamics simulations.

Contribution

It presents a novel approach to quantify non-affine microscopic strain via perturbation expansion of anisotropic PDFs in real and reciprocal space.

Findings

Microscopic strain can be calculated in shear and extension flows.

Method applicable to small-angle scattering and molecular dynamics.

Provides a new tool for analyzing non-equilibrium soft matter.

Abstract

The molecular rearrangements of most fluids under flow and deformation do not directly follow the macroscopic strain field. In this work, we describe a phenomenological method for characterizing such non-affine deformation via the anisotropic pair distribution function (PDF). We demonstrate now the microscopic strain can be calculated in both simple shear and uniaxial extension, by perturbation expansion of anisotropic PDF in terms of real spherical harmonics. Our results, given in the real as well as the reciprocal space, can be applied in spectrum analysis of small-angle scattering experiments and non-equilibrium molecular dynamics simulations of soft matter under flow.