Determining materials properties of natural composites using molecular simulation

Abstract

Layered double hydroxides (LDHs) have a wide range of potential uses due to their ability to intercalate anionic species, including poly-anionic biopolymers. Atomistic simulations can provide considerable insight into these nano-structured materials, particularly given the recent advance in high-performance computing facilities and scalable simulation codes that has enabled simulations virtually free of finite size effects. In this work we present our findings of large-scale (>100 000 atoms) molecular dynamics simulations of Mg–Al LDHs intercalated with alginate oligomers. We have investigated the effect of two different alginate oligomer chain lengths upon the materials properties of these LDH composites. In addition to this we have explored finite size effects through the use of three different system sizes for each alginate oligomer, the largest of which contains ∼240 000 atoms. We estimate the average bending modulus of the systems to be 3 × 10⁻¹⁹ J. However, we find the smallest alginate oligomer in our study dampens the undulations of the LDH sheets at long wavelengths, which confers a greater interlayer compressibility due to the small alginate molecules bridging the interlayer spacing. The initial orientation of larger alginate oligomers is found to have an impact on the Young's moduli of the composite materials over the timescales considered in this work. We find the average in-plane Young's modulus to be approximately 40 GPa for the total composite materials and 135 GPa for the LDH sheets alone.