Molecular Simulation of Strain Dependence of Vibrational Frequencies for Montmorillonite Clay and Analysis of Strain Transfer in a Polymer−Clay Nanocomposite

Abstract

Molecular dynamics simulations are used to determine the vibrational density of states for a model montmorillonite clay as well as the spectral shifts with applied strain for significant peaks in the 1000−1300 cm-1 range. Under uniaxial deformation with fixed lateral dimensions, the spectral shifts are found to be around −29 and −40 cm-1/% strain in the clay, with little dependence on direction of applied strain within the plane of the clay platelet. Using Eshelby's method, a strain transfer efficiency of 5.6% is predicted for the nanocomposite with 5 wt % exfoliated clay. This results in a predicted spectral shift of −1.6 to −2.2 cm-1/% macrostrain in the nanocomposite, in reasonable agreement with the experimental results of Loo and Gleason (Macromolecules 2003, 36, 2587).

Cohesive Vibrational and Structural Depiction of Intercalated Water in Montmorillonite

“…The Clayff force field was chosen to model the fully flexible clay lattices as previous studies showed that it reproduces very well the outer unit cell dimensions as well as the dynamical and vibrational properties of smectites. ,, Water was modeled with the rigid SPC/E water model for mixed-layer modeling and with the flexible Ferguson water model for generation of power spectra. Ion pair potentials for interlayer cations were taken from Åqvist for Na + and from Joung and Cheatham for Ca 2+ .…”

Advances in Clayff Molecular Simulation of Layered and Nanoporous Materials and Their Aqueous Interfaces

“…For such a simple principally nonbonded force field, Clayff gives reasonable estimates of the cleavage and surface energy of layered materials 134 but leads to less accurate estimates of elastic properties. 20,60,135 Rutledge and co-workers were the first to investigate the mechanical properties of montmorillonite clay minerals using Clayff, initially investigating the strain dependence on vibrational frequencies 136 and then determining elastic constants of a single clay particle (Figure 3a), 52 as well as expanded clays. 137,138 Coveney and co-workers used large-scale models (more than 100,000 atoms) of montmotillonite 139 and Mg−Al LDH 140 to calculate mechanical properties including bending moduli.…”

Irradiated PVdF-HFP-montmorillonite composite membranes for the application of direct ethanol fuel cells

“…An intensive band observed at 840 cm À1 is attributed to the Al-O stretching modes. 29,30 The peaks observed at 1640 and 3429 cm À1 are attributed to the bending of absorbed water molecules and the -OH of water molecules associated in hydrogen bonding with SO 3 À groups, respectively. Higher intensities observed for the aforementioned peaks of the composite membrane than that of PVdF-PSSA membrane are purely attributed to the highly adsorbed water molecules via the hygroscopic effort of montmorillonite particles.…”