Generating Triaxial Reinforced Epoxy/Montmorillonite Nanocomposites with Uniaxial Magnetic Fields

Abstract

The next step forward, transforming polymer nanocomposites from filled-polymer replacements to designed and engineered materials, necessitates the development of techniques to transform the random or ill-defined nanoscale morphologies into compositionally and spatially engineered hierarchal structures, paralleling that which underpins conventional continuous-fiber-reinforced composites. By exploiting an orthogonal magnetic susceptibility of montmorillonites (MMTs) from different deposits, a three-dimensional morphology composed of orthogonal alignment of aluminosilicate layers is generated from a mixture of montmorillonites and a uniaxial external magnetic field. Depending on the source, MMTs exhibit remnant magnetization arising from antiferro- and ferrimagnetic impurities and align with layers parallel or perpendicular to the field. Within a few minutes, application of static magnetic fields (1.2 or 11.7 T) induces stable alignment of organically modified MMT within an epoxy resin at room temperature. Structural relaxation is orders of magnitude slower, enabling the alignment to be captured during the subsequent cure. Thermal mechanical measurements demonstrate that morphology manipulation impacts the coefficient of thermal expansion (CTE), decreasing CTE the most in the direction of maximum MMT alignment. Knowledge of the detailed mechanism that leads to a change of the magnetic easy axis within layered silicates opens up opportunities to design novel synthetic layered silicates with unusual magnetic properties.