Mesoscale Behavior of Montmorillonite Clay Modified by a Responsive Polymer

Abstract

Responsive polymers can be combined with clay particles to form adaptable, or “tunable,” clay–polymer composites. The purpose of this study is to investigate the potential for “tunability” of a nanocomposite at the mesoscale through changes in material properties—swelling behavior, Atterberg limits, hydraulic conductivity, and shear strength—with varying pH and ionic concentration of the surrounding fluid. The composite was synthesized from a nonionic form of the polymer polyacrylamide and an expansive clay, montmorillonite. An attempt was made to induce changes in behavior of the composite by exposing the material to a selected range of pH and ionic concentration conditions, thereby influencing the conformation (shape and size) of the responsive polymer molecules under different stress levels and solid contents. Behavior was compared for the cases of predicted coiled, partially extended, and extended conformation. The test results demonstrate that conformation of responsive polymer and tunability of composite depends primarily on solution type, stress levels, and solid content. The “tuning” response of a nanocomposite is maximized with a significant change in ionic concentration of the surrounding fluid. Nanocomposite swelling was 30% less than pure clay and had a friction angle 12° greater than pure clay at high ionic concentration. At low or high pH conditions, nanocomposite tunability was limited.