Factors influencing the synthesis of tunable clay–polymer nanocomposites using bentonite and polyacrylamide

Although clay–polymer nanocomposites have been successfully produced in the material science field, they are typically utilized as static structures. That is, no further structural modification is expected due to the irreversible interaction of the polymer and clay particles. Yet, polymer-intercalated clay nanocomposites may be produced with environmentally-responsive polymers such that the final nanocomposites are “tunable”. The conformation of responsive polymers varies with external environmental conditions such as pH, ionic concentration, temperature, and electric field. The purpose of this study is to develop an optimized procedure for synthesizing tunable clay–polymer nanocomposites using an expansive clay mineral (bentonite) and a responsive polymer for the future production of “tunable” clay soils. The nanocomposites were produced using a solution intercalation technique. Variables investigated include synthesizing temperature, clay content, polymer molecular weight, pH, and clay-to-polymer volume ratio. Changes in the basal spacing of montmorillonite were characterized using X-ray diffraction. Intercalation was not found to vary with mixing and drying temperature. The polymer solution pH variation did not cause significant mineral dissolution, evidenced by nuclear magnetic resonance as well as X-ray diffraction. Optimum conditions for the greatest quantity of intercalated structure were at clay content of 0.001, synthesis with a low molecular weight polymer, and clay-to-polymer volume ratio of 2. Measured total specific surface area implies that the interlayer distances of synthesized nanocomposites vary with pH.

Research Highlights
► Variation in mixing and drying temperatures do not affect intercalation.
► Mineral dissolution due to pH-adjusted polymer solutions during mixing is insignificant.
► Clay content, polymer molecular weight and clay-to-polymer ratio affect intercalated structure.
► The most significant factor is the clay-to-polymer volume ratio.