Swelling behavior of polyacrylamide/laponite clay nanocomposite hydrogels: pH-sensitive property

In this study, an investigation is carried out on the influence of varying clay contents (25-43%), pH values (2-11 buffer solutions), heat treatment, temperatures (25-60 °C) and ionic strengths (saline solution, 10^-7-0.1 M) on the water absorbency of polyacrylamide (PAAm)/laponite nanocomposite (NC) hydrogels in the absence of polyelectrolyte. For the influence of pH value on swelling behaviors, a maximum swelling ratio occurs at pH 11. Heat treatment of the hydrogels significantly improved the swelling capacity and created an obvious pH sensitive area (pH 3-4). The swelling capacity of the hydrogels was enhanced by increasing the temperature of the absorbing media. The results of swelling at different ionic strengths also indicate that the ionic strength can considerably weaken the swelling abilities of the NC hydrogels.