Onset of Osmotic Swelling in Highly Charged Clay Minerals.

Delamination by osmotic swelling of layered materials is generally thought to become increasingly difficult, if not impossible, with increasing layer charge density because of strong Coulomb interactions. Nevertheless, for the class of 2:1 layered silicates, very few examples of delaminating organo-vermiculites were reported in literature. We propose a mechanism for this repulsive osmotic swelling of highly charged vermiculites based on repulsive counterion translational entropy that dominates the interaction of adjacent layers above a certain threshold separation. Based on this mechanistic insight, we were able to identify several organic interlayer cations appropriate to delaminate highly charged, vermiculite-type clay minerals. These findings suggest that the osmotic swelling of highly charged organoclays is a generally applicable phenomenon rather than the odd exemption.