Talc’s Duplicity Toward Water

The hydrated magnesium silicate mineral talc is known for being both hydrophilic and hydrophobic—individual water molecules adsorb on talc surfaces whereas water drops bead up. Now, molecular dynamics simulations have revealed the interplay of forces behind talc’s dual nature (J. Am. Chem. Soc., DOI: 10.1021/ja208687a). Benjamin Rotenberg of France’s National Center for Scientific Research and Pierre & Marie Curie University, together with Amish J. Patel of Rensselaer Polytechnic Institute and David Chandler of the University of California, Berkeley, found that at low relative humidity, when just a few water molecules are around, the strength of the adhesive interaction between talc hydroxyl groups and water overcomes the favorable entropy of having water in the vapor phase. At high humidity, the adhesive interaction is not strong enough to overcome the water-water hydrogen bonding that holds water molecules together. The results suggest that other materials, such as zeolites and metal-organic frameworks thought to be hydrophobic, may also adsorb water molecules, the researchers say.