Hydrophobic Dehydration

Technical Details: A classical molecular dynamics simulation where two hydrophobic self-assembled monolayers (hydrocarbon chains stacked together) are seen in the cyan and blue layers.  The water (red and white sections) are modeled using the TIP5P water model.  The x and y dimensions (horizontal direction and into and out of the screen) of the box are fixed and the z-dimension is coupled to an external pressure of 1bar and allowed to increase to accommodate the water leaving the hydrophobic region.  The hydrophobic chains are held fixed otherwise they would collapse into the vacuum formed by the dehydration event.

Concepts Covered: 
Hydrophobicity - The water molecules are more attracted to each other than they are to the hydrophobic plates and thus dehydration occurs.  These dehydration events are at least partially responsible for the so called "hydrophobic effect" in which hydrophobic molecules tend to aggregate in aqueous environments.  They attract one another on length scales that are much larger than would be predicted by simple van der Waals force models.

Relevant Papers:
Layfield JP and Troya, D, J. Phys. Chem. B, 2011, 115 (16), pp 4662–4670

Giovambattista, N, Rossky PJ, and Debendetti PG, J. Phys. Chem. B, 2009, 113 (42), pp 13723–13734

Fluorine Reacting with a Hydrocarbon SAM

A video of the reaction of impinging fluorine atoms on an alkanethiolate SAM.  The role of secondary collisions in cooling the rotational and translational motion of the product HF can be seen after reaction.

Reaction of Fluorine Atom with Ethane