Wetting of hydrophobic organic surfaces and its implications to organic aerosols in the atmosphere

The interaction between water and organic substances is of extreme importan ce in physical, biological, and geological chemistries. Understanding the i nteractions between water and organic interfaces is one of the earliest che mical quandaries. In this research, self-assembled monolayers (SAMs) were u sed as a tool to investigate the interaction between water molecules and hy drophobic surfaces. Real-time adsorption and desorption kinetics of water o n hydrophobic SAM surfaces was monitored using a new type of field effect t ransistor (FET)-like device called MOCSER (molecular controlled semiconduct or resistor) coated with SAMs, A quartz crystal microbalance (QCM) was used as a complementary technique to give an estimate of total water mass adsor bed. It is shown that water adsorption depends on relative humidity and is reversible. The amount of adsorbed water increased with surface corrugation . The measurements suggest that adsorption takes place as small water clust ers, originating on irregularities on the surface organic layer. Molecular dynamics simulations were carried out to study the interactions of water an d hydrophobic surfaces as well. These simulations also suggest the formatio n of water microdroplets on hydrophobic surfaces, and indicate a strong cor relation between increased surface corrugation and adsorption. This paper e xamines the possible consequences of these interactions on the properties o f organic aerosols in the troposphere.