Effect of Self-Assembling Monolayers (SAMs) on Ice Adhesion to Metals

ABSTRACTIn this research we used an original method to study the role of hydrogen bonding in ice adhesion and to minimize the effect of this mechanism on ice adhesion. We coated metals (Au and Pt) with a mono-molecular layer of specific organic molecules that had either strong hydrophobic properties (CH3(CH2)11SH) or strong hydrophilic properties (OH(CH2)11SH). To determine the contribution of hydrogen bonding to ice adhesion, self-assembling monolayers (SAMs) of varying degrees of hydrophobicity/hydrophilicity were created by mixing the hydrophobic and hydrophilic components. All of the SAMs were composed of similar molecules that differed only in their outermost groups, OH- and CH3-. Thus, when the SAMs were grown on the same substrate (almost atomically smooth metal coatings), any differences in their adhesion to ice were due to differences in the hydrogen bonding between the ice and SAMs. The SAMs structure and quality were examined with scanning force microscopy (SFM) and the degree of the SAM's hydrophobicity/hydrophilicity was characterized by the contact angle of water on the monolayers. We then froze water on the SAMs and measured the shear strength of the ice/SAM/metal interfaces. Possible damage to the interfaces was examined with SFM after the ice had melted. We found a good correlation between the contact angle of water and the ice adhesion strength and determined the fraction of ice adhesion caused by hydrogen bonding.