Relationships between Water Wettability and Ice Adhesion
By Adam J. Meuler, J. David Smith, Kripa K. Varanasi, Joseph M. Mabry, Gareth H. McKinley, and Robert E. Cohen
Ice
formation and accretion may hinder the operation of many systems
critical to national infrastructure, including airplanes, power lines,
windmills, ships, and telecommunications equipment. Yet despite the
pervasiveness of the icing problem, the fundamentals of ice adhesion
have received relatively little attention in the scientific literature
and it is not widely understood which attributes must be tuned to
systematically design “icephobic” surfaces that are resistant to icing.
Here we probe the relationships between advancing/receding water
contact angles and the strength of ice adhesion to bare steel and
twenty-one different test coatings (~200-300 nm thick) applied to the
nominally smooth steel discs. Contact angles are measured using a
commercially available goniometer while the average shear strengths of
ice adhesion are evaluated with a custom-built laboratory-scale
adhesion apparatus. The coatings investigated are comprised of
commercially available polymers and fluorinated polyhedral oligomeric
silsesquioxanes (fluorodecyl POSS), a low surface energy additive known
to enhance liquid repellency. Ice adhesion strength correlates strongly
with the practical works of adhesion required to remove liquid water
drops from the surfaces (i.e., with the quantity [1 + cos θrec]),
and the average shear strength of ice adhesion was reduced by as much
as a factor of 4.2 when bare steel discs were coated with fluorodecyl
POSS- containing materials. We argue that any further appreciable
reduction in ice adhesion strength will require textured surfaces, as
no known materials exhibit receding water contact angles on smooth/flat
surfaces that are significantly above those reported here (i.e., the
values of [1 + cos θrec] reported here have essentially reached a minimum for known materials).