  Hydrophobic interactions have been studied in detail in the past based on
hydrophobic polymers, such as polystyrene (PS). Because fluorinated materials
have relatively low surface energy, they often show both oleophobicity and
hydrophobicity at the macroscopic level. However, it remains unknown how
fluorination of hydrophobic polymer influences hydrophobicity at the
microscopic level. In this work, we synthesized PS and fluorine-substituted PS
(FPS) by reversible addition-fragmentation chain transfer polymerization
method. Contact angle measurements confirmed that FPS is more hydrophobic than
PS at the macroscopic level due to the introduction of fluorine. However,
single molecule force spectroscopy experiments showed that the forces required
to unfold the PS and FPS nanoparticles in water are indistinguishable,
indicating that the strength of the hydrophobic ffect that drives the
self-assembly of PS and FPS nanoparticles is the same at the microscopic level.
The divergence of hydrophobic effect at the macroscopic and microscopic level
may hint different underlying mechanisms: the hydrophobicity is dominated by
the solvent hydration at the microscopic level and the surface-associated
interaction at the macroscopic level.
