Underwater Adhesion of a Stimuli-Responsive Polymer
on Highly Oriented Pyrolytic Graphite: A Single-Molecule Force Study
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Abstract
Exploration
aiming to understand how a single polymer chain interacts
with interested solid–water interface and its dependence on
the environmental stimulus is critical, as it is important for a variety
of scientific research and practical applications, such as underwater
adhesives or smart systems for controlled attachment/detachment. Here,
by single molecule force spectroscopy (SMFS), results on underwater
adhesion of a single stimuli-responsive polymer chain on a model hydrophobic
surface are reported. Salt concentration was used as an effective
stimulus for the transition of the stimuli-responsive polymer from
hydrophilic (solvophilic) hydrated state to hydrophobic (solvophobic)
state in SMFS experiment. The probed equilibrium single-molecule adhesion
force that changed from 45 to 76 pN with increasing salt concentration
were free of other interactions that are responsible for cohesions,
indicating that solvent quality is critical in determining the strength
of single-molecule interfacial adhesion. Moreover, the derived simple
quantitative thermodynamic model by combining single-molecule detachment
mechanics with hydration free energy illustrated that higher single-molecule
adhesion force was resulted from higher solvation/hydration free energy.
The experimental study and theoretical analysis presented in this
work quantitatively revealed the role of hydrophobic and more general
solvophobic interactions in single-molecule level and shed light on
the molecular structure optimization for desired applications, such
as underwater adhesives or smart interfaces