Entropic barriers in nanoscale adhesion studied by variable temperature chemical force microscopy

Area of Science:

• Physical Chemistry
• Surface Science
• Biophysics

Background:

• Intermolecular interactions govern condensed phase phenomena.
• Solvent contributions to interaction energy barriers are often underestimated.
• Hydrogen bonding plays a critical role in molecular recognition and protein folding.

Purpose of the Study:

• To investigate the influence of temperature and solvent polarity on hydrogen bond strength.
• To challenge the conventional view of secondary solvent contributions.
• To elucidate the role of entropic effects in intermolecular interactions.

Main Methods:

• Variable temperature force microscopy was employed.
• Experiments were conducted using carboxylic acid groups as model hydrogen bonds.
• Measurements were performed in both polar (ethanol) and nonpolar solvents.

Main Results:

• Interaction strength between carboxylic acid groups increased with temperature in ethanol.
• Interaction strength decreased with temperature in a nonpolar solvent.
• A kinetic model quantitatively explained the observed force-temperature trends.

Conclusions:

• Solvent layers forming on surfaces upon bond detachment contribute significant entropy.
• The observed reversal in force-temperature dependence indicates a transition between thermodynamic and kinetic unbinding regimes.
• Entropic barriers from solvent-surface interactions are prevalent in diverse systems.