Adhesive Force between Hydrophilic Surfaces in Alcohol-Water Solutions.

Area of Science:

• Surface Science
• Colloid and Interface Science
• Physical Chemistry

Background:

• Understanding molecular interactions and adhesion is crucial for material science and engineering.
• Water-alcohol mixtures are common in industrial processes and biological systems.
• The role of adsorbed layers and surface roughness in adhesion requires detailed investigation.

Purpose of the Study:

• To investigate the molecular-scale interaction and adhesive forces between mica and SiO(2) surfaces in water-alcohol mixtures.
• To determine the influence of alcohol chain length, concentration, and surface roughness on adhesion.
• To elucidate the dominant mechanism driving adhesion in these systems.

Main Methods:

• Atomic Force Microscopy (AFM) was employed to probe interactions at the molecular scale.
• Experiments were conducted using various water-alcohol mixtures (ethanol to 1-hexanol).
• Analysis involved measuring adhesive forces and correlating them with surface properties and solution composition.

Main Results:

• Alcohols longer than 1-propanol form vertically adsorbed monolayers on hydrophilic surfaces at sufficient concentrations.
• Adhesive forces are maximized at a specific water-to-saturated water weight fraction ratio (approximately 0.25), irrespective of the alcohol type.
• Adhesion is significantly reduced on rough surfaces compared to smooth surfaces.

Conclusions:

• The dominant adhesive force originates from water bridging between surfaces, exceeding van der Waals forces.
• This water bridging mechanism is supported by thermodynamic predictions from the Laplace equation and Kelvin relation.
• Surface structure, including adsorbed alcohol layers and roughness, critically influences the magnitude of adhesive forces.