Developing a general interaction potential for hydrophobic and hydrophilic interactions

Area of Science:

• Surface Science
• Physical Chemistry
• Colloid Science

Background:

• Existing theories like DLVO (Derjaguin-Landau-Verwey-Overbeek) do not fully capture all forces between surfaces.
• Hydrophobic and hydrophilic interactions require a more general model to explain observed attractions and repulsions.

Purpose of the Study:

• To develop and validate a general interaction potential for both hydrophobic and hydrophilic surfaces.
• To incorporate additional forces beyond DLVO theory into a unified model.

Main Methods:

• Review of direct force measurements on various hydrophobic and hydrophilic surfaces.
• Development of a general interaction potential: W(D) = -2γ(i)Hy exp(-D/D(H)).
• Utilizing the surface forces apparatus (SFA) for hydrophobic interaction measurements.

Main Results:

• The proposed potential, using the nondimensional Hydra parameter (Hy), accurately describes interactions.
• The interaction energy decays exponentially with a decay length (D(H)) of approximately 0.3-2 nm.
• The potential correctly models attractive hydrophobic forces (Hy > 0) and repulsive hydrophilic forces (Hy < 0).

Conclusions:

• The developed interaction potential provides a quantitative account for forces not covered by DLVO theory.
• The model is applicable to a broad range of surfaces, including mica, silica, and lipid bilayers.
• Direct force measurements validate the proposed potential for describing hydrophobic and hydrophilic interactions.