Measuring Colloidal Forces With Atomic Force Microscopy 1: Salt Influence on Hydrophobic and Hydrophilic Interactions

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Colloidal forces govern the stability and behavior of particles in suspensions.
• Understanding these forces is critical for industrial, biological, and environmental applications.
• Salt concentration significantly influences colloidal interactions.

Purpose of the Study:

• To present basic concepts and protocols for studying colloidal interactions at different salt concentrations.
• To demonstrate the use of Atomic Force Microscopy (AFM) for measuring these forces.
• To detail data processing and fitting using an extended Derjaguin-Landau-Verwey-Overbeek (DLVO) model.

Main Methods:

• Functionalization of silica substrates with a hydrophobic fluorocarbon (FOTS) via chemical vapor deposition (CVD).
• Characterization using sessile drop method, electrophoretic light scattering, AFM imaging, and scanning electron microscopy (SEM).
• Force-distance measurements using AFM in various salt solutions.

Main Results:

• Successful preparation and characterization of a well-defined colloidal system.
• Measurement of hydrophobic and hydrophilic interactions in salt solutions.
• Demonstration of data processing and fitting with the extended DLVO model.

Conclusions:

• AFM provides a robust method for studying colloidal forces as a function of salt concentration.
• The presented protocol enables detailed analysis of surface and interparticle interactions.
• The extended DLVO model effectively describes the observed colloidal behavior.