Control of the colloidal depletion force in nonionic polymer solutions by complexation with anionic surfactants

Area of Science:

• Colloid and Surface Science
• Polymer Science
• Physical Chemistry

Background:

• Depletion and structural forces are critical in colloidal systems.
• These forces are influenced by depletant charge, size, and concentration.
• Nonionic polymers and ionic surfactants can form complexes, potentially altering these forces.

Purpose of the Study:

• To investigate the synergistic effects of nonionic polymers and ionic surfactants on depletion and structural forces.
• To determine how complex formation between Pluronic F108 and sodium dodecylsulfate (SDS) influences these forces.
• To understand the role of concentration and electrolyte on these interactions.

Main Methods:

• Colloidal probe atomic force microscopy was used to measure forces between a silica sphere and plate.
• Experiments were conducted in solutions of Pluronic F108 (nonionic polymer) and SDS (anionic surfactant).
• Pyrene solubilization, ion-selective electrode analysis, and dynamic light scattering characterized complex formation, charge, and size.

Main Results:

• Synergistic enhancement of depletion attraction and repulsive forces was observed within a specific SDS concentration range.
• This enhancement was primarily attributed to the charging of F108/SDS complexes.
• Force interactions above the synergistic SDS range were similar to polymer-free SDS solutions due to unbound SDS micelles.

Conclusions:

• Noncovalent complexation of nonionic polymers and ionic surfactants can significantly enhance colloidal forces.
• The observed synergy is dependent on the concentration of both components and background electrolyte.
• Understanding these complex interactions is crucial for controlling colloidal assembly and stability.