Spontaneous nucleation on flat surface by depletion force in colloidal suspension

Area of Science:

• Colloid science
• Materials science
• Surface chemistry

Background:

• Colloidal crystals form via sedimentation of particles onto surfaces.
• Polymer-induced depletion forces influence colloidal interactions.
• Understanding nucleation is crucial for controlling crystal structure.

Purpose of the Study:

• Investigate polymer-induced depletion forces on colloidal nucleation during sedimentation.
• Determine the effect of polymer concentration on nucleation and crystal growth.
• Clarify the role of particle-surface interactions versus particle-particle interactions in nucleation.

Main Methods:

• Experimental observation of colloidal particle sedimentation on a flat surface.
• Systematic variation of polymer concentration to induce attractive depletion forces.
• Analysis of polycrystalline colloidal crystal formation, grain size, and contact angle.
• Numerical reproduction of the nucleation process using rate equations.

Main Results:

• Sedimentation yields polycrystalline colloidal crystals.
• Above a threshold polymer concentration, spontaneous nucleation increases, reducing grain size.
• No dependence of contact angle on polymer concentration was observed.
• Particle-surface interactions significantly influence spontaneous nucleation.

Conclusions:

• Attractive depletion forces, modulated by polymer concentration, control colloidal crystal nucleation and grain size.
• Surface interactions play a dominant role in spontaneous nucleation, more so than inter-particle forces.
• The nucleation process can be accurately modeled using rate equations, providing a predictive tool.