Direct measurements & simplified models of colloidal interactions & diffusion with adsorbed macromolecules

Area of Science:

• Colloid and Surface Science
• Soft Matter Physics
• Nanotechnology

Background:

• Understanding colloidal particle behavior near interfaces is crucial for many applications.
• Adsorbed macromolecules significantly influence particle interactions and dynamics.
• Existing models often struggle to accurately capture these complex interactions.

Purpose of the Study:

• To investigate the 3D trajectories of colloidal particles near interfaces with and without adsorbed macromolecules.
• To quantify position-dependent energy and diffusivity landscapes.
• To develop and validate models for colloidal transport in macromolecular layers.

Main Methods:

• Total internal reflection microscopy to track particle trajectories in three dimensions.
• Evanescent wave scattering to measure motion normal to surfaces.
• Image analysis for sub-diffraction limit lateral motion detection.
• Equilibrium and non-equilibrium analyses of particle dynamics.

Main Results:

• Accurate quantification of electrostatic and hydrodynamic interactions for bare colloids and surfaces.
• Precise measurement of conservative forces between adsorbed macromolecular layers.
• Identification of position-dependent energy and diffusivity landscapes.
• Demonstration that measured diffusivities necessitate novel models for spatially varying permeability.

Conclusions:

• Established analytical theories accurately describe interactions on bare surfaces.
• Novel models are required to explain diffusion within adsorbed macromolecular layers.
• The study provides a framework for predicting and designing colloidal transport in the presence of adsorbed macromolecules.