Stability and Anomalous Aggregation in Suspensions of Polymer-Grafted Nanoparticles

Area of Science:

• Colloidal physics
• Polymer thermodynamics
• Materials science

Background:

• Polymer-grafted nanoparticles (PGNPs) bridge polymer and colloidal systems.
• Understanding PGNP behavior requires studying polymer conformation and solvent interactions.
• Structural stability, phase transitions, and aggregation kinetics are key properties.

Purpose of the Study:

• To investigate how polymer conformation and solvent interactions influence PGNP behavior.
• To analyze structural stability, phase transitions, and aggregation kinetics.
• To quantify PGNP phase behavior and aggregation rates.

Main Methods:

• Synthesized gold nanoparticles (AuNPs) grafted with polystyrene of varying molecular weights.
• Suspended PGNPs in cyclohexane and studied temperature-dependent transitions.
• Utilized time-dependent dynamic light scattering for aggregation kinetics analysis.

Main Results:

• PGNPs showed a two-step transition: polymer corona contraction followed by aggregation below the upper critical solution temperature.
• Aggregation kinetics followed a diffusion-limited aggregation process.
• Hydrodynamic size increased with time (power law exponent α ≈ 1/3), lower than typical colloidal systems.

Conclusions:

• Polymer conformation and solvent interactions significantly impact PGNP structural stability and phase transitions.
• The observed aggregation exponent suggests contributions from long-range interactions and grafted layer viscoelasticity.
• Findings quantify PGNP phase behavior, integrating polymer thermodynamics and colloidal physics.