Shear induced relaxation of polymer micelles at the solid-liquid interface

Area of Science:

• Materials Science
• Physical Chemistry
• Polymer Science

Background:

• Pluronic F127 (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)) forms complex micellar structures in aqueous solutions.
• Understanding the behavior of these solutions under shear and near interfaces is crucial for applications in drug delivery and nanotechnology.

Purpose of the Study:

• To investigate the influence of shear rates on the crystalline structure and correlations of F127 polymer micelles.
• To examine the relaxation dynamics of F127 micelles near hydrophilic and hydrophobic silicon walls after shear cessation.
• To elucidate the interplay between wall-particle interactions and shear forces at the liquid-interface boundary.

Main Methods:

• Rheology using a cone/plate geometry to measure flow properties.
• Surface-sensitive grazing incident neutron scattering to probe micellar structure and correlations.
• Controlled application and cessation of shear to observe relaxation dynamics.

Main Results:

• The crystalline structure of polymer micelles weakened at low shear rates but correlations strengthened at higher shear rates.
• A slow relaxation of micelles was observed near a hydrophilic silicon wall (strong interaction).
• A fast relaxation of micelles occurred near a hydrophobic silicon wall (weak interaction).

Conclusions:

• Shear forces significantly alter the micellar structure and ordering of F127 solutions.
• The nature of the wall interaction (hydrophilic vs. hydrophobic) dictates the micelle relaxation dynamics post-shear.
• Wall-particle interactions play a critical role, competing with shear forces at the interface.