<i>kT</i>- &amp; <i>fN</i>- Scale Polymer Brush Interactions: Theory vs Experiment for Aqueous Polyethylene Glycol Layers

We report direct sensitive measurements of separation dependent energy and force between aqueous polyethylene glycol (PEG) brushes, which are compared to scaling and self-consistent field theories with complete independently characterized polymer solution properties. By nonintrusively measuring and analyzing Brownian collisions between polymer coated colloids and surfaces using total internal reflection microscopy, we directly measure PEG brush interactions in physiological ionic strength aqueous media with nanometer-, kT-, and femtonewton-scale resolution. The measured brush interactions agree with the self-consistent field theory model with no adjustable parameters. By considering small-compression of polymer brushes due to kT-scale free energy changes, a simplified exponential interaction potential between brush coated colloids and surfaces is developed to also accurately capture the direct measurements using the same polymer solution properties. Our findings demonstrate the self-consistent field theory and a simple generalizable potential validated against directly measured PEG brush interactions, which can be used to reliably predict and interpret interactions between polymer brush coated colloidal particles in diverse materials and applications.