Near-Surface Motion and Dynamic Adhesion during Silica Microparticle Capture on a Polymer (Solvated PEG) Brush via Hydrogen Bonding

Abstract

Surface modification by “polymer brushes” (dense end-tethered chains) is a strategy to create a steric barrier against colloidal aggregation or bioadhesion or to facilitate lubrication. The approach requires good brush solvation; however, even in a good solvent, brush chains can adhere certain objects. An important example is the hydrogen bonding of silica to PEG (poly(ethylene glycol)) chains in water. To probe how hydrogen bonding at the brush periphery facilitates adhesive capture of flowing particles, we employ a model system comprising silica microspheres on biorepellant PEG brushes sufficiently thick to screen interactions with the underlying substrate. We find that capture of silica spheres on PEG brushes is slower and less efficient than the transport-limited rate and can be hindered by the addition of salt and by flow, up to wall shears at least 500 s–1. Individual flowing silica microparticles adhere gradually to the PEG brush (presumably by increasing the numbers of H-bonds), so that the partic...