1 research outputs found
Nanoscopic Interfacial Hydrogel Viscoelasticity Revealed from Comparison of Macroscopic and Microscopic Rheology
Deviations between
macrorheological and particle-based microrheological
measurements are often considered to be a nuisance and neglected.
We study aqueous poly(ethylene oxide) (PEO) hydrogels for varying
PEO concentrations and chain lengths that contain microscopic tracer
particles and show that these deviations reveal the nanoscopic viscoelastic
properties of the particle–hydrogel interface. Based on the
transient Stokes equation, we first demonstrate that the deviations
are not due to finite particle radius, compressibility, or surface-slip
effects. Small-angle neutron scattering rules out hydrogel heterogeneities.
Instead, we show that a generalized Stokes–Einstein relation,
accounting for an interfacial shell around tracers with viscoelastic
properties that deviate from bulk, consistently explains our macrorheological
and microrheological measurements. The extracted shell diameter is
comparable to the PEO end-to-end distance, indicating the importance
of dangling chain ends. Our methodology reveals the nanoscopic interfacial
rheology of hydrogels and is applicable to different kinds of viscoelastic
fluids and particles