Disentangling bulk polymers from adsorbed polymers using the quartz crystal microbalance

At sufficient adhesion energy, polymers may adsorb irreversibly at an interface, with many adhesion sites per polymer and significant changes in their conformation. In addition to irreversibly adsorbed polymers there may be reversibly adsorbed polymers, which are in dynamic equilibrium with bulk polymers, and which have fewer adhesion sites per polymer and less significant conformational changes. In this work, we simultaneously determine the viscoelasticity of irreversibly adsorbed polymers, reversibly adsorbed polymers, and bulk polymers. To this end, we combine hydrodynamic modelling with quartz crystal microbalance-dissipation (QCM-D) measurements involving an adsorbing target surface and a non-adsorbing, i.e., passivated surface. We apply the method to polyethylene glycol adsorption at the water–silica interface. The results demonstrate that the viscoelasticity of the reversibly adsorbed polymers is similar to that of the bulk polymers, whereas the irreversibly adsorbed polymers are less elastic. This is the first approach to decouple these viscoelastic contributions, which provides a new analytical tool to quantify the kinetics and conformation of reversibly adsorbed polymers, shedding light on polymer dynamics near interfaces.