Probing Viscoelastic Properties of Polymer Boundary Layers in Solutions

Abstract

Viscoelastic properties of polymer boundary layers in solutions can be drastically different from that of the corresponding polymer solutions due to the interactions of the polymers and the solid surfaces and the confinement on the interfaces. We have used quartz crystal resonator technique to systematically investigate mechanical behaviors and viscoelasticities of boundary layers of polymer solutions under different conditions. The quartz crystal resonator technique probes the solution boundary layer with a thickness approximately equal to the viscous penetration depth adjacent to the surface of the quartz crystal. In most cases relevant to chemical and biological applications, the penetration depth ranges from nanometers to a few micrometers. In this talk, we will present results on polyethylene glycol (PEG) solutions and polystyrene sulfonate sodium (PSSS) solutions with different molecular weights and different concentrations. The results show that the viscosity and the shear modulus of a polymer solution boundary layer increase with the polymer concentration in the solution. The increase depends on the molecular weight and the molecular configuration. The results are analyzed in terms of the scaling theory proposed by de Gennes for polymer solutions. For solutions with large PEG molecules the viscoelastic properties of their solution boundary layers are distinctly different from that of corresponding bulk solutions. These behaviors can be explained in terms of solid-like behaviors due to an increased concentration of PEGs next to the quartz crystal and the interactions between polymers and the interface.