Colloidal motion in confined viscoelastic systems

In this work we report measurements of the effect of confinement on the motion of colloidal particles immersed in a confined viscoelastic fluid and on the mechanical properties of this medium. The fluid is a polymer solution in the semidilute regime, having colloidal particles dispersed within as probes. The mean squared displacement of the probes, determined by particle tracking using videomicroscopy, is used to determine the mechanical moduli of the fluid as it is confined. We find that both moduli, the elastic and the viscous, increase as confinement is more severe but the increment in the elastic modulus is proportionally larger.