A NANORHEOLOGICAL STUDY OF ADSORBED POLYMER LAYERS

In this paper, a means of determining the viscoelastic properties of a dsorbed polymer layers under compression is presented. The technique a llows rheological properties to be measured on a nanoscopic scale, and revolves around the use of a Surface Force Apparatus (SFA) that has b een specially modified for such a purpose. The experiments were carrie d out by applying an oscillatory motion to one mica surface and monito ring the response of the second confining surface to this motion. The coupling of the motion between the two surfaces is characteristic of t he material in the gap and allows the viscoelastic properties of the m aterial to be determined as a function of its confinement. In developi ng such a technique, the aim was to bridge the gap between the nanosco pic (equilibrium) view obtained from surface force measurements and th e macroscopic (dynamic) view obtained from traditional rheological mea surements. Results obtained on a PEO/PS system in toluene and a PMMA/P HSA system in a decahydranaphthalene solvent are presented here. The r esults indicate a significant change in the behavior of the system fro m being predominantly viscous away from polymer overlap to being predo minantly elastic where there is overlap.