Effect of tip radius on the nanoscale viscoelastic measurement of polymers using loss tangent method in amplitude modulation AFM

Abstract

We study the influence of tip radius on the viscoelastic characterization of polymers using a recently developed loss tangent (tan δ) method operated in amplitude modulation atomic force microscopy (AM-AFM) mode. By decreasing the tip radius, we found that AM-AFM tan δ of a homogeneous polystyrene film decreased close to the bulk limit value, which can be ascribed to a reduced effect of the probe/sample adhesive interaction for a smaller tip. Decreasing the tip radius also shifted the tan δ values of nanostructured blocks in a poly(styrene-b-isoprene-b-styrene) triblock copolymer film to their bulk limits, but in different trends for glassy styrene and rubbery isoprene blocks. Besides minimizing the effect of the adhesive interaction, we demonstrate that reducing the tip radius being smaller than the characteristic size of nanostructured domains is critical to obtain their true tan δ image.