Tip-sample interactions in dynamic force microscopy of polyvinyl alcohol films

Dynamic force microscopy (DFM) was performed in air on ultrathin polyvinyl alcohol (PVA) films. Nominal non-contact and intermittent solid contact reg imes are identified in measurements of amplitude and phase as a function of the mean distance from the sample. Evidence suggests that the nominal non- contact regime is divided into two subregimes: true non-contact, in which o nly long-range attractive forces exist, and intermittent fluid contact, inv olving brief penetration of the tip into a fluidized zone at the tip-polyme r interface. Viscous fluid damping differs among three mesoscopic film comp onents, producing variable 'resistance' to intermittent solid contact. As a result, some components of the film are imaged in intermittent fluid conta ct and others in intermittent solid contact, within a single image. Approac h-withdrawal amplitude hysteresis correlates with amplitude damping, and is consistent with component-specific surface fluidity (meniscus formation). Differences in surface fluidity are interpreted in terms of relative crysta llinity. (C) 2000 Society of Chemical. Industry.