Tip-sample Interactions in Dynamic Force Microscopy of Polyvinyl Alcohol Films


Greg Haugstad
Center for Interfacial Engineering
University of Minnesota, Minneapolis, MN 55455

Wayne L. Gladfelter
Department of Chemistry
University of Minnesota, Minneapolis, MN 55455

Richard R. Jones
Avery Dennison, Fasson Roll North America
Painesville, OH 44077


Abstract

Dynamic force microscopy (DFM) was performed in air on ultrathin polyvinyl alcohol (PVA) films. Nominal non-contact and intermittent solid contact regimes 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 only long-range attractive forces exist, and intermittent fluid contact, involving brief penetration of the tip into a fluidized zone at the tip-polymer interface. Viscous fluid damping differs among three mesoscopic film components, producing variable "resistance" to intermittent solid contact. As a result, some components of the film are imaged in intermittent fluid contact and others in intermittent solid contact, within a single image. Approach-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 crystallinity.