Atomic force and optical force microscopy: applications to interfacial microhydrodynamics

Atomic force microscopes (AFM) and related scanning probe microscopes are m ost commonly used for imaging interfaces and measuring surfaces and colloid al forces. More recently, their use in probing mechanical and viscoelastic properties of macromolecules and fluids near interfaces has begun to receiv e attention. Here, we examine the dissipative responses of an AFM cantileve r and of a spherical particle used as a probe in an optical force microscop e (OFM). as a first step in the eventual development of AFMs and OFMs for m icrorheological measurements near interfaces. We focus specifically on meas urements of probe motions normal to the substrate in viscous fluids in orde r to examine the accuracy of simple models for the oscillations of the cant ilever in the case of AFMs and for testing the accuracy of measurements in the case of OFMs. The advantages and disadvantages of the two techniques an d some of the outstanding issues are also discussed. (C) 2000 Elsevier Scie nce B.V. All rights reserved.