Advances in Colloid and Interface Science Ž . 96 2002 213230 Capillary forces between surfaces with nanoscale roughness Yakov I. Rabinovich, Joshua J. Adler, Madhavan S. Esayanur, Ali Ata 1 , Rajiv K. Singh, Brij M. Moudgil  Department of Materials Science and Engineering and Engineering Research Center for Particle Science and Technology, 205 Particle Science and Technology Bldg., Uni  ersity of Florida, P.O. Box 116135, Gaines  ille, FL 32611-16135, USA Abstract Ž . The flow and adhesion behavior of fine powders approx. less than 10 m is significantly affected by the magnitude of attractive interparticle forces. Hence, the relative humidity and magnitude of capillary forces are critical parameters in the processing of these materials. In this investigation, approximate theoretical formulae are developed to predict the magnitude and onset of capillary adhesion between a smooth adhering particle and a surface with roughness on the nanometer scale. Experimental adhesion values between a variety of surfaces are measured via atomic force microscopy and are found to validate theoretical predictions.  2002 Elsevier Science B.V. All rights reserved. Keywords: Adhesion; Surface force; Capillary; Nanoscale; Roughness; Atomic force microscope; Rela- tive humidity Contents 1. Introduction ............................................... 214 2. Theory .................................................. 215 2.1. Adhesion to surfaces with nanoscale roughness .................... 215  Corresponding author. Tel.: 1-352-846-1194; fax: 1-352-846-1196. Ž . E-mail address: bmoudgil@erc.ufl.edu B.M. Moudgil . 1 Currently affiliated with the Department of Materials Science and Engineering, Gebze Institute of Technology, Turkey. 0001-868602$ - see front matter  2002 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 0 1 - 8 6 8 6 01 00082-3