ORIGINAL PAPER AFM measurements of forces between silica surfaces Hasan Guleryuz • Arne K. Røyset • Ingeborg Kaus • Claudine Filia`tre • Mari-Ann Einarsrud Received: 19 December 2011 / Accepted: 10 March 2012 / Published online: 23 March 2012 Ó Springer Science+Business Media, LLC 2012 Abstract Interaction forces and adhesion between a silica sphere and a flat silica surface in aqueous electrolyte solutions were investigated by atomic force microscopy. The forces were measured as a function of surface sepa- ration, pH and NaCl concentration as the surfaces were approaching each other. The adhesion force was deter- mined upon retraction with respect to pH, NaCl concen- tration and contact time. The magnitude of the long range repulsive force was decreasing with decreasing pH. A short range repulsive force was observed at pH = 2, but no long range repulsive forces were observed at this pH. Force measurements showed that adhesion of silica surfaces in water was obstructed by short and long range repulsive forces. Adhesion was enhanced when both the long and the short range repulsive force was mitigated. A maximum adhesion force of 7.8 mN/m was measured at pH = 12.5 when the short range force vanished and the long range repulsive force was reduced by increasing the NaCl concentration. At pH = 12.5, the work of adhesion was calculated to be 1.2 mJ/m 2 according to the Derjaguin– Muller–Toporov (DMT) model. Adhesion energy was much less at pH = 2 (0.3 mJ/m 2 ) due to persistive short range repulsion. Keywords Silica  AFM  Colloidal probe  Adhesion  Chemical force spectroscopy 1 Introduction Colloidal silica sols and silica gels have a wide range of industrial use in making catalysts, adsorbents, casting moulds, ceramics, paper, textile fibres, paints, coatings, etc. [1]. In order to have good control over the manufacturing processes, colloidal stability of silica sols and the transition from sol to gel states have been extensively studied over decades by rheological and light scattering techniques [1]. Earlier studies have shown that colloidal silica sols remain stable for a long time around the isoelectric point of silica before gel transition starts [1]. Therefore, the unusual colloidal behaviour of silica sols has driven researchers to utilise more subtle methods to elaborate the interactions between the silica particles. Surface force apparatus (SFA) and atomic force microscope (AFM) have been used to investigate the interaction forces between the silica sur- faces enclosed in a module which enables simulation of the sol chemistry and colloidal processing conditions [2–4]. Dispersibility, aggregation and gelation of the particles depend on adhesive interparticle forces which hold them together [5]. SFA and AFM force measurements have also been beneficial for investigating the adhesion forces between the contacting surfaces. Therefore, SFA and AFM methods have provided significant insight for the process- ing of colloidal silica sols [2, 3, 6, 7]. SFA has been used to study adhesion of silica surfaces in ambient air and in aqueous solutions. Vigil et al. [8] reported that the adhesion of contacting hydroxylated silica surfaces was enhanced by increasing the humidity of the environment and prolonging the contact time. The effect of H. Guleryuz  M.-A. Einarsrud (&) Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway e-mail: mari-ann.einarsrud@material.ntnu.no A. K. Røyset  I. Kaus SINTEF Materials and Chemistry, 7465 Trondheim, Norway C. Filia`tre Institut UTINAM UMR CNRS 6213, Universite´ de Franche-Comte´, 25030 Besanc¸on, France 123 J Sol-Gel Sci Technol (2012) 62:460–469 DOI 10.1007/s10971-012-2750-6