Measurement of van der Waals forces by atomic force microscopy between surfaces of silicon nitride, gold, and Langmuir-Blodgett films of polymerized 10,12-nonacosadiynoic acid

The atomic force microscope (AFM) was originally developed to produce high-resolution images of non-conducting materials. In recent years, it has become an important tool for studying intermolecular forces between surfaces with small contact areas. In this research, van der Waals' forces were measured between surfaces of silicon nitride, gold, and polymerized Langmuir-Blodgett (LB) films of the lithium salt of 10,12-nonacosadiynoic acid. AFM tips were successfully coated using LB deposition. This research also examined the ability of the AFM to predict Hamaker coefficients by fitting the force data to the van der Waals' force equation.; A great deal of work has been done using liquid as the interacting medium in force experiments. Less attention has been given to force experiments in air or vacuum due to complications caused by capillary condensation from ambient moisture. A nitrogen-purging method is used in this research to minimize the effects of ambient moisture.; Fitting the force data to the van der Waals' force equation for each system produced reasonable values (that is, correct order of magnitude) of the Hamaker coefficient. The Hamaker coefficient for the Si₃N ₄ tip/Si₃N₄ substrate system obtained in this work is a factor of 1.3 to 2 higher than the literature values. The Hamaker coefficient for the gold tip/ gold substrate system is a factor of 1.2 to 2.3 higher than the literature values. The force data for the LB tip/ LB substrate system show a very good fit to the van der Waals' force equation. This is promising for future studies of forces using LB-coated tips, especially since the SEM images indicate that the LB film remains intact during the force experiments.; Much work has been done with tips that have gold coatings and selfassembled films in liquid environments, but no literature exists on tips coated with LB films. The present work on LB-coated tips opens up numerous opportunities to systematically study the interfacial forces between monolayer films of different functionalities such as amine or amide groups. The information gained in this way will be valuable in many areas by increasing the understanding of interfacial forces.