| Adhesion plays a significant role in the overall properties and behavior of many natural and man-made systems. It is often a difficult task to achieve a fundamental understanding of the adhesion between two solid surfaces as a number of variables can affect the adhesion between two surfaces, including the surface physicochemical properties and environmental conditions. New techniques in adhesion force measurement and analysis are utilized to study the factors that affect adhesion and the underlying mechanisms directly.; The scanning probe microscope (SPM) is one of the primary instruments used to measure the adhesion between a particle and another surface directly, as well as investigate the variation of physicochemical properties across a surface. A new technique that produces maps of particle-surface adhesion is used in conjunction with other SPM imaging techniques to correlate the spatial variation in the surface physicochemical properties with that of the particle-surface adhesion. The utility of this method is demonstrated using a lactose particle and a gelatin capsule from a pharmaceutical dry powder inhalation system.; When two rough surfaces adhere, the force of adhesion will be determined by the contact between the asperities of each surface. Measurement of the average asperity-asperity adhesion force has, up to this point, been difficult at best. The SPM is able to selectively probe specific ranges of force by varying the cantilever spring constant. A statistical analysis method is combined with the selective probing ability of the SPM to measure not only the average force of a single atomic bond, but also the average asperity-asperity adhesion force in model papermaking and de-inking systems.; The nature of the cellulose surface, and how particles adhere to it, has been a topic of debate for a number of years. Recently, a new model, called the dangling tail model, proposes that molecular chains of cellulose extend away from the surface in aqueous solutions. The SPM is used to directly measure the interaction forces between colloidal particles of regenerated cellulose and carbon black. Not only is the existence of cellulose chains confirmed by application of the colloidal probe technique, but the chains are also found to be sensitive to solution conditions and play a critical role in the interactions between cellulose surfaces and other particles.; While the SPM can be used to measure adhesion and friction between a surface and a micron-sized particle, larger surfaces require the use of a molecular tribometer. Molecular tribometers can measure mechanical properties of thin organic films between solid surfaces, but they are unable to measure the molecular dynamics of the lubricant molecules between solid surfaces undergoing shear. The MASIF surface force apparatus can be combined with laser spectroscopic techniques to provide information on the mechanical properties and the molecular dynamics simultaneously. A prototype molecular tribometer based on the MASIF has been designed and fabricated. The results obtained during the evaluation of the prototype tribometer are utilized in making recommendations for the next phase of development. |
