ABSTRACT
The statistical method developed by Beebe and co-workers [51, 52] for determining the force of a single chemical bond between a cantilever tip and a sample surface was extended to the analysis of the adhesion force between a lactose particle and a gelatin capsule surface. The method is based on the assumption that the total adhesion (pull-off) force is the sum of discrete bond or interaction forces. Multiple adhesion force measurements should then follow a Poisson distribution, so that a plot of the force variance versus the mean force should be linear with a slope which corresponds to the individual bond force and a zero intercept. If nonspecific long-range forces such as those which occur in colloidal systems are present, then the intercept will be negative. Furthermore, if the discrete bond force is not constant due to varying bond position and orientation or varying chemical composition, there will be curvature in the plot of the variance versus mean force. This method utilizes the natural variability in the tip (or colloidal particle) and sample surface asperities, and it does not require a priori assumptions of the tip (or particle) radius or knowledge of the tip (or particle)-sample surface contact area.
