Study of Adhesion Forces by AFM

Recently, Bowen et al. [27,28] and Hilal and Bowen [29] and Hilal et al. [30] applied the APM technique to study adhesion at the membrane sinface. The measurement of interaction forces between a colloid probe and a membrane smface allows quantification of the electrostatic double layer interactions when the colloid probe approaches the membrane surface, and of the adhesion force (van der Waals interaction force) when the colloid probe is withdrawn after it has been in contact with the membrane surface. Quantification of the interaction forces involved in fouling and chemical cleaning of fouled membranes is very important in order to imderstand the mechanism of fouling and to develop a favorable membrane for water treatment. 

Aim and his coworkers [31] attempted to show macroscopic models can be successfully applied to measure the adhesion forces by AFM. Butt et al. [16] wrote a review on measuring surface forces in an electrolyte solution with 7LFM. Local surface properties like the surface charge density or micromechanical properties can be determined by AFM. 

For microscopy, the most commoiJy used probes are the sharp microfabricated silicon nitride or silicon tips. These tips provide high resolution when measming sm-face forces. But it is difficult to determine the surface geometry of these probes as the tip area is less than 10 nm [31,32]. Besides this, the surface chemistry of silicon nitride tips, which are most frequently used for force measurement, is very complex [33-35]. 

The problems of unknown surface geometry and chemistry of the conventional probes can be solved by attaching smooth micrometer-sized spheres to the cantilever. For a sphere of radius R and a flat surface, a simple equation (Eq. 7.1) relates the measured force F to the interaction energy per unit cirea Va [16]  

Polymeric films (or membranes) are favorable materials to study adhesive properties with AFM. Electronic controls and software used to record the force-versus- 

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