Atomic force microscopy at rigid interfaces

FIGURE 4.2. A schematic of an atomic force microscope, comprising a piezo mbe, a cantilever, a sample or substrate to image and an optical lever using a laser and four-quadrant photodiode. A colloidal probe (radius 5 pm) is added to the end of the cantilever for direct force measurement. For imaging application, the probe is absent and the tip is rastered across the surface. 

FIGURE 4.3. The extraction of separation distance Do from the linear compliance region. Reprinted from Ref. [67], with permission from Elsevier. 

The cantilever deflection d is related to the total force F on the particle via F = Kcd, where is the cantilever spring constant. By employing a basic distance balance 

The cut-off distance Dc for rigid surfaces is sufficiently so small that it is commonly neglected in the display of force versus separation curves. This cut-off distance may not be neghgible in the presence of absorbed layers of surfactant or polymers, compressed between the surfaces thus it is common to report apparent separation distance on AFM measurements [27]. 

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The goal of this chapter is to provide an overview of the measurement of colloidal forces at liquid/Iiquid interfaces, using predominately atomic force microscopy (AFM)-First, some of the types and origins of the relevant colloidal forces are introduced. This is followed by a general description of the operation of AFM at rigid interfaces. The next sections focus on forces at liquid/Iiquid interfaces, beginning with a discussion of other measuring techniques employed at liquid/Iiquid interfaces, followed by a summary of... 

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