Theoretical Models for Surface Forces and Adhesion and Their Measurement Using Atomic Force Microscopy

Abstract

The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of AFS, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution.

Characterisation of dry powder inhaler formulations using atomic force microscopy

“…(9)). These generally depend on the separation distance, D, the effective radius, R * , and the Hamaker constant, A (Israelachvili, 2011;Leite et al, 2012):…”

“…Leite et al (2012) demonstrated that the film thickness per se has a negligible effect which is taken into account by the Hamaker constant. The Hamaker constant is based on the chemical and physical characteristics of the tip, the Fig.…”

“…There is also a significant difference between performing the measurements in air or gaseous atmospheres and in liquid. Thus, both the specific environmental and experimental parameters and the free surface energy of the material have to be considered (Cappella and Dietler, 1999;Leite et al, 2012). A clear distinction between all these factors is impossible without substantial effort (the ideal experiment would require completely smooth and homogeneous surfaces with welldefined properties and strictly controlled experimental settings).…”

“…From the snap-off force the work of adhesion can be calculated once the radius is known (Bhushan, 2003). However, all adhesion theories are based on simplifications and assumptions (Leite et al, 2012) and the limitations of the models (summarised below) should be kept in mind when interpreting the data.…”

Modeling the coverage of an AFM tip by enzymes and its application in nanobiosensors

“…inhibitors, antigens) can be used to build nanobiosensors with AFM. The design of an effective sensor, however, requires understanding of the specific interactions leading to detection signals, such as those generated by enzyme-inhibitor pairs [3][4][5][6]. Owing to the complexity of the enzyme-substrate interaction, in silico studies are now employed, including molecular dynamics (MD) simulations [7][8][9].…”