Dipolar force adhesion

Another interaction occurs between dipoles in molecules. Dipoles arise when the electrons of a chemical bond between atoms are not shared equally, thus creating positive and negative charge centers in the molecule. The interaction forces between permanent dipoles of polar molecules depend on the strength of the two dipoles, and decrease with the sixth power of the distance between their centers. Clearly, the dipolar interaction of polymeric adhesives will be strong when they carry polar chemical groups. 

We have already encountered the concept of thermodynamic adhesion and its related terms such as the work of adhesion. The term is applied to a defined model system and does not take into consideration conditions before or after the formation of the interface, the presence of random flaws or defects in the system, or the bulk physical properties of the components, all of which are of primary importance in the practical application of the concept of adhesion. It is related to molecular interactions such as van der Waals, dipolar, and electrostatic forces but does not consider mechanical or chemical interactions as defined above. It is therefore not a very useful concept in terms of practical adhesion problems, but it serves as a good theoretical tool and to indicate a maximum force or work that a given interface may be expected to transmit before failure (i.e., separation) occurs. 

The adsorption theory of adhesion attributes adhesive strength to the action of London dispersion forces, combined in many instances with contributions from other forces (dipolar, polar or primary bonding) Calculations indicate that, in spite of their relatively low strength compared with the other types of bonding, these force can account for far greater strengths than are ever achieved experimentally. It is because all these forces are... 

Additionally, AFM tips were held in contact with the samples for different dwell times, and force curves were collected for the analysis of the influence of dwell times on the sample viscoelasticity. To study dipolar interactions on adhesion hysteresis, methyl- and hydroxyl-functionalized AFM tips were used. 

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