Mechanical bonding first appeared in the 1960s when Wasserman and Schill synthesised catenanes and Harrison and Harrison synthesised rotaxanes, this was followed by the pioneering use of template methods for mechanically interlocked molecular architectures by Sauvage.
A mechanical bond alters the chemistry of the sub-components of catenanes and rotaxanes, with the steric hindrance of reactive functionalities increasing, while the strength of the non-covalent interactions between the components is altered.
The increased strength of non-covalent interactions is known as the ‘catenand effect’ and is more pronounced in smaller interlocked systems, where more degrees of freedom are lost compared to larger systems.
The increased steric hindrance associated with mechanical bonding can also lower the kinetic reactivity of products, allowing for the isolation of otherwise reactive intermediates. Being able to alter chemical reactivity without changing the covalent structure has led to MIMAs being investigated for several technological applications, including protecting organic dyes from environmental degradation.
Mechanical bonds cannot be easily separated without breaking or distorting the chemical bonds between atoms, although they are only as strong as the weakest chemical bond.
Mechanical bonding uses inter-fibre factors such as friction, which results in entanglement, to create web strengthening. Processes for mechanical bonding include needle punching, whereby specially-designed needles are pushed and pulled through a material to entangle the fibres within. Another method, hydro-entanglement (also knwn as spunlacing) uses high pressure water jets to interlace the fibres.
Mechanical bonding doesn’t only provide a strong method for joining materials but can also allow for the study and determination of the strength of industrial steel. Used with materials like cobalt and titanium, mechanical bonding can indicate whether a surface or material has been correctly prepared to achieve a level of strength capable of fending off the harmful effects of corrosion.
Mechanical bonding can also be used for joining dissimilar materials like glass to metal. In such instances, the surface roughness of the materials creates a frictional force that binds them together while the glass penetrating surfaces, pores or cavities creates a greater surface area for the surfaces to lock together.
Mechanical bonding is used by industry to form strong joins between materials, improving their strength and resistance to damage and corrosion. As an adhesive method, mechanical bonding physically locks materials together through surface crevices that increase the available surface area for the mechanically interlocked molecules to work.
Unlike chemical bonding, a mechanical bond does not share or transfer electrons between the materials.