What is cohesion

Cohesion or cohesive attraction  is the action of like molecules sticking together by the means of attraction forces. These attraction forces are usually of the electric type: van der Waals forces, hydrogen bonds, covalent bonds.

When these forces overcome the dispersive action of the entropic forces (of thermodynamic pressure), the molecules stick together. In the absence of cohesive forces, atoms and molecules would disperse into the atmosphere.

Also, gravity is a force of attraction that makes atoms, molecules and solid particles stick together into planets and stars.

Attraction forces create a potential well of energy, they trap particles using negative potential energy.

A barrier of positive potential energy is found at each side of the potential well and the particles need energy supplied from the surroundings to climb out of this well and to break the bonds:

(photo source: commons.wikimedia.org)

The constant that defines the strength differs for each force. For gravity is the smallest (G = 6.674×10−11 N⋅m2/kg2 ), while for the electric force it is the largest (ke = 8.9875517873681764×109 N·m2/C2 ).







While cohesion is the action of similar molecules attracting each other, adhesion is the action of molecules with different properties of attracting each other:

(photo source: www.adhesiveandglue.com)

Cohesion opposes the dispersive action of thermodynamic pressure and thus produces order out of disorder.

Also, the lowest potential energy configuration of every attraction force is the crystal, a periodic ordered arrangement of particles.



(photo source: www.doitpoms.ac.uk)