Mixing may be defined as a unit operation that aims to treat two or more components, initially in an unmixed or partially mixed state, so that each unit (particle, molecule, etc.) of the components lies as nearly as possible in contact with a unit of each of the other components.
If this is achieved, it produces a theoretical ‘ideal’ situation, i.e. a perfect mix. However, this situation is not normally practicable, is actually unnecessary and, indeed, is sometimes undesirable.
How closely it is attempted to approach the ‘ideal’ situation depends on the product being manufactured and the objective of the mixing operation. For example, when mixing a small amount of a potent drug in a powder mix, the degree of mixing must be of a high order to ensure a consistent dose. Similarly, when dispersing two immiscible liquids or dispersing a solid in a liquid, a well-mixed product is required to ensure product quality/stability. In the case of mixing lubricants with granules during tablet production, however, there is a danger of ‘overmixing’ and the subsequent production of a weak tablet with an increased disintegration time.
The article: https://pharmatech-rx.com/mixing/
Mixing is a unit operation that combines two or more components to form a uniform mixture where all particles are evenly distributed.