Diffusion transport
While diffusion transport takes no energy for the motion the necessary energy expenditure for the capture from the solution and permanent fixture to the target surface must not be overlooked.
Diffusion transport speed is faster when temperature is higher but the temperature is limited by what the transported molecule can survive and the boiling point of the solvent (if unpressurized).
Diffusion transport speed is distance dependent. The farther the slower it gets.
Diffusion on a lower dimensional subspace (e.g. a lipid membrane) can improve the situation. That is diffusion transport can be sped up by reducing the dimensionality of freedom of motion and or restricting the range of motion to regions.
In biology motors work often by prevention of back reactions.
If taken to the extreme one ends up with a one dimensional path with unidirectional erratic motion with unpredictable times for forward steps.
By coupling many of these together in the background one ends up with predictable and continuous forward motion which is essentially what a machine phase systems is.
