Bulk Materials - Molecular Transport Phenomena

Page 1

Free Diffusion

-SLOW process of movement of substance due to RANDOM thermal motion

- moves from HIGH to LOW

Xrms= average distance moved by molecules

Dab = diffusion constant for molecules A in SUBSTANCE B. (ink molecules in water)

Osmosis and Dialysis

Semipermeable Membrane

-May have small pores and allow ONE TYPE of molecule to pass through, OR which may DISSOLVE/REACT with molecules passing through.

Osmosis

-Transport of water through semi-permeable membrane from high conc to low conc

-CAN create substantial pressure diff across membrane.

Osmotic Pressure

-Back pressure that stop osmosis if one solution is pure water

- can be LARGE

Relative Osmotic Pressure

-Back pressure that stops osmosis if neither solution is pure water.