Osmometers osmosis

Osmosis is the passage of a pure solvent into a solution separated from it by a semipermeable membrane, which is permeable to the solvent but not to the polymeric solute. The osmotic pressure n is the pressure that must be applied to the solution in order to stop the flow. Equilibrium is reached when the chemical potential of the solvent is identical on either side of the membrane. The principle of a membrane osmometer is sketched in Figure 2. 

Willibald Gottlob Schmidt (1828-77), a school teacher," found that animal membranes are less permeable to colloids than to sugar or salts. In (IV) Graham describes what he calls a dialyseVy based on his work on osmosis (see p. 652). He used a small bell-jar, formerly used as an osmometer , closed... 

Generally speaking, the bilayer lipid membrane (BLM or planar lipid bilayer) is semipermeable, meaning that some molecules are allowed to pass freely (diffuse) through the structure. The lipid bilayer is virtually impermeable to large molecules, relatively impermeable to small ions and polar molecules. Specifically, osmosis, a diffusion phenomenon, can be easily observed in a device called osmometer in which a membrane separating two... 

Vapour pressure depression and membrane osmometry are the most common methods to determine the polyer-solvent interaction parameter. The latter method will be described briefly. In a membrane osmometer a dilute polymer solution has been separated from pure solvent by means of a membrane. The membrane is penneable for solvent molecules but not for polymer molecules. Due to a chemical potential difference solvent molecules will diffuse from the diluted phase to the concentrated phase and this results in a pressure increase which is called the osmotic pressure ti (see also section VI - 2 for a more detaUed description of osmosis). The osmotic pressure is given by... 

When a solution is separated from the pure solvent by a semi-permeable membrane i.e. a membrane that permits the passage of solvent molecules but not of solute molecules, the solvent molecules always tend to pass through the membrane into the solution. This general phenomenon is known as osmosis, and the flow of solvent molecules leads to the development of an osmotic pressure which at equilibrium just prevents further flow. The equilibrium osmotic pressure, n, can be measured using a capillary osmometer such as that shown schematically in Fig. 3.9. 

---