Osmometry with membranes permeable to solute

Abstract

Simultaneous measurements of osmotic pressure and permeation of solute have been made for a nonfractionated polystyrene with a number of membranes of widely different permeability. It is shown that, even after many days, no real equilibrium is reached in an osmometer with a membrane permeable to part of the polymer. The theory of equilibria in such osmometers is developed and shows that, in first approximation, the distribution of permeating solute over the two osmometer cells is not affected by the presence of nonpermeating solute. In second approximation, this distribution is affected indeed, but in this approximation the osmotic pressure is not affected by this unequal distribution. Some short‐time experiments also show that when the number of permeated molecules is negligible (t → 0) the contribution of a molecular species to the osmotic pressure is less than the value given by equilibrium thermodynamics if the membrane is not completely impermeable to that molecular species. This phenomenon is in accordance with the theory of permeability of membranes based upon nonequilibrium thermodynamics.

SEC Absolute Molar Mass Detection by Online Membrane Osmometry

“…For M n = 3100 g/mol a 50% pressure drop was observed after 12 min. Care must be taken when permeating polymers are measured, since even an infinitely fast osmometer does not allow the measurement of the correct osmotic pressure due to the Staverman effect …”

“…Care must be taken when permeating polymers are measured, since even an infinitely fast osmometer does not allow the measurement of the correct osmotic pressure due to the Staverman effect. 10 SEC Online Detection. To test the suitability of the osmometer as an online flow detector for SEC, a concentration series of PS (5250) with c i ) 0.99, 2.54, 5.00, and 10.32 g/L was prepared and V i ) 0.1 mL of the solutions were injected into the SEC apparatus.…”

Polyacrylonitrile capillary membranes for membrane osmometry

“…For M n = 11 500 g/mol there is a significant deviation, which is caused by polymer permeating through the membrane and thus reducing the measured osmotic pressure. Due to the Stavermann effect [13] permeating polymer does not allow the measurement of the true osmotic pressure, even with an infinitely fast osmometer. The accessible molecular weight range is significantly increased, when compared to the glass membrane, from 80 to 20 kg/mol, while still retaining the fast response time.…”

Automatic Osmometer for Determination of Number Average Molecular Weights of Polymers.

“…Dow Styron 666. Figure 5 shows that in the case of the untreated polymer, initially half of the total osmotic pressure is due to the lowmolecular weight species; the apparent molecular weight, here to an even greater extent than for PAMS 1 and 2 (Figure 6), depends on the characteristics of the membrane, and is a "reflection-average molecular weight" (14,15).…”