Measuring Osmotic Pressure of Poly(ethylene glycol) Solutions by Sedimentation Equilibrium Ultracentrifugation

Abstract

The osmotic pressure of aqueous poly(ethylene glycol) (PEG) solutions (400 and 8000 g/mol) was measured by sedimentation equilibrium (SE) ultracentrifugation over a concentration range of 0-50 wt % and over a temperature range of 10-40 °C. We have developed a procedure to cover a large polymer concentration range by performing a series of ultracentrifugation experiments at different loading concentrations. The SE data agreed well with previous measurements made using a vapor pressure osmometer. To facilitate conversion from concentration to osmotic pressure, the data were fitted to multivariable polynomial expressions as a function of the PEG-to-water ratio G and temperature T. The osmotic pressure of PEG solutions decreases with increasing temperature. We attribute this behavior to the release of structured water associated with the PEG chains which compared to bulk water has a lower entropy.

Mechanical confinement regulates cartilage matrix formation by chondrocytes

“…To modulate osmotic pressure in the culture medium, 400 Da polyethylene glycol (PEG 400, TCI America, MA) was added to the culture media in different amounts, as done previously 58,59 . Briefly, different concentrations of sterilized PEG 400 were added to culture media following encapsulation of chondrocytes into gels with a relaxation time of 436 seconds with an initial modulus of 3kPa.…”

Quantification of thermodynamics of aqueous solutions of poly(ethylene glycols): Role of calorimetry

“…The data obtained from these studies are well documented by Wohlfarth [5]. The most widely used methods for activity measurements are vapor pressure osmometry [6], laser-light scattering [7], isopiestic method [7,8], dew point method [9], and sedimentation technique [10]. Different methods of measurements differ in terms of their accuracy as well as the range of temperature and composition in which each is applicable.…”

“…(2) and (3) into Eqs. (10) and (11), one can obtain following equations, which govern the phase equilibria:…”

“…. ., n) are estimated from the reported data on the activity of water in PEG solutions [6][7][8][9][10]. The data for a single temperature (base temperature) is used.…”

“…Every technique has a relatively narrow range of temperature and polymer compositions over which it is accurate. For example, the sedimentation technique is accurate only at lower temperatures (<313 K) [10], whereas vapor pressure osmometry is valid only above the temperature of about 313 K [6].…”