Water Potential of Aqueous Polyethylene Glycol

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Abstract
Water potential (.psi.w) values were determined for aqueous colloids of 4 molecular sizes of polyethylene glycol (PEG) using freezing-point depression and vapor-pressure deficit methods. A significant 3rd-order interaction existed between the method used to determine .psi.w, PEG molecular size and concentration. At low PEG concentrations, freezing-point depression measurements resulted in higher (less negative) values for .psi.w than did vapor-pressure deficit measurements. The reverse was true at high concentrations. PEG in H2O did not behave according to van''t Hoff''s law. .psi.w was related to molarity for a given PEG but not linearly. .psi.w varied with the molecular size of the PEG. The .psi.w of PEG in H2O may be controlled primarily by the matric forces of ethylene oxide subunits of the PEG polymer. The term matricum was proposed for PEG in soil-plant-water relation studies.