Calibration of the osmotic technique of controlling suction with respect to temperature using a miniature tensiometer

Abstract

The osmotic technique was calibrated at various temperatures (20–40 °C) using a high-capacity tensiometer. The effect of temperature on the calibration curve of the high-capacity tensiometer in the positive range has been found to be insignificant, i.e., about 0.03%/°C. The measurement at ambient temperature shows that the suction value is not significantly dependent either on the molar mass of polyethylene glycol (PEG) or on the molecular weight cutoff (MWCO) of the semipermeable cellulose membrane. On the other hand, the matric suction measured in the present work by tensiometer was lower than the total suction found in the literature measured by psychrometer. This shows that the so-called membrane effects must be characterized by not only the crossing of PEG molecules but also other complex phenomena. The calibration at controlled temperatures showed a slight suction decrease of 1%/°C. One possible explanation for this decrease is that increasing the temperature decreases the viscosity of PEG solutions, possibly accelerating the crossing of PEG molecules. It is also possible that increasing the temperature changes the physicochemical properties of the PEG solutions, resulting in a suction decrease.