Temperature of maximum density of water in hydrophilic confinement measured by transient grating spectroscopy

We report heterodyne detected transient grating measurements on water confined in the hydrophilic porous glass Vycor7930 in the range of temperature from -15 to 90 degrees C. With this experiment we are able to obtain the temperature of the water maximum density by measuring the temperature when the water thermal expansion coefficient vanishes. We found, similarly to what is already reported in the literature in hydrophobic confinement, that the temperature of the maximum density shifts to lower temperatures. We obtain this maximum at -1 +/- 1 degrees C. No experimental evidence of a shift of the temperature of maximum density in hydrophilic systems has been previously reported.