Capillary water shrinkage

Water in Wood Sorbed and Capillary Water, and Shrinkage.804... 

The shrinkage resulting from the loss of capillary water results in the elastic deformation, depending on the elasticity modulus of the paste. The reduction of elasticity modulus with the increase of w/c ratio leads to the rise of this deformation. 

Figure 3.2 Principle of the development of the volumetric proportions of the constituents of the cement paste during hydration. CS chemical shrinkage. Volumes is for cement V p, capillary water gel water, V, solid hydration products. (Based on Powers, T. C., Industrial and Engineering Chemistry, 27(7), 790-794, 1935.)...

For gels of finer dimensions, such as transparent fine-stranded gels, the capillary pressures are too high for water to be pressed out. Such gels can also release water, but this is mostly due to syneresis, which is related to aggregation of the network beyond the gel point and subsequent shrinkage. The water will be squeezed out because of the decrease in volume of the gel network and there will simply be less space available. 

As soon as the particles arrive in mutual contact, the shrinkage is practically complete. The water level is depressed into the pores and water is supplied to the surface by diffusion of vapour through capillary pores. Since the water is transferred from irxreasing distances, the overall drying rate (expressed as the amount of water removed per unit time) decreases (curve section B—C—O in Fig. 170). 

One might anticipate that if the water in the cell wall were to be frozen and then the ice were to be subliminated off there should be no liquid capillary tension, no cell wall shrinkage and it should be possible to create a porous cell wall. However, sublimating the water molecules from the cell wall at -20°C does not prevent collapse of the internal pore structure (Merchant, 1957). This implies that the cell wall water is not actually frozen at this temperature the cell wall still shrinks and very little internal surface is created. Indeed there is evidence (Tarkow, 1971) that at least some adsorbed water does not lose the mobility characteristic of the liquid phase until very low temperatures (<-80°C). Of course water in the lumens behaves like bulk water and freezes at a temperature between -0.1°C and -2.0°C, depending on the concentration of dissolved sugars in the sap. 

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