Swelling during drying

The amount of swelling and contraction in smectites is quite dramatic. Typically, soils containing large amounts of this type of clay will develop cracks that are 30 cm wide at the surface and greater than 100 cm deep, and these cracks will allow surface material to fall into them during dry periods. This characteristic is so unique that these types of soils are given their own name. They are called Vertisols the name is taken from the concept that material from the surface falls to the bottom of the cracks, resulting in inversion of the soil. 

The conditions of swelling during the measurement undoubtedly have an important bearing on crystallinity estimates. Area determinations by Assaf, Haas and Purves89 indicate that up to 98% of the surface of moist cellulose is obliterated by direct drying while about 75% remains (39) A. G. Assaf, R. H. Haas and C. B. Purves, J, Am. Chem. Soc., 08, 68 (1944). 

Swelling of dry GPC beads takes up to several hours and may be accelerated by heating (cf Table 3.2). Take care that sufficient solvent is available during swelling (as a rule of thumb twice the expected volume). 

Modified starches tend to swell more after contact with water due to a weakened granular structure. Their suspensions have higher viscosity, lower maximum suspension solids and a slower settling rate. Suspension solids and viscosity are also affected by mechanical starch damage during drying. 

Immobiline gels are cast in slaTndard vertical cassettes on GelBond PAG supports. After polymerization the gel must be washed to remove unreacted catalysts and unpolymerized Immobilines. The gel swells during this process and must be dried back to its original weight. It is, therefore, much preferable to use a rehydratable gel system, where after washing the gel can be dried, stored and rehydrated for use (see above). 

Figure 8 shows the evolution of the swelling during saturation under a vertical load of 1 MPa at two different temperatures for samples of initial dry density 1.70 g/cm . The increase of water permeability and the decrease of swelling capacity of the bentonite with temperature can be observed. 

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