Stress from re-immersion of partially dried gel

When liquid evaporates from a gel, capillary tensile pressure (suction) develops in the liquid and corresponding compressive forces are imposed on the solid network, leading to contraction. At any point up to the time when shrinkage stops, the pores remain full of liquid. If, during that stage, the gel is immersed into liquid, the capillary pressure is suddenly relieved at the surface of the body, so the compressive forces on the network are eliminated and the network tends to expand elastically. The expansion of the surface creates compressive stresses near the surface and tensile stresses inside the body. These stresses can be great enough to cause cracking. In this paper, the stresses caused by re-immersion of a partially dried cylinder of gel are analyzed. The stresses are shown to be greatest at the axis of the cylinder, where fracture is observed to originate. By reducing the pressure at the surface slowly (as by exposing the gel to a humid atmosphere), the stresses can be kept low, so that the partially dried gel can be safely re-immersed.