The following are some effective methods to solve the drying shrinkage problem when preparing coatings by sol-gel method:
Optimize formula
Add inorganic fillers: Select suitable inorganic fillers such as nano silica, alumina, zirconia, etc., and evenly disperse them into the sol. These fillers can occupy a certain space, play a supporting role in the drying and shrinkage process of gel, limit the excessive shrinkage of gel, and also enhance the overall performance of the coating, improve its high temperature resistance and mechanical properties.
Introducing plasticizers: for example, using some organic small molecule plasticizers such as phthalates. Plasticizer can reduce the rigidity of gel and make it more flexible when drying, so as to reduce the internal stress caused by shrinkage and alleviate the occurrence of cracks.
Improve the process
Control drying conditions: Adopt a slow drying method by reducing the drying temperature, controlling the environmental humidity, and extending the drying time to allow the solvent to evaporate more smoothly. This can avoid cracks caused by uneven shrinkage inside and outside the gel due to rapid evaporation of solvent. For example, the coated sample can be placed in a drying oven with constant temperature and humidity, set a lower temperature and appropriate humidity, and gradually complete the drying process.
Multiple coating: Do not attempt to apply thicker coatings at once to achieve the desired thickness, but instead apply thin coatings in multiple batches. After each coating, allow it to fully dry and cure, so that the shrinkage degree of each layer is relatively small. The subsequent stacked coatings can to some extent compensate for the small defects that may occur in the previous layer, reduce the occurrence of shrinkage cracks as a whole, and also ensure the quality and thickness requirements of the coating.
Using additives
Use of cross-linking agent: add an appropriate amount of cross-linking agent, such as organic silane coupling agent, to promote the construction of a more stable and elastic cross-linking system during the formation of the gel network structure. This cross-linking structure can better withstand the internal stress caused by drying shrinkage, prevent gel from cracking due to shrinkage, and improve the integrity and stability of the coating.
Adding surfactants: surfactants can improve the surface properties of the sol, adjust its surface tension, and make the solvent volatilization more uniform. When gel is dried, the shrinkage of each part tends to be consistent, reducing cracks and other defects caused by excessive local shrinkage differences, and ensuring the uniformity and integrity of the coating.
Post processing reinforcement
Heat treatment optimization: Suitable heat treatment is carried out on the dried coating, followed by annealing at an appropriate temperature to eliminate residual stress inside the coating, repair small cracks that may have appeared, improve the microstructure of the coating, make it denser, further reduce the adverse effects of drying shrinkage, and improve the quality and performance of the coating.
External force constraint: During the drying process of gel, some fixtures and other tools can be used to properly fix and constrain the substrate coated with gel to limit its deformation in the shrinkage direction, so as to reduce the cracks caused by shrinkage and other problems. However, it should be noted that the applied external force should not be too large to avoid damage to the coating and substrate.

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High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.