In mortar materials, due to the low viscosity of the slurry, bubbles rise due to buoyancy, and the liquid film of bubbles moves towards the surface due to gravity, resulting in a pressure difference. The thickness of the film becomes thinner and thinner, and the bubbles eventually burst. The self defoaming method of this cement-based material itself cannot meet the comprehensive performance requirements of products such as self compacting concrete or self leveling mortar, and suitable defoamers must be selected for further defoaming treatment.
The functions of defoamers include inhibiting foam and defoaming. Bubble suppression refers to the disordered distribution of molecules on the liquid surface after adding defoamers to the system, which suppresses the formation of elastic films, i.e. the generation of bubbles. Defoaming means that when a large number of bubbles are generated in the system, the defoamer is added, and its molecules immediately diffuse on the foam surface, rapidly diffuse, form a thin double film layer, further diffuse, penetrate, and invade in layers, thus replacing the thin wall of the original foam film. Due to its low surface tension, it is easy to flow towards liquids with high surface tension, causing the liquid film to rapidly thin. At the same time, the bubbles are subjected to strong tensile forces from the surrounding film layer with high surface tension, causing an imbalance in the force on the bubbles and thus eliminating them. The insoluble defoamer molecules in the system then re reach the surface of another bubble membrane, repeating this process. During the process of mixing dry mixed mortar with water, the introduced air is trapped in the wet mortar to form bubbles. Meanwhile, additives such as water reducers, redispersible latex powders, and cellulose ethers all have hydrophilic functional groups, which can reduce the surface tension of liquids, cause bubble aggregation, and increase the stability of bubbles.
Defoamers have certain specificity and specificity. The foaming mechanism and process conditions of each foaming system are different, and the required defoamers are also different. However, regardless of which defoamer is used, it should have the following characteristics:
(1) Strong defoaming ability and low dosage;
(2) Joining does not affect the basic performance of the system;
(3) Low surface tension;
(4) Good balance with the surface;
(5) Good diffusion and permeability;
(6) Good heat resistance, acid and alkali resistance;
(7) Stable chemical properties and strong antioxidant activity;
(8) Good air solubility and permeability;
