Surfactant is a substance that has significantly changed (usually reduced) the surface tension of liquid or the interfacial tension between two phases, and its molecule is composed of two parts: hydrophilic group and hydrophobic group.When the surfactant is added into the aqueous solution, the hydrophilic group in the molecule points to the solution, and the hydrophobic group points to the air, solid or non-polar liquid and makes directional arrangement, forming the directional adsorption film and reducing the surface tension of water and the interfacial tension of two phases.Surface activity was shown in the liquid.
When water slurry after adding polycarboxylate superplasticizer , hydrophobic groups of the poly (carboxylic acid water reducing agent molecules adsorbed on the surface of cement particles, directional point hydrophilic radical aqueous solution, forming a single molecule in the surface of cement particles or multimolecular adsorption film, under the influence of electric repulsion, make originally the cement after adding water due to many factors such as molecular cohesion between cement particles formed flocculation structure open, the bound released a free water in the structure of flocculation, which is produced by poly carboxylic acid molecular adsorption jianshuiji dispersion effect.After adding water to cement, cement particles are wetted by water. The better the wetting, the less amount of water needed to mix with the same performance, and the faster the hydration rate of cement is.When surfactant is present, the surface tension of water and the interfacial tension between water and cement particles are reduced, which makes cement particles easy to be wet and conducive to hydration.At the same time, the molecules of polycarboxylate superplasticizer are adsorbed directionally on the surface of cement particles, and the hydrophilic groups point to aqueous solution, which thickens the solvated layer on the surface of cement particles, increases the sliding ability between cement particles, and plays a lubricating role.If the air-entraining polycarboxylate superplasticizer, the lubrication effect is more obvious.
