Effect Of Conformation Of Polycarboxylate Superplasticizer On Its Dispersion

Polycarboxylate superplasticizer is the most widely used superplasticizer in concrete.It can disperse the particles in the slurry by changing the interaction between particles.Polycarboxylate superplasticizer adsorbed on the surface of cement particles has different conformation,so it will produce different steric repulsion and electrostatic repulsion,which will affect the interaction between slurry particles.Although a lot of research work has been done in the preparation,performance and mechanism of polycarboxylic superplasticizer,the research theory of the conformation of polycarboxylic superplasticizer is not comprehensive,and the explanation of the dispersion mechanism is not perfect.In this paper,the influence of different neutralizing agents,different storage environment and different calcium ion concentration on the dispersion of polycarboxylate superplasticizer was studied,and the dispersion mechanism of polycarboxylate superplasticizer and the Possible conformational changes were analysed.The main research contents and results are as follows:Firstly,polycarboxylate superplasticizer labelled PC1,PC2 and PC3 were prepared by using sodium hydroxide,ethanolamine and ammonia as neutralizing agents,and their effects on the fluidity of cement paste were studied.The molecular structure,ionization degree and hydrodynamics radius of polycarboxylate superplasticizer were measured by infrared spectrum,Zeta potential and dynamic light scattering（DLS）.The influence mechanism of conformational difference of polycarboxylate superplasticizer on dispersion was analysed.The results show that the fluidity and fluidity retention of PC1 are higher than that of PC2 and PC3,and the order of Zeta potential absolute value is PC1 < PC3 < PC2.The order of hydrodynamics radius of three scales of polycarboxylate superplasticizer in aqueous solution（intramolecular aggregates,single molecules and associative molecules）all is PC1 > PC3 > PC2.This may be due to the fact that compared with PC2 and PC3,PC1 has more side chain extension and stronger steric hindrance effect.Secondly,the influence of storage environment of polycarboxylate superplasticizer on the fluidity of cement paste with polycarboxylate superplasticizer was studied.Total organic carbon（TOC）,infrared spectrum,Zeta potential,DLS and X-ray photoelectron spectroscopy（XPS）were used to test the adsorption capacity,adsorption layer thickness,molecular structure,ionization degree,hydrodynamics radius of polycarboxylate superplasticizer.The influence mechanism of different conformation of polycarboxylate superplasticizer on dispersion was analysed.The results show that the fluidity and fluidity retention of cement paste with PC4 stored in acid environment are better than that of cement paste with of PC1 stored in Na OH alkaline environment.The adsorption capacity of PC1 and PC4 on the surface of cement particles is almost the same.The hydrodynamics radius of intramolecular aggregates and single molecules of PC4 is larger than that of PC1.The absolute value of Zeta potential of PC4 is smaller than that of PC1.The adsorption layer thickness of PC4 on the surface of cement particles is larger than that of PC1.From the above results,it can be inferred that compared with PC1,PC4 has more side chain extension,more significant steric hindrance effect and better dispersion performance.Finally,the influence of different calcium ion concentration on fluidity of calcium carbonate slurry,a cement simulant mixed with polycarboxylate superplasticizer,was studied.Adsorption capacity,light transmittance and hydrodynamic radius were measured by TOC,ultraviolet spectrophotometer and DLS,and the action mechanism was analysed.The results show that with the increase of calcium ion concentration,the fluidity of calcium carbonate slurry mixed with polycarboxylate superplasticizer decreases,the adsorption capacity of polycarboxylate superplasticizer decreases,the light transmittance of the solution decreases,and the hydrodynamics radius of a single molecule of polycarboxylate superplasticizer increases.This may be due to the complexation of calcium ions,which increases the molecular fluid radius of polycarboxylate superplasticizer,and at the same time affects the adsorption of polycarboxylate superplasticizer,resulting in the decrease of slurry fluidity.