聚羧酸减水剂在水泥颗粒表面的吸附行为

合成一系列聚羧酸减水剂，探讨不同单体摩尔比对其吸附性能的影响。结果表明，当n(烯丙醇聚氧乙烯醚)∶n(2-丙烯酰胺-2-甲基丙磺酸钠)∶n(丙烯酸)∶n(马来酸酐)=1∶0.14∶3.6∶2.6时，产物吸附性能最优。并利用总有机碳分析技术，研究了不同温度、不同浓度下最优产物在水泥颗粒表面的吸附动力学和热力学。动力学研究结果表明：聚羧酸在水泥颗粒表面的吸附过程符合Lagergren吸附速率方程，吸附速率常数k=0.01594 min-1(30℃)，表观活化能Ea=17.9647 kJ·mol-1。热力学研究结果表明：随温度升高，聚羧酸在水泥颗粒表面的吸附量增大；求得吸附热力学参数分别为ΔHad=-24.788 kJ·mol-1，ΔSad=0.050 kJ·mol-1·K-1，ΔGad=-39.886 kJ·mol-1(30℃)，可知该吸附过程是自发的放热反应。理论上温度升高对吸附不利，但因放出的热量促进水泥水化，导致聚羧酸分子容易掺杂到水化产物中，从而使更多聚羧酸吸附到水泥颗粒表面，令其吸附量反而增大。

Adsorption behavior of polycarboxylate superplasticizer on cement particle surfaces

A series of polycarboxylate superplasticizers were prepared and the effects of mole ratio of different monomers on the adsorption were studied.The experimental results showed that the product was the best when mole ratio of acrylic polyether,2-acrylamide-2-methyl propane sulfonic acid sodium,acrylic acid,and maleic anhydride was 1∶0.14∶3.6∶2.6.Adsorption kinetics and thermodynamics of the best product on cement particle surfaces at different temperatures and concentrations were studied by TOC analysis.The kinetic results showed that the adsorption process followed Lagergren adsorption rate equation.Adsorption rate constant k and activation energy Ea were 0.01594 min-1(30℃)and 17.9647 kJ·mol-1,respectively.Thermodynamic results showed that the adsorption capacity of PC increased with temperature.The thermodynamic parameters obtained are as follows:ΔHad=-24.788 kJ·mol-1,ΔSad=0.050 kJ·mol-1·K-1,ΔG⊙ad=-39.886 kJ·mol-1(30℃),indicating that the adsorption is a spontaneous exothermic process.In theory,higher temperature is not beneficial to adsorption process,but as temperature increases,more PC adsorbs at cement particle surfaces,resulting in larger adsorption capacity.The reason is that the heat released will promote hydration of cement,so that it is easier for PC to dope with hydration products.