Effects and mechanisms of surfactants on physical properties and microstructures of metakaolin-based geopolymer

Abstract

In this study, the effects of five different ionic and nonionic surfactants on the physical properties and microstructures of a metakaolin-based geopolymer (MKG) were investigated. It is the first comprehensive comparative study of the effects of sodium lauryl sulfonate (SLS), alkyl polyglycoside (APG), benzalkonium chloride (BAC), sucrose fatty acid esters (SE), and stearic acid (STA) on MKG. Viscosity, densities, apparent water absorption, and compressive strength were measured, and pore structures, micro-defects, and gels observed through scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). In the MKG slurry, a high affinity of surfactants to liquid-air interfaces increased viscosity and promoted the generation of bubbles. Based on both the ionic types and molecular configurations of the surfactants, stronger adsorption of a surfactant on the surface of the metakaolin resulted in better dispersion of metakaolin particles and a denser microstructure of the MKG. The surfactants with weaker adsorption (SLS and APG) caused higher porosity, a larger pore size, and more micro-defects, while those with stronger adsorption (BAC, SE, and STA) led to relatively lower porosity and denser microstructures. Density, water absorption, and compressive strength were closely related to the total intrusion porosity of the MKG. The mechanisms underlying surfactant adsorption to the surface of metakaolin are proposed. 目的 研究五种离子型和非离子型表面活性剂(十二烷基磺酸钠、烷基糖苷、苯扎氯铵、蔗糖脂肪酸酯和硬脂酸)对偏高岭土基地聚合物的物理性能和微观结构的不同影响。并从表面活性剂对偏高岭土的吸附能力方面提出相关的机理模型,分析不同影响产生的原因。 创新点 1. 首次全面比较并研究上述五种表面活性剂对偏高岭土基地质聚合物的影响。2. 从作用机理上提出:地聚合物性能与特定分子构型的表面活性剂的吸附能力密切相关。 方法 1. 通过浆体的粘度,养护28天后样品的密度、表观吸水率和抗压强度表征地聚合物物理性能。2. 通过扫描电镜观测地聚合物微观缺陷和凝胶结构。3. 通过压汞试验和扫描电镜观察相结合的方法表征地聚合物孔隙特征。4. 进行相关机理分析。 结论 1. 所有表面活性剂均能提高浆料粘度并引入气泡。苯扎氯铵具有最强的增粘能力,而烷基糖苷具有最强的气泡引入能力。2. 具有特定分子构型的表面活性剂,由于其对偏高岭土的吸附能力而影响地聚合物的物理性能和微观结构;吸附能力弱的十二烷基磺酸钠和烷基糖苷会导致高的孔隙率,松散的微观结构和更多的微观缺陷。吸附能力强的苯扎氯铵、蔗糖脂肪酸酯和硬脂酸导致相对较低的孔隙率和致密的微观结构。3. 地聚合物的密度、吸水率和抗压强度的变化趋势与总孔隙率相吻合,反映出微观和宏观、外部和内部结构的一致性。