层状复合金属氢氧化物-聚丙烯酸钠水分散体系的双絮凝现象及机理探讨

Double Flocculation in Aqueous Dispersion of Layered Double Hydroxide Particles Induced by Sodium Polyacylate

研究了聚丙烯酸钠(PAAS)对镁铝型层状复合金属氢氧化物(MgAl-LDH)的胶体水分散体系稳定性的影响.利用总有机碳(TOC)分析技术测定了PAAS在LDH颗粒上的吸附量,并利用ζ电位表征了LDH颗粒的电性质.实验结果表明,在质量分数为1%的LDH水分散体系中加入0.006～2.400mmol/LPAAS,随着PAAS浓度的增加,LDH-PAAS混合体系出现了絮凝-分散-再絮凝变化.同时,随着PAAS浓度的增加,PAAS在LDH颗粒上的吸附导致颗粒ζ电位由正减至0,并进一步负向增加,颗粒间静电斥力先减小后增加,因此体系先絮凝再分散.随着LDH颗粒负电性的进一步增强,未吸附的PAAS引发颗粒间产生的空缺引力成为体系再次絮凝的主要原因.对吸附PAAS的LDH颗粒的红外光谱分析表明,PAAS主要通过—COO-与LDH的相互作用而吸附在颗粒上.

The effect of sodium polyacrylate（PAAS） on the stability of aqueous dispersion of Mg/Al layered double hydroxide（MgAl-LDH） nanoparticles was studied.The adsorption of PAAS on LDH particles was determined by total organic carbon（TOC） analysis and the electrical properties of LDH particles were characterized by ζ potential measurement.The experimental results show that the LDH-PAAS mixtures appeared to be flocculation-dispersion-reflocculation as the PAAS concentration increased from 0.006 to 2.400 mmol/L in a 1.0%（mass fraction） LDH aqueous dispersion.At first,the ζ potential of LDH particles changed from positive to zero and then to negative with the increase of PAAS concentration,which was due to the adsorption of PAAS on LDH surfaces.As a result,the electrostatic repulsion between LDH particles firstly decreased and then increased.Therefore,the PAAS LDH mixture first flocculated and then dispersed.When the PAAS concentration further increased,the LDH particles remained negatively charged,and the depletion attraction between LDH particles should be the major reason causing the reflocculation of the particles.The examination of FTIR spectra of LDH,PAAS,and LDH after PAAS adsorption suggests that the adsorption of PAAS on LDH particles was mainly through the interaction between the —COO-in PAAS molecules and the LDH particles.