聚羧酸系减水剂对石墨烯分散性的影响

Impact of the microstructure of polycarboxylate superplasticizers on the dispersion of graphene

石墨烯用于水泥基材料不仅可以起到增强增韧作用,还可以提高水泥基体的自感应能力,石墨烯的均匀分散是其在水泥基体中应用的瓶颈问题。在本研究中,笔者合成了4种电荷密度和侧链长度不同的聚羧酸类减水剂(PCEs)。利用紫外分光光谱仪、动态光散射仪、超景深光学显微镜等方法研究了不同结构PCEs对石墨烯分别在去离子水体系和水泥孔溶液体系中分散性的影响,并提出了石墨烯的分散机理。结果表明,在去离子水体系中,高电荷密度的PCE具有更高的静电排斥力,更有利于石墨烯的分散;而具有较低电荷密度和较长侧链的PCE降低了石墨烯的分散性。相反,在水泥孔溶液体系中,对于高电荷密度PCE,由于聚羧酸基团与Ca^2+的桥接效应,降低了PCE间库仑力的排斥作用,从而降低了石墨烯的分散性;对于低电荷密度的PCE,由于聚羧酸基团与Ca^2+的桥接效应不显著,空间位阻发挥主要作用,石墨烯分散性较好。此外,具有较长侧链的PCE在两种体系中均表现出较差的分散效率。总体来说,具有低电荷密度和较短侧链的PCE更适合于制备石墨烯水泥复合材料。

Graphene can not only toughen cement-based materials,but also give them sensing ability.However,the uniform dispersion of graphene in a cement matrix is the major problem in the fabrication process.Four polycarboxylate superplasticizers(PCEs)with different charge densities and side-chain lengths were synthesized and the effects of their microstructures on the dispersibility of graphene in deionized water and in solution in cement pores were examined by UV-V is spectroscopy,dynamic light scattering and optical microscopy with a large depth of field.A mechanism for the dispersion of graphene in the two media was also proposed.In deionized water,PCEs with a higher charge density showed more electrostatic repulsion,which improved the graphene dispersion efficiency.Conversely,PCEs with a lower charge density and longer side-chains gave a lower graphene dispersion.In solution in the cement pores,however,a PCE with a high charge-density produced a low graphene dispersibility,due to a cross-linking Ca^2+-bridging effect.This effect was insignificant in cement pores for a solution containing low charge-density PCEs.Moreover,it was found that PCEs with the longer side-chains produced the worst graphene dispersion efficiency in both media.Overall,PCEs with a low charge density and relatively short side chains are more suitable for the preparation of graphene-composited cement pastes.