Fu Zhixi, Chen Peng, Liu Yang, Li Jiayan
School of Emergency Management and Safety Engineering, China University of Mining and Technology, Beijing100083, China.
Langmuir. 2022 Dec 6;38(48):14607-14614. doi: 10.1021/acs.langmuir.2c01954. Epub 2022 Nov 18.
The aqueous film-forming foam (AFFF) extinguishing agent is suitable for fighting various hydrocarbon fuel fires due to its dual fire-fighting effect of foam and liquid film. Because the action law and microscopic mechanism of inorganic salts on the stabilization process of surfactant-generated AFFF are not perfect, this paper employs an experimental approach to investigate the effects of inorganic salt types and concentrations on sodium dodecyl sulfate-containing foam systems (SDS). Prior to critical micelle concentration (CMC), increasing inorganic salt concentration decreased solution surface tension, but the opposite was true after CMC. The CMC value of an SDS solution decreases as inorganic salt concentration increases, and the "salting effect" of inorganic salt cations also has an effect on the CMC value. Based on the resistance of the liquid film at the gas-liquid interface affecting gas transport, the foam evolution was divided into three stages: foam generation, liquid drainage, and gas transfer. The effect of inorganic salts on these three stages was studied at the molecular level, and it was discovered that the addition of NHCl and MgCl could improve the saturation adsorption at the gas-liquid interface, reduce the surface tension of the surfactant solution, and improve foam stability. Meanwhile, inorganic salts can change the force of gas molecules, so the equilibrium force of gas across the liquid membrane increases as inorganic salt concentration increases. Additionally, the addition of inorganic salts raises the diffusive drainage coefficient, but the gravity drainage coefficient still reigns supreme in the predecay period.
水成膜泡沫（AFFF）灭火剂因其泡沫和液膜的双重灭火作用，适用于扑救各种烃类燃料火灾。由于无机盐对表面活性剂生成的AFFF稳定过程的作用规律和微观机理尚不完善，本文采用实验方法研究无机盐种类和浓度对含十二烷基硫酸钠泡沫体系（SDS）的影响。在临界胶束浓度（CMC）之前，增加无机盐浓度会降低溶液表面张力，但在CMC之后则相反。SDS溶液的CMC值随无机盐浓度增加而降低，无机盐阳离子的“盐析效应”也对CMC值有影响。基于气液界面处液膜对气体传输的阻力，将泡沫演化分为三个阶段：泡沫产生、排液和气体传递。在分子水平上研究了无机盐对这三个阶段的影响，发现添加NHCl和MgCl可提高气液界面的饱和吸附量，降低表面活性剂溶液的表面张力，提高泡沫稳定性。同时，无机盐可改变气体分子的作用力，因此随着无机盐浓度增加，气体穿过液膜的平衡力增大。此外，添加无机盐会提高扩散排液系数，但在衰变前期重力排液系数仍占主导。
