Short-Chain n-Alcohol-Induced Changes in Phase Behaviors of Aqueous Mixed Cationic/Anionic Surfactant System
Short-Chain n-Alcohol-Induced Changes in Phase Behaviors of Aqueous Mixed Cationic/Anionic Surfactant System
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DOI：
10.1021/acs.langmuir.8b00320
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发表时间：
2018-06-26
期刊：
影响因子：
3.9
通讯作者：
Nan, Yan-Qing
中科院分区：
文献类型：
--
作者：
Hao, Li-Sheng;Wu, Jin;Nan, Yan-Qing
研究了短链正醇对1，3-丙二基双(十二烷基二甲基溴化铵)(12-3-12)与十二烷基磺酸钠(AS)混合体系相行为的影响。对于12-3-12/As/H2O混合体系，存在两种含过量阳离子表面活性剂(ATPS-C)的双水相体系。ATPS-C上相中12-3-12与As的摩尔比(MR12-3-12/As)和表面活性剂总浓度(m(T))均小于底相。值得注意的是，乙醇和正丙醇的加入对ATPS-C的影响不同。分子动力学(MD)模拟结果表明，乙醇和正丙醇的助表面活性剂效应不同，其影响也不同。当使用乙醇作为添加剂时，m(T)的不同导致了ATPS-C的两个共存相表面活性剂与乙醇相互作用的不同，从而决定了它们与混合溶剂的结合能力的不同。这是导致第一类ATPS-C乙醇诱导相转化的主要原因。当加入正丙醇时，由于正丙醇具有较强的助表面活性剂作用，除m(T)外，MR12-3-12/AS也是影响12-3-12与AS以及表面活性剂与正丙醇相互作用的关键因素。MD模拟表明，具有较小MR12-3-12/AS的囊泡更容易和更快地形成。这些小泡在ATPS-C底相转移的一定量混合溶剂的作用下，在顶相自发聚集。同时，富含表面活性剂的底相对混合溶剂的竞争阻碍了转移。这两个因素共同作用，导致ATPS-C顶相m(T)随正丙醇的加入而增加，导致正丙醇诱导的相浓度反转，而不是ATPS-C的相反转。在实验结果和分子动力学模拟的基础上，提出了ATPS-C的乙醇诱导相转化机理或正丙醇诱导相转化机理。
The short-chain n-alcohol-induced changes in phase behaviors of aqueous mixed 1,3-propanediyl bis(dodecyl dimethylammonium bromide) (12-3-12) and sodium dodecyl sulfonate (AS) system have been investigated. For the 12-3-12/AS/H2O mixed system, there are two kinds of aqueous two-phase systems with excess cationic surfactant (ATPS-C). The molar ratio of 12-3-12 to AS (MR12-3-12/AS) and the total surfactant concentration (m(T)) in the top phase are smaller than those in the bottom phase of ATPS-C. It is worth noting that the addition of ethanol or n-propanol leads to different influences on the ATPS-C. Molecular dynamics (MD) simulation results illustrate that the different influences ascribe to the difference in the cosurfactant effect of ethanol and n-propanol. When ethanol is used as additive, the difference in m(T) leads to the difference in interactions between surfactants and ethanol for the two coexisting phases of ATPS-C, determining the difference in their combination ability with the mixed solvent. It is the main reason for the ethanol-induced phase inversion of the first kind of ATPS-C. When n-propanol is added, in addition to m(T), MR12-3-12/AS is also a key factor influencing the interactions between 12-3-12 and AS and between surfactants and n-propanol due to the stronger cosurfactant effect of n-propanol. MD simulations indicate that vesicles with smaller MR12-3-12/AS are easier and faster to form. These vesicles spontaneously accumulate at the top phase accompanied by certain amount of mixed solvent transferred from the bottom phase of ATPS-C. Meanwhile, the competition for the mixed solvent arising from the surfactant-rich bottom phase prevents the transferring. The two factors work together to cause the increase of m(T) in the top phase of ATPS-C with the addition of n-propanol, leading to n-propanol-induced phase concentration inversion rather than phase inversion of ATPS-C. On the basis of the experimental results and MD simulations, ethanol-induced phase inversion mechanism or n-propanol-induced phase concentration inversion mechanism of ATPS-C has been proposed.