油酸-正丙醇-水无表面活性剂反相微乳液电导研究

Study on the electrical conductivity of reverse surfactant-free microemulsion composed of oleic acid,propanol,and water

本文对油酸-正丙醇-水三元体系的相行为进行了研究,表明可形成微乳液。由于体系中无传统表面活性剂,故所形成的微乳液为无表面活性剂微乳液。在反相微乳液区,固定正丙醇/油酸体积比(RP/O)为3∶5、1∶1和2∶1,考察了体系电导率(κ)随分散相体积分数(Φd)的变化,结果表明κ随Φd的增大先缓慢增加,后急剧增大,符合渗滤特征。采用电荷涨落模型在低Φd值范围内估算出液滴流体力学半径(Rh)为1.35～1.85nm,随Φd值的增大Rh有所增大。采用渗滤模型探讨了其导电机理,RP/O为3∶5、1∶1和2∶1时拟合出的渗滤特征指数(μ和s)分别为μ=1.28、s=0.49,μ=1.31、s=0.51和μ=1.50、s=0.73,表明所研究体系符合静态渗滤模型。电导率的研究结果表明,无表面活性剂微乳液体系的电导行为与有表面活性剂微乳液体系相似。

Generally,a microemulsion consists of oil,water,surfactant and sometimes cosurfactant.Herein,we report a novel surfactant-free microemulsion（denoted as SFME）,consisting of oleic acid（oil phase）,water and propanol without the amphiphilic molecular structure of traditional surfactant.The phase behavior of the ternary system was investigated and a single-phase microemulsion region and a two-phase region were formed.In the reverse microemulsion region,the variation of electrical conductivity（κ）as a function of droplet volume fraction（Φd）was examined at two constant propanol/oleic acid volume ratios（RP/O）of 3∶5,1∶1 and 2∶1,respectively.The results show that with the increase of Φd,the κ values increase slowly,followed by a sharply increase,which is consistent with percolation character.On the basis of charge fluctuation model,the hydrodynamic radius（Rh）of droplets were estimated to be 1.35～1.85 nm,and the Rh value increase with increasing Φd.The conductive mechanism of the reverse SFME was investigated by percolation model,and it was found that it might be described with static percolation model.The electrical conductivity behaviour of surfactant-free microemulsion is similar to the traditional microemulsion containing surfactant.