Spectrometric Study of AOT-Hydrolysis Reaction in Water/AOT/Isooctane Microemulsions Using Phenolphthalein as a Chemical Probe

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• 作者：Shiyan Mao ; Zhiyun Chen ; Dashuang Fan ; Xueqin An ; Weiguo Shen
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：January 12, 2012
• 年：2012
• 卷：116
• 期：1
• 页码：158-165
• 全文大小：398K
• 年卷期：v.116,no.1(January 12, 2012)
• ISSN：1520-5215

文摘

The kinetics of the alkaline hydrolysis of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in water/AOT/isooctane microemulsions has been studied by monitoring the absorbance change of the phenolphthalein in the system with time. The apparent first-order rate constant k_obs has been obtained and found to be dependent on both the molar ratio of water to AOT 蠅 and the temperature. The dependences of k_obs on 蠅 have been analyzed by a pseudophase model which gives the true rate constants k_i of the AOT-hydrolysis reaction on the interface and the partition coefficients K_wi for the distribution of OH^{鈥?/sup> between aqueous and interface pseudophases at various temperatures; the latter is almost independent of the temperature and 蠅. The temperature dependences of the reaction rate constants k_obs and k_i have been analyzed to obtain enthalpy 螖H鈮?/sup>, entropy 螖S鈮?/sup>, and energy E_a of activation, which indicate that the distribution of OH鈥?/sup> between aqueous and interface pseudophases increases 螖S鈮?/sup> but makes no contribution to E_a and 螖H鈮?/sup>. The influence of the overall concentration of AOT in the system on the rate constant has been examined and found to be negligible. It contradicts with what was reported by Garc铆a-R铆o et al.(1) but confirms that the first-order reaction of the AOT-hydrolysis takes place on the surfactant interface. The study of the influence of AOT-hydrolysis on the kinetics of the alkaline fading of crystal violet or phenolphthalein in the water/AOT/isooctane microemulsions suggests that corrections for the AOT-hydrolysis in these reactions are required.}