Hydrophilic Alcohol Ethoxylates as Efficiency Boosters for Microemulsions

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• 作者：Christian Frank ; Henrich Frielinghaus ; J&#xfc ; rgen Allgaier ; Dieter Richter
• 刊名：Langmuir
• 出版年：2008
• 出版时间：June 17, 2008
• 年：2008
• 卷：24
• 期：12
• 页码：6036 - 6043
• 全文大小：1064K
• 年卷期：v.24,no.12(June 17, 2008)
• ISSN：1520-5827

文摘

Highly amphiphilic polyalkane−PEO diblock copolymers drastically increase the solubilization capacity of surfactants in microemulsions if they are used in small quantities as additive to the surfactant. This effect goes along with an additional reduction of the already very low interfacial tension between water and oil. Lamellar phases, which usually develop when the surfactant becomes more efficient, are suppressed to a large extent. In this work we use another type of additive, namely hydrophilic alcohol ethoxylates. These amphiphiles are identical with the previously used block copolymers with respect to the hydrophilic moiety. However, they contain only small hydrocarbon groups ranging from C₈ to C₁₈. A typical example from the hydrophilic alcohol ethoxylates is C₁₂E₁₀₀. Both additive types increase surfactant efficiency equally with respect to mass fraction in the mixture. Because the alcohol ethoxylate additives decorate the surfactant film only on the aqueous side, they influence the curvature of the surfactant membrane or, in other words, the temperature behavior of the microemulsion. Together with nonionic surfactants, however, the shift of the one-phase region to higher temperatures is only a few degrees Celcius. Just as with the polyalkane−PEO block copolymers, the hydrophilic alcohol ethoxylates suppress lamellar phases. This behavior is especially pronounced if the hydrophobic groups are small or the PEO chains are long. We found that hydrophobic units as short as C₈ are sufficient to largely anchor the PEO chains at the interface. If C₁₂ or C₁₈ hydrocarbon unit are used instead, the PEO chains are fully interfacially active, even if the hydrophilic chain contains up to about 500 EO units. We applied the new additives in bicontinuous and in droplet microemulsions and used nonionic, as well as ionic, surfactants, namely C₁₀E₄ and AOT. In contrast to polyalkane−PEO blockcopolymers the new additives are easy to synthesize and are commercially available. Therefore, they might be interesting in applications.