The effect of ethylene oxide number (EON) polydispersity on the phase behavior of alkyl ethoxylates has been well documented in the surfactant literature. These previous studies show that polydisperse alkyl ethoxylates appear more hydrophilic as the surfactant concentration decreases or as the oil-to-water ratio increases. This becomes a troubling issue considering that most surfactant formulations undergo dilution during use, and they experience a wide range of water-to-oil volume ratios. Within the hydrophilic–lipophilic difference framework, the surfactant hydrophobicity is assessed via the sigma (σ) term (also known as the characteristic curvature or Cc). In this work, the effect of surfactant concentration on the apparent value of sigma (σ_app) is evaluated as a function of surfactant concentration. The experimental observations are then explained using a bifunctional model for alkyl ethoxylates that consider the dual nature of polar oils (free alcohol and low EON ethoxymers) as surfactants and as oil components. A segregation-based model and a partition-based model are implemented to account for the distribution of the ethoxymers in the surfactant pseudophase and the oil phase. Combining these distribution models with the bifunctional model and a group contribution model for sigma, one can predict the σ term versus surfactant concentration for a given water/oil ratio, starting from the EON distribution of the surfactant. The practical applications of the model are discussed.

中文翻译：

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表面活性剂浓度对多分散烷基乙氧基化物疏水性的影响

环氧乙烷值 (EON) 多分散性对烷基乙氧基化物相行为的影响已在表面活性剂文献中得到充分证明。这些先前的研究表明，随着表面活性剂浓度的降低或油水比的增加，多分散烷基乙氧基化物的亲水性更强。考虑到大多数表面活性剂配方在使用过程中会发生稀释，这成为一个令人不安的问题，并且它们的水油体积比范围很广。在亲水-亲油差异框架内，表面活性剂疏水性通过 sigma ( σ ) 项（也称为特征曲率或 Cc）来评估。在这项工作中，表面活性剂浓度对 sigma ( σ _app) 被评估为表面活性剂浓度的函数。然后使用烷基乙氧基化物的双功能模型解释实验观察结果，该模型考虑极性油（游离醇和低 EON 乙氧基聚合物）作为表面活性剂和油组分的双重性质。实施基于分离的模型和基于分配的模型来解释乙氧基在表面活性剂假相和油相中的分布。将这些分布模型与双功能模型和 sigma 的组贡献模型相结合，可以从表面活性剂的 EON 分布开始，预测给定水/油比的σ项与表面活性剂浓度的关系。讨论了模型的实际应用。