Tisor Omoakhe, Muzzio Michelle, Lopez David, Lee Sunghee
Department of Chemistry, Iona College , 715 North Avenue, New Rochelle, New York 10801, United States.
Langmuir. 2015 Feb 24;31(7):2112-9. doi: 10.1021/la5049419. Epub 2015 Feb 13.
Understanding the interaction of a surfactant assembly with surrounding ionic compositions is critical in controlling the nanostructure formed by amphiphilic systems. In this study, we investigated the influence of specific anions upon the character of the crystallization process of a model inorganic salt (K2SO4) in an aqueous microdroplet (10-100 μm) in the presence of monolayers of monoelaidin (ME), monovaccenin (MV), monoolein (MO), and monolinolein (ML) assembled at a water-decanol interface. In particular, control monolayers of each monoglyceride at the water-oil interface did not accelerate nucleation (i.e., act as a template) of the crystallization of K2SO4. However, in the presence of 1-10 mM exogenous anions, certain types of monoglycerides did induce nucleation. The influence of the anions was consistent with the Hofmeister series. Monoglyceride monolayers in combination with chaotropic anions, such as SCN(-), imparted a euhedral crystal habit with a relatively lower C(onset), while kosmotropic anions showed less notable changes in the crystallization characteristics. However, this specific anion effect was seen only for monolayers of ME, MV, and MO but not for ML. This enhancement of nucleation-inducing ability upon addition of chaotropic anions appears to be related to the degree of chain splay: the larger the chain splay, the less anion efficiency in enhancing the templating capability. Our findings indicate that the improved nucleation-enhancing capabilities may originate from mutual interactions between anions and the monolayer, allowing the monoglyceride monolayers to adapt to a modulated self-assembled structure resulting in the greatest degree of control over K2SO4 crystallization.
了解表面活性剂聚集体与周围离子组成的相互作用对于控制两亲体系形成的纳米结构至关重要。在本研究中，我们研究了特定阴离子对模型无机盐（K2SO4）在水 - 癸醇界面组装的单油酸甘油酯（ME）、单反式油酸甘油酯（MV）、单油酸甘油酯（MO）和单亚油酸甘油酯（ML）单层存在下的水性微滴（10 - 100μm）中结晶过程特征的影响。特别是，每种甘油单酯在水 - 油界面的对照单层并未加速K2SO4结晶的成核（即不作为模板）。然而，在存在1 - 10 mM外源阴离子的情况下，某些类型的甘油单酯确实诱导了成核。阴离子的影响与霍夫迈斯特序列一致。甘油单酯单层与离液序列高的阴离子（如SCN(-)）结合，赋予了具有相对较低C(起始)的自形晶体习性，而促离子序的阴离子在结晶特性方面显示出不太明显的变化。然而，这种特定的阴离子效应仅在ME、MV和MO的单层中观察到，而在ML中未观察到。添加离液序列高的阴离子后成核诱导能力的增强似乎与链展开程度有关：链展开越大，增强模板能力的阴离子效率越低。我们的研究结果表明，成核增强能力的提高可能源于阴离子与单层之间的相互作用，使甘油单酯单层能够适应调制的自组装结构，从而对K2SO4结晶实现最大程度的控制。
