Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

05 October 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


Developing better separation technologies for rare earth metals is important for a sustainable economy. However, the chemical similarities between rare earths make their separations difficult. Identifying molecular scale interactions that amplify the subtle differences between the rare earths can be useful in developing new separation technologies. Here, we describe ion-dependent monolayer to inverted bilayer transformation of extractant molecules at the air/aqueous interface. The inverted bilayers form with Lu3+ ions but not with Nd3+. By introducing Lu3+ ions to preformed monolayers, we extract kinetic parameters corresponding to the monolayer to inverted bilayer conversion. Temperature-dependent studies show Arrhenius behavior with an energy barrier of 40 kcal/mol. The kinetics of monolayer to inverted bilayer conversion is also affected by the character of the background anion, although anions are expected to be repelled from the interface. Our results show the outsized importance of ion-specific effects on interfacial structure and kinetics, pointing to their role in chemical separation methods.


liquid-liquid extraction
Langmuir monolayers
inverted bilayers
lanthanide separation
ion-specific effects
amphiphile aggregation
vibrational sum frequency generation
ion adsorption

Supplementary materials

Supporting Information for Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface
Supplemental information for the main article. Additional VSFG, XFNTR, and XR results are described.


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.