Equilibrium state model for surfactants in oils: Colloidal assembly and adsorption

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2023-01-15
Major/Subject
Mcode
Degree programme
Language
en
Pages
12
783-794
Series
Journal of Colloid and Interface Science, Volume 630
Abstract
An equilibrium state model addressing the aggregation and adsorption of colloidal assemblies in apolar solvents (oils) via monomer exchange is presented. The model is based on the previously reported step-wise aggregation response of fatty acids and monoglycerides in bio-oils, and captures surface crowding via scaled particle theory (SPT). The sensitivity of key observables - mean aggregation number, adsorbed surfactant amount, and free monomer concentration - to model parameters is demonstrated. Fits to molecular modelling based aggregation and adsorption data of oleic acid and monoolein reveal that the model accurately reproduces chemically specific aggregate exponential distributions in both bulk and surface phases, even outside of its parameterization conditions. A biased state model, where the initial bulk aggregation step (dimer formation) differs from other steps results in a notable improvement in accuracy. Fits to various phospholipid adsorption isotherms demonstrate the applicability of the model toisotherm type experimental data. The fits reveal either monolayer or aggregate like adsorption structures, depending on surfactant head group charge. The presented model provides an easily accessible, computationally feasible means to estimate colloidal assembly and adsorption in oil environments, and enables assessment of surfactant aggregation propensity and adsorption energetics.
Description
Funding Information: This work was partly financed by the Fortum and Neste Foundation project 20210130 and Academy of Finland through its Centres of Excellence Programme (2022–2029, LIBER) under project No. 346111. Computational resources by CSC IT Centre for Science, Finland, RAMI – RawMatTERS Finland Infrastructure, and Aalto Science-IT project are also gratefully acknowledged. M.S. is grateful for the support by the FinnCERES Materials Bioeconomy Ecosystem and use of the Bioeconomy Infrastructure at Aalto. We thank Dr. Markku Laatikainen and Prof. Tuomo Sainio for the raw data corresponding to Ref. [14] which enabled explicit comparison of the model to the experimental adsorption isotherms.
Keywords
Adsorption, Aggregation, Colloids in oil, Reverse micelles, Scaled particle theory, Self-assembly, Surfactants
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Citation
Vuorte , M , Kuitunen , S , Van Tassel , P R & Sammalkorpi , M 2023 , ' Equilibrium state model for surfactants in oils: Colloidal assembly and adsorption ' , Journal of Colloid and Interface Science , vol. 630 , pp. 783-794 . https://doi.org/10.1016/j.jcis.2022.09.153