Unravelling the interactions between surface-active ionic liquids and triblock copolymers for the design of thermal responsive systems

Germán Pérez-Sánchez, Filipa A. Vicente, Nicolas Schaeffer, Inês S. Cardoso, Sónia P.M. Ventura, Miguel Jorge, João A.P. Coutinho

Research output: Contribution to journalArticle

Abstract

The tunable properties of surface-active ionic liquids
(SAILs) and Pluronics are dramatically magnified by combining them
in aqueous solutions. The thermo-controlled character of both,
essential in the extraction of valuable compounds, can be fine-tuned
by properly selecting the Pluronic and SAIL nature. However, further
understanding of the nanoscale interactions directing the aggregation
in these complex mixtures is needed to effectively design and control
these systems. In this work, a simple and transferable coarse-grained
model for molecular dynamics simulations, based on the MARTINI
force field, is presented to study the impact of SAILs in Pluronics
aggregation in aqueous solutions. The diverse amphiphilic characteristics
and micelle morphologies were exemplified by selecting four
archetypical nonionic Pluronicstwo normal, L-31 and L-35, and two reverse, 10R5 and 31R1. The impact of the alkyl chain length
and the headgroup nature were evaluated with the imidazolium-based [C10mim]Cl and [C14mim]Cl and phosphonium-based
[P4,4,4,14]Cl SAILs. Cloud point temperature (CPT) measurements at different Pluronic concentrations with 0.3 wt % of SAIL in
aqueous solution emphasized the distinct impact of SAIL nature on the thermo-response behavior. The main effect of SAIL addition
to nonionic Pluronics aqueous solutions is the formation of Pluronic/SAIL hybrid micelles, where the presence of SAIL molecules
introduces a charged character to the micelle surface. Thus, additional energy is necessary to induce micelle aggregation, leading to
the observed increase in the experimental CPT curves. The SAIL showed a relatively weak impact in Pluronic micelles with relatively
high PPG hydrophobic content, whereas this effect was more evident when the Pluronic hydrophobic/hydrophilic strength is
balanced. A detailed analysis of the Pluronic/SAIL micelle density profiles showed that the phosphonium head groups were
positioned inside the micelle core, whereas smaller imidazolium head groups were placed much closer to the hydrophilic PEG
corona, leading to a distinct effect on the cloud point temperature for those two classes of SAILs. Herein, the phosphonium-based
SAIL induces a lower repulsion between neighboring micelles than the imidazolium-based SAILs, resulting in a less pronounced
increase of the CPT. The model presented here offers, for the first time, an intuitive and powerful tool to unravel the complex
thermo-response behavior of Pluronic and SAIL mixtures and support the design of tailor-made thermal controlled solvents.

Original languageEnglish
Pages (from-to)7046-7058
Number of pages13
JournalJournal of Physical Chemistry B
Volume124
Issue number32
Early online date20 Jul 2020
DOIs
Publication statusPublished - 13 Aug 2020

Keywords

  • copolymers
  • self-assembly mechanism
  • MARTINI framework
  • polymer structure

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