In this paper, we develop a new coarse-grained model, under the MARTINI framework, for Pluronic block copolymers that is able to describe the self-assembly mechanism and reproduce experimental micelle sizes and shapes. Previous MARTINI-type Pluronic models were unable to produce realistic micelles in aqueous solution, and thus our model represents a marked improvement over existing approaches. We then applied this model to understand the effects of polymer structure on the could point temperature measured experimentally for a series of Pluronics, including both normal and reverse copolymers. It was observed that high PPG content leads to dominant hydrophobic interactions and a lower cloud point temperature, while high hydrophilic PEG content shields the micelles against aggregation and hence leads to a higher cloud point temperature. As the concentration increases, the effect of polymer architecture (normal vs reverse) starts to dominate, with reverse Pluronics showing a lower cloud point temperature. This was shown to be due to the increased formation of cross-links between neighboring micelles in these systems, which promote micelle aggregation. Our results shed new light on these fascinating systems and opens the door to increased control of their thermal responsive behavior.

Besides the good performance, the downstream process based in thermo-responsive systems was shown to be efficient and of lower environmental impact.

Aqueous micellar two-phase systems (AMTPS) hold a large potential for cloud point extraction of biomolecules but are yet poorly studied and characterized, with few phase diagrams reported for these systems, hence limiting their use in extraction processes. This work reports a systematic investigation of the effect of different surface-active ionic liquids (SAILs)-covering a wide range of molecular properties-upon the clouding behavior of three nonionic Tergitol surfactants. Two different effects of the SAILs on the cloud points and mixed micelle size have been observed: ILs with a more hydrophilic character and lower critical packing parameter (CPP < /) lead to the formation of smaller micelles and concomitantly increase the cloud points; in contrast, ILs with a more hydrophobic character and higher CPP (CPP ≥ 1) induce significant micellar growth and a decrease in the cloud points. The latter effect is particularly interesting and unusual for it was accepted that cloud point reduction is only induced by inorganic salts. The effects of nonionic surfactant concentration, SAIL concentration, pH, and micelle ζ potential are also studied and rationalized.

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.

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