Abstract
Hypothesis
Polyoxometalates (POMs) are metal oxygen clusters with a range of interesting magnetic and catalytic properties. POMs with attached hydrocarbon chains show amphiphilic behaviour so we hypothesised that mixtures of a nonionic surfactant and anionic surfactants with a polyoxometalate cluster as headgroup would form mixed micelles, giving control of the POM density in the micelle, and which would differ in size and shape from micelles formed by the individual surfactants. Due to the high charge and large size of the POM, we suggested that these would be nonideal mixtures due to the complex interactions between the two types of surfactants. The nonideality and the micellar composition may be quantified using regular solution theory. With supplementary information provided by small-angle neutron scattering (SANS), an understanding of this unusual binary surfactant system can be established.
Experiments
A systematic study was performed on mixed surfactant systems containing polyoxometalate-headed amphiphiles (K10[P2W17O61OSi2(CnH2n+1)2], abbreviated as P2W17-2Cn, where n = 12, 14 or 16) and hexaethylene glycol monododecyl ether (C12EO6). Critical micelle concentrations (CMCs) of these mixtures were measured and used to calculate the interaction parameters based on regular solution theory, enabling prediction of micellar composition. Predictions were compared to micelle structures obtained from SANS. A phase diagram was also established.
Findings
The CMCs of these mixtures suggest unusual unfavourable interactions between the two species, despite formation of mixed micelles. Micellar compositions obtained from SANS concurred with those calculated using the averaged interaction parameters for P2W17-2Cn/C12EO6 (n = 12 and 14). We attribute the unfavourable interactions to a combination of different phenomena: counterion-mediated interactions between P2W17 units and the unfolding of the ethylene oxide headgroups of the nonionic surfactant, yet micelles still form in these systems due to the hydrophobic interactions between surfactant tails.
Polyoxometalates (POMs) are metal oxygen clusters with a range of interesting magnetic and catalytic properties. POMs with attached hydrocarbon chains show amphiphilic behaviour so we hypothesised that mixtures of a nonionic surfactant and anionic surfactants with a polyoxometalate cluster as headgroup would form mixed micelles, giving control of the POM density in the micelle, and which would differ in size and shape from micelles formed by the individual surfactants. Due to the high charge and large size of the POM, we suggested that these would be nonideal mixtures due to the complex interactions between the two types of surfactants. The nonideality and the micellar composition may be quantified using regular solution theory. With supplementary information provided by small-angle neutron scattering (SANS), an understanding of this unusual binary surfactant system can be established.
Experiments
A systematic study was performed on mixed surfactant systems containing polyoxometalate-headed amphiphiles (K10[P2W17O61OSi2(CnH2n+1)2], abbreviated as P2W17-2Cn, where n = 12, 14 or 16) and hexaethylene glycol monododecyl ether (C12EO6). Critical micelle concentrations (CMCs) of these mixtures were measured and used to calculate the interaction parameters based on regular solution theory, enabling prediction of micellar composition. Predictions were compared to micelle structures obtained from SANS. A phase diagram was also established.
Findings
The CMCs of these mixtures suggest unusual unfavourable interactions between the two species, despite formation of mixed micelles. Micellar compositions obtained from SANS concurred with those calculated using the averaged interaction parameters for P2W17-2Cn/C12EO6 (n = 12 and 14). We attribute the unfavourable interactions to a combination of different phenomena: counterion-mediated interactions between P2W17 units and the unfolding of the ethylene oxide headgroups of the nonionic surfactant, yet micelles still form in these systems due to the hydrophobic interactions between surfactant tails.
| Original language | English |
|---|---|
| Pages (from-to) | 608-618 |
| Number of pages | 11 |
| Journal | Journal of Colloid and Interface Science |
| Volume | 578 |
| Early online date | 4 Jun 2020 |
| DOIs | |
| Publication status | Published - 15 Oct 2020 |
Bibliographical note
Funding Information:Funding: A. Di. thanks University of Bath and China Scholarship Council for supporting her PhD studies. The authors would like to thank the ISIS Neutron and Muon Spallation Source for the award of beam time on beamline LARMOR and LOQ (experiment nos. 1810278 and 1720185) that contributed to the results presented here. The raw SANS data can be found at DOI: 10.5286/ISIS.E.RB1810278 and 10.5286/ISIS.E.RB1720185, while the CMC data and reduced SANS data supporting this paper can be found in the University of Bath Research Data Archive, 2019 DOI: 10.15125/BATH-00845.
Funding Information:
This work benefited from the use of the SasView application, originally developed under NSF Award DMR-0520547. SasView also contains code developed with funding from the EU Horizon 2020 programme under the SINE2020 project Grant 654000.
Publisher Copyright:
© 2020 Elsevier Inc.
Keywords
- Hexaethylene glycol monododecyl ether
- Micellar composition
- Polyoxometalate amphiphiles
- Small angle neutron scattering
- Unfavourable mixing
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Biomaterials
- Surfaces, Coatings and Films
- Colloid and Surface Chemistry
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Dataset for "Antagonistic Mixing in Micelles of Amphiphilic Polyoxometalates and Hexaethylene Glycol Monododecyl Ether"
Di, A. (Creator), Schmitt, J. (Creator), Ma, K. (Creator), Alves Da Silva, M. (Creator), Elstone, N. (Creator), Mahmoudi, N. (Creator), Li, P. (Creator), Washington, A. (Creator), Wang, Z. (Creator), Errington, J. (Creator) & Edler, K. (Creator), University of Bath, 10 Jun 2020
DOI: 10.15125/BATH-00845
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