Antagonistic mixing in micelles of amphiphilic polyoxometalates and hexaethylene glycol monododecyl ether

DOI: 10.1016/j.jcis.2020.06.007

Authors: Andi Di (University of Bath) , Julien Schmitt (University of Bath; UMR 3080 CNRS / Saint-Gobain CREE) , Kun Ma (ISIS Neutron and Muon Source) , Marcelo A. Da Silva (University of Bath) , Naomi S. Elstone (University of Bath) , Najet Mahmoudi (ISIS Neutron and Muon Source) , Peixun Li (ISIS Neutron and Muon Source) , Adam Washington (ISIS Neutron and Muon Source) , Zi Wang (ISIS Neutron and Muon Source) , R. John Errington (Newcastle University) , Karen J. Edler (University of Bath)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Colloid And Interface Science

State: Published (Approved)
Published: June 2020

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 non-ionic surfactant and anionic surfactants with a polyoxometalate cluster as headgroup would form mixed micelles, giving control of the POM density in the micelle, but 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, 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 small angle neutron scattering (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.

Journal Keywords: polyoxometallate amphiphiles; hexaethylene glycol; monododecyl ether; unfavourable mixing; micellar composition; small angle neutron scattering

Subject Areas: Chemistry

Diamond Offline Facilities: Tensiometer (Kruss DSA 100)

Facility: ISIS

Added On: 10/06/2020 10:23

Discipline Tags:

Surfaces Physics Physical Chemistry Soft condensed matter physics Chemistry Organic Chemistry

Technical Tags: