Probing competitive interactions in quaternary formulations

Omar T Mansour; Beatrice Cattoz; Richard K Heenan; Stephen M King; Peter C Griffiths

doi:10.1016/j.jcis.2015.04.068

Probing competitive interactions in quaternary formulations

J Colloid Interface Sci. 2015 Sep 15:454:35-43. doi: 10.1016/j.jcis.2015.04.068. Epub 2015 May 11.

Authors

Omar T Mansour¹, Beatrice Cattoz¹, Richard K Heenan², Stephen M King², Peter C Griffiths³

Affiliations

¹ Faculty of Science and Engineering, University of Greenwich, Medway Campus, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK.
² Science and Technology Facilities Council, ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 OQX, UK.
³ Faculty of Science and Engineering, University of Greenwich, Medway Campus, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK. Electronic address: p.griffiths@greenwich.ac.uk.

PMID: 26002337
DOI: 10.1016/j.jcis.2015.04.068

Abstract

Hypothesis: The interaction of amphiphilic block copolymers of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) group with small molecule surfactants may be "tuned" by the presence of selected alcohols, with strong interactions leading to substantial changes in (mixed) micelle morphology, whilst weaker interactions lead to coexisting micelle types.

Experiments: The nature and the strength of the interactions between Pluronic P123 (EO20PO70EO20) and small molecule surfactants (anionic sodium dodecylsulfate, SDS, C12SO4Na), (cationic dodecyltrimethylammonium bromide, C12TAB) and (non-ionic polyoxyethylene(23)lauryl ether, Brij 35, C12EO23OH) is expected to depend on the partitioning of the short, medium and long chain alcohols (ethanol, hexanol and decanol respectively) and was probed using tensiometry, pulsed-gradient spin-echo nuclear magnetic resonance (PGSE-NMR) and small-angle neutron scattering (SANS).

Findings: The SANS data for aqueous P123 solutions with added alcohols were well described by a charged spherical core/shell model for the micelle morphology. The addition of the surfactants led to significantly smaller, oblate elliptical mixed micelles in the absence of alcohols. Addition of ethanol to these systems led to a decrease in the micelle size, whereas larger micelles were observed upon addition of the longer chain alcohols. NMR studies provided complementary estimates of the micelle composition, and the partitioning of the various components into the micelle.

Keywords: PGSE-NMR; Pluronic micelle; SANS; Small molecule surfactant.