Temperature- and pH-Dependent Shattering: Insoluble Fatty Ammonium Phosphate Films at Water–Oil Interfaces

Joe Forth, David J. French, Andrei Gromov, Stephen King, Simon Titmuss, Kathryn Lord, Mike Ridout, Pete Wilde, Paul S. Clegg

Research output: Contribution to journalArticlepeer-review

Abstract

We study the films formed by tetradecylamine (TDA) at the water–dodecane interface in the presence of hydrogen phosphate ions. Using Fourier transform infrared spectroscopy (FTIR), interfacial shear rheology, confocal fluorescence microscopy, cryo-scanning electron microscopy (cryo-SEM), and small-angle neutron scattering (SANS), we find that between pH 5 and 8 tetradecylammonium cations bind to hydrogen phosphate anions to form needle-shaped crystallites of tetradecylammonium hydrogen phosphate (TAHP). These crystallites self-assemble into films with a range of morphologies; below pH 7, they form brittle, continuous sheets, and at pH 8, they form lace-like networks that deform plastically under shear. They are also temperature-responsive: when the system is heated, the film thins and its rheological moduli drop. We find that the temperature response is caused by dissolution of the film in to the bulk fluid phases. Finally, we show that these films can be used to stabilize temperature-responsive water-in-oil emulsions with potential applications in controlled release of active molecules.
Original languageEnglish
Pages (from-to)9312-9324
Number of pages13
JournalLangmuir
Volume31
Issue number34
Early online date11 Aug 2015
DOIs
Publication statusPublished - 1 Sep 2015

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