Temperature- and pH-Dependent Shattering: Insoluble Fatty Ammonium Phosphate Films at Water-Oil Interfaces.
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.
School of Physics and Astronomy, University of Edinburgh , Edinburgh EH9 3FD, U.K.
Joe
J
Forth
School of Physics and Astronomy, University of Edinburgh , Edinburgh EH9 3FD, U.K.
David J
DJ
French
EaStChem, School of Chemistry, University of Edinburgh , Edinburgh EH9 3FJ, U.K.
Andrei V
AV
Gromov
STFC ISIS Facility, Rutherford Appleton Laboratory , Harwell Oxford Campus, Didcot OX11 0QX, U.K.
Stephen
S
King
School of Physics and Astronomy, University of Edinburgh , Edinburgh EH9 3FD, U.K.
Simon
S
Titmuss
School of Biological Sciences, University of Edinburgh , Edinburgh EH9 3BF, U.K.
Kathryn M
KM
Lord
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, U.K.
Mike J
MJ
Ridout
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, U.K.
Pete J
PJ
Wilde
School of Physics and Astronomy, University of Edinburgh , Edinburgh EH9 3FD, U.K.
Paul S
PS
Clegg
D000473:Alkanes / Q000737:chemistry*; D005223:Fats / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009821:Oils / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D012995:Solubility; D013696:Temperature; D014867:Water / Q000737:chemistry*
D000473:Alkanes; D005223:Fats; D009821:Oils; D010710:Phosphates; C024788:ammonium phosphate; D014867:Water; C007548:n-dodecane