Development of positron and neutron experimental techniques for the investigation of hierarchical materials

The experimental investigation of polymer coatings is of great interest, partly due to
their use in corrosion protection. Epoxy-amines are currently used extensively as in-
dustrial corrosion-resistant coatings. However, these systems contain volatile organic
chemicals with severe environmental and health side effects and are therefore being re-
placed by water-based latex coatings. This thesis investigates epoxy-amine and water-
based coatings using positron annihilation lifetime spectroscopy (PALS) and spin-echo
small angle neutron scattering (SESANS). In the process, both techniques have been
developed and their use for the investigation of corrosion-resistant coatings has been
tested.
The PALS instrument in Sheffield has been upgraded and a new data fitting proce-
dure was established. This instrument was then used to investigate corrosion-resistant
epoxy coatings alongside molecular dynamics simulations. Two characteristic free-
volume void diameters were identified at 4.7 ˚A and 7.0 ˚A using PALS and a similar
two-peak distribution was identified by molecular dynamics.
SESANS is a recently developed neutron scattering technique with access to infor-
mation on larger length scales than conventional scattering. This technique therefore
requires a new calibration sample. Multiple samples were trialled including various
nanoparticle dispersions and colloidal crystals. The samples suggested for future cali-
brations of the device are 500 nm SiO2 colloidal crystals and polystyrene nanoparticle
dispersions.
SESANS is then used to investigate water-based latex coatings. These systems
require the use of surfactants for latex particle stability, however, residual surfactants
in the final film can cause defects and create pathways for corrosion reactants to pene-
trate the film. Surfactant distribution is therefore of great interest in corrosion-resistant
coatings. Using a deuterated latex to gain contrast, the distribution of a range of sur-
factants were investigated and the internal structure of dried latex films was measured.
Thanks to the unique length scales available to SESANS large (micron-sized) ellipsoidal
surfactant clusters were identified and their size distribution was determined.