The Relationship between Charge Density and Polyelectrolyte
Brush Profile Using Simultaneous Neutron Reflectivity and In Situ
Attenuated Total Internal Reflection FTIR
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Abstract
We
report on a novel experimental study of a pH-responsive polyelectrolyte
brush at the silicon/D<sub>2</sub>O interface. A poly[2-(diethylamino)ethyl
methacrylate] brush was grown on a large silicon crystal which acted
as both a substrate for a neutron reflectivity solid/liquid experiment
but also as an FTIR-ATR spectroscopy crystal. This arrangement has
allowed for both neutron reflectivities and FTIR spectroscopic information
to be measured in parallel. The chosen polybase brush shows strong
IR bands which can be assigned to the N–D<sup>+</sup> stretch,
D<sub>2</sub>O, and a carbonyl group. From such FTIR data, we are
able to closely monitor the degree of protonation along the polymer
chain as well as revealing information concerning the D<sub>2</sub>O concentration at the interface. The neutron reflectivity data allows
us to determine the physical brush profile normal to the solid/liquid
interface along with the corresponding degree of hydration. This combined
approach makes it possible to quantify the charge on a polymer brush
alongside the morphology adopted by the polymer chains