Probing Interfaces between
Pharmaceutical Crystals
and Polymers by Neutron Reflectometry
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Abstract
Pharmaceutical powder engineering often involves forming
interfaces
between the drug and a suitable polymer. The structure at the interface
plays a critical role in the properties and performance of the composite.
However, interface structures have not been well understood due to
a lack of suitable characterization tool. In this work, we have used
ellipsometry and neutron reflectometry to characterize the structure
of such interfaces in detail. Ellipsometry provided a quick estimate
of the number of layers and their thicknesses, whereas neutron reflectometry
provided richer structural information such as density, thickness,
roughness, and intermixing of different layers. The combined information
allowed us to develop an accurate model about the layered structure
and provided information about intermixing of different layer components.
Systematic use of these characterization techniques on several model
systems suggests that the nature of the polymer had a small effect
on the interfacial structure, while the solvent used in polymer coating
had a large effect. These results provide useful information on the
efforts of engineering particle properties through the control of
the interfacial chemistry