Structural characterization of thin hydroxypropylcellulose films. X-ray reflectivity studies.

Thin solid films of hydroxypropylcellulose (HPC) have been investigated using synchrotron X-ray reflectivity. Evidence of preferential alignment of HPC molecules at the substrate surface is obtained. In the surface region the liquid crystalline domains ofHPC are preferentially oriented parallel to the substrate, whereas in the bulk they are mostly distributed randomly. Incorporation of colloidal particles in the film-substrate region destroys the preferential alignment. It is also found that in conditions of restricted geometry (very thin films), a minimum film thickness is required to produce lateral packing order perpendicular to the substrate surface.