Modification of surface properties of thin polysaccharide films by low-energy electron exposure

The effect of low-energy electron irradiation on thin layers of two different polysaccharide materials, namely amylose and chitosan, has been investigated. Modification of the samples occurs at electron energies as low as 5 eV. In the case of amylose, a change in the wetting properties is observed upon exposure. Loss of oxygen from the hydroxyl groups and consequent formation of a hydrocarbon material is responsible for this effect as revealed by analysing the samples before and after electron exposure by means of reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). It is shown that the amide side groups in chitosan are more reactive than the hydroxyl groups and consequently dominate the modifications in this case. Additional experiments by high-resolution electron energy loss spectroscopy (HREELS) on thin condensed films of the model compound α-d-glucose show that facile oxidation of the saccharide occurs in the presence of O2. Traces of O2 as a residual gas can therefore be held responsible for the formation of carboxyl groups that are observed by RAIRS in samples of amylose after electron exposure.