Intramolecular segregation in polymers and macromolecules studied by low-energy ion scattering

• Published in: Surface science 2001, Vol.482, p.1235-1240
• Main Authors: Reijme, M.A., Maas, A.J.H., Viitanen, M.M., Denier van der Gon, A.W., Brongersma, H.H., Bosman, A.W., Meijer, E.W.
• Format: Article
• Language: English
• Subjects: Low energy ion scattering (LEIS); Plasma processing; Surface segregation; X-ray photoelectron spectroscopy
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/S0039-6028(01)00990-6

The intramolecular segregation in several generations of poly(propylene imine) dendrimers and oxygen plasma modified HDPE was studied with low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). Although the different generations of poly(propylene imine) dendrimers contain almost the same atomic carbon to nitrogen (C/N) ratio, it is shown that this ratio at the outermost surface depends strongly on the generation of the dendrimer. The conformation of a dendrimer is probably related to the flexibility of the bis(3-aminopropyl)amine endgroups, which becomes lower for higher generations. Furthermore, the formation of a metallodendrimer, by complexation of CuCl 2 with the amine endgroups of a fourth generation dendrimer (D4), was followed with LEIS. Compared to pure CuCl 2, a relatively high copper concentration and a high atomic copper to chlorine ratio was found at the surface of the metallodendrimer. The high copper concentration and the reduced sterical hindrance by chlorine demonstrate the high potential of the metallodendrimers as catalytic material. The hydrophobic surface of HDPE can be made hydrophilic by treating it in an oxygen plasma. During such a treatment, oxygen containing functional groups are introduced at the surface, which improves wetting and thus adhesion. Unfortunately, the effect of an oxygen treatment is only temporary, an effect referred to as ageing or hydrophobic recovery. LEIS has been used to study this ageing process. We were able to follow the surface oxygen concentration as a function of the time between the plasma treatment and the LEIS analysis. Combined information obtained from LEIS and XPS measurements indicates that the ageing is mainly confined to the outermost atomic layers. Moreover, the ageing process depends strongly on the exact experimental conditions.