Preparation and Properties of Surface Modified Thin Polymer Films

Doktorsavhandling, 2002

This thesis deals with preparation, modification and characterisation of thin polymer films. Most of the work has been performed using thin films of high-density polyethylene (HDPE) as a model system for systematic surface modifications by glow discharge plasma and UV/ozone treatments. First, a reproducible method, hot spin coating, to prepare thin films of the highly crystalline HDPE was established. The obtained films were thoroughly characterised with respect to film thickness, chemical composition, morphology and substrate dependence. The following characterisation methods were used during the thesis work: Contact angle measurements, electron spectroscopy for chemical analysis (ESCA), optical microscopy, atomic force microscopy (AFM), AFM colloid surface probe, time-of-flight secondary ion mass spectrometry (TOF-SIMS), ellipsometry, quartz crystal microbalance (QCM) and streaming potential measurements. A study of the effect of ozone (generated by UV-light) treatment of these films was performed. The ozone not only modifies the surface properties by oxidation and incorporation of oxygen species into the HDPE films but also "etches" away the polymer layer. UV-light exposure alone resulted only in minor degradation, i.e. the presence of ozone is critical to cause destruction and loss of material. The HDPE films were also modified by argon and oxygen plasma. In contrast to other reports of argon-plasma treated polymer substrates, we were able to treat the films with argon plasma without oxygen incorporation, as measured with in situ XPS. Moreover, properties such as degree of oxygen incorporation as a function of plasma treatment time, oxygen saturation levels, ageing, and modification depth have been studied. In another study, the possibility to obtain chemically patterned surfaces by plasma treatment of HDPE films through different masks was explored. In a more applied study, plasma polymerised thin films of acetaldehyde and allylamine were prepared as substrates for control of biological interactions via surface modification. The objective was to explore the role of physico-chemical surface properties for surface/protein/cell interactions by employing aminodextran coatings to the plasma polymers.