Plasma aminofunctionalisation of PVDF microfiltration membranes. Comparison of the in plasma modifications with a grafting method using ESCA and an amino-selective fluorescent probe

Microfiltration membranes of polyvinylidenefluoride (PVDF) are promising materials for the development of functional polymeric membranes. The aim of this work is the investigation of typical plasma processes such as continuous plasma, pulse plasma and plasma graft polymerisation concerning their effect of functionalisation with primary amino groups using a mixture of nitrogen and hydrogen, ammonia, allylamine and diaminocyclohexane. The relative amounts of surface-incorporated nitrogen and primary amino groups are determined using electron spectroscopy and the binding of a selective fluorescent probe (Atto Tag FQ). No correlation of the relative amount of surface-bound nitrogen, determined by ESCA, and the relative amount of primary amino groups, determined with Atto Tag FQ, is found. The interpretation of the chemical shift of nitrogen with ESCA is limited. This is due to the unknown ionisation states of the primary amino groups resulting in peak shifts and their overlap with various other nitrogen compounds. The comparison of experiments performed with the same electric energy input but different powers show that the formation of primary amino groups on the surface of PVDF is higher, the lower the power of the plasma is. The formation of primary amine groups is maximised when a grafting method is applied. We explain this phenomenon as a fragmenting plasma effect. This results in an increased abstraction of hydrogen at higher plasma intensities and an augmented formation of a greater variety of nitrogen compounds. Furthermore the effectiveness of diaminocyclohexane as precursor is higher than allylamine, resulting in a higher grafting density.