Molecular dynamics in grafted layers of poly(γ-benzyl-L-glutamate)

Broadband dielectric spectroscopy (10-1 Hz - 106 Hz) has been employed to study the molecular dynamics of poly-(γ-benzyl-L-glutamate) (PBLG) in the bulk and prepared as ultra-thin grafted film. In order to contact the ultra-thin layer, two techniques were applied : (i) the evaporation of aluminium electrodes directly on the sample and (ii) the use of a solid electrode. The latter was prepared by evaporating aluminium on freshly cleaved mica sheets. Both in the bulk and in the grafted layer two relaxation processes are observed : (i) the fluctuation of the helical main chains ("chop-stick-motion") and (ii) the dynamic glass transition of the side chains. This second process is found to be slightly slowed down in the grafted layer. In case of evaporated electrodes, the "chop-stick-motion" could not be observed in the grafted layer

Molecular dynamics in confining geometries

The molecular dynamics of confined (low molecular weight and polymeric) systems is determined by the counterbalance between surface- and confinement-effects : Due to the interaction with the (inner) surfaces (e.g. the formation of H-bonds, grafting, physisorption) the molecular dynamics is slowed down, resulting in an increase in the glass transition temperature of the system. In contrast the confinement may induce an increase in "free volume'' thus making the molecular dynamics faster than in the bulk. This causes a decrease in the glass transition temperature. This counterbalance will be exemplified by employing broadband dielectric spectroscopy (10-2Hz - 109Hz) to study the molecular dynamics of the low molecular weight liquid ethylene glycol being contained in zeolites of different topology