SOLVENT VAPOUR MEDIATED INTERDIFFUSION AND
ADSORPTION PROCESSES IN THIN POLYMER FILMS
R.L. Thompson J.T. Lenthall and R.W. Richards
Dept. of Chemisty, University of Durham, South Road, Durham, DH1 3LE.
The thermal interdiffusion of linear polymers is well-understood in terms of chain
reptation. Similarly, the adsorption behaviour of end-functionalised polymers is also a
mature area of study in annealed solid films. Whilst it is also possible to achieve self
assembly of polymers by exposure to solvent vapour, this process is far less well
understood than the equivalent thermal annealing process.
We have conducted a series of experiments in which thin (100 – 1000 nm) polystyrene
films have been exposed to solvent vapour. Using deuterium labelling and ion beam
analysis, interdiffusion between layers of these polymers has been characterised (see
figure, below). The influences of temperature and polymer molecular weight on
polymer diffusion coefficient have been measured and compared with thermal
annealing. We have also examined the ability of surface active end-functionalised
polymers to diffuse to the surfaces of blended films.
Our results show that that polystyrene interdiffusion can occur in micron thick films,
simply by exposing the film to solvent vapour at near-ambient temperatures. This
phenomenon can be exploited to achieve surface and interfacial adsorption of
functional polymers. The merits and limitations of solvent vapour mediated
interdiffusion will be discussed.
1.0
unexposed
60 s
90 s
0.8
dps
0.6
0.4
0.2
0.0
-50
0
50
100
150
200
250
300
350
depth / nm
Figure: Concentration versus depth profile of deuterium labelled polystyrene in a trilayer
‘sandwich’ following exposure to cyclohexane vapour at 35 °C. With continued exposure, the
film approaches a homogeneous state.