W. Richard Bowen and Nidal Hilal 4

230 8. ATOMIC FORCE MICROSCOPy ANd POLyMERS ON SURFACES
(a)
(b)
FIgurE 8.3 Schematic drawing of a polymer brush in (a) good solvent conditions and
(b) poor solvent conditions. Upon the change of the solvent conditions, the polymer chains
could self-organise in nanoscale aggregates of small groups of polymer chains instead of
collapsing individually.
between the thiol and gold, end-grafting the chain, while its backbone is
not affected by the inert Au surface (negligible physisorption). A system
based on several molecular weights of various thiol-terminated polymers
chemisorbed on gold substrates from dilute solutions at different incubation
times was used in order to investigate the different structural regimes
of such end-grafted polymer monolayers and submonolayers [18–20]. The
gold substrates were immersed in the polymer solutions for a designated
duration and upon removal from the solution were rinsed exhaustively
with fresh toluene and subsequently dried under a stream of argon. The
AFM imaging was performed in water in contact mode at very low force
set-point; capillary forces were avoided since both the sample and the
cantilever/tip were immersed in water.
In Figure 8.4, we show a three-dimensional AFM topography map
of a gold substrate sample prepared by immersion in a toluene solution
of thiol-terminated polystyrene, PS-SH (concentration 0.1 mg ml –1 ,
weight-average molecular weight M w� 144 000 g mol –1 ), for 45 min. It
was imaged by AFM in water (bad solvent for PS). The gold substrate
morphology of flat gold terraces separated by valleys and channels can
be observed, while well-separated globular polymer islands on top of the
terraces can be clearly seen.
Although the height of the polymeric islands can be deduced directly
from AFM topography images, their lateral size is usually overesti-
mated owing to the convolution between the volumes of the tip apex
and the polymeric island. One can employ deconvolution methodologies