W. Richard Bowen and Nidal Hilal 4

(a)
Good solvent:
swollen state
8.3 ENd-gRAFTEd POLyMER CHAINS 229
(c) (d)
Bad solvent:
collapsed state
FIgurE 8.2 (a) A swollen polymer chain in the ‘bulk’ solution and (b) in a collapsed
globular state upon the change of the solvent conditions from good to bad. (c,d) The same
transition for an end-grafted polymer chain with negligible affinity for the solid surface
(mushroom regime).
In the following sections, we will be demonstrating the AFM capability
to give answers to these and other similar questions using specific examples
of chemisorbed or physisorbed polymer chains on solid surfaces from
dilute polymer solutions. Owing to the characteristic nanometre-scale size
of single chains and thickness of polymer monolayers, any inhomogeneity,
aggregation, instabilitity and dewetting effects of such layers can be
readily and directly probed by atomic force microscopy, which is based on
piezoelectric transducers and sharp probing tips mounted on microfabricated
cantilevers that scan the interrogated surface and are simultaneously
monitored by the laser beam deflection technique while a feedback loop
controls the distance between the probing tip and sample.
8.3 EnD-grAFtED PoLymEr ChAInS
An efficient way of attaining purely end-grafted polymer chains is to
use thiol-terminated macromolecules, i.e. polymer chains ending in –SH,
and gold substrates. In this case, one achieves a quite strong chemical bond
(b)