The nucleation of calcium phosphate crystals from a weakly supersaturated c
alcium phosphate solution on the surface of polyelectrolyte multilayers was
investigated in dependence on the chemical nature of the outermost layer.
Scanning angle reflectometry was used to follow in situ the initial stages
of the nucleation kinetics. The multilayers were constructed by alternate a
dsorption of poly(styrene sulfonate) (PSS) and poly(allylamine) (PAH), lead
ing to oppositely charged surfaces. It was verified that films terminating
with either PSS or PAH exhibited a negative or positive 5-potential, respec
tively. Surprisingly, both types. of surface layers induced a nucleation pr
ocess for supersaturations smaller than the one observed on the bare silica
surface. According to the literature, such an effect should only be expect
ed on a negatively charged surface. Infrared spectroscopy showed that the n
ucleated crystals are hydroxyapatite (OHAP) or octacalcium phosphate (OCP)
but not dicalcium phosphate dihydrate (DCDP) which is found on bare silica
surfaces. On both PSS and PAH surfaces, the nucleation processes started on
ly after a given induction time. The evolution of the induction times with
different supersaturations was analyzed within the framework of the classic
al nucleation theory. The effective surface free energies of the formed cry
stals were estimated to be on the order of 32 mJ.m(-2) on a multilayer term
inating with PSS and to be about 37 mJ.m(-2) on a multilayer terminating wi
th PAH. A mechanism for the enhanced nucleating effect of such polyelectrol
yte surfaces is proposed.